Paul Reich
Royal Adelaide Hospital
Acting Principal Physicist

Wendy Harriss-Phillips
Senior Medical Physicist
Royal Adelaide Hospital

John Lawson
Acting Chief Physicist
Royal Adelaide Hospital

Background and Purpose

In-vivo dosimetry is an important component to radiotherapy as it aims to verify that the prescribed dose is what is actually delivered to the patient .This is especially important in brachytherapy due to the reproducibility requirements associated with customised treatments (e.g. surface moulds) combined with steep dose gradients associated with the radioactive source. The aim of this work is to present our methodology and results for in-vivo dosimetry performed on surface mould HDR brachytherapy patients at the RAH since 2014.

Methods

In-vivo dosimetry is performed at the RAH using thermoluminescence dosimetry (TLD) or film dosimetry on our HDR surface mould patients as requested by our clinicians [1, 2]. Since 2014, 8 patients received HDR brachytherapy to sites ranging from the face and head to arm and leg extremities. In-vivo dosimetry was performed on 6 of these patients.

HDR brachytherapy is administered to our surface mould patients using a MicroSelectron ® remote afterloader equipped with an Ir-192 radioactive source. CT based treatment planning is performed with Oncentra® Brachy treatment planning system (using the AAPM TG 43 based dose algorithm). The TLDs or films are placed on the treatment area of the patient at day 1 of treatment. The position of the detectors is localised using anatomical landmarks on the patient (e.g. tattoos, scars). Depending on the vicinity of the treatment site to critical structures or organs (e.g. eyes), additional detectors are placed on these tissues as requested by the clinician. The dose measured from the irradiated detectors is compared to the dose calculated from the treatment planning system.

Results

On average (across 6 patients), the dose measured at the surface of the patient was within approximately ±10 % (range of ± 3 - 15 % ) of the dose prescribed to the patient. For all 6 patients, the dose measured at critical structures or organs were within clinically safe levels.

Conclusions

Our in-vivo dosimetry program for HDR surface mould brachytherapy at the RAH has provided us with valuable information and confidence on the dose delivered to our patients. Performing in-vivo dosimetry has also informed us on where improvements can be made in our methodology.

References

1. Radiation Oncology Practice Standards. A Tripartite Initiative. 2011.

2. Radiation Oncology Practice Standards. A Tripartite Initiative. Supplementary Guide. 2011.


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