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Abstract
The accuracy of dose calculations at extended SSD is of significant importance in the dosimetric planning of total body irradiation (TBI). In a first step toward the implementation of electronic, multi‐leaf collimator compensation for dose inhomogeneities and surface contour in TBI, we have evaluated the ability of the Eclipse AAA to accurately predict dose distributions in water at extended SSD. For this purpose, we use the Eclipse AAA algorithm, commissioned with machine‐specific beam data for a 6 MV photon beam, at standard SSD (100 cm). The model was then used for dose distribution calculations at extended SSD (179.5 cm). Two sets of measurements were acquired for a 6 MV beam (from a Varian linear accelerator) in a water tank at extended SSD: i) open beam for 5 × 5, 10 × 10, 20 × 20 and 40×40 cm2 field sizes (defined at 179.5 cm SSD), and ii) identical field sizes but with a 1.3 cm thick acrylic spoiler placed 10 cm above the water surface. Dose profiles were acquired at 5 cm, 10 cm and 20 cm depths. Dose distributions for the two setups were calculated using the AAA algorithm in Eclipse. Confidence limits for comparisons between measured and calculated absolute depth dose curves and normalized dose profiles were determined as suggested by Venselaar et al. The confidence limits were within 2% and 2 mm for both setups. Extended SSD calculations were also performed using Eclipse AAA, commissioned with Varian Golden beam data at standard SSD. No significant difference between the custom commissioned and Golden Eclipse AAA was observed. In conclusion, Eclipse AAA commissioned at standard SSD can be used to accurately predict dose distributions in water at extended SSD for 6 MV open beams.PACS numbers: 87.53.Kn, 87.55.D‐, 87.55.de, 87.56.ng
Highlights
91 Hussain et al.: a 3D pencil beam superposition-convolution algorithm (AAA) algorithm at extended SSD media, and especially at interfaces, the AAA algorithm has been shown to be consistently more accurate than the pencil beam convolution (PBC) algorithm.[9,10,14,15,16]For the commissioning of the Eclipse treatment planning system, the manufacturer advises that the SSD used for treatment planning calculations does not exceed 30% of the SPD used during commissioning of the Eclipse AAA algorithm
If an SSD exceeding the range of 30% is routinely used, it is recommended to acquire another set of measurements at an extended SSD, and to recommission the Eclipse AAA algorithm under these conditions
Based on the limitations of the Eclipse configuration algorithm, the maximum SPD that is allowed for complete beam data storage is 140 cm.[17]. In the present study, we assess the capability of the Eclipse AAA to accurately predict dose distributions at distances beyond 140 cm in water while using the beam model commissioned at standard SSD (100 cm) with machine specific beam data
Summary
For the commissioning of the Eclipse treatment planning system, the manufacturer advises that the SSD used for treatment planning calculations does not exceed 30% of the SPD (source to phantom distance) used during commissioning of the Eclipse AAA algorithm. If an SSD exceeding the range of 30% is routinely used, it is recommended to acquire another set of measurements at an extended SSD, and to recommission the Eclipse AAA algorithm under these conditions. Based on the limitations of the Eclipse configuration algorithm, the maximum SPD that is allowed for complete beam data storage is 140 cm.[17] In the present study, we assess the capability of the Eclipse AAA to accurately predict dose distributions at distances beyond 140 cm in water while using the beam model commissioned at standard SSD (100 cm) with machine specific beam data. Measured and calculated depth dose curves and dose profiles were compared using the criteria established by Venselaar et al[18]
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