Radiotherapy

Question 1

what is radiotherapy?

Answer 1

treatment of cancer using ionising radiation, such as x-rays, gamma rays, high energy electrons and protons

Question 2

what are the principles of radiotherapy?

Answer 2

• mutation and abnormal proliferation of cells; malignant
• cellular level; main problem is spread
• ionising radiation imparts energy to cells = particles to be released from atoms
• RT disrupts biological molecules and has potential to kill cells
• DNA damage

Question 3

DNA damage

Answer 3

two types, direct and indirect
- mainly indirect; water molecules in and around cells impacted by radiation to produce free radicals
- may interact with O2 = more damage to cells as superoxide radicals
- ideal is to create ds-break of polynucleotides in DNA
- harder to repaid + multiple ds breaks = cell death

Question 4

radiotherapy and the cell cycle

Answer 4

• cancer cells tend to divide more frequently than normal cells
• cell cycle repeat more often
• most sensitive in M-phase chromosomes dividing / DNA replication
• G1 phase in which cell gets ready for DNA synthesis, S-phase DNA replication, G- phase when cell prepares for mitosis, M-phase where cell division takes place

Question 5

what happens to normal cells during RT treatment?

Answer 5

• damaged too
• fractions of radiation = ds breaks too
• sub-lethal damage can be better repaired by normal cells
• fractionation allows normal cells to recover
• damage to normal cells = toxicities

Question 6

what are toxicities or side effects of damage to normal cells?

Answer 6

• acute or early; during RT and up to 6 weeks after
• chronic or late; after 3 months of completeing RT
  impacts quality of life and survivorship

Question 7

what are the 4R’s of radiobiology?

Answer 7

• repair
• repopulation
• reassortment
• reoxygenation

Question 8

radiobiology; repair

Answer 8

normal cells better at repairing DNA damage than cancer cells. Fractionantion enables repair.

Question 9

radiobiology; repopulation

Answer 9

by tumor cells with sublethal damage. Each fraction must cause more damage to tumor cells than it can repopulate. Normal cells also repopulate

Question 10

radiobiology; reassortment

Answer 10

of cells into different stages of cell cycle (M phase) due to fractionation enables more cells to be damage

Question 11

radiobiology; reoxygenation

Answer 11

tumors can have hypoxic centres, O2 essential for superoxide radicals (indirect damage). Fractionation enables oxygenation (also Hb crucial).

Question 12

what acute toxicities arise from damage to normal cells?

Answer 12

• tissues with fast turnover = toxicities sooner
• can be short lived and patients recover
  -Radical RT trade off toxicities for cure. Minimise or palliative
• consent and careful person-centred management

Question 13

what late toxicities arise from damage to normal cells?

Answer 13

• less frequent cell cycle rates
• remain with patient so much be minimised for radical, less crucial for palliative
• consent (can cause malignancy for <1%)

Question 14

future for RT treatment

Answer 14

• adaptive plan of the day
• personalised RT
• shorter treatment courses
• early detection standard
• prevention
• survivorship
• QoL