Performance characteristics of a microMOSFET as anin vivodosimeter in radiation therapy

Abstract

The commercially available microMOSFET dosimeter was characterized for its dosimetric properties in radiotherapy treatments. The MOSFET exhibited excellent correlation with the dose and was linear in the range of 5-500 cGy. No measurable effect in response was observed in the temperature range of 20-40 degrees C. No significant change in response was observed by changing the dose rate between 100 and 600 monitor units (MU) min(-1) or change in the dose per pulse. A 3% post-irradiation fading was observed within the first 5 h of exposure and thereafter it remained stable up to 60 h. A uniform energy response was observed in the therapy range between 4 MV and 18 MV. However, below 0.6 MeV (Cs-132), the MOSFET response increased with the decrease in energy. The MOSFET also had a uniform dose response in 6-20 MeV electron beams. The directional dependence of MOSFET was within +/-2% for all the energies studied. The inherent build-up of the MOSFET was evaluated dosimetrically and found to have varying water equivalent thickness, depending on the energy and the side of the beam entry. At depth, a single calibration factor obtained by averaging the MOSFET response over different field sizes, energies, orientation and depths reproduced the ion chamber measured dose to within 5%. The stereotactic and the penumbral measurements demonstrated that the MOSFET could be used in a high gradient field such as IMRT. The study showed that the microMOSFET dosimeter could be used as an in vivo dosimeter to verify the dose delivery to the patient to within +/-5%.

Image guided IMRT dosimetry using anatomy specific MOSFET configurations

“…The reproducibility values at the dose levels of 100 cGy, 50 cGy and 1 cGy were found to be 0.7%, 1% and 2.1%, respectively. These reproducibility results are an improvement compared to the previously reported values (9) . This improvement can be attributed to the new mobileMOSFET automated readout system.…”

“…The active detection area of the MOSFET is 0.04 mm 2 . The detailed structure and technical aspects and design of MOSFET detectors have been described previously by several authors 9 , 12 …”

Small field electron beam dosimetry using MOSFET detector

“…MOSFET dosimeters have been widely studied for photon beam dosimetry ( 8 – 14 ) and have been used extensively for in vivo clinical dose measurements, ( 11 , 12 , 15 – 19 ) as well as for small field photon dosimetry. ( 20 ) MOSFET systems have recently been investigated for use in electron beam dosimetry, ( 21 – 23 ) as well.…”

Clinical results of entrance dose in vivo dosimetry for high energy photons in external beam radiotherapy using MOSFETs

“…MOSFETs have also been evaluated as an in vivo dosimeter, and have been found to be suitable as an in vivo dosimeter [17][18][19] . Comparisons between diodes and MOSFETs have been made with a build up cap showing that the total uncertainty with diodes is similar to that of MOSFETs for entrance dose in vivo dosimetry measurements 20 .…”