Radiotherapy Flashcards
Mechanism of radiotherapy
Direct: electron breaks DNA, induces mitotic cell death at time of cell division
Indirect: electrons produce free radicals
Define gray (gy)
Amount of energy deposited (joule/kg)
Represents dose
Define fraction
Number of doses given?
Neo-adjuvant radiation
Given prior to curative treatment
Definitive radiation
Main curative modality
Adjuvant radiation
After curative treatment
Examples of contexts for neo-adjuvant therapy
Rectal cancer: treat pelvic LNs prior to surgery
Soft tissue sarcoma: eradicate microscopic disease prior to surgery
Oesophageal cancer: downsize tumour prior to surgery
Examples of contexts for adjuvant therapy
Breast cancer: post-op to treat microscopic disease
Head and neck cancer: after neck dissection to trat microscopic disease
Lymphoma: treat sites of original bulky disease
Radical radiotherapy
Intent to provide cure Higher doses (50-80 gy) over shorter treatment time
Palliative radiotherapy
Intent to provide symptom control, not cure
4 indications for palliative radiotherapy
Pain relief
Control of fungation/ulceration
Reduction of mass effect
Haemostasis
Dose per fraction traditionally 2Gy/day. Why?
Radiobiology!
4Rs of radiobiology
Repair
Redistribution
Reoxygenation
Repopulation
Repair
DNA can be repaired post-radiation; normal cells repair radiation damage, unlike tumours (repair mechanisms impaired)
Maximal time for repair is 4 hours (can double up on one day)
Redistribution
Different phases of cell cycle have variable radiosensitivity
Giving radiation of days means that previously resistant cells may be sensitive on another day and be knocked out then; more are killed when treatment is fractionated
