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ADVANCED IMAGING
| Question | Answer |
|---|---|
| Where should the marker/notch be placed on patient in US? | Marker/notch should point towards patients right side or their head (or in between for oblique views). |
| What is the movement and rotation in the Y-Axis called in US? | Sliding + rocking |
| What is the movement and rotation in the X-Axis called in US? | Sweeping + fanning |
| What is the movement and rotation in the Z-Axis called in US? | Compression + rotation |
| What are the 5 main transducer types | Curvilinear, linear array, intracavity, phased array, transoesophageal |
| Applications of curvilinear transducers | abdo/gynae applications = lower frequency transducers |
| Applications of linear array transducers | wide applications – vascular, eyeballs, musculoskeletal |
| Applications of intracavity transducers | transvaginal - visualisation of uterus and ovaries |
| Applications of phased array transducers | cardiac applications (small footprint that pans out for imaging between rib spaces) |
| Explain the transverse scan plane in US | Splits body sup/inf. Marker placed on PATIENTS RIGHT SIDE. On the image, the left = patients right. Anatomy closest in image to transducer is anterior, deeper anatomy = posterior |
| Explain the sagittal scan plane in US | Splits body left/right. Marker placed towards head. Left of image = superior, right = inferior Anatomy close to transducer is anterior, deeper = posterior |
| Explain the coronal scan plane in US | Splits body ant/post. Transducer on patients side (r or l) with marker towards head. Left of image = superior, right = inferior Anatomy closest to transducer in image = lateral, bottom = medial |
| What is the longitudinal plane of viewing in ultrasound | The longitudinal plane of viewing divides the body into sections along the long axis e.g. sagittal and coronal planes. |
| • Explain the difference between scan planes on the body and on the organ. | The longitudinal plane of an organ may not be a longitudinal plane on the body as many organs are not placed on the axial plane e.g. kidneys have oblique orientation and their longitudinal plane is not same as longitudinal plane on the body. |
| What is gain in ultrasound? | Increased gain = processes more incoming echoes = brighter image Decreased gain = less incoming echoes are processed = generally darker auto-gain presets exist for each anatomy scan preset |
| What is time/depth gain compensation | Adjusts brightness of image at specific depths Left = decreased brightness, right = increased brightness |
| What is depth in US? | Controls the pulse repetition period - the longer the period, the greater the penetration depth |
| What is frequency | res = resolution, gen = general, pen = penetration Resolution produces a higher frequency beam (greater resolution) at the expense of penetration Penetration produces a lower frequency beam (greater penetration) at the expense of resolution |
| Define focus in US | Focus is the narrowest part of the beam which provides greatest lateral resolution [ |
| In US, why do we manually adjust the depth of focus so that the target structure is visualised within the focal zone | a) the reflector gives rise to a stronger echo (as the beam is highest intensity) b) beam width is narrowest (best lateral resolution as minimises overlapping echoes) |
| Define compound imaging in US | Uses multiple lines of sight to improve spatial resolution Clears up margin of structures and reduces strength of artefacts |
| Define XRES (precision) in US | Mathematical algorithm that helps to reduce image noise (X1 -> 5 (smooth)) System assesses neighboring lines of sight and checks that the echoes received are also displayed in adjacent beam |
| What is dynamic range in US | Controls how many shades of grey are visible in the ultrasound image A lower dynamic range will show increased contrast (black and white images) A higher dynamic range will show decreased contrast with many shades of grey |
| What is harmonics in US | Harmonics decrease image artefacts, increases signal to noise ratio |
| Define spatial resolution and list the two types in US | – ability to differential small structures on a B-mode image Axial resolution Lateral resolution |
| What affects spatial resolution in US | Spatial resolution is affected by beam characteristics, and resolution of the viewing monitor |
| Define axial resolution | the closest distance two structures can be along the axis of the beam and which can still be seen as separate entities |
| What is the primary determinant of axial resolution | Axial resolution is determined by spatial pulse length (which itself is affected by frequency and transducer design) |
| formulas for axial resolution and spatial pulse length | A.R. = ½ SPL (SPL = no. of cycles x wavelength) A shorter SPL is better, as shorter pulses allow the ultrasound to distinguish between reflectors that are closer together. A shorter pulse length reduces the overlap of echoes from adjacent structures |
| What are the two secondary determinants of axial resolution | Axial resolution is also affected by output power and gain Increased power or gain means that the effective pulse length increases as the low amplitude at the end of the echo are magnified and detected OPTIMISED BY HIGH FREQUENCY AND LOW POWER/GAIN |
| Define lateral resolution | the closest distance two structures can be at 90 degrees across the axis of the beam at the same depth, and which can still be seen as separate entities |
| What is lateral resolution dependent on? | Beam width -> LR increased with reduced beam width |
| What is contrast resolution in US | ability to differentiate tissues of different echogenicity |
| What influences contrast resolution in US | background noise, backscatter interference and slice thickness Thinner slices better as echoes from surrounding tissue are less likely to overwrite the lesion (also depends on characteristics of machine and transducer construction) |
| What is temporal resolution in US | ability to resolve rapidly moving structures (dependent on frame rate) |
| What influences temporal resolution in US | High frame rates are required to provide increased temporal resolution (sometimes at expense of other features) |
| What is colour resolution in US | the spatial resolution of the Doppler colour display when defining moving substances e.g. blood |
| What is the doppler effect | the frequency of waves detected by an observer changes if the source is moving towards or away from them. waves moving towards are squeezed - shorter wavelength, higher freq (blue shift) waves moving away = stretched = longer wavelength and lower freq |
| how does the doppler effect apply in u/s waves (doppler shift) | blood towards transducer = reflected waves compressed and received freq is HIGHER than transmitted freq. blood moving away produces stretched waves and lower received frequency Doppler shift = difference between transmitted freq and received freq. |
