RadCalc 3D algorithms to evaluate TPS dose on planning CT
Pasquale Tamborra, Erica Martinucci, Raffaella Massafra, Marco Bettiol, Caterina Capomolla, Annarita Zagari and Vittorio Didonna
Journal: Medical Physics
First published: 19.11.2018
Before the approval of any IMRT or VMAT treatment plan, QA tests are needed to reveal potential errors such as an inaccurate calculation of the dose distribution, the failure of the record-and-verify system or the delivery system of the linear accelerator. Currently the method adopted to compare the measured dose distribution with the TPS calculated dose distribution is gamma analysis. However gamma analysis has been shown to be ineffective for the clinical evaluation of treatment plans. We proposed and tested a new method (the Isodose Structures method) alternative to gamma analysis.
Different errors were introduced in thirty-three error-free Head and Neck plans. The modified plans were recalculated using TPS software and the dose distributions obtained were compared to those of the original (error-free) plans. The comparison was performed using gamma analysis and the new method. The target was to calculate overall and organ specific gamma passing rates as well as the Overlapping Ratio (OR) and Volume Ratio (VR) factors of the Isodose Structures method for each error -included plan.
Eight of the thirty -three plans passed both the gamma analysis and the Isodose Structures (IS) analysis, ten plans did not pass either of them , while thirteen plans which did not pass the IS analysis, passed the gamma analysis. Two plans which did not pass gamma, passed IS analysis. Furthermore, DVH metrics could not detect the low agreement between the dose distributions of two error -free plans and the respective modified plans. In this case , the IS analysis also allowed us to detect clinically meaningful differences between measured and TPS dose distributions.
The IS method analysis clearly showed a high efficiency in detecting clinically relevant differences between TPS and measured dose distributions not seen in gamma analysis and in DVH based metrics. Therefore IS analysis proved to be a valid tool , alternative to gamma analysis for dose comparison in patient -specific QA test.
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