Experimental evaluation of pencil beam algorithm by measurements of dose distributions of protons traversing an L-shaped phantom

A proton dose-calculation method has been developed on the basis of the pencil-beam algorithm (PBA), which is expected to improve the precision of the conventional method based on the broad-beam algorithm (BBA). In order to verify the accuracy of calculation by the PBA, dose distributions formed by a horizontal proton beam traversing a phantom with an L-shaped horizontal cross section were measured using a silicon semiconductor detector (SSD) in a water vessel. The results of the measured dose distributions agree well with the ones calculated using the PBA within an rms error of 2.3%. Therefore, the dose-calculation method by the PBA is useful and applicable to actual treatment planning of the proton therapy.