Gustafsson, H and Vial, P and Kuncic, Z and Baldock, C and Denham, JW and Greer, PB, Direct dose to water dosimetry for pretreatment IMRT verification using a modified EPID, Medical Physics, 38, (11) pp. 6257-6264. ISSN 0094-2405 (2011) [Refereed Article]
Copyright 2011 Am. Assoc. Phys. Med
Purpose: Electronic portal imaging devices (EPIDs) are high resolution systems that produce electronic dose maps with minimal time required for equipment setup, and therefore potentially present a time-saving alternative for intensity modulated radiation therapy (IMRT) pretreatment verification. A modified commercial EPID was investigated operated with an opaque sheet blocking the optical signal produced in the phosphor layer as a precursor to a switched mode dual dosimetry-imaging EPID system. The purpose of this study was to investigate the feasibility of using this system for direct dose to water dosimetry for pretreatment IMRT verification.
Methods: A Varian amorphous silicon EPID was modified by placing an opaque sheet between the Gd2S2O:Tb phosphor layer and the photodiode array to block the optical photons. The EPID was thus converted to a direct-detecting system (dEPID), in which the high energy radiation deposits energy directly in the photodiode array. The copper build-up was replaced with dmax solid water. Sixty-one IMRT beams of varying complexity were delivered to the EPID, to EDR2 dosimetric film and to a 2D ion chamber array (MapCheck). EPID data was compared to film and MapCheck data using gamma analysis with 3%, 3mm pass criteria.
Results: The fraction of points that passed the gamma test was on average 98.1% and 98.6%, for the EPID versus film and EPID versus MapCheck comparisons, respectively. In the case of comparison with film, the majority of observed discrepancies were associated with problems related to film sensitivity or processing.
Conclusions: The very close agreement between EPID and both film and MapCheck data demonstrates that the modified EPID is suitable for direct dose to water measurement for pretreatment IMRT verification. These results suggest a reconfigured EPID could be an efficient and accurate dosimeter. Alternatively, optical switching methods could be developed to produce a dual-mode EPID with both dosimetry and imaging capabilities.
|Item Type:||Refereed Article|
|Keywords:||electronic portal imaging device, film, 2D array, dosimetry, IMRT, sliding window, verification|
|Research Division:||Physical Sciences|
|Research Group:||Medical and biological physics|
|Research Field:||Medical physics|
|Objective Group:||Other health|
|Objective Field:||Other health not elsewhere classified|
|UTAS Author:||Baldock, C (Professor Clive Baldock)|
|Web of Science® Times Cited:||11|
|Deposited By:||Strategic Research Funding|
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