| What is colour doppler | Overlays doppler info onto a standard B-mode grey scale image, allowing visualisation of blood follow with a selected ROI Calculation of mean doppler shift - assigns a colour based on that average shift |
| Describe colour maps in US | Red = flow towards transducer Blue = flow away (but this can be reversed) Within each colour band, lighter or brighter shades usually represent higher average velocities, whereas darker shades represent lower velocities. - AVERAGE PICTURE |
| What is 'power doppler' | Displays amplitude (power) of doppler signal, NOT mean frequency shift Highly sensitive to low velocity flow and small vessels, often revealing flow not visible on standard colour doppler Does not show direction of flow, no absolute velocity value |
| What is variance in US | A display that measures the width of the Doppler shift range within a region High variance indicates wide spread of velocities (turbulent or disturbed flow ie downstream stenosis) coloured in green |
| what is a pulse-wave (spectral) doppler | An extension of colour doppler that produces a spectral waveform over time, enabling quantitative assessment of blood velocity at a specific location |
| Clinical example of pulse-wave doppler | obsestric ultrasound: sample umbilical artery within umbilical cord where the waveform reflects blood low from fetus through placenta. changes in waveform/velocity can indicate altered placental resistance / impaired placental function |
| List the basic scan parameters for CT image acquisiton | mAs, kV, FOV, slice thickness/interval, pitch |
| In CT, what is patient dose dependent on | mAs - higher mAs = more dose kV - higher kV = better penetration, lower noise but decrease in soft tissue contrast FOV Slice width/thickness scan length patient factors: weight, size, mobility |
| List the advantages / clinical benefits of the MRI Linac / MR in IGRT | Superior target delineation and precision (soft-tissue visualisation), real time 2d/3d tracking (gating w/out surrogates), early (intra-treatment) response assessment and normal tissue toxicity, adaptive treatment throughout treatment, no IR Research |
| (ICRU 97) MRI guided vs x-ray guided imaging | Pre-txt image-guidance - Both routinely available, MRI superior soft-tissue During txt - MRI routinely available, limited spatio-temporal acquisiton - x-ray emerging, reliance on marker as a surrogate Functional imaging - MRI growing, x-ray none |
| what is MRI excitation | If you apply an RF pulse at the same spinning frequency (Lamour) – the spins will tip into the transverse plane where they are “visible” to the receiver coils |
| Where do we find hydrogen protons in the body | in water, fats and lipids, proteins and macromolecules |
| what is t1 relaxation | • Relaxation back to z • Spin-Lattice EXPONENTIAAL |
| what is t2 relaxation | • Dephasing of transverse plane • Spin-Spin interaction EXPONENTIAL |
| what is t2* relaxation | • Local field inhomogeneity • Bone-air-tissue interfaces FASTER THAN T2 |
| what determines a substances t1 relaxation rate | the higher the mobility, the longer the t1 relaxation time |
| list from short to long t1 relaxation time (bright to dark) | liver, spinal cord, white matter, cartilage, gray matter, blood |
| what determines a substances t2 relaxation rate | constricted tissues have shorter t2 times (spins are more likely to bump or collide) |
| list from short to long t2 relaxation time (dark to bright) | bone, cartilage, river, kidney, white matter, spinal cord, gray matter, blood |
| how does echo time effect T2 signal | T2 signal is greater with a longer echo time |
| what is FLAIR | Flair is a t2 sequence that supresses CSF and pulls out white matter lesions |
| describe t2* relaxation times | different types of material sitting close together (air-bone-tissue) cause local field changes. always faster than T2. can manipulate this to see things that will cause local field shifts like iron and calcification |
| what is SWI | susceptibility weighted image - sensitive to blood and calcification |
| why do we use MRI in RT | • improved ST visualisation + delineation - reduces contour uncertainty • non-invasive, better for repeated scanning • Better for paediatric patients • Some artefacts in CT (dental fillings) are better on MR • Moving organs can be visualised |
| MRI contradindications | • Certain implants not compatible (pacemakers, aneurysm clips etc) • Claustrophobia • Certain implants, while safe, cause problems in the image • Gd contrast agent – allergic reactions, NSF |
| describe changes in workflow when using MRI sim | MRI and CT sim - ideally on same day - one venous access for contrast • MR – Tumour delineation • CT – Dose calculation • MR segmentation (if possible) |
| which order for CT/MRI sim | • MR bore is more restrictive – if done first patient positioning will be compatible • Reduces need for deformable registrations • If CT has occurred first – use body markings for positioning • Be aware of ink- can cause signal loss on MR |
| what are the additional considerations for MRI sim | flat table needed, compatible immobilisation device, coils may need to fit over mask/equipment (further away from coils - lower SNR), coils can deform patient surface, fiducial markers, bore size |
| what should we consider when choosing MR protocol for sim | consider SNR - small voxels required for radiotherapy but this means less signal and lowers SNR or longer scan time |
| what is the risk of having too large/too small MRI volume | • Too large – distortion increases, scan time increases • Too small – missed target or image registration fails • Make sure target volume is in isocentre to reduce distortion • Same slice positioning for all images - helps w registration |
| how do distortions arise in MRI | • B0 homogeneity • Magnetic susceptibility • Air-tissue interfaces • Tissue-bone interfaces • Metal implants • Chemical shift artefacts • Distance from the isocentre • Pulse sequence and parameters |
| how do we reduce distortions in MRI | • Apply 3D distortion correction in protocol (2D as last resort) • Use new sequences with improved imaging around metallic implants • Lower field MRI • 0.5T and 0.06T MRI systems • Offset by advances in AI in reconstruction and signal boosting |
| how do we account for motion in MRI | gating: respiratory or cardiac gating |
| describe respiratory gating in MRI | • Can set acquisition to acquire either at inspiration or expiration • Set a threshold level so it knows when to acquire |
| describe cardiac gating in MRI | • MR-compatible ECG leads • Acquire at some part of the diastole- systole cycle • Set a threshold level so it knows when to acquire (R-wave) • Set a delay so it knows which part of the cycle you’d like |
| how do malignant tumours appear in MRI | more heterogenous in signal, with possible oedema. increased angiogenesis and cell density, reduced water flow, contrast ring |
| benefit of t2 weighted imaging in oncology | high water content = high signal, cancers have low signal if they have dense cellularity (high grade) |
| benefit of t1 weighted imaging in oncology | visualises haemorrhage |
