Radiation Therapy Flashcards
What are the three indications for radiation therapy?
Incompletely resected tumours, Non-resectable tumours and pain control.
How does radiation therapy affect cells?
Direct and indirect damage to DNA (direct to DNA, and indirect by producing free radicals which then damage DNA).
What are the three possible pathways a cell can take when hit with radiation? Which is desirable?
1) Proliferation of cells (undesirable)
2) Cell death (most desirable)
3) Alive but unable to divide (beneficial in RT)
In what unit is radiation measured? How does the amount of grey’s delivered affect the cell response?
Grey’s. 10Gy-100Gy to cause intermitotic death.
What are the 4R’s of radiation?
Repair, repopulation, re-oxygenation and redistribution.
What is fractionation?
The total dose of radiation used to treat a tumour is usually divided into a number of fractions.
Why is fractionation important? How do the 4R’s fit in?
Fractionation spares normal tissues because it allows REPAIR of sublethal damage and REPOPULATION. It increases damage to tumour cells because of REOXYGENATION and REDISTRIBUTION.
How does fractionation help the repair of normal tissues?
It is assumed that tumour cells are less able to repair DNA. Therefore by adding another dose, it spares repaired normal cells, and kills non-repaired tumour cells.
How does fractionation help the repopulation of normal tissues?
RT can stimulate cell division by cells by “accelerated repopulation”. In normal tissues, this is kept under control by homeostatic mechanisms.
How does fractionation help to increase the damage to tumour cells by reoxygenation?
Tumour has poorly oxygenated necrotic centre which is not radiosensitive. Oxygenated cells are radiosensitive, between doses it allows necrotic centre to become oxygenated.
How does fractionation help to increase the damage to tumour cells by redistribution?
Cells are more radiosensitive to RT in M/G1/G2. Time between doses gives time for cell to move from S to more sensitive stages.
What types of radiation can be used in radiotherapy? Which machines can use them?
Orthovoltage: Photons (X-rays), not really used.
Cobalt-60: Photons (Gamma rays)
Megavoltage “Linear accelerator”: Photons (X-rays) or Electrons.
What are the characteristics of using photons in radiotherapy?
Highly penetrative, slow dose reduction, penetrates normal tissue. Needs CT based treatment planning. Fixed energy.
What are the characteristics of using electrons in radiotherapy?
Various energies, not very penetration, good for superficial use. e.g. injection site sarcoma. Rapid dose reduction.
What is the protocol in curative radiation therapy? What kind of side affects does curative RT produce?
More low doses, usually has ACUTE side effects rather than late side effects.
What are the absolute indications for curative radiation therapy? What kinds of tumours would it be used as the primary treatment?
When RT shows better results than other therapies. Primary Tx in Nasal tumours, brain tumours (palliative doesn’t work), oral tumours (SCC), epulis.
In what types of tumours is curative radiation used as post surgery adjuvant RT?
Soft tissue sarcomas, feline injection site sarcoma (usually needed to cure)
What is the protocol in palliative radiation therapy? What kind of side affects does palliative RT produce?
Few big fractions used, more likely to cause late effects, but usually don’t expect them to live that long.
What two types of radiation therapy protocols?
Curative and palliative.
What types of tumours might you use palliative radiation therapy on?
Radiosensitive tumours that are highly metastatic e.g. histiocytic sarcoma, oral melanoma, haemangiosarcoma, MCT grade III
