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Poster ‐ 21: Verification of Monitor Unit Calculations for Breast Field‐In‐Field Three‐Dimensional Conformal Radiotherapy Plans
Author(s) -
Kosztyla Robert,
Pierce Greg,
Ploquin Nicolas,
Roumeliotis Michael,
Schinkel Colleen
Publication year - 2016
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4961795
Subject(s) - eclipse , monitor unit , field size , nuclear medicine , field (mathematics) , dosimetry , physics , radiation treatment planning , radiation therapy , optics , mathematics , medicine , radiology , astronomy , pure mathematics
Purpose: To determine the source of systematic monitor unit (MU) calculation discrepancies between RadCalc and Eclipse treatment planning software for three‐dimensional conformal radiotherapy field‐in‐field breast treatments. Methods: Data were reviewed for 28 patients treated with a field‐in‐field breast technique with MU calculations from RadCalc that were larger than MU calculations from Eclipse for at least one field. The distance of the calculation point from the jaws was measured in each field's beam's‐eye‐view and compared with the percentage difference in MU (%ΔMU) between RadCalc and Eclipse. 10×10, 17×13 and 20×20 cm 2 beam profiles were measured using the Profiler 2 diode array for 6‐MV photon beams and compared with profiles calculated with Eclipse and RadCalc using a gamma analysis (3%, 3 mm). Results: The mean %ΔMU was 1.3%±0.3%. There was a statistically‐significant correlation between %ΔMU and the distance of the calculation point from the Y jaw (r=−0.43, p<0.001). RadCalc profiles differed from measured profiles, especially near the jaws. The gamma pass rate for 6‐MV fields of 17×13 cm 2 field size was 95%±1% for Eclipse‐generated profiles and 53%±20% for RadCalc‐generated profiles (p=0.01). Conclusions: Calculations using RadCalc for field‐in‐field breast plans resulted in MUs that were larger than expected from previous clinical experience with wedged plans with calculation points far from the jaws due to the position of the calculation point near the jaws in the beam's‐eye‐view of each field.