Dean Cutajar
Centre for Medical Radiation Physics, University of Wollongong
Research Fellow

Iliana Peters
Masters Student
Centre for Medical Radiation Physics, University of Wollongong

Ryan Brown
Medical Physics Registrar
St George Cancer Care Centre, The St George Hospital

Andrew Howie
Senior Medical Physicist
St George Cancer Care Centre, The St George Hospital

Joel Poder
Senior Medical Physicist
St George Cancer Care Centre, The St George Hospital

Joseph Bucci
Radiation Oncologist
St George Cancer Care Centre, The St George Hospital

Alex Pogossov
Physicist
Centre for Medical Radiation Physics, University of Wollongong

Anatoly Rosenfeld
Director of Centre for Medical Radiation Physics
Centre for Medical Radiation Physics, University of Wollongong

Background and Purpose Real-time ultrasound planned HDR prostate brachytherapy has been introduced at St George Cancer Care Centre. A verification of the doses delivered to the rectal wall during the treatment is desired. MOSkin detectors, based on miniature MOSFET devices, have been used to monitor the rectal doses during prostate radiotherapy (both brachytherapy and EBRT). The ability to read out the detectors in real-time, as well as the versatility of the devices allows them to be utilised for verification of the doses delivered to the rectal wall. A new MOSkin wireless dosimetry system has been developed to improve the functionality of the MOSkin detectors for clinical application, as an upgrade to the previous MOSkin readout system, which has been in regular use for over 12 years. This includes adding wireless data transmission out of the treatment room, automatic temperature variation correction and automatic signal detection. Methods Comprehensive studies were performed to commission the new MOSkin wireless dosimetry system for clinical HDR brachytherapy trials, in direct comparison with the previous MOSkin readout system, including readout reproducibility, detector lifetime, signal variation (creep), dose dependence, angular dependence and temperature dependence. A full in-phantom treatment dose verification was performed to simulate a real-time ultrasound planned HDR prostate brachytherapy treatment, using 3 MOSkin detectors mounted to a TRUS probe, within a CIRS prostate phantom. These measurements were validated against TLDs and film. Results The new MOSkin wireless dosimetry system showed an improvement over the previous system, with a 20% increase in detector lifetime, improved readout reproducibility and signal variation (due to the automatic signal detection), and reduction in angular dependence (±1.5% within the angles of ±60°). Within the simulated HDR treatment, the new system reproduced the planned rectal wall doses to within experimental error of the previous system, with a maximum discrepancy of 6% and a maximum distance to agreement of 1.2mm, and were closer to the predicted doses than both TLDs and film. This is most likely due to the high dose gradients at the points of measurement. Conclusions The new MOSkin wireless dosimetry system, with real-time wireless transmission of data, temperature variation correction and automatic signal detection/stabilisation has been commissioned for in-vivo verification of rectal wall doses during real-time ultrasound planned HDR prostate brachytherapy. Clinical measurements are being prepared, with the goal of measuring the rectal wall doses in 4 locations simultaneously. These trials are under ethics review and will commence upon approval.


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