Experimental evaluation of ALFARD treatment planning system for 6 MV photon irradiation: A lung case study

Abstract

Purpose: Simple inhomogeneity correction methods available in a number of currently applied treatment planning systems are not accurate enough for dose calculations in lung irradiations. The purpose of this study was to evaluate the accuracy of the ALFARD treatment planning system in dose calculations for lung irradiation. Material and methods: An anatomic thorax phantom and a 6 MV photon beam were used for our irradiation. Our set-up consisted of an anterior single field for the left lung of a thorax phantom with field sizes of 5 أ— 5 cm2 and 10 أ— 10 cm2. The percentage depth doses for each point in the lung were measured by a Pinpoint ionization chamber and calculated by the ALFARD treatment planning system. The results of calculations and measurements were compared. Results: The ALFARD calculations overestimated measurements at all points and field sizes. The magnitude of error increased with depth of the calculation point from 2.7% to 17.3% for the field size of 5 أ— 5 cm2. The error for 5 أ— 5 cm2 was approximately twice as high as that for 10 أ— 10 cm2. Conclusions: The ALFARD treatment planning system cannot calculate the dose in the lung accurately. This may be due to inherent deficiencies of the effective path length method, which is implemented in the ALFARD treatment planning system.