SU‐GG‐T‐303: Evaluation of An Implantable MOSFET Dosimeter for Use with Hypo‐Fractionated External Beam Treatments

Purpose: Evaluate the performance of an implantable MOSFET dosimeter designed for hypo‐fractionated protocols. Method and Materials: The DVS® implantable dosimeter has been developed for use with external beam radiotherapy. A new version is currently under development for use with hypo‐fractionated protocols (DVS‐HFT*). This dosimeter is pre‐calibrated for use at body temperature in a dose per fraction range of 340–1200 cGy. The dosimeter response was evaluated in a water phantom at 37°C to validate the accuracy as a function of dose. Since delivery times for high dose fractions can vary, a study of the response as a function of treatment time was performed. In addition, dose rate dependency for high doses was evaluated. Final dosimeter accuracy was validated by delivering simulated hypo‐fractionated treatments on a body phantom at 37 °C. Two dosimeters each (total six) were irradiated inside the phantom with a breast BID plan at 340 cGy per fraction (10 fx), two prostate IMRT plans at 700 cGy per fraction (5 fx) using 6 MV and 18 MV. Results: The dosimeter had minimum dependency on dose fraction size from 340 to 1200 cGy. Phantom testing found a response accuracy of <6% for 50 dosimeters tested with different doses and fractionation schemes. Dose rate dependence measurements in the range of 300 to 600 MU/min showed <0.6% variability. The dosimeter was found to have a slight dose response fall off as a function of fraction number for irradiation times larger than 1 hour. Simulated clinical treatments on six dosimeters resulted in an overall accuracy of −0.65% (σ=1.9%). Conclusion: Hypo‐fractionated treatments have fewer fractions requiring increased treatment accuracy. Phantom testing suggests that the DVS‐HFT could be used to measure the dose per fraction delivered helping optimize hypo‐fractionated treatments. *Not FDA cleared for use in the US Research sponsored by Sicel Technologies, Inc.