(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: To understand the impact of MLC miscalibration on organs at risk (OARs) near treatment sites where margins between the target volume and OAR volume(s) are minimal and to validate the Anatomy (ScandiDos) OAR DVH tools.
Methods: Using Eclipse treatment planning system (TPS, Varian), treatment plans were generated for two treatment sites in which surrounding OARs typically abut, or overlap the tumor volume [(cavernous sinus (SRS) and spine (SBRT)]. Once the treatment plan was created, an in-house program was used to modify the base plan by uniformly shifting the MLCs by a known amount (i.e. 0.5 mm, 1 mm, 3 mm, and 5 mm), representing an error in MLC position during delivery of the treatment. The modified plans were re-imported into the TPS. DVHs for each plan were re-evaluated and considered to be the baseline to validate Anatomy. Subsequently, each plan was delivered and measured using the Delta4 Phantom+ IMRT QA phantom and the Delta4 Discover transmission detector. The data was analyzed by Anatomy software and compared to the baseline results obtained by the TPS.
Results: The Anatomy software utilizing data from both the Delta4 Phantom+ and the Delta4 Discover devices were able to demonstrate (typically within 5% to 10%) the predicted impact on both PTV and OARs for the cavernous sinus SRS plan. While Anatomy with Delta4 Phantom+ and Delta4 Discover agreed with the TPS for the PTV, Anatomy with Discover more closely trended with the TPS for the cauda equina than did the Delta4 Phantom+ in the spine SBRT plan.
Conclusion: The Anatomy software with Delta4 Discover transmission detector can be used to estimate the clinical impact to patients for MLC miscalibration.
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