Helical tomotherapy (HT) can provide highly conformal dose distribution through multiple-beam irradiation. Evaluation of such dose distribution is essential to ensure the quality of radiotherapy. In this study, we evaluated the performance of measuring the 3D dose distribution delivered by the HT using an N-Isopropylacrylamide (NIPAM) polymer gel dosimeter (PGD) and optical computed tomography (CT) with ring artifact correction. The 3D dose distribution of a real clinical case of cerebral arteriovenous malformation was measured using the NIPAM PGD. The irradiated PGD was scanned using an optical CT scanner 24-hr after dose delivery. The ring artifact correction was performed by median filtering of the acquired optical CT images in polar coordinates. The optical CT images without and with ring artifact correction were compared. The converted dose distributions from the optical CT images were compared with those generated from a treatment planning system using a gamma evaluation. Results show that the NIPAM PGD could accurately record the dose distribution delivered by the tomography. Also, ring artifact correction with proper filter length could effectively reduce the artifacts and improve the uniformity of the measured dose distribution. The pass rate of the measured dose distribution calculated using a three-dimensional gamma evaluation with 3%/3 mm criteria from 89.2% to 99.7% after ring artifact correction. We concluded that the NIPAM PGD and optical CT with ring artifact correction could be useful for pre-treatment verification of the HT.
