Dynamics of Vaginal Cuff Displacement Due to Bladder Filling in Adjuvant Pelvic Irradiation for Uterine Cancers

Abstract

RTOG Consensus contouring guidelines for IMRT recommend combining two separate clinical target volumes (CTV) for vaginal cuff based on full and empty bladders to create an ITV (Internal Target Volume). In this study, we report the magnitude of vaginal cuff position displacement when going from an empty to full bladder in post-operative patients with uterine cancers. We examined 42 patients treated with pelvic irradiation at our institution for post-operative uterine cancers FIGO stage I - IIIC. The median age was 67 years (range 41 to 81). Patients were simulated in the supine position using appropriate immobilization. A urinary catheter was inserted, and the bladder was drained to obtain the initial empty bladder (EB) scan. After this, the bladder was filled with diluted contrast (200-300 cm3), and a second full bladder (FB) CT scan was obtained. The amount of bladder fill was determined depending on the volume tolerable by the individual patient. Average Rectal distension in the AP direction was 28.9 ±7.5 mm. The vaginal cuff was visualized on the CT scans by injecting a mixture of contrast and lubricant. The EB and FB CT scans were co-registered before contouring. Target volumes and normal structures were contoured according to RTOG contouring atlas. For each patient, the vaginal cuff wall position displacement in all directions for FB in reference to EB was measured. Additionally, the vaginal cuff width and thickness at a reference level (1 cm inferior to the apex) for EB and FB were also measured. In representative patients, weekly CBCT images were obtained to assess bladder volume at treatment. The average bladder volume from FB CT scans was 272.9 cm3(range 197.5 to 485.7). The average and maximum values for vaginal cuff wall displacement due to FB relative to its position on the EB scan are summarized in Table 1. The vaginal cuff displacement appears to be more favored in the cranial direction. At the reference level, the vaginal cuff width and thickness values were 59.6 ± 12 mm, 16 ± 4.9 mm for EB and 65.8 ±12.8 mm, 12.6 ± 4.1 mm for FB, respectively. CBCT data revealed that the bladder volumes at treatment did not exceed FB nor were below EB values at simulation. Our study data quantify magnitude of vaginal cuff positional variation with bladder filling from EB to FB state. The use of a urinary catheter in all patients eliminated the need for repeat scans during CT/simulation to obtain true EB and FB scans. As also supported by our study limited CBCT data, the use of a urinary catheter to drain bladder as well as determine FB volume ensures that the intra-treatment bladder volumes never exceed nor fall below the FB and EB bladder volumes at simulation and thereby guarantees that the maximum vaginal cuff position variation has been accounted in the ITV generation.Abstract 2750; Table 1Vaginal Cuff Wall Displacement, mmRight WallLeft WallAnterior WallPosterior WallCranialCaudal(Mean ±SD)7.7 ±5.56.6 ±3.66.7 ±2.67.0 ±2.57.7 ±5.50.8 ±1.2Maximum20.314.718.514.522.52.5 Open table in a new tab