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Low Measurement Variation Small Field Dosimetry: A Practical Method to Measure Dose Area Products (DAP)

M Held

M Held*, A Sudhyadhom , UCSF, San Francisco, CA


SU-I-GPD-T-545 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To minimize the variation of small field dosimetry by evaluating a method to acquire dose area products (DAPs) using commercially available hardware and software.

Methods: Four commonly used small field radiation detectors (PinPoint3D ion chamber, W1 scintillator, EDGE Detector diode, and microDiamond) were used to measure the small field DAPs on a cone-based radiosurgery system. A large uniform field of irradiation was created as the composite of a semi-continuous distribution of hundreds of small-field beams. The dosimeters were placed inside a phantom using custom-built stereotactically localized cubes for each device. DAPs and single point output factors (SPOFs) were measured for field sizes down to 7.5 mm for each dosimeter.

Results: The PP3D, W1, and EDGE all measured small field DAPs consistent with each other to within 2% for all delivered fields. The scintillator showed a 50% deviation for the 7.5 mm field DAP. Out-of-field measurements showed a highly non-linear dose response for the scintillator for low dose-rate radiation compared to the other detectors. Comparable SPOFs spanned a range of 16% for the 7.5 mm field across these devices.

Conclusion: In this work, we show that small field DAP-based measurements can be acquired using commercially available hardware and software. These measurements may be dosimeter independent as long as the dosimeter does not exhibit non-linear dose rate dependence. The PinPoint3D ion chamber, microDiamond, and EDGE detector were found to be suitable devices for these DAP measurements. The scintillator shows large variation between in- and out-of-field dose linearity and may not be suitable for small field DAP measurements, most likely due to a dose-rate dependence for out-of-field/low dose-rate radiation. DAP dosimetry has the potential to increase the accuracy and decrease the variability of small field dosimetry.

Funding Support, Disclosures, and Conflict of Interest: This work was in part supported by Sun Nuclear Corporation.

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