A comparison between two-dimensional ion chamber array and EDR2 film for intensity modulated planning of helical tomotherapy

Objective: The aim of this work is to compare the performances of EDR2 film dosimetry with two-dimensional ion chamber array (2DICA) in quality assurance (QA) procedures and to investigate the origin of possible discrepancies between the two methods. Methods: A 2DICA, I' mRT MatriXX and MULTICube equivalent solid water phantom from IBA Company were used to verify the dose distribution of 15 tomotherapy plan cases. The combined phantom which includes EDR2 film on the array was set up to measure the dose distribution from coronal and sagittal orientations. After the irradiation, the dose distributions of 2DICA and film were compared with those calculated in the planning system for verification. The results and efficiency were evaluated independently in the two methods. Results: The mean number of points satisfying γ parameter ≤1 in the coronal and sagittal planes was 97.00%±1.56% and 95.98%±2.52% (t=-2.22, P=0.043) and 98.28%±1.55% and 95.42%±1.99% (t=0.75, P=0.464) of the 15 cases respectively for 2DICA and EDR2 film. The ratio of more than 90% and 95% were 93.3% and 66.7%. The results we presented show a very good agreement between the two methods when used to assess the dose distribution between calculated and measured doses, and a certain degree of correlation (r=0.14, P=0.001). Conclusions: The 2DICA may effectively replace both film and ion chamber dosimetry in routine IMRT QA. The good agreement between 2DICA and EDR2 film may give a possible check regularly just as a gold standard. (authors)