| benefit of DWI weighted imaging in oncology | measures microstructure by looking at movement of water. cancers with tightly packed cells will restrict the motion of water. restricted water = bright. in the brain, compression of white matter can be mapped with diffusion |
| benefit of dynamic contrast enhancement in oncology | contrast (gadolinium) injected, followed by t1 weighted image. signal inc as contrast agent flows. inc blood flow = greater malingnayc. leaky capillaries / blood brain barrier = tumour |
| benefit of magnetic resonance spectroscopy in oncology | measures metabolites in-vivo. e.g. choline and creatine concentrations which can increase in tumours |
| what is MRI diffusion | • Random thermal motion (“Brownian motion”) • Will displace over time • Provides information about the microstructure. • Water cannot diffuse as far as it can in normal tissue • Diffusion weighted image – signal is brighter than normal |
| what is perfusion in MRI | • Dynamic Contrast Enhancement (DCE) • Image before injection, then inject contrast agent • Scan continuously while contrast moves through the body • T1 weighted images, contrast is bright • See the “wash-in” and “wash-out” of the contrast |
| outcome of perfusion in MRI | • Outcomes: Uptake curve, time to peak, mean transit time, tissue perfusion, tissue blood volume, delayed contrast image. • more aggressive tumours - quicker uptake curves • Delayed contrast images can often help to determine the border of the tumour |
| prostate MRI protocol | platinum fiducial markers, bladder and bowel prep with buscopan, cover prostate, SVs, rectum and bladder, t1 |
| glioma MRI protocol | • Thermoplastic masks • Head coil (20 ch) • or flex coils depending on the type of mask • Chin-to-chest measures from the CT so head tilt can be duplicated • Same central slice position t2 flair, gdt1w MPRAGE |
| head and neck MRI protocol | • Flex coils (to fit over 5 point mask) • Protocol: T1, Post-contrast T1, T2, Dynamic Perfusion, Diffusion Helped outline tumour, and visual the retropharyngeal lymph nodes |
| pancreas MRI protocol | • Respiratory guided radiation therapy • End expiration to match target delivery • Arterial and Venous for tumour delineation T1 post gd arterial phase, t1 post gd venous phase, ADC map |
| liver MRI protocol | • Large flex coil + bridge, spine array • T1 3D GRE radial (better for motion artefacts) • Hepatobilary contrast (gadoxetic acid) • Free breathing protocol with respiratory gating • ‘binning’ of acquisition |
| cervix brachytherapy MRI protocol | • Insert MR marker into applicator ring • Clamp urinary catheter just before scan. t2 TSE |
| rectum MRI protocol | • Patient Preparation: Empty bladder 30 mins before scan, then drink 700ml • Foot and head fixation pads T2 TSE or t2 space |
| lung MRI protocol | • Free breathing protocol using UTE (ultra short echo time) • Same central slice to CT to minimise registration problems • Protocol would include • tumour motion assessment (T2-Trufi) • Contrast perfusion • Diffusion |
| musculoskeletal MRI protocol | site dependent flex coils and devices - t2 water only, post contrast t1, t2 HASTE |
| limits of PET/MRI | • Issues – attenuation compensation, motion detection and correction, partial volume correction |
| advantages of PET/MRI | • Lower radiation dose compared to PET/CT • Great for follow up or paediatric scanning |
| portable low field MRI | • Can a low field system be used for SIM? • 64mT field strength • Rolls to the bedside • Faster turnaround for the patient • Less claustrophobic • Children’s parents can sit with them safely |
| why is MRI attractive for oncology imaging beyond high soft-tissue contrast | • Mapping of tissue characteristics (T1/T2) • Microstructure information looking at diffusion of water • Fibre tracking in the brain • Tissue perfusion and angiography • Temperature mapping • Metabolic mapping with spectroscopy |
| describe u/s as a diagnostic tool | for initial detection + characterisation of solid tumours: abdo/pelvic organs - liver, pancreas, kidneys, breast, prostate. real‑time, cross‑sectional imaging without ionising radiation, advantageous for repeat follow‑up, younger or pregnant pts. |
| examples of u/s as image guidance in RT | elekta clarity: tracks prostate pos without ionising radiation time-resolved 3d us: record intrafraction motion - detailed motion trajectories to support margin reduction + adaptive strategies assess bladder filling and restal distention pre-treatment |
| u/s applications in gynaecological RT | Transabdo and transvag u/s can assist in localising uterus and ovaries to guide placement of brachy apps Accurate visualisation helps to optimise applicator geometry and reduce unintended dose to OARs (bladder/bowel) |
| Describe MRI zones | zone 1 - publicly accessible area zone 2 - waiting room, reception, screening and change room zone 3 - low magnetic field, corridors outside room and console zone 4 - actual room |
| What is a basic gradient echo localiser | short TR and short TE, flip angle 20 degrees. Short scan time (9 secs) Basic image, three planes of viewing. Used to localise scans. ACPC line for axial scan plane localisation |
| What is a T2 turbo spin echo | long TR and TE, scan time ¬ 2 mins, 150 degree flip angle. BRIGHT CSF, grey matter lighter than white matter |
| What is a T2 hybrid FLAIR | long TR and TE, grey matter lighter than white, dark CSF -> good for white matter plaques ie. MS |
| What is a T1 inversion recovery | (for contrast of grey/white matter). Shorter 200 TR, 900 TE (improves contrast of grey/white matter). Grey matter darker than white matter. Classic T1 weighting |
| what are MRI coils | Transmit coils generate the RF field to excite hydrogen protons, built into scanner for uniform excitation. Receive coils, often surface coils, detect weak MR signal from tissue, maximizing SNR. Modern systems use transmit-receive coils for both functions |
| complete MRI contraindications | older pacemakers and anyeurism clips |
| 2d vs 3d mri acquisition | |
| describe T1 sequences | short TR and TE, anatomical detail |
| describe T2 sequences | long TR and TE, highlights fluid and pathology (inflammation) |
| explain FOV distortion in MRI | |
| list types of MRI coils and considerations in RT | flex array coils, hand coils, knee coils, head coils may compress patient -> registration, mask may not fit in head coil |
| cons of contrast enhanced CT | second scan acquired, more time and radiation, resource load (staff needed) |
| Define 'contrast' | radiopaque substances administered orally, rectally or intravenously during medical imaging that enhance visualisation of organs (or hypovascular lesions) |
| phases of contrast enhancement | pre contast, arterial phase 35-40 secs (early 15-20, late 34-42/early portal), hepatic portal phase |
| Outcomes/pros of contrast enhancement in RT | Help to identify pathology by enhancing contrast between lesion and normal structures -> increased confidence in volumes / target delineation -> dose escelation -> improved dosimetric accuracy and minimised dose to critical structures |
