In vivo dosimetry with semiconductors in medium dose rate (MDR) brachytherapy for cervical cancer.

PURPOSE

This study was performed to evaluate the role of in vivo dosimetry with semiconductor detectors in gynaecological medium dose rate brachytherapy, and to compare the actual doses delivered to organs at risk (as measured using in vivo dosimetry) with those calculated during treatment planning.

MATERIALS AND METHODS

Doses to the rectum and bladder were measured in a group of patients with cervical carcinoma using semiconductor detectors and compared to the doses calculated using a treatment planning system. 36 applications of brachytherapy at dose rates of 1.8-2.3 Gy/h were performed in the patients.

RESULTS

The mean differences between the measured and calculated doses were 3 % for the rectum and 11 % for the bladder.

CONCLUSIONS

The main reason for the differences between the measured and calculated doses was patient movement. To reduce the risk of large errors in the dose delivered, in vivo dosimetry should be performed in addition to treatment planning system computations.