Room: Exhibit Hall
Purpose: To examine the anatomic position of point B in CT-based HDR brachytherapy for cervical cancer, and to assess the relationship between point B dose and the dose delivered to pelvic lymph nodes.
Methods: Forty-nine HDR applications were performed on 49 patients with FIGO Stage IB-IVB cervical cancer at Kyushu University Hospital from February 2013 to January 2016. For all cases, planning CT images were obtained after applicator insertion, and planning and treatment were performed by using Plato (Elekta AB, Stockholm, Sweden). The obtained planning CT images were imported to Oncentra Brachy (Elekta AB, Stockholm, Sweden), point A (dose prescription, 6 Gy) and point B were set according to the Manchester method. The pelvic lymph nodal regions (external iliac, internal iliac, and obturator) were contoured and the anatomic positions of 98 points B in 49 patients were examined on 3D view. DVH parameters (D100, D90, D50, D2cc, D1cc, and D0.1cc) were calculated for each lymph nodal region, compared with the point B dose. For statistical analysis, two-sided paired t test and Pearson correlation coefficients were used. The significant level was set at 5%.
Results: The mean dose to point B was 1.70Â±0.18 Gy. For the anatomical position, 51 (52%) and 21 (21%) points of 98 points B were in obturator and internal iliac nodal region, respectively. The DVH analysis indicated low degree of correlation overall, and all values were significantly different from point B doses, except D0.1cc of the external iliac nodal group (1.60Â±0.37 Gy, p = 0.0594) and D1cc of the internal iliac nodal group (1.60Â±0.39 Gy, p = 0.0711).
Conclusion: We investigated the anatomical location of point B in patients with uterine cervical cancer who underwent brachytherapy, and the DVH analysis reveals that point B dose is poor surrogate for the dose delivered to pelvic lymph nodes.