Advantages of brachytherapy

The probability of local tumour control increases with increasing radiation dose, however, so does the probability of normal tissue damage. Brachytherapy allows the delivery of a highly localized radiation dose to a small tumour volume, increasing the chance of local control. There is a sharp fall off of radiation dose in the surrounding normal tissue, therefore, the risks of complication are reduced.

The overall duration of brachytherapy is relatively short, and can vary from a minute or two to several days depending on dose rate, prescribed dose and treatment distance from the radiation source. Constant low dose rate irradiation (below 1.0 Gy/hr) takes advantage of the different rates of repair and repopulation of normal and malignant tissue to produce differential cell killing. Hypoxic cells are relatively resistant to radiation treatment. Reoxygenation may occur during low dose rate radiotherapy with initially resistant hypoxic cells becoming well aerated and sensitive. Often in brachytherapy treatments, the dose distribution within tumour volume is not homogeneous. Treatment is often prescribed to the minimum dose received around the periphery of the treated volume. Areas close to the radiation sources in the centre of the tumour volume often receive up to twice this dose. Hypoxic cells are situated in avascular, sometimes necrotic, areas in the centre of tumours and the higher doses received here help to compensate for the relative radioresistance of these hypoxic cells. Irregular shaped tumours can be treated by judicious positioning of radiation sources and critical surrounding normal tissues can be avoided. At higher dose rate (above 12.0 Gy/hr) the radiobiological issues considerations are similar to those of external beam treatments.

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