Radiotherapy

Question 1

What is radiotherapy?

Answer 1

• Use of ionising radiation in the management of cancer
• Loco-regional treatment and therefore has curative potential in the absence of distant metastatic spread and may be delivered as the sole treatment modality

Question 2

What is the most common form of radiotherapy used in the UK?

Answer 2

• External beam radiotherapy using photons/x-rays most common

Question 3

Explain the science that underpinns how radiotherapy works?

Answer 3

• X-rays pentrate deep into body tissue
• they produce secondary electrons and free radicals which cause DNA damage to both cancer cells and normal cells
• Normal cells can often repair DNA damage and therefore survive
• Cancer cells unable to repair =cell detah at time of cell division or apoptotic cell death

Question 4

Explain how radiotherapy is delivered?

Answer 4

• Series of small doses called fractions rather than single large dose
• Number of fractions and dose (Gy) given in each fraction depends on treatment intent
• Radical/curative treatment require large doses of radiotherapy overall
• Palliative radiotherapy, primarily given to alleviate symptoms, delivered in smaller number of fractions and lower total dose

Question 5

What is done in the pre-treatment before radiotherapy is given?

Answer 5

1. Diagnosis and imaging
2. Discussion at MDT
3. Patient consents to radiotherapy
4. Patient immobilisation
5. Planning CT scan done

Question 6

What is done for planning the treatment of radiotherapy?

Answer 6

1. Disease delineation by clinical oncologist
2. Additional margins added for microscopic disease, treatment set up and motion
3. Complex treatment plans developed by medical physics team in collaboration with clinicians

Question 7

What is done in the treatment delivery and follow up of radiotherapy?

Answer 7

1. Patient attends for daily treatments
2. Treatment delivery and verification by radiographers monitored daily
3. Clinical review during treatment by clinicl oncologist/nurse
4. Long term follow up

Question 8

What is delineated on each CT slice? What margins are added?

• GTV
• CTV
• PTV

Answer 8

• Gross tumour volume
• Clinical target volume
• Planning target volume

Question 9

What are the acute side effects of radiotherapy? When can you develop them?

Answer 9

• Develop usually after first 5-10 fraction
• Side effects increase during treatment and hit peak in first few weeks
• Side effects:
  
  • localised skin reaction
  • oral mucositis
  • diarrhoea

Question 10

What are the late side-effects that develop from radiotheapy? When do they develop?

Answer 10

• Develop at least 3 months after radiotherapy and sometimes manifest years later
• Often irreversible and may wosen over time
• Side effects:
  
  • lont term toxicity : lung fibrosis, skin atrophy and infertility
  • Risk of second malignancy developing
  • teratogenic and should be avoided in woman who are pregnant

Question 11

What is brachytherapy?

Answer 11

Form of radiation treatment where radiation sources are placed within or close to the tumour. Allow delivery of localised high radiation dose to a small tumour.

Question 12

What are the two most common types of brachytherapy?

Answer 12

1. Intracavitiy: radiactive material placed inside body cavitiy i.e. uterus and cervix
2. Interstitial: material put into target i.e. prostate

Question 13

What are radioisotoped? USed in which cancer?

Answer 13

• Is an unstable form of a chemical element, which emits radiation when it decays and therefore is another method of radiation delivery
• Most commonly used form is radioactive iodine, used in thyroid cancer