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Investigation of a Synthetic Diamond Detector for Tomotherapy Dosimetry

C Knill

C Knill1*, V Zakjevskii2 , A Nalichowski1 , R Halford1 , M Snyder1,2 , L Zhuang2 , J Burmeister1,2 , (1) Karmanos Cancer Institute, Detroit, MI, (2) Wayne State University School of Medicine, Detroit, MI


SU-E-T-485 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Tomotherapy treatments are characterized by rotational deliveries of flattening-filter free fields resulting in high-gradient dose distributions. Small volume, rotationally independent detectors are needed for accurate dosimetry. PTWs microDiamond detector, with its small sensitive volume (0.004mm³), could potentially be an ideal detector for Tomotherapy. The microDiamond detector was tested against a small volume Exradin A1SL ion chamber for Tomotherapy open-field and IMRT commissioning measurements.

Methods: Custom detector holders were fabricated to allow A1SL and microDiamond measurements in the Tomotherapy Cheese phantom and a square solid water phantom. The microDiamond rotational dependence within the Tomotherapy phantom was tested by incrementally rotating the detector in between static-gantry angle Tomotherapy irradiations. Longitudinal Tomotherapy profiles, for all field sizes, were measured with the microDiamond and A1SL detectors at 1.5cm depth in the square phantom, and compared to film. Detector axes were aligned parallel to table motion. Per TG-119 recommendations, both detectors were calibrated to known doses in phantoms and used to measure high-dose points in TG-119 H&N and Prostate plans. The measurements were compared to the treatment planning system and subsequently compared to published TG-119 confidence limits.

Results: The microDiamond angular dependence was less than 0.5%. The average difference between the detectors and film-measured longitudinal profile 80-20% penumbras were 0.03+/-0.04mm and 1.36+/-0.22mm for the microDiamond and A1SL, respectively. The average difference between the detector and film-measured field sizes were 0.07+/-0.01mm and 0.09+/-0.02mm for the microDiamond and A1SL, respectively. The measured confidence limits were 0.023 and 0.015 for microDiamond and A1SL, respectively. TG-119 reported a confidence limit of 0.034.

Conclusion: The microDiamond measured open-field longitudinal Tomotherapy profiles more closely resembled film measurements, compared with the A1Sl chamber. Furthermore, the microDiamond was shown to have low angular dependence and both detectors were able to accurately measure the high-dose points in TG-119 H&N and prostate plans.

Funding Support, Disclosures, and Conflict of Interest: Our institution has research grants with PTW.

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