Abstract
Recently, the developers of Eclipse have recommended the use of ionization chambers for all profile scanning, including for the modeling of VMAT and stereotactic applications. The purpose of this study is to show the clinical impact caused by the choice of detector with respect to its ability to accurately measure dose in the penumbra and tail regions of a scanned profile. Using scan data acquired with several detectors, including an IBA CC13, a PTW 60012, and a Sun Nuclear EDGE Detector, three complete beam models are created, one for each respective detector. Next, using each beam model, dose volumes are retrospectively recalculated from actual anonymous patient plans. These plans include three full‐arc VMAT prostate plans, three left chest wall plans delivered using irregular compensators, two half‐arc VMAT lung plans, three MLC‐collimated static‐field pairs, and two SBRT liver plans. Finally, plans are reweighted to deliver the same number of monitor units, and mean dose‐to‐target volumes and organs at risk are calculated and compared. Penumbra width did not play a role. Dose in the tail region of the profile made the largest difference. By overresponding in the tail region of the profile, the 60012 diode detector scan data affected the beam model in such a way that target doses were reduced by as much as 0.4% (in comparison to CC13 and EDGE data). This overresponse also resulted in an overestimation of dose to peripheral critical structure, whose dose consisted mainly of scatter. This study shows that, for modeling the 6 MV beam of Acuros XB in Eclipse Version 11, the choice to use a CC13 scanning ion chamber or an EDGE Detector was an unimportant choice, providing nearly identical models in the treatment planning system.PACS number: 87.55.kh
Highlights
175 Gersh et al.: Clinical impact of detector choice region, suggesting the importance of dose to this region for beam modeling
This study examines the clinical impact of detector choice for profile scanning, with emphasis placed on accuracy in the penumbra and tail regions
Studies related to dosimetric accuracy have been performed concerning small-field dosimetry as it relates to the modeling of beams for use in stereotactic applications.[4,5] While accurate small-field dosimetry is important for stereotaxy, a broader-scope manifestation of this phenomenon is demonstrated when scanning beam profiles for beam modeling of treatment planning systems, where accurate dosimetry in the penumbra and the tail is important
Summary
175 Gersh et al.: Clinical impact of detector choice region, suggesting the importance of dose to this region for beam modeling. This study examines the clinical impact of detector choice for profile scanning, with emphasis placed on accuracy in the penumbra and tail regions. While accurate small-field dosimetry is important for stereotaxy, a broader-scope manifestation of this phenomenon is demonstrated when scanning beam profiles for beam modeling of treatment planning systems, where accurate dosimetry in the penumbra and the tail is important. Previous studies concerning this specific case clearly show that a broadening of a beam’s penumbra can be substantial when comparing measurements using different detectors.[4-9]. Plans are reweighted to deliver the same number of monitor units, and mean dose to target volumes and organs at risk are calculated and compared
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