Two-dimensional ion chamber array in dose verification for intensity modulated planning of helical tomotherapy

Abstract

Objective To investigate the feasibility of dose verification of intensity modulated (IM) planning of helical tomotherapy (HT) using two-dimensional ion chamber array (2DICA),and develop an efficient way to validate the dose delivered under the parameters mirroring those during the treatment. Meth-ods A 2DICA,I'mRT MatriXX and MULTICube equivalent solid water phantom from IBA company were used to verify the dose distribution of 10 IM planning. The combined phantom was set up to measure the dose distributions on coronal and sagittal surface. The precise setup of phantom was guided by HTMVCT images. After the irradiation, the measured dose distributions on the coronal and sngittal plane were compared with those calculated by the IM planning system for verification. The results were evaluated and the feasibility of the different measuring methods was studied. Results The dose distribution measured by the MatriXX 2DICA was well consistent with that calculated by the treatment planning system. The errors between the measured dose and predicted dose in the selected points were within ±3%. In the comparison of the pixel-segmented ionization chamber versus treatment planning system using the 3 mm/3% γ criteria, the passing ratio of pixels with γ parameter ≤1 was 97.76% and 96.83%, respectively. Conclusions MatriXX is a-ble to measure the absolute and relative dose distributions simultaneously,which can be used for dose verifi-cation of IM planning. Key words: Helical tomotherapy; Two-dimensional ion chamber array; Equivalent solid water phantom; Dose verification.