Room: Exhibit Hall
Purpose: Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETs) have recently been proposed for use in radiation therapy. The purpose of this study is to evaluate the feasibility of using MOSFETs for in-vivo skin dose measurements during high energy photon and electron irradiation with bolus.
Methods: Measurements were made using dual-bias TN-502RD MOSFETs which were connected to a portable dosimeter with bias set at standard sensitivity. To reduce systematic differences, separate calibration factors were used for photons and electrons. A total of 70 patient measurements were performed for photon and 109 for electron fields with various treatment techniques (3D, IMRT, et.al.). MOSFET measurements on patients were compared to those measured using thermoluminescent dosimeters (TLDs) and/or calculated from the clinical Eclipse planning system (TPS) for photons or a hand calculation for electrons.
Results: In photon treatments, 80% agreed with the calculated value within 5% and 8.6% were outside the 8% tolerance range. In electron fields, 80.7% agreed with the calculated value within 5% and 8.3% were outside the 8% tolerance range. The measurements that were outside the 8% tolerance range were repeated and repeated measurements were all within 8%. 28 of 70 photon and 15 of 109 electron measurements were also compared with TLD measurements performed separately. The agreement between MOSFETs and TLDs were all within 8%. The patient measurements that displayed larger discrepancies between MOSFETs and calculated values showed similar behavior for TLD measurements. This discrepancy may be due to limitations of the MOSFET system, TPS calculation algorithm limitations or measurement setup.
Conclusion: The accuracy, small size and ease of placement of MOSFETs makes them feasible for skin dose measurement under bolus with the added advantage of delivering immediate results compared to TLDs. This study concludes that the portable MOSFET system can provide a useful clinical dosimetry technique for in-vivo skin dose measurement.