| contrast flow rate | - Influenced by patient weight and volume of contrast administered - SI unit = mL/s Larger volume administered = faster flow rate |
| Patient ineligibility to contrast | - Known allergy to contrast - Abnormal renal function - Renal function assessed > 1 month of planned injection Diabetes managed with metformin |
| Two types of contrast reaction | Anaphylactoid, chemotoxic (nephro and cardiotoxicitiy, neuro), or vasovagal |
| Symptoms of mild, moderate and severe media reactions | mild = flushing, nausea, puritis, vomiting, headache. usually resolve without txt Moderate = severe vomiting, broncospasm, respiratory systems, oedema, vasovagal Severe = hypovolaemic shock, respiratory and cardiac arrest, severe anaphylaxis |
| risk factors for contrast reaction | CHF, Sickle Cell Anaemia, Nephrotic syndrome, Polycythemia and myeloma, Dehydration, Phaeochromocytoma, Extremely anxious patients, Asthma, Pregnancy, Hyperthyroidism, Breast feeding, Myasthenia Gravis |
| Symptoms of post contrast allergies | dizziness, naus/vom, itching and hives |
| define extravasation and mgmt | leakage of IV drug from vein into tissue - Stop infusion - Aspirate from cannula - Remove cannula - Elevate affected extremity (above heart) - Apply hot pack with towel Observe for 2-4 hours if volume exceeds 25mLs (outpatients) |
| risk factors of extravasation | - Obesity - Large vol Small or damaged veins |
| sites for IV contrast sim | - Lung - Oesophagus - Mediastinal nodes - Liver - Pancreas Metastatic brain lesions enhance tumour visualisation -> improves targewt delineaion -> minimise dose to OAR |
| types of contrast | • Iodine based non-ionic chemical • Pre-loaded syringes • Syringes kept in an incubator @ 37 degrees • Intravenous administration |
| Role of RO in contrast administration | request renal function test, educate patient (RF, SE), discuss allergies/contraindications, obtain consent, discuss cannulation site, request contrast enhancement phases, attach tubing to canula, start pressure injector, monitor, disconnect + flush line |
| Role of nurses in contrast administration | day prior: contact patient and remind water, check RFT prep resus equipment and reversal drugs, remove cannula, montior, patient education |
| sim protocol steps using contrast | Position patient, RO connect tubing to cannula, setup CT scan protocols, ensure double scan available, perform 1 st scan (planning dataset), RO and RT start injector and scanner simultaneously per timings, No RO = No Contrast Scan perform 2nd scan |
| what does NSQHS say about contrast / ADR responsibilities | re adverse drug reactions. we must document a patient's hx of medicine allergies/ADR in the health care record and organisation wide incident reporting system, as well as reporting to TGA in accordance w requirements |
| what does MRPBA say about CT contrast responsibilities | 1. perform ct imaging safely 2. deliver efficient, effective and culturally safe person-centred care (including recognising circumstances of impending or acute physiological deterioration including anaphylaxis...), trained in anaphylaxis mgmt |
| What does RANZCR say about CT contrast responsibilities | for those administering contrast must be: R36. trained in recognition of contrast media rxns/procedures for treating rxns R37. trained in basic life support including CPR, advanced life support where possible |
| Role of RTS in contrast administration | RTs are involved in monitoring and educating patient + timing scan acquisiton with appropriate contrast enhancement phase |
| additional MRI capabilities for oncology imaging | Mapping of tissue characteristics (T1/T2) • Microstructure information looking at diffusion of water • Fibre tracking in the brain • Tissue perfusion and angiography • Temperature mapping • Metabolic mapping with spectroscopy |
| Define inter fraction motion and list examples | Motion that occurs between fractions Patient setup changes regardless of immobilization and localization methods — do they get on the bed the same every day? Is today's normal breathing/bladder filling the same as yesterday's/tomorrow's? |
| Define intra fraction motion and list examples | Motion that occurs during a fraction Typically related to voluntary + involuntary motion (wiggling, scratching, respiration, peristalsis, coughing, sneezing, swallowing) |
| How do immobilisation devices affect motion mgmt | • Reduce setup errors and (hopefully) increase comfort • Can be source of anxiety (e.g. masks, compression) which may exacerbate motion |
| How does bladder and bowel prep affect motion mgmt | • Consistency of filling/emptying known to improve positional reproducibility of pelvic organs, including targets (e.g. prostate, small bowel) • Filling difficult to reproduce (dependent on uncontrolled factors) |
| How does compression/BH techniques affect motion mgmt | • Reduce abdominal or chest motion due to respiration • Potentially increase baseline shifts (setup errors) • May try too hard to achieve protocols and becomes source of anxiety |
| How does education affect motion mgmt | • Patient understanding of positioning equipment and preparation protocols increases compliance • May try too hard to achieve protocols and becomes source of anxiety |
| Cons of lung positioning in sim | Arms above head -> no dose through arms, more beam angles available for planner, improved target coverage, improved normal tissue sparing X Not suitable for all (arthritis, mobility, injury) X Difficult to hold X Collision risk with elbows |
| Where is lung motion greatest | Motion increases towards the diaphragm and is largest in the liver -60% lung tumours move < 1 cm -35% between 1 and 2 cm -5% move > 2 cm |
| Describe how CT scanning speed and tumour motion speed affect motion artefacts | If CT scanning speed << tumor motion speed -> smeared tumor image If >> tumor motion speed -> tumor position and shape captured at an arbitrary breathing phase If = tumor motion speed tumor -> position and shape heavily distorted |
| Describe 4dct | Images taken at POIs along long. axis (slow pitch), obtained by RPM, ABC, compression belt or SGRT, images sorted based on corresponding breathing signals ("binning"), 3DCT datasets are produced corresponding to a particular breathing phase or amplitude |
| Limitations of 4DCT | Only a snapshot of respiratory motion, repeat 4dct is likely to give different result |
| Advantages of 4dct | Improves estimate of tumour shape and trajectory, minimises motion artefacts due to relative motion (interplay) between CT acquisition and the object |
| Pelvis positioning at sim + prep | Arms on chest -> no dose through arms, more beam angles available for planner, improved target coverage, improved normal tissue sparing X Collision risk need reproducible anatomy: consistent B+B • Demonstrated worse outcomes w rectal distension |
| Gynae filling protocols | • Bladder + rectal filling during chemorads is variable despite protocol, blad larger on post-chemo days • Blad > 300 cm3 at sim not reproducible. deviation > 130 cm3 from planned = CTV motion outside PTV • patient prep w bladder volume 150 – 300 cm3 |
