Dosimetric verification of brain and head and neck intensity-modulated radiation therapy treatment using EDR2 films...

The evaluation of the agreement between measured and calculated dose plays an essential role in the quality assurance (QA) procedures of intensity-modulated radiation therapy (IMRT).

The purpose of this study is to compare performances of the two dosimetric systems (EDR2 and I'matriXX) in the verification of the dose distributions calculated by the TPS for brain and head and neck dynamic IMRT cases.

The comparison of cumulative fluence by using Kodak extended dose rate (EDR2) and I'matriXX detectors has been done for the evaluation of 10 brain, 10 head and neck IMRT cases treated with 6 MV beams. The parameter used to assess the quality of dose calculation is the gamma-index (g -index) method. The acceptance limits for g calculation we have used are 3% and 3 mm respectively for dose agreement and distance to agreement parameters. Statistical analyses were performed by using the paired, two-tailed Student t-test, and P< 0.01 is kept as a threshold for the significance level.

The qualitative dose distribution comparison was performed using composite dose distribution in the measurement plane and profiles along various axes for TPS vs. EDR2 film and TPS Vs I'matriXX. The quantitative analysis between the calculated and measured dose distribution was evaluated using DTA and g-index. The percentage of pixels matching with the set DTA and g values are comparable for both with EDR2 film and I'matriXX array detectors. Statistically there was no significant variation observed between EDR2 film and I'matriXX in terms of the mean percentage of pixel passing g for brain cases (98.77 +/- 1.03 vs 97.62 +/- 1.66, P = 0.0218) and for head and neck cases (97.39 +/- 2.13 vs 97.17 +/- 1.52%, P = 0.7404).

Due to simplicity and fast evaluation process of array detectors, it can be routinely used in busy departments without compromising the measurement accuracy.