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Application of the Dose Magnifying Glass to Proton Radiosurgery

A Wroe

A Wroe1*, J Wong2, A Teran1, M Lerch2, M Petasecca2, R Schulte1, A Rosenfeld2, (1) Loma Linda University Medical Center, Loma Linda, CA, (2) University of Wollongong, Wollongong, NSW,

TH-A-137-3 Thursday 8:00AM - 9:55AM Room: 137

Purpose: To evaluate the performance of a pixelated-Silicon detector for proton radiosurgery applications and determine a methodology for response correction as a function of proton energy/LET.

Methods: Proton radiosurgery requires metrology apparatus that have a high spatial resolution and a stable (or well characterized) response to LET. To meet this need the dose magnifying glass or DMG was developed at the University of Wollongong. This device is a pixelated silicon strip detector comprising an array of 128 phosphor implanted n+ strips on a p-type silicon wafer. A 100μm pitch device was tested with proton radiation to evaluate its performance. The DMG was mounted in a water tank and irradiated with various discrete energies to develop correction factors as a function of proton energy. Depth dose and lateral profiles of various proton radiosurgery beams were then collected for comparison with standard metrology techniques.

Results: The DMG performed well providing real-time depth dose and lateral profile information. The device did over-respond to proton dose especially below 100MeV resulting in over-estimation in the spread-out Bragg peak region of almost 30%. This over-response could be accounted for using a power law correction, the parameters of which were established for a range of discrete proton energies down to 20MeV. Using the central channel of the DMG, accurate depth dose profiles proton fields to 1mm diameter were obtained without errors associated with partial volume sampling, while the full array could be used to provide real time profile information of fields below 1.5cm diameter without the need for detector scanning.

Conclusion: The DMG is a potentially useful device for proton therapy, in particular in providing real-time data for small fields associated with SRS. Further work is required to better characterize the performance of the device as a function of depth/LET before it can be used clinically.

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