SU-F-T-170: Patient Surface Dose Measurements Using Optically Stimulated Luminescence Dosimeters in Scanning Proton Beam Therapy for Breast Cancer

Authors


Abstract

Purpose:

To establish patient surface dose dosimetry for scanning proton beam therapy (SPBT) for breast cancer using optically stimulated luminescence dosimeters (OSLD).

Methods:

OSLDs were calibrated with SPB under the similar conditions as the treatments for breast cancer. A range shifter (RS) of 5 cm water equivalent thickness (WET) was used. The air gap from the surface of the range shifter to the surface of the phantom was 15 cm. A uniform planar dose generated by nominal energy of 118 MeV was delivered. The range of 118 MeV proton beam after the 5cm RS is approximately 5 cm in water, which is the common range for breast treatments. The OSLDs were placed on the surface of high density polyethylene slabs, and a bolus of 1.06 cm WET was used for buildup. A variety of dose levels in the range of 0.5 to 8 Gy were delivered. Under the same condition, an ADCL calibrated parallel plate (PP) chamber was used to measure the reference dose. The correlation between the output signals of OSLDs and the reference doses was established. The calibration of OSLD was verified against the PP chamber measurements for two SPBT breast plans calculated for two patients.

Results:

the least squares fitting for the OSLD calibration curve was a polynomial function to the order of 2 in the range of 0.5 to 8 Gy (RBE). The differences between the dose measured with OSLDs and PP chamber were within 3% for the two breast proton plans.

Conclusion:

the calibrated OSLDs under the similar conditions as the treatments can be used for patient surface dose measurements.

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