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Investigation of the Accuracy of Two-Dimensional Dose Distributions Measurement From High-Dose-Rate Brachytherapy Ir-192 Source Using Multiple-Diode-Array Detector (MapCheck2)

J Taguenang

J Taguenang1*, T De La Fuente Herman1 , S Ahmad1 , I Ali1 , (1) Oklahoma Univ. Health Science Ctr., Oklahoma City, OK.


SU-E-T-223 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To investigate the dosimetric accuracy of multiple-diode-array detector (Mapcheck2) for high-dose-rate brachytherapy Ir-192 source. The two-dimensional (2D) dose distributions measured with MapCheck2 were validated with EBT2 Gafchromic film measurement and AAPM task-group-43 (TG-43) modeling.

Methods: 2D-dose distributions from Ir-192 source were measured with MapCheck2 and EBT2-films. MapCheck2 response was corrected for effects: directional dependence, diode and phantom heterogeneity. Optical density growth of the film was controlled by synchronized scanning of the film exposed to Ir-192 and calibration films exposed to 6 MV linac beams. Similarly, MapCheck2 response was calibrated to dose using 6 MV beams. An empirical model was developed for the dose distributions measured with Mapcheck2 that considered directional, diode and phantom heterogeneity corrections. The dose deposited in solid-state-detectors was modeled using a cavity theory model for the diode. This model was then validated with measurements using EBT2-films and calculations with TG-43.

Results: The response of MapCheck2 has been corrected for different effects including: (a) directional dependence of 0-20% over angular range 0o-90o, (b) phantom heterogeneity (3%) and (c) diode heterogeneity (9%). The corrected dose distributions measured with MapCheck2 agreed well with the measured dose distributions from EBT2-film and with calculations using TG-43 within 5% over a wide range of dose levels and rates. The advantages of MapCheck2 include less noisy, linear and stable response compared with film. The response of MapCheck2 exposed to 192Ir-source showed no energy dependence similar to its response to MV energy beam. Detection spatial-resolution of individual diodes was 0.8x0.8 mm2, however, 2D-MapCheck2 resolution is limited by distance between diodes (7.07 mm).

Conclusion: The dose distribution measured with MapCheck2 agreed well within 5% with that measured using EBT2-films; and calculations with TG-43. Considering correction of artifacts, MapCheck2 provides a compact, practical and accurate dosimetric tool for measurement of 2D-dose distributions for brachytherapy Ir-192.

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