Program Information
Suitability Study of a Unique 3D Dosimeter for Commissioning Radiation Treatment Machines
Y Roed1,2*, R Tailor2 , L Pinsky1 ,G Ibbott2 , (1) University of Houston, Houston, TX, (2) UT MD Anderson Cancer Center, Houston, TX
Presentations
SU-E-T-716 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose:
To determine the suitability of a methacrylic acid-based MAGAT gel dosimeter to serve as a 3D commissioning tool
Methods:
Different sized MAGAT gel dosimeters were fabricated in-house to perform dose response, depth dose and dose rate measurements using an orthovoltage treatment unit. Dose response data were obtained by irradiating dosimeters to six dose levels at three different effective beam energies. Depth dose measurements were taken using one dose at one energy. Dose rate dependence was measured by varying only distances for the gel irradiations while dose level and energy remained unchanged. A Bruker Biospecs 4.7T MRI scanner was used to acquire spin-spin relaxation rates on axial slices at different depths throughout each dosimeter 24h after irradiation.
Results:
The dose response curves exhibited a separation when compared for the measured energies. MAGAT depth dose data, normalized to ion chamber data at 2 cm depth, showed an increasing divergence with increasing depth. The dose rate decreased when distances were increased and demonstrated a significant dose rate dependence of the measurements. Consequently, dose rate corrections were applied to all measurements, thus, aligning the dose response curves for all three energies and reducing the divergence between MAGAT and ion chamber depth dose data.
Conclusion:
The MAGAT dosimeter was intended to serve as a 3D commissioning tool for testing radiation treatment plans of small fields with steep dose gradients and complex treatment volumes. A suitable detector for commissioning needs to be dependent on dose but independent of dose rate. This study, however, showed a dose rate dependence of up to 30% eliminating the current composition of MAGAT as a suitable dosimeter. Further investigations of chemical compositions need to be performed.
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