Treatment optimization with concurrent SBRT and intracavitary brachytherapy for locally advanced cervical cancer

This work is aimed at investigating treatment planning strategies to optimally combine stereotactic body radiation therapy (SBRT) with intracavitary brachytherapy (ICBT) for the treatment of locally advanced cervical cancer. Forty patients (stage IIB - IIIB) previously treated with combined SBRT and ICBT were randomly selected for this retrospective study. All patients were CT- and MR-scanned with a ring applicator in situ. HR-CTV and OARs were contoured according to fused CT and MR images. Several ICBT plans were generated for each patient based on different dose prescription points, and then a matching SBRT plan was generated for each ICBT plan. The dose distribution of each composite plan was analyzed with a focus on the doses received by 90% and 100% of the target volume (D₉₀ and D₁₀₀), the target volume receiving 100% of the prescription dose (V_100%), and the doses received by 2 cc and 40% of the OARs (D_{2 cc} and D₄₀). As the distance, d, between the prescription point and the tandem varied within 1.0 and 1.9 cm, the D₉₀, D₁₀₀ and V_100% for the target, as well as D_{2 cc} and D₄₀ for the bladder and rectum approached their optimal values for d value between 1.0 and 1.4 cm. When designing a combined ICBT + SBRT plan, one should measure the size of the cervix and set the prescription isodose line 1.0 to 1.4 cm away from the tandem for the ICBT plan first and then optimize the SBRT plan based on the ICBT dose distribution to achieve the best target coverage and critical structures sparing.