Abstract

INTRODUCTION

The success of treatment in breast radiotherapy depends on the correct irradiation of the target volume and correct positioning of patient. Patient positioning and repeatability of treatment at each fraction were investigated. In this way, the reduction of radiation implemented to the patient for portal imaging was also investigated.

METHODS

Positioning in breast cancer patients with 3D surface imaging was performed using the Catalyst optical surface guide system. Then, scans with kV-based CBCT were used to determine deviations in the patient position between the two systems. The laser-based optical surface and CBCT scans were performed in 475 fractions.

RESULTS

The mean and maximum deviation amounts for each patient and all of the 475 fractions were obtained in lateral, longitudinal and vertical axes. The mean differences between Catalyst and CBCT values in the 475 fraction were 0.24±0.22cm in the lateral axis, 0.36±0.28cm in the longitudinal axis and 0.22±0.20cm in the vertical axis. The maximum differences between Catalyst and CBCT values were obtained 1.28cm in lateral axis, 1.54cm in longitudinal axis and 1.30cm in vertical axis. If only the Catalyst was used for 26 patients, a margin of 5mm was implemented to clinical target volume, treatment could be performed in lateral axis at 89.05%, in longitudinal axis 74.52% and in vertical axis at 90.52% confidence interval.

DISCUSSION AND CONCLUSION

Reproducibility of the treatment and accurate positioning of the patient are very important in breast radiotherapy. Catalyst system is a simple, fast, repeatable and accurate solution for patient setup. It can be used effectively to minimize random daily setup errors and reduce radiation implemented to the patient for external portal imaging. CBCT and Catalyst should be used simultaneously in the first few fractions. If the deviations between the two systems are low, the number of CBCT should be reduced, taking into account the full treatment of the patient.