SU‐FF‐T‐357: Clinical Implementation of the OneDosePlusTM MOSFET Detector for in Vivo Dose Measurement

Abstract

Purpose: To demonstrate the clinical implementation of the OneDosePlus™ MOSFET detector for in vivo dose measurement. Method and Materials: The ratio of the mean dose reported by OneDosePlus™ MOSFETs placed on the surface of a 90 cm × 30 cm × 9 cm water‐equivalent plastic phantom to the mean dose measured by an ionization chamber placed at dmax within the phantom, was determined as a function of (i) gantry angle and detector orientation, (ii) square‐field size, (iii) SSD, (iv) wedge angle, (v) monitor units, and (vi) dose rate, over clinically relevant ranges, and separately for the 6 MV and 15 MV beams of our clinical linear accelerator. A least‐squares straight‐line fit was performed to the response ratio as a function of each of these parameters in turn, and normalized to the ratio evaluated under reference conditions ((i) 0°, (ii) 10 cm, (iii) 100 cm, (iv) 0°, (v) 100, (vi) 400 MU min−1). From these, a formalism was derived to predict the dose reading by OneDosePlus™ and its uncertainty for arbitrary treatment fields for comparison with the treatment planning system prediction. Results: At 6 MV (15 MV), in order to achieve agreement with the ionization chamber, corrections of <3.5% (<11.5%) to the reported OneDosePlus™ dose are required at 0° gantry angle across the full clinical range of all other variables, increasing rapidly as the gantry rotates beyond 50° to 27.5% (22.1%) at 80°. For non‐zero gantry angles, OneDosePlus™ was found to exhibit a stronger angular dependence when its contacts pointed towards the linac head. Conclusion: The OneDosePlus™ MOSFET is well‐suited to in vivo dose measurement, providing a highly convenient alternative to TLDs and diodes. Provided that appropriate corrections are made, verification of the expected dose should be possible to within 3.3% (6 MV) and 3.7% (15 MV) for arbitrary treatment fields.