Conical collimators are effective and readily available accessories for the field shaping of small stereotactic fields, however the measurements required to accurately characterise the smallest radiation fields are difficult and prone to large errors. Furthermore, there is little published commissioning data to compare measurements against. The aim of this investigation was to commission the cone dose calculation algorithm of a Varian Eclipse treatment planning system for a Varian 5mm conical collimator attached to a Varian TrueBeam linear accelerator that had been beam-matched to the Varian Golden Beam Data (GBD). Tissue maximum ratios (TMRs), off-axis ratios (OARs), and the output factor (OF) were measured using a PTW 60019 microDiamond and a PTW 60018 SRS Diode detector. Results were compared to the GBD for this collimator, radiochromic film measurements, and an output factor measured during an independent audit by the Australian Clinical Dosimetry Service. Film dosimetry was used to evaluate Eclipse dose calculations in a solid water phantom and end-to-end accuracy with an anthropomorphic head phantom. A PTW BEAMSCAN water phantom was used to collect the data, and output correction factors were derived from IAEA TRS-483. Gamma analysis was used to compare measured TMRs and profiles, and to compare Eclipse dose planes with film dosimetry results. Good agreement was obtained between the measurements with the two detectors, and with the various comparisons carried out to confirm both measurement accuracy and planning system configuration. It was decided to configure Eclipse with the microDiamond OF and the SRS Diode measured TMR and OAR data.

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