Arc Therapy – The Next Big Thing in Radiation Therapy

Radiation therapy is all about management of side effects while delivering a curative dose to the tumour site. The advent of ‘arc therapy’ for the treatment of brain tumours is a huge step forward in minimising healthy tissue radiation exposure while still effectively treating the tumour site.

In radiation therapy, the ultimate outcome is to deliver a maximum dose of radiation to the tumour site with the surrounding tissues receiving no exposure. In real life this is next to impossible independent of the radiation modality used (both kilovoltage or megavoltage external beam delivery modalities experience this problem under different conditions). Surrounding tissue cannot be conveniently ‘removed’ during irradiation and inevitably some exposure to healthy tissue occurs.

The introduction of a new technique termed ‘arc therapy’ has provided a breakthrough in radiation therapy at the Southern Animal Referral Centre. Arc therapy is used in the treatment of brain tumours and employs a device which safely rotates the head around an axis centred on the tumour. Lasers and CT imaging are used to position the patient and rotation axis isocentrically around the tumour. The device then continuously rotates the head around an arc for the duration of treatment.

In the recent past brain tumours have been treated from three different aspects (two lateral and one dorsal) with a total of three beams. This technique meant that the skin and surrounding healthy tissue exposed to each beam received only one third of the radiation dose as compared to a single beam protocol. The tumour still received the full dose.

Arc therapy provides a further improvement to this technique by further distributing the radiation exposure of healthy tissue over an arc of almost 180 degrees while still maximising the exposure to the tumour site.

The arc therapy technique means that healthy cranial tissue receives even less exposure to radiation than a multiple-beam technique. This further decreases side effects to surrounding healthy tissue while still delivering a curative dose to the tumour site.

For brain tumours, the median survival time for dogs and cats with radiation therapy is 18 months. Without radiation therapy the median survival time is 2 months.

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