Dosimetric Verification in Radiosurgery with Linac Non-Coplanar ARC Beams

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Abstract
A method to verify the imparted dose to small brain lesions in radiosurgery treatments of non-coplanar arcs of radiation beams is presented. This technique consists of the assessment of the integral dose at an inner point of the head, obtained from surface measurements. With this aim, a hairband shaped device fitting the patient's head has been designed, which includes a line of thermoluminescence dosemeters (1 x 1 x 1 mm3, TLD-100). Moreover, a series of algorithms allowing the calculations of the target dose, derived from experimental measurements performed at the surface, has been elaborated. This procedure has been carried out in two steps: the first one, called the static model, establishes the relation between the readings registered by the TLDs and the dose at the reference depth, assuming fixed beams. The second part, called the dynamic model, takes into account the kinetics of the arc therapy. The results obtained in an experiment using a cylindrical phantom showed a mean discrepancy of 6.5% between the dose values calculated from the model and those found experimentally. Taking into account the great variety of sub-processes involved with this technique, this value can be considered acceptable.

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