Journal of Medical Physics
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Year : 2019  |  Volume : 44  |  Issue : 3  |  Page : 156-175

Out-of-field dose calculation by a commercial treatment planning system and comparison by monte carlo simulation for varian TrueBeam®

1 Department of Physics, Banasthali University, Jaipur, Rajasthan, India
2 Division of Radiation Physics, Regional Cancer Center, Thiruvananthapuram, Kerala, India
3 Department of Radiation Oncology, Aster Medcity, Kochi, Kerala, India

Correspondence Address:
Mr. N S Shine
“Shangri-La,” Alathara, Sreekariyam P.O., Thiruvananthapuram - 695 017, Kerala
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jmp.JMP_82_18

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Purpose: The calculation accuracy of treatment planning systems (TPSs) drops drastically when the points outside the field edges are considered. The real accuracy of a TPS and linear accelerator (linac) combination for regions outside the field edge is a subject which demands more study. In this study, the accuracy of out-of-field dose calculated by a TPS, used with a TrueBeam® (TB) linac, is quantified. Materials and Methods: For dose calculation, Eclipse™ version 13.7 commissioned for TB machine was used. For comparison, Monte Carlo (MC) methods, as well as the measurements, were used. The VirtuaLinac, a Geant 4-based MC program which is offered as a cloud solution, is used for the generation of input phase-space (PS) files. This PS file was imported into PRIMO (PENELOPE based MC program) for the simulation of out-of-field dose. Results: In this study, the accuracy of the out-of-field dose calculated by a TPS for a TB linac was estimated. As per the results in comparison with MC simulations, the TPS underestimated the dose by around 45% on an average for the off-axis-distance range considered in this study. As the off-axis distance increased, the underestimation of the dose also increased. Conclusion: In this work, it was observed that the TPS underestimates doses beyond the edges of treatment fields for a clinical treatment executed on a TB machine. This indicates that the out-of-field dose from TPSs should only be used with a clear understanding of the inaccuracy of dose calculations beyond the edge of the field.

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