Quantitative Evaluation of Dosimetric Accuracy of a Multiple-Diode-Array Detector (MapCHECK2) for High-Dose-Rate Ir-192 Brachytherapy
J Taguenang*, T De La Fuente Herman, J Young, S Ahmad, I Ali, Oklahoma Univ. Health Science Ctr., Oklahoma City, OKSU-E-T-113 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
Purpose: To evaluate dosimetric accuracy of a multiple-diode array detector (MapCHECK2 ) for high-dose-rate (HDR) brachytherapy Ir-192 source using two-dimensional dose distributions measured with MapCHECK2, EBT2 Gafchromic films, and TG-43 calculations.
Materials and Methods: Plans with different patterns of dwell positions and times were delivered to MapCHECK2 and EBT2 films using a remote afterloader Ir-192 HDR brachytherapy Nucletron system. A catheter was placed between phantom slabs with Gafchromic films and the MapCHECK2 positioned 2cm above and 2cm below the source dwell positions, respectively. The dose distributions were also calculated with TG-43 using the phantom setup and I-192 source parameters to compare with dose measurements from MapCHECK2 and film.
Results: Dose distributions measured with MapCHECK2 and calculated with TG-43 were within 5% agreement. Similarly, the dose distributions measured with MapCHECK and EBT2 film agreed within 5% in the range from 10-800 cGy. However, for doses larger than 800 cGy, EBT2 films saturated. In the low range, for doses below 10 cGy, the MapCHECK2 and film measurements were noisy and deviated up to 15% from the TG-43 calculations. The advantage of MapCHECK2 over Gafchromic film is linear response and stability over a wide range of dose levels and dose rates produced from Ir-192 sources. No over-response of MapCHECK2 dose from Ir-192 was observed. The 2D dose distributions from MapCHECK2 are obtained with small detectors and high spatial resolution at positions where the diode detectors are located. However, the separation of the detectors (7 mm) limits the overall spatial resolution of MapCHECK2 in comparison with films.
Conclusion: MapCHECK2 provided accurate measurements of 2D-dose distributions from HDR Ir-192 source as validated by TG-43 calculations and EBT2 measurements. The response of MapCHECK2 was linear over a wide range of dose levels and dose-rates while the response of EBT2 Gafchromic film was non-linear and unstable.