Investigation of a pulsed current annealing method in reusing MOSFET dosimeters for in vivo IMRT dosimetry.
OBJECTIVE
To explore the feasibility of pulsed current annealing in reusing metal oxide semiconductor field-effect transistor (MOSFET) dosimeters for in vivo intensity modulated radiation therapy (IMRT) dosimetry.


METHODS
Several MOSFETs were irradiated at d(max) using a 6 MV x-ray beam with 5 V on the gate and annealed with zero bias at room temperature. The percentage recovery of threshold voltage shift during multiple irradiation-annealing cycles was evaluated. Key dosimetry characteristics of the annealed MOSFET such as the dosimeter's sensitivity, reproducibility, dose linearity, and linearity of response within the dynamic range were investigated. The initial results of using the annealed MOSFETs for IMRT dosimetry practice were also presented.


RESULTS
More than 95% of threshold voltage shift can be recovered after 24-pulse current continuous annealing in 16 min. The mean sensitivity degradation was found to be 1.28%, ranging from 1.17% to 1.52%, during multiple annealing procedures. Other important characteristics of the annealed MOSFET remained nearly consistent before and after annealing. Our results showed there was no statistically significant difference between the annealed MOSFETs and their control samples in absolute dose measurements for IMRT QA (p = 0.99). The MOSFET measurements agreed with the ion chamber results on an average of 0.16% ± 0.64%.


CONCLUSIONS
Pulsed current annealing provides a practical option for reusing MOSFETs to extend their operational lifetime. The current annealing circuit can be integrated into the reader, making the annealing procedure fully automatic.
Department of Radiation Oncology, Sun Yat-Sen University Cancer Center and State Key Laboratory of Oncology in Southern China, Collaborative Innovation Center of Cancer Medicine, Guangzhou 510060, China.
Guang-Wen
GW
Luo
Department of Radiation Oncology, Sun Yat-Sen University Cancer Center and State Key Laboratory of Oncology in Southern China, Collaborative Innovation Center of Cancer Medicine, Guangzhou 510060, China.
Zhen-Yu
ZY
Qi
Department of Radiation Oncology, Sun Yat-Sen University Cancer Center and State Key Laboratory of Oncology in Southern China, Collaborative Innovation Center of Cancer Medicine, Guangzhou 510060, China.
Xiao-Wu
XW
Deng
Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW 2522, Australia.
Anatoly
A
Rosenfeld
D002138:Calibration; D004867:Equipment Design; D005240:Feasibility Studies; D006258:Head and Neck Neoplasms / Q000532:radiotherapy; D008954:Models, Biological; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods*; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation* / Q000379:methods*; D015203:Reproducibility of Results