Cancer Treatment: Radiotherapy

Question 1

total body irradiation

Answer 1

• having bone marrow/stem cell transplant
• leukaemias or lymphomas

Question 2

radiotherapy delivery methods

Answer 2

• radioisotopes (brachytherapy)
• radiolabelled compounds
• external beams (X-ray, charged particles)
• classical external beam uses X-ray

Question 3

conventional RT

Answer 3

• fractionated therapy (same efficacy BUT fewer side effects)
• each fraction given from a different direction, to minimise damage to surrounding tissues
• uses linear accelerators (LINACS)

Question 3

hypofractionation

Answer 3

• multiple fractions per day

Question 4

accelerated fractionation

Answer 4

• high doses over a quicker time

Question 5

when is RT used

Answer 5

• curative stand-alone treatment
• shrinking cancer before surgery (neo-adjuvant)
• reduce risk of cancer returning after surgery (adjuvant)
• complement chemotherapy
• control symptoms and improve QoL in palliative care

Question 6

brachytherapy

Answer 6

• can be used in most soft tissue tumours, most common are prostate/uterus/cervix
• insertion of radioactive isotope (usually iridium) beads directly in tumour
• alpha/beta emitters
• treatment lasts 2-5 days and patient remains in hospital for this time

Question 7

EBRT

Answer 7

• linac uses microwaves to accelerate electrons to produce high energy X-rays
• shaped as they exit by multi-leaf collimator
• conforms to shape of patients tumour
• beam can be rotated around patient so radiation can be delivered from range of angles

Question 7

intensity modulated radiation therapy

Answer 7

• uses computer-controlled linacs deliver precise radiation dose to tumour
• can use much higher doses on tumour but lowers overall effect on healthy tissues
• reduces treatment toxicity
• requires longer daily treatment time and additional planning and safety checks
• most used to treat prostate, head and neck and CNS cancers, but has been used in many others (eg. breast)

Question 8

RT toxicities

Answer 8

number, type and severity of side effects depends on treatment site, type of RT, total dose, does per fraction and overall treatment times
can cause both acute and chronic (progressive) side effects

Question 9

what does radiation damage

Answer 9

• DNA (double strand breaks)
• cell membrane and lipid peroxidation
• 2/3 damage comes from free radicals produced not the radiation itself

Question 10

common early side effects

Answer 10

• fatigue, skin problems, eating/digestion problems, nausea/vomiting, headaches

Question 11

late side effects

Answer 11

• rare
• permanent and progressive
• cognitive changes
• kidney changes
• joint problems
• spinal cord changes
• lung changes
• secondary cancer
• infertility

Question 12

X-rays and oxygen

Answer 12

• O2 enhances radiation effects
• peroxynitrite SSBs
• cannot be repaired
• hypoxic cells much more resistant to RT
• multiple fractions allows reoxygenation, allowing gradual killing of hypoxic cells

Question 13

sensitivity and cell cycle

Answer 13

• cycling cells more sensitive than non-cycling cells
• M phase most sensitive
• late S phase most resistant
• fractionating allows redistribution

Question 14

sensitivity and dna repair

Answer 14

• cancer cells more sensitive than halethy as often have damaged DNA repair genes

Question 15

4 Rs of RT

Answer 15

• reoxygenation
• redistribution
• repair
• repopulation

Question 16

5th R

Answer 16

• radiosensitivity
• immaure cells more sensitive
• as mitotic activity increases, so does radiosensitivity
• exception is lymphocytes