kV reference dosimetry in Australia and New Zealand: Survey results and trends

To assess the number of radiotherapy kilovoltage (kV) units in service, their clinical utilization, and methodology and equipment used for absorbed dose determination across Australia and New Zealand.

A survey was sent to 61 Australian and New Zealand radiotherapy providers in the second half of 2023.

Fifty-seven responses were received, with 43 departments having kV units and providing beam quality data for 185 therapeutic kV beams 20-300 kVp. Percentage depth dose curves were compared between five clinical beams with 100 kVp and 2.13-6.28 mm Aluminum half value layers (HVLs), demonstrating large differences that can occur between beams with the same kVp. Eighteen departments provided clinical utilization data for their kV units, with a total of 4458 treatment courses and their corresponding kVp reported. All departments complied with national and international recommendations with respect to the equipment used for reference dosimetry of kV beams; 77% of ionization chambers used for absorbed dose determination were of Farmer-type, with the remaining 23% being plane parallel soft x-ray chambers. Methods of derivation of air-kerma calibration factors varied, with 73% of respondents using a draft document disseminated by the Australian Primary Standards laboratory, 23% using HVL alone, and 6% using other methods.

The results of this survey provide a snapshot of kilovoltage radiation therapy use and the number of kV units across Australia and New Zealand. This data can be used as a point of reference for future investigations into clinical utilization and reference dosimetry methods across Australia and New Zealand or for comparisons with other countries, facilitating standardization of reference dosimetry practice for kilovoltage units.