Principles of radiotherapy

Question 1

What is radiotherapy?

Answer 1

Using ionising radiation to treat cancer and sometimes benign disease like pituitary adenomas

Question 2

What is the units of radiation?

Answer 2

Gray (Gy)

Question 3

How does radiotherapy work?

Answer 3

-The x-ray penetrate tissue
- Loosely bound electrons are knocked out of orbit, free radicals are formed, chemical bond are broken
- This causes damage to DNA that then results in cell death

Question 4

What are the 2 types of radiation waves used in radiotherapy?

Answer 4

X-ray and Gamma rays

X-rays are man made
Gamma rays are emitted from a radioactive isotope

Question 5

What are the different methods of giving radiotherapy?

Answer 5

External Beam radiotherapy (most patients)

Brachytherapy
- Applicators inserted into tumour or into body cavity
- Permanent e.g. 125-Iodine seeds implant for prostate cancer
- Temporary e.g. applicators inserted into uterus and vagina to treat cervical cancer with192Iridium

Question 6

What are the different indications for radiotherapy?

Answer 6

• Curative therapy for primary tumour
  Eg. lung, prostate, cervix, skin, head & neck, bladder, lymphoma
• Adjuvant therapy after surgery to primary and/or regional lymph nodes
  Eg. breast, lung, endometrium
• Palliative therapy
  Eg. bone metastases, local recurrences, fungating tumours
  -Total Body Irradiation
  Eg. Leukaemia → kill off all white cells in bone marrow → bone marrow transplant

Question 7

What are the doses for radiotherapy?

Answer 7

• Radical doses (curative intent):
  60 – 70 Gy (solid tumours)
  40 Gy (lymphoma) must be given in small daily fractions (max 2 Gy) so radical treatments take 6 – 7 weeks
• Palliative doses:
  8 Gy single fraction (#) for a bone metastasis
  20 Gy in 5 fractions for many other sites

Question 8

What is the mechanism behind late radiotherapy reactions?

Answer 8

• The inflammatory response to the damage caused by radiation resulting in microvascular damage and fibrosis
• There is continued cell loss

Question 9

What are some examples of late effects of radiotherapy?

Answer 9

• cataracts as a child (RT)
• Bilateral slipped femoral epiphyses as a child (steroids)
• Hypothyroidism developed as a child (RT)
• Primary ovarian failure (RT and chemo)
• Hypertension and mild renal impairment (probably both)