Treatment planning for high dose rate brachytherapy of cervical cancer based on total dose constraints.

OBJECTIVES: To compare the inverse planning optimization based on total dose constraints versus conventional treatment plan (point A planning method) for cervical carcinoma, and evaluate the benefit of CT-based image-guided brachytherapy.

METHODS: We prospectively analyzed data of 10 consecutive patients with cervical cancer treated with external beam radiotherapy to the whole pelvis (45 Gy in 25 fractions) followed by high-dose-rate (HDR) brachytherapy (21 Gy in 3 fractions). For treatment planning of HDR brachytherapy, the basic equations of the linear-quadratic model were used to calculate the physical dose for each brachytherapy fraction needed to achieve a given total iso-effective dose for the whole treatment. Specific dosimetric parameters are evaluated for high risk (HR CTV), intermediate risk (IR CTV) clinical target volumes, and organs at risk (OARs).

RESULTS: In conventional plans, the HR CTV was well covered in only 15/31, and the IR CTV in 7/31 of the brachytherapy implants, while dose constraints of OARs bladder and rectum were respected in 28/31 and 14/31 implants. After optimization, the HR CTV and IR CTV dose constraints were respected in all the implants, and the bladder and rectum of cases dose constraints were respected in 25/31 and 17/31 of cases.

CONCLUSIONS: Point A is a poor surrogate of target dose. Significant differences between point doses and dose volume histogram parameters indicate the need for inverse planning in image-guided brachytherapy of cervical cancer.