| Types of motion management in planning (types of scans) | 1. FB CT - Deformed tumour shape - Large PTV margin to account for uncertainties 2. FB, 4DCT with ITV - Medium PTV 3. FB or BH, 4DCT using gating (in or ex) - Small ptv 4. FB, 4DCT - mid vent approach - small PTV (easy or txt delivery) |
| On txt, how does IGRT affect motion management | Reduces uncertainties and maximises reproducibility of txt delivery by: improving setup accuracy and accounting for organ motion Minimises PTV margins, thereby reducing overall irradiated volume and sparing NTT and reducing rad-related complications |
| Dangers of IGRT motion mgmt | • Tightly conformed dose distributions are at increased risk of missing the moving target • With IMRT and IGRT, we can more precisely irradiate the intended target. • REMEMBER, this is dangerous if the target is poorly delineated! |
| What is the IGRT interplay effect? | interplay between organ motion and leaf motion for the delivery of IMRT with an MLC. Depending on the phase relative to the leaf motion, the PTV can receive very different dose values. |
| describe kv imaging | • Widespread adoption of kiloVoltage (kV) imaging • Now standard equipment within LINAC hardware • Relatively low imaging dose • Efficient means of isocentre verification |
| describe fiducial markers | • Routinely used for localising prostate irradiation • Relatively low imaging dose • Aims to overcome prostate motion due to: • Bladder filling • Rectal filling, and • Patient motion |
| strengths of fiducial markers | • Surrogate of prostate motion • Very fast method of localisation • Staff have great confidence when alignment • Very low intra- and inter-observer variability |
| limitations of fiducial markers | expense, invasive procedure, ineligible patients, evaluation of nearby organs and target deformation is difficult, hard to differentiate gas vs SV motion |
| describe ct on rails | diagnostic ct opposite/orthogonal, single couch rotates between machines, assumes fixed relationship between iso of linac/CT |
| limitations of ct on rails | couch sag that occurs at CT gantry, potential movement during rotation of couch, associated time lag |
| describe mvct | no additional arms required, low contrast, high-density images without artefact (e.g. prosthetic hips), same isocentre, dose several times greater than kV |
| describe cbct | • Much more than daily isocentre localisation • Able to monitor patient throughout treatment • Volumetric rather than few discrete points • Learning when to replan (adapt) treatment: disease progression, disease response, weight loss |
| describe fiducial markers matching for prostate | Fiducial makers proven to reduce interobserver variability CBCT of seminal vesicles, bladder and rectum provide vital information to proceed safely Recommend complementary use of fiducials + volumetric imaging with CBCT for daily localisation |
| Describe plan of the day e.g. bladder + prostate + cervix | Initial plan has generous margins based on sim CT (empty bladder). Initial fxs treated w soft-tissue match. First 5 fx CBCTs used to create small, average, large bladder vol (plan library). Adaptive RT allows reduction of margins and reducing dose to NTT |
| Define SGRT | • Utilises ceiling mounted 3D cameras • Reference surface model is produced from either: - importing contours from CT data, or acquiring a 3D surface at simulation. At each fx, the system images the current patient pos and couch shifts are calculated |
| Describe 'remove the mask' using SGRT | up to 50% of patients experience mask anxiety • Aim to use surface-mapping technology to achieve a sub-degree and submillimetre surface tracking accuracy. • Allows easy access to raw surface images with high temporal resolution. |
| beam gating vs target tracking | beam gating; beam on only when target in desired phase tracking: treatment beam follows target during the whole cycle |
| describe prostate electromagnetic guidance | MLCs tracking system combines real-time position signal with the plan to adjust leaf positions to adapt the plan to new target pos coverage improved, margins reduced |
| **describe lung electromagnetic guidance | implants into lung - invasive, risk of infection, uncomfortable |
| describe ultrasound guidance for RT treatment | relatively poor reputation after initial implementation due to interobserver variability and inaccurate treatment localisation. nowadays, inexpensive, non-IR real time guidance method e.g. clarity |
| describe clarity (general) | U/s probe calibrated to isocentre enables volumetric image to be automatically fused and provides additional information for contouring quick patient alignment, scanning (prostate, breast, gynae) can monitor changes over time e.g. lumpectomy cavity |
| describe clarity (prostate) | • Can be used to robotically scan the prostate and surrounding anatomy during treatment delivery • Continuous real-time targeting |
| ****markerless tracking for SBRT lung | central lung tumours - inc central airway toxicity 3d monitoring of proximal bronchial tree helps manage risk by tracking position/motion w/out reflective/implanted markers |
| ***describe mgRT | |
| define anaphylaxis | any acute onset illness with typical skin features + involvement of respiratory/cardiovascular and/or persistent, severe gastrointestinal symptoms. or any acute onset of hypotension/bronchospasm (even if skin features not present) |
| skin features of anaphylaxis | urticarial rash, erythema/flushing, angiodoema |
| signs and symptoms of anaphylaxis | difficult/noisy breathing, tongue swelling, swelling/tightness of throat, wheeze or persistent cough, hoarse voice, collapse, abdo pain/vom |
| signs of mild/moderate allergic reaction | swelling of lips/face/eyes, hives or welts, tingling mouth, abdo pain/vom |
| vasovagal episode vs anaphylaxis | VE immediate vs 15 mins anaphylaxis (can be immediate), normal breathing with VE, laboured anaphylaxis, brachycardia vs tachycardia, clammy skin for VE vs red and itchy anaphylaxis |
| panic attack vs anaphylaxis | anxiety attack has no urticaria, itching, hoarseness, stridor, wheezing, couching, hypotension or collapse |
| what does the aus commission on safety and quality in health care say about anaphylaxis mgmt (first 3 dot points) | 1. prompt recognition of anaphylaxis 2. immediate injection of intramuscular adrenaline 3. correct pt positioning 4. access to autoinjector in all healthcare settings 5. obs time (at least four hours or overnight) 6. discharge mgmt and documentation |
| describe the pharmacology of adrenaline | stimulates a+b recept. -vasocon: raises BP, reduces mucosal oedema -raise HR, inc cardiac contraction - stimulate lungs to relax muscles - inhibits mast cells to dec release of inflam med overall reverse hypotension, breathlessness and allergic rxn |
| positioning of anaphylaxis pts | fatality can occur within minutes if a patient stands, walks or sits suddenly patient must lie flat or semi-reclined with legs outstretched - assists return of venous blood |
