Radiotherapy Flashcards
Can radiotherapy be a sole treatment modality?
Yes i.e. prostate cancer
Can radiotherapy be used throughout all cancer treatment?
Yes - it can be used neoadjuvantly, adjuvantly, in palliation, as a primary treatment, and in conjunction with chemotherapy
Explain the science behind radiotherapy
X-rays are high energy with a short wavelength.
They are delivered by a linear accelerator (LINAC).
X-rays produced secondary electrons and free radicals that cause DNA damage (to cancer and normal cells)
Normal cells can repair damage and survive, cancer cells cannot.
What is a radiation dose denoted by?
the unit Gray (Gy)
Describe a common radiotherapy schedule for a H&N cancer patient with curative intent
70Gy in 35 fractions over 7 weeks
Describe some factors that influence the level of tumour kill and toxicity of radiotherapy
- treatment issues - total dose, overall treatment time etc
- co-morbidities - diabetes, smoking
- Intrinsic radio-sensitivity of the tumour, tumour hypoxia, tumour re-population
Which tumours are radiosensitive?
Seminoma, Hodgkin’s
Which cancer is relatively radio-resistant even at high doses?
Glioblastoma multiform
What is chemotherapy called when given along side radiotherapy?
Concurrent chemotherapy
What are the advantages of using concurrent chemotherapy?
- Improves efficacy of the radiotherapy treatment without having to significantly increase the dose of radiotherapy
- Makes the cells more sensitive to radiation
What are the disadvantages to concurrent chemotherapy?
These regimens are associated with increased radiation-related side effects
What is the most common external beam radiotherapy in the Uk?
3D-conformal radiotherapy
What does 3D-conformal radiotherapy entail?
The patient has individually planned radiotherapy based on the 3D shape of their tumour
Needs to be in the same position - may need head mask or tattoos
How is the tumour target defined?
The gross tumour volume has a margin added for microscopic disease spread = clinical target volume
Another margin is added to allow for minor daily variations in patient and tumour position = planning target volume
What is the planning target volume?
The total area of tissue being irradiated - combines the clinical target volume, with another margin to allow for minor patient movement
What are side effects in radiotherapy related to?
The anatomical area being irradiated i.e. the thorax will not cause diarrhoea
When do acute side effects occur?
Usually after 5-10 fractions
Describe acute side effects
Tend to increase during treatment and peak in first few weeks
Generally reversible
Examples oral mucositis, diarrhea, skin reactions
Describe late reactions
Develop 3 months after radiotherapy and sometimes years later
Often irreversible and worsen over time, difficult to treat, need MDT and sometimes surgery
Examples of late side effects
Fibrosis, blood vessel damage, lung fibrosis, skin atrophy, infertility
Who has the highest risk of developing a secondary malignancy due to radiotherapy?
Younger patients treated for a good prognosis cancer
Can radiotherapy be given to pregnant women?
No - it is teratogenic (causes birth defects)
What is brachytherapy?
A form of radiation where radiation sources are placed within or close to the tumour
What are the advantages of brachytherapy?
allows delivery of a localised high radiation dose to a small tumour volume, increasing the chance of tumour control, whilst minimising the dose to surrounding normal tissue.
What cancers are commonly treated by brachytherapy?
Prostate cancer, gynaecological cancers, oesophageal cancer and H&N
What are the two main types of brachytherapy?
Intracavity - the radioactive material is placed inside a body cavity such as the uterus and cervix
Interstitial - where the material is put into target, such as the prostate
What advice does a patient receiving brachytherapy need?
They are radioactive, having radioactive substances inside them - no sex etc.
What is a radioisotope?
A radioisotope is an unstable form of a chemical element, which emits radiation when it decays and is another method of radiation delivery.
What is the most commonly used form of radioactive iodine?
I-131
What cancer is I-131 used in?
Thyroid cancer
What happens after someone has had I-131?
They must remain in a lead lined room for 4 days or until the radiation they are emitting is low enough to not to provide risk to others
