Bess Sutherland
Radiation Oncology Centres
Medical Physicist

Guy Godwin
Director of Physics, ROC QLD
Radiation Oncology Centres

Danielle Tyrrell
Site Senior Medical Physicist
Radiation Oncology Centres

Background and Purpose

Electronic brachytherapy involves the use of a high dose rate (HDR) x-ray source placed close to, or in contact with, an area requiring radiation therapy treatment. The benefits of electronic brachytherapy include the low energy and high dose rate, resulting in minimal room shielding requirements and treatment times in the order of 2-3 minutes. The sharp penumbra, accurate source positioning, and steep fall-off makes brachytherapy suitable for superficial lesions. Additionally, electronic brachytherapy can be used without the additional radiation safety considerations associated with brachytherapy radioisotopes.

The Esteya® (Elekta Brachytherapy, Veenendaal, The Netherlands) operates at a single tube voltage of 69.5 kVp. The system selects one of three available dose rates to keep treatment times to approximately 2 minutes. Circular applicators of 10 mm – 30 mm diameter are available for treatment.

This work presents the commissioning and clinical use of the first Esteya® unit in Australia.

Methods

The Esteya® system was commissioned following recommendations from Candela-Juan et al. Tests included output reproducibility, dose linearity, half-value layer (HVL) determination, percentage depth dose (PDD), effective source to surface distance (SSD), and applicator factor measurements. The flatness, symmetry, and penumbra for each applicator was measured with EBT3 film. Absolute dosimetry was performed in-air following the American Association of Physicists in Medicine (AAPM) Task Group 61 (TG-61) recommendations. The Esteya® QA check device sensitivity was also tested using foils to simulate output variation.

Results

Results from commissioning are presented. The Esteya® unit was found to have reproducible output and the dose was seen to be linear with time for all three dose rates. The unit was found to have a sharp penumbra < 1 mm for all applicators. Applicator factors were compared to the Esteya® internal applicator factors as well as to published data.

Absolute dosimetry was performed following the AAPM TG-61 protocol using an ARPANSA calibrated PTW 23342 0.02cc soft x-ray chamber in-air. The HVL was determined to be 1.7 mm Al and the dose rate for all three mA settings was found to be within 2% of the tube certificate.

Conclusions

The Esteya® system has been commissioned for clinical use for superficial lesions.

References

Candela-Juan C et al. Commissioning and periodic tests of the Esteya® electronic brachytherapy system, J Contemp Brachytherapy 2015; 7, 2:189-195

Ma CM et al. AAPM protocol for 40-300 kV X-ray beam dosimetry in radiotherapy and radiobiology, Med Phys 2001; 28: 868-893


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