| steps of managing anaphylaxis (ASCIA guidelines) | 1. remove allergen, stay with pt, assistance, locate injector 2. lay person flat 3. give injector 4. oxygen if avail 5. call ambo/mert 6. 5 mins, more adrenaline if needed 7. observation (at least 4 hours) 8. commence cpr at any time if needed |
| when to use adrenaline | not needed for general non-anaphylactic rxns (skin rash/ angiodoema). but, if in doubt give adrenaline. no serious or permanent harm is likely to occur from administering if not anaphylactic. antihistamines/hydrocortisone not rec for mgmt in an emergency |
| how to administer epipen | form fist around epipen and pull off blue safety release. hold leg still and place orange to anterolateral thigh (with or without clothing). push down hard until a click is felt and hold for 3 seconds |
| how to administer anapen | pull off black needle shield, pull off grey safety cap from red button, place againt outer mid-thigh (with or without clothing), press red button until it clicks and hold for 3 seconds |
| how to use ampoules | hold vial with blue dot facing you. with dom hand, place thumb on dot, index finger opp. snap vial away from body. use protective tools (e.g. amp openers) if available + add layer of protec (gloves, gauze) use plastic vials or syringers where poss |
| how to use adrenaline nasal spray | do not pull/push plunger until ready to give dose. do not test or prime, each nasal spray only has one dose. can give a second nasal spray after 5 mins, in the SAME NOSTRIL |
| what is deep learning segmentation | utilizes ai to automatically delineate tumors and healthy tissues (organs-at-risk) on planning CT or MRI scans. It drastically reduces contouring time and inter-observer variability, though clinical review and manual corrections remain essential. |
| What is TR in MRI | Repetition time = time between pulses, controls T1 weighting |
| What is TE in MRI | Echo time = time to signal measurement, controls T2 weighting |
| Describe TR/TE characteristics of a T1 image | Short TR and Short TE |
| Describe TR/TE characteristics of a T1 image | Long TR and long TE |
| 6 components of MRI safety | 1. Magnet always on - projectile risk 2. RF energy/heating - tissue heating, burns 3. Gradient fields - peripheral nerve stimulation, hearing damage 4. Implants and metal 5. Patient prep - screening orm 6. Emergency = quench |
| MRI sim workflow overview | CT Sim (including acquisition of patient consent) -> MRI sim (scan in CT pos using identical immobilisation devices) -> MR for RT planning (high geometric accuracy, thin slice thickness) |
| steps of MRI sim implementation | 1 establish scanner location 2 MRI safety and training 3 laser bridge and positioning 4 MDT |
| 1.5 vs 3T | 3T = superior contrast, higher SNR, supports MR only planning, susceptible to geometric distortion/artefact, larger footprint and requires quench 1.5T = lower SNR, geometrically stable, less sensitive to artefact, may not require quench |
| what are 1.5 and 3T machines best suited for | 1.5 - departments with space constraints or standard fusion workflows 3 - high precision contouring and multi-site RT workflows |
| MRI-sim staffing and responsibilities | 1. patient prep. explain procedure and safety screening, change into scrubs 2. scanning (admister contrast if needed, confirm coverage, assess qual and add sequences) 3. post-scan (discharge pt, send images to PACS and complete documentation) |
| Why are standardised sequences used in MR sim | - Standardised sequences for geometrically accurate images - Sequence optimisation Reduce variability |
| head and neck MRI sim | T1 and T2, contrast administered. challenges with claustrophobia and patient compliance, movement artefact |
| brain MRI sim | mask, pre and post contrast T1, T2 + flair for GBM |
| prostate MRI sim | single body coil and coil bridge, can scan before or after CT. B+B prep assessed on console if after CT. T2 localiser, T2 space and T1 diffusion. challenges with movement artefact (peristalsis) and timing of bladder prep |
| spine MRI sim | most patients in a full body vacbag - coil challenges. considerations around patient arm clearance |
| liver/abdo MRI sim | arms up in vacbag, replicate BH, 3D T1 vibe arterial, venous and delayed, T2 fat sat and DWI - contrast and in BH/FB LABOUR INTENSIVE |
| future focus for MRI sim | intra-treatment imaging and mid-treatment response assessment (weekly scans), MR only workflow (synCT), auto-contouring and functional MRI |
| positives and negatives of sCT workflow | pos: improved ST, reduced reg error, no IR, reduce patient appt, ED for dose calc without CT neg: requires robust site-based QA, not avail for all body areas, FOV limitations in larger pts, potential failure with unusual anat/metal |
| define CT | Computer-generation of sectional images using radiation transmission measurements obtained as the beam makes multiple projections through a section of the patient. |
| role of CT in oncology (general) | diagnosis, staging, sim, guidance for intervention, monitoring treatment response, follow-up |
| role of CT in RT | accurate determination of inhomogeneities, provides accurate structure identification, 3d/4d data and ct numbers for planning calcs, DRRs, CBCTs |
| Describe CT cross sectional images | Data that forms the CT slice are further sectioned into elements called pixels Width is x Height is y |
| Describe CT detectors | detectors convert x-ray photons into electrical signal, electrical signal is converted into digital signal and fed into the computer -> image reconstruction process |
| main components of CT | tube and housing, filters, collimators and detectors |
| define SFOV | = scan field of view - Diameter (40cm, 80cm) Determines how many detector rows we use |
| define DFOV | = display field of view 10 vs 20 If we display less we magnify SFOV should be = DFOV |
| define HU | numbers used to define relative attenuation coefficients for each voxel of tissue as compared to the attenuation coefficient of water |
| relo b/w LAC and beam energy (kVP) | Highest kvP = 120-140kvP where the LAC is consistent. Effective energy of the beam is 50-70keV |
| What is the effective energy of a CT beam | Imaging beams are heterogenous - not all photons have same energy EE is the energy of a poly-energetic beam that has the same penetrating ability as a mono-energetic beam of a specific maximum energy EE keV = 1/2 - 1/2 of max photon energy |
| CT numbers for bone, water, air | bone = 1000 (white) water = 0 (gray) air = -1000 (black) |
| describe CT window width and level | window width = how many shades of gray can we see at a specified window LEVEL (tunes in to region of interest) narrow window width = accentuates differences |
| How many diff WW/WL does a thorax CT require | 3 - one for mediastinum, one for lungs and one for ribs/calcifications |
| Lung window width / level | Level = -400 to -500 Width = 1000 |
| Bone window width / level | Level = 500, width = 2000 |
| Soft tissue width / level | Level = 50-60, level = 400 |
