ESTRO 2023 - Abstract Book

S1434

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ESTRO 2023

Conclusion The DICOM reference surface generated from TPS CT dataset can achieve near-to-zero positioning accuracy regardless of the CT slice thickness and HU. The results provide great confidence in utilizing DICOM reference surface generated from TPS as a reference surface in our clinic. Studies on other factors that could impact on the DICOM surface such as calibration, camera thermal stability, CBCT image reconstruction, respiratory phase and CT voxel could be further investigated in the future.

PO-1719 Can SunCHECK™ Patient replace phantom based SRS plan verification?

N. Shiravand 1 , A. Starke 1 , J. Poxon 1 , S. Wheeler 1 , N. Macdougall 1

1 Barts Health NHS Trust, Radiotherapy Physics, London, United Kingdom

Purpose or Objective SRS plans require high delivery accuracy due to the small volumes and steep dose gradients involved. The accuracy of both TPS calculation and treatment delivery are verified by a pre-treatment measurement with a detector array: a time consuming process. The SunCHECK Patient platform offers an independent 3D dose calculation module (DoseCHECK) and EPID based measurement for pre-treatment verification (PerFRACTION). The aim was to establish if DoseCHECK and PerFRACTION are sufficiently sensitive to detect clinically significant errors in SRS HyperArc plans and thereby replace array verification. Materials and Methods Six previously treated, single lesion, SRS HyperArc patient plans were selected, covering a range of PTV volumes (1.2 - 15.3 cc), fraction doses (8 - 20Gy) and beam energies (6MV and 10FFF). Deliberate errors were written into treatment DICOM plan files to simulate potential corruption in the planning process and plan delivery errors. Plans were exported to MATLAB to introduce MLC errors into one leaf bank to simulate patient plan corruption. Six erroneous plans were created for each patient:

• central MLC leaf retracted by 1.0 mm and 2.0 mm; • central five MLC leaves retracted by 0.5 mm and 1.0 mm • all MLC leaves retracted by 0.5 mm and 1.0 mm.

The modified plan files were sent to SunCHECK (with their original dose, structure set and CT files). DoseCHECK compared its dose calculation on the corrupted plan file(s) with the original TPS dose. PerFRACTION compared its corrupted plan dose calculation with measured EPID dose from the original plan. Plans were reported as a pass or fail using local gamma analysis parameters: 5% dose difference, 1mm DTA, 30% threshold, 95% pass rate.

Results