Ramaq Al-Qadhi
Centre for Medical Radiation Physics, University of Wollongong
PhD Student

Andrew Howie
Senior Medical Physicist
St George Cancer Care Centre, Kogarah

Joseph Bucci
Radiation Oncologist
St George Cancer Care Centre, Kogarah

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

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

Background and Purpose:

Rectal doses may be of concern during HDR prostate brachytherapy. The close proximity of the rectal wall to the prostate leads to a high probability of delivering too much dose to the rectum. Post-treatment complications occur due to overdosing to rectal wall. CMRP/STGCCC have undertaken rectal dose measurements in the past using MOSFET based dosimeters (MOSkin). MOSkin detectors are designed to measure the doses on interfaces, hence are ideal for in-vivo dosimetry of the rectal wall. MOSkin dosimeters, however, are disposable (use once), with diodes offering a reusable solution. Skin diodes have recently been developed, which embed a diode within a MOSkin package, giving the ability to measure interface doses with a versatile detector. We propose the integration of a skin diode array within a plastic sheath, which allows both the housing of the diodes against the rectal wall as well as the accommodation of a trans rectal ultrasound probe for treatment. This work aims to develop a system for measurement of anterior rectal wall doses during high dose rate prostate brachytherapy (HDR BT).

Methods:

The Epitaxial Skin Diode detector was designed at the Centre for Medical Radiation Physics (CMRP), Wollongong. The dimension of the diode is 2x2mm2 with central sensitive area 1x1mm2. In phantom measurements performed with the skin diodes and an Ir-192 radioactive source to verify several fundamental parameters of the detectors, such as depth-dose response, angular dependence, sensitivity and reproducibility.

Results:

The skin diode depth-dose response was in agreement (to within experimental error) of TG43 calculated values. The angular response showed a variation of ±7% between the angles ± 60°, with an average angular dependence of ±3%. The results indicate the skin diode shows promise as a tool to measure the dose to the rectal wall during HDR brachytherapy dosimetry.

Conclusions:

Skin diodes embedded within a plastic sheath offer a new, permanent solution to in-vivo rectal dose measurements during HDR prostate brachytherapy. The skin diode measurements were not as accurate as equivalent measurements with MOSkins, however, at this early stage in development, re-engineering the packaging will improve these. Further development and experimental trials will proceed to advance the technology to a clinical stage.


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