| What is MDCT | Multi-Detector Computed Tomography uses multiple rows of detectors to acquire, with high speed, detailed 3D cross-sectional images of the body's internal structures in a single, fast rotation |
| Describe helical scanning + advantages | continually rotating x-ray tube, constant x-ray output, uninterrupted table movement -> eliminates interscan delay, ability to optimise contrast administration, reduces respiratory mis-registration and motion artifacts |
| What is pitch | CT table travel distance per 360 rotation of the x-ray tube, divided by the x-ray beam collimation width When feed is identical, pitch = 1 (ideal) |
| How does changing pitch effect dose | Half pitch = 2x dose 2x pitch = 1/2 dose |
| How does pitch affect scan time | slower table movement (smaller pitch) = slower scan time faster movement (higher pitch) = faster scan time |
| describe pitch in mdct | pitch in mdct is the table movement per rotation divided by beam width. beam width is determined by multiplying the number of slices by slice thickness |
| problems of data acquisition in mdct | no defined slice, localisation of particular slice is difficult, projection data is inconsistent |
| how to reduce patient dose in CT | reduce scan vol, choose optimal technical factors for dose/quality, automatic tube current modulation, pitch, limit thin slices |
| function of SCOUT | define scan range, check for artefacts, ensure patient pos and alignment, radiation dose modulation (density data) |
| why does a scout have low mA | 20mAs = low = don’t need high anatomical detail, don’t want artefacts Single projection and direction (AP and LAT) |
| benefit of automatic dose modulation algorithms | It will modulate the dose to this unique patients shape - ensures adequate image contrast using the lowest dose possible |
| how does changing the kV affect the dose | Increased kV = increased penetration, less absorbed dose, more photons reaching detector - DECREASED PATIENT DOSE |
| disadvantages of MR-Linac | • Longer treatment times • Treatment is recalculated and adapted to suit the fraction • Machine limitations- Field size, positioning, • Patient selection • Cost +++ |
| Why is it good to use MR-Linac for adaptive treatment (NTCP and TCP) | If we can visualise tumour better, we can reduce margins, decrease NTT dose, increase radiation dose and increase TCP |
| Describe elekta unity | - Superconducting closed bore MR system - 1.5 Tesla magnet - High SNR and CNR - RF coils receive signal well from patient - B0 coils split into 2 interconnecting coils Small helium annulus connecting either end |
| What is the faraday cage | MR components need to be inside the faraday cage to stop RF interference from outside tx room. All linac components need to be outside cage to avoid interfering with MR image quality. Isolates linac and MR, maintaining full functionality of both systems |
| Workflow screening of MR Linac | Patients must be safety screened • At least three times • implants can be considered MR safe or MR conditional. • An abbreviated version is obtained before each fx • Mosaiq will not allow the linac to turn on until screening assessment complete. |
| MR Linac sim process in Townsville | Avoid skin to skin contact, obtain a reference CT and MR, suggest reference MR obtained prior to CT, reference MR position must match CT positioning, indexed positioning equipment. Positioning equipment must be MR safe |
| Reference MR image for MR Linac | - Images used for dose calculation need to include the whole patient contour - Larger FOV increases the scan duration - 3D image acquisition to reduce scan duration (may not be as crisp as a 2D image) Need to acquire daily treatment dataset |
| Why do we need a reference planning CT for MR Linac | Reference planning CT needed to derive electron densities System can do a pixel-by-pixel dose calculation Doses calculated on the MR use a bulk density correction for the region within the contour - e.g. bone bulk density, bowel bulk density |
| Due to Mr Linac fixed height and transverse couch position: iso considerations | needs to be close to target as possible and let MLCs do rest of the work Weary of beam entry through couch or coils, position of pipe -> IMRT beam arrangement |
| how does the geometric distortion of MRI images affecg PTV creation | Increases as distance from magnetic isocentre increases. -Might have to increase PTV size to ensure target volume is within. 20cm away from iso , additional mm margin |
| What is the electron return effect | Electron scatter effected by B0/Lorentz force observed at tissue-air boundaries. Causes inc surface dose at beam entry/exit and asymmetry of beam penumbra - backscatter into patient Can be modelled/controlled in TPS - multiple beams minimise effect |
| What is the ESE | Unobstructed electrons (e.g. exit scatter) travel in the direction of B0 (or opposite) More significant with an inclined or curved patient surface (especially HN, chest, extremities) CAN BE MITIGATED BY BOLUS |
| Describe ATP | Establish a virtual isocentre from rigid registration with daily MRI. No contours edited, same dose objectives as reference plan. Warm start calculation |
| 4 types of ATP | Original segments, adapt segments, optimise weights, optimise shapes |
| Describe original segments | Copies the original shapes from your reference plan to the new adapted isocentre and recalculates dose. Field weights and shapes remain unchanged. |
| Describe adapt segments | Segment aperture morphing is applied. Segments are adjusted to match the new target position relative to the reference plan. MU, beam weights and segment numbers the same |
| Describe optimise weights | SAM is applied. Segments are adjusted to the match the new target position and are reweighted. The number of segments is the same. Warm start parameters can be weighted to target or OAR |
| Describe optimise shapes | SAM is applied. Segments are adjusted to match the new target position relative to the reference plan. The shape of segments are optimised to suit the reference plan. Warm start parameters can be weighted to target or OAR |
| Describe ATS | Daily MRI registered with planning CT Establish "Virtual Isocentre" Allows deformable contour registration Contours can be edited In ATS we can plan off planning MRI, structures are forced to an assigned RED - important stage in planning |
| Describe cost functions in ATS | Full interaction with cost functions. Segment shape optimisation combines segments and refines to better match constraints. time increases in contouring, calculation and delivery |
| MR Linac patient monitoring | Verification MR prior treatment and post treatment Additional MR images can be acquired during the planning process Patient monitoring scan throughout treatment: Balance Fast Field Echo (bFFE) or • Balance Turbo Field Echo (bTFE) scan • 2D acquisition |
| Dose accumulation for MRgART | No strategies commercially available Difficult when irradiated volumes in one fx may not be relevant in next - max doses in diff locations each fx. Option: spatially warp dose dis for each fx onto primary image -> accurate sparing of OARs, dose esc |
