Effect of beam spoiler on radiation dose in the build-up region for 6-MV X-ray

Abstract

Purpose

To determine the effects of a lucite spoiler on the dose distribution in the build-up region for 6-MV X-rays.

Methods and Materials

Build-up depth-dose measurements were performed for 6-MV X-ray beams generated in a Mevatron KD2 accelerator. Dose distributions were measured with a parallelplate ionisation chamber 5 × 5, 10 × 10, 15 × 15 and 20 × 20-cm fields sizes at 100 cm SSD. Measurements were performed either for open or for 15, 30, 45 and 60 degrees wedged beams. The spoiler was placed at three different spoiler-water phantom distances of 10, 15 and 20 cm.

Results

The spoiler increased the surface and the build-up dose and shifted the depth of the maximum dose toward the surface. The smaller is the spoiler-phantom distance the larger is the influence of the spoiler on the dose distribution in the build-up region.

Conclusions

The spoiler changed the dose distribution in the build-up region. It allowed using a 6-MV X-ray beam for breast treatment and for all other cases in which the superficial dose should be high enough.