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Poster — Thurs Eve‐03: Dose verification using a 2D diode array (Mapcheck) for electron beam modeling, QA and patient customized cutouts
Author(s) -
Ghasroddashti E,
Sawchuk S
Publication year - 2008
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 - 10.1118/1.2965922
Subject(s) - imaging phantom , pinnacle , quality assurance , nuclear medicine , materials science , radiation treatment planning , physics , medical physics , optics , medicine , radiation therapy , radiology , external quality assessment , pathology
Purpose: To assess a diode detector array (MapCheck) for commissioning, quality assurance (QA); and patient specific QA for electrons. Method and Materials: 2D dose information was captured for various depths at several square fields ranging from 2×2 to 25×25cm 2 , and 9 patient customized cutouts using both Mapcheck and a scanning water phantom. Beam energies of 6, 9, 12, 16 and 20 MeV produced by Varian linacs were used. The water tank, beam energies and fields were also modeled on the Pinnacle planning system obtaining dose information. Mapcheck, water phantom and Pinnacle results were compared. Relative output factors (ROF) acquired with Mapcheck were compared to an in‐house algorithm (JeffIrreg). Inter‐ and intra‐observer variability was also investigated Results: Profiles and %DD data for Mapcheck, water tank, and Pinnacle agree well. High‐dose, low‐dose‐gradient comparisons agree to within 1% between Mapcheck and water phantom. Field size comparisons showed mostly sub‐millimeter agreement. ROFs for Mapcheck and JeffIrreg agreed within 2.0% (mean=0.9%±0.6%). Conclusion: The current standard for electron commissioning and QA is the scanning water tank which may be inefficient. Our results demonstrate that MapCheck can potentially be an alternative. Also the dose distributions for patient specific electron treatment require verification. This procedure is particularly challenging when the minimum dimension across the central axis of the cutout is smaller than the range of the electrons in question. Mapcheck offers an easy and efficient way of determining patient dose distributions especially compared to using the alternatives, namely, ion chamber and film.