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

Dean Cutajar
Lecturer
University of Wollongong

Anna Romanyukha
PhD Student
University of Wollongong

Tebarak Al-Salmani
Masters Student
University of Wollongong

Joel Poder
Senior Medical Physicist
St George Cancer Care Centre

Iolanda Fuduli
PhD Student
University of Wollongong

Marco Petasecca
Senior Lecturer
University of Wollongong

Joseph Bucci
Radiation Oncologist
St George Cancer Care Centre

Annamaria Cerrotta
Physicist
National Cancer Institute, Milan, Italy

Carlo Fallai
Physicist
National Cancer Institute, Milan, Italy

Emanuele Pignoli
Physicist
National Cancer Institute, Milan, Italy

Mauro Carrara
Physicist
National Cancer Institute, Milan, Italy

Introduction

Treatment verification of all brachytherapy procedures is recommended to provide optimal outcomes for the patients. In-vivo tracking of the source location would be the most ideal method of treatment verification for HDR brachytherapy, however the ability to routinely perform this is greatly limited by the complexity of the procedures themselves. One such procedure is gynaecological brachytherapy, incorporating the multichannel vaginal cylinder (MVC) applicator. By embedding diodes within the cylindrical applicator, the HDR source location within the applicator may be tracked in real-time during the dose delivery.

Materials and Methods

A prototype MVC applicator, based on the commercially available MVC applicator (Elekta Brachytherapy, Veenedaal, NL), was produced with a 30 mm diameter, containing 1 central channel and 7 peripheral channels. Three epitaxial diodes of size 1.5 mm x 1.5 mm x 0.5 mm were embedded below the radial surface of the applicator, in 120 degree intervals, 35 mm, 37 mm and 39 mm from the applicator tip. An in-house electrometer was developed to measure the induced current within each diode at a frequency of 50 Hz. By measuring the current in each diode, the location of the source could be reconstructed using a pre-calibrated depth-signal function. The applicator was placed inside a large PMMA phantom to provide full scattering conditions. 10 clinical plans were delivered to the applicator with the reconstructed and ideal dwell position and times compared, to enable evaluation of the prototype applicator.

Results

For the 10 delivered plans, there were a total of 181 dwell positions in the central catheter and 106 dwell positions in the peripheral catheters. The mean dwell position discrepancies between the reconstructed and planned positions were 0.2 ± 0.4 mm for the central channel and 0.0 ± 0.8 mm for the peripheral channels. The mean time discrepancies were -0.1 ± 0.2 s for dwell positions in the central catheter and 0.0 ± 0.1 s for dwell positions in the peripheral catheters. Limitations in the system were identified where the dwell positions were within 3 mm of a diode. In this case, volume averaging effects of the diode inhibited the system from distinguishing 2 separate dwell positions.

Conclusion

The developed prototype for source tracking in gynaecological procedures has shown great potential for the system to be used clinically, as well as the technology to be translated to other applicator styles without changing the protocol of the procedures.


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