Australasian level III dosimetric intercomparison using a purpose built anthropomorthic phantom

Full text: Comparison of the absolute dose given at a reference point is defined as a level I dosimetric intercomparison. Level III dosimetry methodology will verify radiotherapy treatment from patient data acquisition through to planning and treatment (figure 1). The CCRR (Centre for Clinical Radiation Research) at the Department of Radiation Oncology, Mater Hospital, Newcastle, in collaboration with TROG (Trans-Tasmin Radiation Oncology Group), is undertaking a combined level I/III dosimetry intercomparison project as a follow up to a previous study performed in 1999, which involved 19 Australian and New Zealand centres. A purpose-built anthropomorphic pelvic phantom has been designed and constructed for anatomical accuracy and dosimetric reproducibility. Clinically-relevant points were located throughout the phantom for TLDs to be placed and the centre of the prostate was identified as the location for point-measurement with a small-volume ionization chamber. Radiotherapy centres throughout Australia and New Zealand were invited to voluntarily participate and 32 sites expressed an interest. After initial testing and development of study protocol in mid-2004, site visits will commence. The phantom will be transported to each department and accompanied by a physicist and additional member of CCRR staff. The study requires CT, simulation, planning and treatment of the phantom for prostate and rectal treatments. The project will require one day at each treatment centre with (in addition to access to equipment) the time of one local radiation oncologist, radiation therapist and physicist. Protocols for performing phantom irradiations have been developed, as well as a protocol for the undertaking of a Level I dosimetry measurement (basic accelerator output) at each centre. Plans are underway for the use of the SWAN software for analysis of treatment plans collected at each centre. This study will provide substantial clinical and dosimetric information regarding structure outlining, local irradiation techniques, geometric and dosimetric accuracy, dose distributions in realistic phantom, the accuracy of different treatment planning systems as well as the feasibility of multi-centre dosimetry studies. Each centre will receive an individual dosimetry report but cumulative results will only be reported and published in an anonymous form. Copyright (2004) Australasian College of Physical Scientists and Engineers in Medicine