| what is nuclear medicine | unsealed radioactive substances are administered (orally, IV, inhalation) in the form of a radiopharmaceutical for diagnosis and treatment of disease non-invasive imaging aimed at capturing functional and metabolic images |
| how do radioisotopes decay/become detected by the scanner | radioisotope decays to emit energy in the form of gamma radiation that can be detected by rhe gamma camera or PET/CT scanner scintillation detectors convert energy deposits to light signal -> electronic signal |
| how is radioactive decay quantified | Becquerel = 1 decay per second. Megabecquerels Half life is the length of time that it takes for an element to decay to half its activity |
| what emissions do we image in nuc med | gamma rays and positron decay - annihilation coincidence detection (2x 511 keV photons) must have sufficient energy to be able to penetrate greater than 10cm of tissue |
| discuss effects of high photon energy and long half life on image res | limits amount of activity we can administer results in lower photon flux -> additional imaging time -> compliance and motion artefacts -> reduced resolution |
| pitfalls of SPECT alone | low resolution leads to decreased reporting confidence, acquisition times long with motion problems, superimposition of structures with a lack of bony/anatomical landmarks |
| Role of SPECT/CT in RT | LDCT for attenuation correction, image co-reg and pathology localisation Easily imported into RT planning systems - improved delineation of GTV (incorp metabolic pathology) - define NTT and pathology -> dose sparing |
| radiation safety in nuc med | ALARA - LDCT - as low as practicable. interpretable images required but do not need to be high res TIME DISTANCE SHIELDING |
| patient safety in PET | rest the patient in a shielded room for uptake time - minimises public exposure and reduces FDG muscle uptake - half lives 68-2 hours means after procedure one half life has passed and pt safe to be in public |
| how are radioisotopes/radiopharmaceuticals created | created by bombarding stable target materials with subatomic particles in a nuclear reactor or particle accelerator, and then chemically tagging the resulting radioactive atoms onto specific biological carrier molecules |
| How does PET differ from SPECT in machine instrumentation | Ring of detectors with timing windows for better resolution in imaging (different to SPECT) |
| why is there more FDG uptake in malignant tissues | increased glyocolysis is a distinct marker of malignant tumours compared to normal tissue - over expression of membrane glucose transporters, especially GLUT1 - increased hexokinase activity - decreased levels of glucose-6-phosphate |
| What is standardised uptake value | simple reproducible index for quantifying glucose utilisation by measuring activity of tracer in organ (region of interest activity x body weight / injected dose) - value compared to liver may be influenced my image noise, low res, ROI bias |
| SUV of pathology | 2.0 - 2.5 |
| Describe PET/MRI | metabolic info from PET with superior soft tissue visualisation technical issues associated with PET detectors in magnetic field |
| what needs to be considered when performing a PET/CT for radiation therapy fusion | positioning -> arms up or down, head tilt, flat pallet or curved scanner pallet |
| what are the common pitfalls of molecular imaging that can affect RT planning accuracy | registration errors, brown fat, patient movement, differences in breathing patterns (breath hold vs FB), high density contrast agents |
| describe rigid reg vs deformal reg for PET/CT fusion to RT planning CT | LDDT fused to planning CT -> spatial transformation applied to respective PET (translation and rotation) deformable reg allows for fusion beyond trans/rot. they 'warp' PET data set to match reference image -> rigorous QA required |
| define theranostics | pairing PET/SPECT imaging agents to identify whether a cancer specific membraine protein is strongly expressed in a tumour AND a therapeutic radiopharmaceutical (alpha or beta emitting radionuclide) administered at a therapeutic dose level |
| describe FDG uptake process | FDG crosses cellular membrane via glucose transporters and is then phosphorylated by hexokinase. FDG does not undergo further and is trapped within the cell, allowing for imaging |
| areas of high and low FDG uptake | brain high uptake=cortical and cerebellar grey matter low=white matter and ventricular system liver, spleen, mediastinum (vessels), kidney, ureter, bladder, muscles and bone marrow variable: heart, stomach, uterus, thymus, oesophagus |
| prep for FDG pet | 6 hour fast, no exercise 24-48 hours, diabetics must discuss with dpt to ensure appropriate insulin levels |
| DO WE NEED TO KNOW DIFFERENT TRACERS FOR DIFFERENT AREAS/CANCERS / criteria etc | **********PROSTATE, meningioma ETC |
| describe alpha and beta radiation in theranostics | Alpha have higher energy and higher LET -> double strand breaks Beta primarily effects DNA by indirect formation of free radicals and reactive oxygen species. single strand breaks formed |
| how does molecular imaging allow target dose escelation | delineation of biologic tumour sub-volumes |
| how is PET/CT useful in GBM assessment response | MRI provides anatomical and structures info however RT treatment incuded changes are difficult to distinguish from profressive tumour. amino acid PET imaging can be a valuable tool that allows for differentation between pseudo and teue progression |
| why is MRI contrast used | alters appearance of tissues of interest to enhance clinically relevant info structures. Improves diagnostic confidence in: pathology, inflammation, infection, measurements such as relative perfusion/function |
| How does gadolinium affect normal flowing blood | Normally flowing blood has high free fluid content: long T1 recovery , dark on T1 Gadolinium changes the intrinsic frequency of blood much closer to the Lamor frequency, SHORTENS THE T1 recovery time of blood considerably -> brighter on T1 |
| What is the contrast enhancement proportional to | CONTRAST ENHANCEMENT OF TISSUE IS DIRECTLY PROPORTIONAL TO: - Local vascular concentration - Molar concentration and associated T1 relaxivity of the contrast agent Dependent on strength of main magnetic field |
| 3 common applications of contrast | basic enhancement vs non enhancement, dynamic contrast enhancement (using known vascular pathways and physiologic functions, arterial/venous phases), dynamic perfusion mapping (T1 or T2* changes over time) |
| patient consent form for gadolonium | survey on allergies and previous use, pregnancy risk, medical conditions, opp to ask questions |
| DO WE NEED TO KNOW ALL TYPES OF CONTRASTS | ************** |
| which patients are at highest risk of contrast reaction | Previous reaction to a gadolinium chelate, iodinated contrast, other medical or non-medical substances; Have asthma; Are pregnant Are lactating and/or Are patients with end-stage, severe, and (possibly) moderate renal failure? |
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jrichardss