The Australasian College of Physical Scientists and Engineers in Medicine (ACPSEM) Radiation Oncology Specialty Group (ROSG) formed a series of working groups in 2011 to develop position papers for guidance of radiation oncology medical physics practice within the Australasian setting. These position papers are intended to provide guidance for safe work practices and a suitable level of quality control without detailed work instructions. It is the responsibility of the medical physicist to ensure that locally available equipment and procedures are sufficiently sensitive to establish compliance to these position papers. The recommendations are endorsed by the ROSG, have been subject to independent expert reviews. For the Australian audience, these recommendations should be read in conjunction with the Tripartite Radiation Oncology Practice Standards [1, 2]. This publication presents the recommendations of the ACPSEM OPACS and OIS Working Group (OISWG) and has been developed in alignment with other international associations. However, these recommendations should be read in conjunction with relevant national, state or territory legislation and local requirements, which take precedence over the ACPSEM position papers. It is hoped that the users of this and other ACPSEM position papers will contribute to the development of future versions through the Radiation Oncology Specialty Group of the ACPSEM.

Purpose: The purpose of this technical study was to evaluate how the effect of changing beam energies for one to multiple fractions of a patient's plan affected the overall dose delivered to the planning target volume (PTV) and surrounding organs at risk (OAR's). Method: In this study, twenty-eight patient plans from treatment sites including the oesophagus, prostate, lung, spine, rectum, bladder, chest, scapula, and breast were evaluated in the Philips Pinnacle treatment planning system (TPS), of these 14 were originally planned with 15MV and 14 with 10MV. Each of these plans were substituted with a single to multiple fractions with 10MV and 15MV respectively while keeping the original monitor units the same. Results: It was determined that when the number of fractions of the substituted beam energy remained at one fifth or less of the overall fractions a change of dose of less than 2% to the PTV could be maintained. The OAR's dose, when the plan had 20% of its fractions substituted with a different energy, were found to change by on average up to 3.5% and 2.3% for original plan energies of 15MV and 10MV respectively. The dose change calculated in the TPS was then verified using ion chamber measurements for bladder and oesophagus treatment plans. Conclusion: Results appear to indicate that the site of treatment was not an important factor when changing energy but the overall number of fractions versus the number of fractions substituted with an alternative energy was fundamental. These results may be clinically useful when a radiotherapy department have machines with different photon energies. In the event of a break down, when a patient needs to be urgently treated, it may be possible to treat them on another machine with a different energy, without an immediate recalculation in the TPS. This decision would depend upon the percentage of fractions of their overall treatment needing to be treated before the machine was repaired.

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An increasing number of cancer treatment centres are using in vivo dosimetry as a quality assurance tool for verifying dosimetry as either the entrance or exit surface of the patient undergoing external beam radiotherapy. Equipment is usually limited to either thermoluminescent dosimeters (TLD) or semiconductor detectors such as p-type diodes. The semiconductor detector is more popular than the TLD due to the major advantage of real time analysis of the actual dose delivered. If a discrepancy is observed between the calculated and the measured entrance dose, it is possible to eliminate several likely sources of errors by immediately verifying all treatment parameters. Five Scanditronix EDP-10 p-type diodes were investigated to determine their calibration and relevant correction factors for entrance dose measurements using a Victoreen White Water-RW3 tissue equivalent phantom and a 6 MV photon beam from a Varian Clinac 2100C linear accelerator. Correction factors were determined for individual diodes for the following parameters: source to surface distance (SSD), collimator size, wedge, plate (tray) and temperature. The directional dependence of diode response was also investigated. The SSD correction factor (CSSD) was found to increase by approximately 3% over the range of SSD from 80 to 130 cm. The correction factor for collimator size (Cfield) also varied by approximately 3% between 5 x 5 and 40 x 40 cm2. The wedge correction factor (Cwedge) and plate correction factor (Cplate) were found to be a function of collimator size. Over the range of measurement, these factors varied by a maximum of 1 and 1.5%, respectively. The Cplate variation between the solid and the drilled plates under the same irradiation conditions was a maximum of 2.4%. The diode sensitivity demonstrated an increase with temperature. A maximum of 2.5% variation for the directional dependence of diode response was observed for angle of +/- 60 degrees. In conclusion, in vivo dosimetry is an important and reliable method for checking the dose delivered to the patient. Preclinical calibration and determination of the relevant correction factors for each diode are essential in order to achieve a high accuracy of dose delivered to the patient.