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

OBJECTIVE 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. CONCLUSION 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.