Radiotherapy Dose Fractionation

Chapter 6 - The Essentials in Radiation Oncology for Brain Tumours

Radiotherapy Dose Fractionation

Standard RT practice: small daily fractions of 1.6–2.0 Gy per fraction up to 60 Gy in 30 fractions (being considered the limit of radiation tolerance with a risk of radiation-induced structural damage <5%). Increasing the dose or dose per fraction is associated with a marked increase in the risk of damage.

Toxicity-“equivalent” altered fractionation regimens:

  • Hypofractionation: larger doses per fraction over a shorter treatment time to an overall lower dose, OR
  • Hyperfractionation: Multiple smaller doses, generally twice a day over the same or shorter period.

Such regimens require testing for equivalent effectiveness in terms of survival and tumour control.

Adverse Effects of Radiotherapy

Fractionated RT is well tolerated, with principal acute side effects including hair loss and tiredness. Doses beyond tolerance can lead to radiation necrosis (more frequently seen following large single doses of radiation; it is uncommon following conventional fractionated RT).

Conventional doses may lead to mild functional impairment, noted as decline in cognitive function; it is more pronounced in young children, following treatment of large volumes of brain and with the use of large doses per fraction. Avoidance of hippocampus is being tested as a potential means of sparing cognitive function.

Cranial RT is associated with a small risk of developing a second radiation-induced tumour, and with an increased risk of cerebro- vascular accident (CVA).

Medical Management During Radiotherapy

Fractionated cranial RT is generally well tolerated without the need for prophylactic corticosteroids or anticonvulsants.

Low-dose corticosteroids such as dexamethasone can be used for symptoms of increased intracranial pressure and for apparent deterioration of a focal deficit specific to the site of the tumour, all assumed to be due to radiation-induced oedema.

For large single-fraction radiosurgery, a short course of corticosteroids is generally recommended. No specific treatment is required or recommended for post-treatment tiredness/somnolence, as this is a transient phenomenon with full spontaneous recovery.

Revision Questions

  1. What different fractionation regimens can be used for radical RT of malignant glioma?
  2. What dose of corticosteroids (dexamethasone) should be given during RT?
  3. Is hypofractionated RT safer or more toxic than conventional fractionated RT?

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Last update: 18 September 2017