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TrueBeam Small Field Dosimetry Using Commercial Plastic Scintillation and Other Stereotactic Detectors

R Pino

R Pino1*, F Therriault-Proulx2 , X Wang2 , J Yang2 , S Beddar2 , (1) Houston Methodist Hospital, Houston, Texas (2) University of Texas MD Anderson Cancer Center, Houston, Texas


SU-E-T-423 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

To perform dose profile and output factor (OF) measurements with the Exradin W1 plastic scintillation detector (PSD) for small fields made by the high-definition multi-leaf collimator (MLC) on the TrueBeam STx system and to compare them to values measured with an IBA CC01 ionization chamber and a Sun Nuclear Edge detector diode for 6 MV photon beams.

The Exradin W1 is a new small volume near-water equivalent and energy independent PSD manufactured by Standard Imaging, Inc. All measurements were performed in an IBA Blue Phantom water tank. Square MLC-shaped fields with sides ranging from 0.5 cm to 2 cm and jaw-shaped fields with sides ranging from 1 cm to 40 cm were measured using an SAD setup at 10 cm depth. Dose profile and percent depth dose (PDD) measurements were also taken under the same conditions for MLC fields 0.5x0.5 and 1x1 cm2 in size with jaws at 2x2cm2. The CC01 and W1 were vertically mounted.

OFs measured with the W1 for jaw only square fields were consistent with the ones measured with a Farmers PTW TN33013 ion chamber (1.8% maximum deviation). OF and penumbra measurement results are presented below. PDDs measured for all detectors are within 1.5% for the 0.5x0.5 cm2 and within 1% for the 1x1 cm2 MLC fields.
Output factors:
MLC size W1 CC01 EDGE
0.5cm 0.555 0.541 0.585
1.0cm 0.716 0.702 0.733
1.5cm 0.779 0.761 0.777
2.0cm 0.804 0.785 0.796
Penumbras (mm):
MLC size W1 CC01 EDGE
0.5cm 2.7 2.9 2.5
1.0cm 3.0 3.4 2.7

OFs measured for small MLC fields were consistent with the ones measured with the other stereotactic detectors. Measured penumbras are consistent with detector size. The Exradin W1 PSD is an excellent choice for characterizing MLC-shaped small beam dosimetry used for stereotactic radiosurgery and body radiation therapy.

Funding Support, Disclosures, and Conflict of Interest: Sam Beddar would like to disclose a NIH/NCI SBIR Phase II grant (2R44CA153824-02A1) with Standard Imaging, Title: "Water-Equivalent Plastic Scintillation Detectors for Small Field Radiotherapy"

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