Luc BEAULIEU
Université Laval

Scintillating Optical Fibers as High Precision, Small Area Dosimeters in Radiation Therapy

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Radiotherapy treatment planning aims at delivering a high and uniform dose to the target volume while sparing surrounding normal tissues as much as possible. With the advent of Intensity Modulated Radiation Therapy (IMRT) the tumors can be literally dose-"painted". However with such a precision, quality assurance (QA) has become a long and tedious process. IMRT involves a large number (over 100) of small segments. Each segment can have low (1 cGy) to high (few tens of cGy) dose levels. While QA processes are necessary to experimentally confirm the dose predicted by treatment planning algorithms, only a limited number of solutions are available for the simultaneous measurement of the absolute dose in multiple points with a high spatial resolution.

We are proposing a new solution to this problem by building an absolute dose detection system based on scintillating optical fibers. Such detectors can have a very small detection volume, can be used in various geometries and can be scaled up to easily include a few hundreds individual units. Moreover, scintillating fibers are water-equivalent (the medium of reference in radiation therapy) and cost only a few cents per mm. A consistent and elegant solution to the problem of substracting the Cerenkov light production (noise on the measurements) has been found. The method is based on the simultaneous measurement of the light output using color filters. Furthermore, using a CCD camera solves the problem of reading hundreds of such detectors in a simple and easy-to-use form.

*In collabaration with: L Archambault Université Laval et Centre Hospitalier Universita,L Gingras Université Laval et Centre Hospitalier Universita,R Roy Université Laval.