SU‐E‐T‐316: Dosimetric Effects Resulting From Increased MLC Error and Expanded Dose Dynamic Leaf Tolerances in Sliding Window IMRT

TL;DRAbstract

Purpose: To examine the dosimetric effects on the target dose coverage of MLC error (actual vs. planned position) for sliding window IMRT treatment plans. Methods: Dynalog files from a treated 7 field H&N sliding window IMRT plan were imported into a Dynalog to .mlc converter. The errors of the MLC's were multiplied by factors of f= 5, 10, 50, and 500 while capping the dose dynamic leaf tolerance at 0.2cm (Eclipse TPS default). Resulting .mlc files were imported into the TPS to study the changes in dose after increasing the magnitude of MLC error. Additionally, the dose dynamic leaf tolerance was expanded to 0.3cm, 0.4cm, and 0.5cm for each case. Results: For the linac investigated, A and B MLC error was found in the direction opposite to MLC motion, toward the X1 jaw. This systematic shift in the MLC position results in a shift of the dose distribution per field when the inherent error is multiplied by a factor. The complete treatment plan had maximum and minimum dose differences

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