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A Comparative Study of Dose Calculation Algorithms for In-Field and Out-Of-Field Conditions

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P Ramachandran

p ramachandran1*, A Tajaldeen2 , K Roozen3 , D Taylor4 , D Wanigaratne5 , M Geso6 , (1) ,,,(2) RMIT University & Peter MacCallum Cancer Centre, Melbourne, Vic, (3) Peter MacCallum Cancer Centre, Bentleigh East, VIC, (4) Peter MacCallum Cancer Centre, Bentleigh East, VIC, (5) Peter MacCallum Cancer Centre, Bentleigh East, VIC, (6) Royal Melbourne Institute of Technolog, Bundoora Victoria,


SU-I-GPD-T-420 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: In radiotherapy, dose calculation algorithms play an important role in delivering precise dose to the target volume. Prior to clinical use, the accuracy of dose calculation algorithm needs to be validated against measurement under / for different inhomogeneous conditions. In this study, we have compared four different dose algorithms: Pencil Beam convolution, (PBC) AcurosXB, Anisotropic Analytical Algorithm (AAA) and Collapsed Cone Convolution Algorithm (CCC).

Methods: The study was conducted on a Varian 21iX linear accelerator for both 6 and 18 MV X-rays. The measurement was conducted using a 0.6 cc ionization Farmer type chamber in geometric solid water phantom with inhomogeneity inserts (IPSM phantom).. The chamber was placed at six different positions and three different field sizes 3x5, 5x5 and 10x10 were defined for both in-field and out-of-field measurements. The measurements were performed for open, physical wedge and enhanced dynamic wedge fields at 90° and 270° degree gantry angles. Water equivalent, lung, ribs and dense bone inserts were used to study the accuracy of dose calculation algorithms for the above geometries. Dose calculation was performed using AAA, PBC, AcurosXB algorithms and CCC compared against the measured dose.

Results: The mean difference between measurement and the dose calculations algorithms with water equivalent insert for PBC, AcurosXB, AAA and CCC were -1.57 ± 0.81, -0.96 ± 0.65, -1.50 ± 0.61 and -0.77 ± 0.69 respectively. Similarly, the mean difference beyond lung insert for PBC, AcurosXB, AAA and CCC were 0.68 ± 1.21, -0.40 ±, 1.20, -1.8 ± 0.82 and -0.1 ± 1.03 respectively.

Conclusion: Our results show that CCC and AcurosXB algorithm are closer to the measurements as compared to AAA and PBC for a majority of the field conditions for water equivalent, lung and ribs inserts. CCC algorithm resulted in better agreement with measurement for out-of-field points.

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