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Radiobiology
| Question | Answer |
|---|---|
| Acute effects | Determined by fraction size AND overall treatment time |
| Late effects | Determined primarily by fraction size |
| Kick in time | - Refers to the acceleration of repopulation in H&N cancers after 28 days - H&N cancers and other fast-growing tumours should finish the radiation course no more than 28 days after day 1 - Better to delay treatment start than introduce delays during |
| Standard fractionation | 1.8-2Gy |
| Hyperfractionation | - Smaller doses per fraction (>1.8Gy) - Delivered more than once a day - Increased opportunity for redistribution and reoxygenation - Lower OER - Different sparing of late-reacting normal tissues |
| Accelerated fractionation | - Standard fraction dosage is delivered in a shorter overall treatment time - e.g. bidaily - Spares early reactions - Allows adequate reoxygenation in tumours - Increase in locoregional control and late effects |
| Accelerated repopulation | - Treatment with any cytotoxic agent can cause surviving tumour cells to divide faster than before - Therefore, a longer overall treatment time compromises the effectiveness of the later fractions |
| Hypofractionation | - Higher dose per fraction - Delivered once a day or less e.g. prostate patients 60Gy in 20 |
| Unscheduled interruptions | - SCC H&N and lung patients can have reduced local control of 1-1.4% with just a one-day interruption - ^^ patients should not have a treatment course >42 days |
| causes of unscheduled interruptions | 1. Machine and staff availability (breakdowns) 2. Public holidays 3. Transport problems (ambulance, transport services) 4. Medical problems 5. Social circumstances |
| Minimising effects of interruptions | 1. Adequately staffing 2. Treating bidaily before public holidays/weekends 3. Efficient communication with ambulance services 4. Management of side effects 5. Psychological and support work |
| Category 1 patients | Refers to radical patients with tumours that have significant prolongation affects - H&N SCC - Lung NSCLC and SCLC - Oesophageal cancers - Medulloblastomas - Anal SCCs |
| Category 2 patients | Refers to slower growing radical tumours whose treatment should not be prolonged more than 2 days - Bladder TCC - SCC of the cervix |
| Managing interruptions for category 1 | - Category 1 patients should be moved to another machine (no breaks ideally, better for patients with complex plans and machine dependencies to be converted to a conventional plan instead) |
| Managing interruptions in general | - Accelerated scheduling: BDs (unless fraction size is > 2.2Gy) - Increase total dose/dose per fraction by delivering more Gy per fraction or adding extra ones |
| Considerations | - Conccurent chemo (should BDs be delivered on the same day?) - Previous treatment - SABR - Proton/brachy |
| Radioprotectors | - Chemicals that reduce the biological effects of radiation - Exert their effect by scavenging free radicals and thereby reducing the free-radical damage to DNA - Most effect for IR characterised by low LET |
| Radiosensitisers | - Chemicals that increase the biological effects of radiation e.g. chemo |
| Retreatment | - Techniques like SABR, brachy and stereotactic radiosurgery are best, consider: 1. Initial chemo 2. Time since 3. Tissues and organs involved - Reirradiation of 50-60Gy within a few years or initial RT improves local control but with severe toxicity |
Created by:
chloe.donaldson