Surface Dose in the Treatment of Breast Cancer with Helical Tomotherapy

Abstract

Investigation of the effects of breathing motion- and misregistration-induced errors on the superficial dose in the treatment of breast cancer using helical tomotherapy (HT). Surface dose measurements were performed with thermoluminescence dosimetry (TLD). Two treatment plans with different planning target volume (PTV) definitions of the left breast were used: PTVskin had its ventral border exactly on skin level, while PTVair included also a 10-mm extension ventral to the PTVskin. With a thoracic static phantom, misregistration errors in an HT were simulated. A dynamic phantom was used to simulate a breathing patient during HT. Surface doses of breast cancer patients were measured both for an HT (179 points) and a conventional three-dimensional conformal treatment (70 points). In the static phantom misregistration setup, dose deviations of -31.9% for PTVskin to +35.4% for PTVair could be observed. The dynamic phantom measurements resulted in surface dose deviations from those in a static position between 0.8% and 3.8% without a significant difference for the PTV definitions. The measured surface doses on patients averaged (mean +/- standard deviation) 1.65 +/- 0.13 Gy for the HT and 1.42 +/- 0.11 Gy for the three-dimensional conformal treatment. HT enables a homogeneous and reproducible surface dose with small dose deviations in the treatment of breast cancer. HT is a feasible method to treat breast cancer under free shallow breathing of the patient using a treatment plan with a ventral PTV border on the skin level.