Dean Cutajar
University of Wollongong
Lecturer

Ryan Brown
Medical Physics Registrar
St George Cancer care Centre

Andrew Howie
Senior Medical Physicist
St George Cancer Care Centre

Joel Poder
Senior Medical Physicist
St George Cancer Care Centre

Kristine Schreiber
Radiation Therapist
St George Cancer Care Centre

Andrej Bece
Radiation Oncologist
St George Cancer Care Centre

Anatoly Rosenfeld
Distinguished Professor
University of Wollongong

Joseph Bucci
Radiation Oncologist
St George Cancer Care Centre

Introduction

St George Cancer Care Centre has been performing real time ultrasound based HDR brachytherapy of the prostate for the past two years. This involves the delivery of two treatment fractions, one week apart, with each fraction involving the implantation, planning and radiation delivery in the one theatre session. This may be streamlined further by moving to a single fraction treatment. To analyse the efficacy of moving to a single fraction, the accuracy of the treatment needs to be evaluated. This involves not only planning studies and phantom measurements, but in-vivo dose measurements to fully validate the method. To provide in-vivo measurements, the rectal doses have been monitored using MOSkin detectors mounted on the transrectal ultrasound (TRUS) probe.

Materials and Methods

For each fraction of a real time TRUS based HDR brachytherapy of the prostate, the TRUS probe was fitted with 4 MOSkin detectors, placed 1.5 cm apart, along the right hand edge of the probe, 90° to the longitudinal transducer. The probe and MOSkin detectors were then placed inside an ultrasound balloon before insertion within the patient. After the TRUS guided HDR catheters have been inserted and the treatment plan constructed and optimised, the TRUS probe is rotated 90°, placing the MOSkin detectors against the anterior rectal wall. The doses delivered to the rectal wall are monitored in real time and compared to the planned doses at these locations. Readout and analysis of the MOSkin measurements is performed every three seconds for the duration of the radiation delivery, using a newly developed wireless MOSkin readout system, incorporating temperature fluctuation correction and automatic measurement triggering.

Results

The first patient measurements were performed in late September, 2018. Initial results indicate the measured rectal doses are within 5% of planned doses and have a distance to agreement of within 2mm. The results of the first three months of the trial will be presented.

Conclusions

Real time ultrasound planning based HDR brachytherapy of the prostate has been shown to be a more streamlined treatment modality than conventional CT based HDR prostate brachytherapy. In-vivo rectal dose measurements have shown the current treatment protocol produces rectal doses within accepted uncertainty of the treatment plan doses. The trial will be performed over a six month period, with the results constantly evaluated.


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