2664 Impact of Bladder Volume and Uterine and Vaginal Geometric Factors on the Irradiated Dose to the Bladder and Small Intestine in Cervical Cancer Patients Treated With Image Guided Brachytherapy G. Kasuya, T. Toita, T. Ariga, H. Shiina, Y. Kakinohana, J. Heianna, and S. Murayama; Ryukyus University, Nishihara-cho, Japan Purpose/Objective(s): To evaluate the impact of bladder volume and uterine and vaginal geometric factors on the D2cc value of whole bladder, bladder lining, and small intestine in cervical cancer patients treated with CT-based image-guided high-dose rate intracavitary brachytherapy (HDR- IGBT). Materials/Methods: We retrospectively analyzed 148 consecutive HDR- IGBT sessions in 49 cervical cancer patients (stages IB1, IB2, IIB, IIIB, and IVA [n Z 12, 6, 18, 12 and 1, respectively]). Median age was 59 years (range, 27-86). A planning CT was performed at 1.25 mm slice thicknesses under inserted CT/ MR compatible tandem-ovoid applicators. A 6 Gy dose was delivered at point A. In 120 sessions, normal saline was instilled into the bladder (100-200 ml) to decrease the intestinal dose, and the urethral catheter was clamped. The anterior wall thickness of the uterine cervix (AWTC) and cranio-caudal vaginal wall distance (VWD) above the su- perior aspect of the pubic bone to the vaginal fornix were measured on the sagittal image in which the tandem lumen was sufficiently visible. All sessions were divided into 2 groups based on AWTC and VWD by two ways, and we evaluated relationships among the D2cc value for whole bladder, bladder lumen, and small intestine or bladder volume. Chi-square test and t-test were used to compare the ratio and average, respectively. A p < 0.05 was considered statistically significant. Results: Median D2cc for small intestine, whole bladder, and bladder lumen was 3.6, 5.6, and 4.7 Gy (range Z 0.1-7.2, 2.0-10.3, and 1.6-8.4 Gy), median AWTC and VWD were 11 and 30 mm (range Z 0-36 and 0- 66mm), and median bladder volume was 130 ml (range Z 37-396 ml) in the 148 sessions. Two groups were created (48 sessions: both AWTC less than 11 mm and VWD > 30 mm; 100 remaining sessions). Between the groups, a D2cc for the small intestine > 6 Gy was observed in 11 sessions and 1 session, respectively (p < 0.001). Of these 12 sessions, bladders were distended in 10; the VWD was more than 40 mm in all 10. We created another 2 groups (24 sessions: both AWTC < 11 mm and VWD < 30 mm; 124 remaining sessions). Between the groups, a significant dif- ference was observed in average D2cc values for whole bladder (6.9 Gy vs. 5.4 Gy; p < 0.001) and bladder lumen (5.7 Gy vs. 4.5 Gy; p < 0.001). Of the 148 sessions, the D2cc for bladder lumen was more than 6Gy in 13. Of these, all AWTC and VWD values were < 10 and 32 mm, respectively, and bladders were distended in 11 sessions. Conclusions: A short AWTC has an impact on high-dose irradiation for the small intestine and bladder in cervical cancer patients treated with HDR- IGBT. A long VWD, combined with a short AWTC, causes high-dose irradiation to the small intestine due to insufficient movement on the cranial aspect of the small intestine, despite bladder distention. In case of a short VWD combined with a short AWTC, the bladder wall and bladder lining are subjected to high-dose irradiation due to bladder distention. Author Disclosure: G. Kasuya: None. T. Toita: None. T. Ariga: None. H. Shiina: None. Y. Kakinohana: None. J. Heianna: None. S. Murayama: None. 2665 Overall Rectum and Bladder Doses (D2cc and D0.1cc) When Integrated EBRT and HDR Brachytherapy Doses for Cervical Cancer by Accounting for Organ Deformations Y. Kim, K. Cheung, D. Wang, C.J. Mart, A. Sheybani, W. Sun, and S. Bhatia; University of Iowa Hospitals and Clinics, Iowa City, IA Purpose/Objective(s): It is hypothesized when voxel-by-voxel doses are tracked accounting for organ deformation, the integrated maximal organs- at-risk (OAR) doses (D2cc and D0.1cc) of EBRT and HDR brachytherapy (BT) (Integrated-TECH) can be significantly different from that by simple summation of maximum doses from EBRT and HDR-BT DVH (DVH- TECH). Materials/Methods: Six cervical cancer patients who received EBRT and HDR-BT were retrospectively analyzed. Three patients received para- metrial boost while one patient received both parametrial and paraaortic boost. The overall prescription dose to high risk CTV D90 was 86  12 Gy 10 in EQD2 (a/b Z 10). A 3T MRI-guided volume-optimization planning technique was used for all HDR-BT plans following GEC- ESTRO recommendations. A CT, EBRT dataset and a MRI, HDR-BT dataset were registered by accounting for organ deformations with using deformable image registration. Afterward, the EBRT and HDR-BT dose maps were combined using the deformation map. The resulting cumulative rectum and bladder D2cc and D0.1cc EQD2 (a/b Z 3) values were compared to those obtained from DVH-TECH. For DVH-TECH, an EQD2 DVH tool was developed in-house to convert initial dose maps into EQD2 maps and differential EQD2 DVH. Differential EQD2 DVHs of EBRTand HDR-BT were combined, and converted into an overall cumulative EQD2 DVH which assumed that D2cc and D0.1cc doses of EBRT and HDR-BT are at the same location. Results: The integrated rectum and bladder D2cc values matched the values from those of DVH-TECH on average within 3%. The integrated rectal D2cc values presented on average -2.3  2.0 % (p Z 0.04) lower than those of DVH-TECH. This was mainly caused due to the D2cc location differences in EBRT and HDR-BT. The integrated bladder D2cc values also showed lower doses (on average -2.4  3.4 %) but did not present statistical difference (p Z 0.14). The integrated D0.1cc values of both rectum and bladder were found to be different by on average -7.7  4.5 % (p Z 0.01) and -13.3  5.4 % (p Z 0.006), respectively, than DVH- TECH. The maximum point doses (D0.1cc) had larger changes than D2cc when tracking voxel-by-voxel dose accumulation. However, since D0.1cc is not robust to the way of generating DVH, D2cc is the recommended metric to evaluate overall OAR doses from EBRT and HDR. Conclusions: The simple combined DVH-TECH was able to estimate the integrated OAR D2cc doses within on average 3% differences when compared to the Integrated-TECH. Author Disclosure: Y. Kim: None. K. Cheung: None. D. Wang: None. C.J. Mart: None. A. Sheybani: None. W. Sun: None. S. Bhatia: None. 2666 The Addition of Brachytherapy to Adjuvant External Beam Radiation Improves Survival in Cervical Cancer Patients Following Surgery S. Felder, O. Pail, S. Appel, Y. Korach, J. Goldstein, Z. Symon, and Y.R. Lawrence; Sheba Medical Center, Ramat Gan, Israel Purpose/Objective(s): Adjuvant external beam radiation therapy (EBRT) is often delivered to women with cervical cancer following surgery. The clinical benefit of adding vaginal-cuff brachytherapy (BT) to EBRT is unclear, and there are no agreed-upon indications or consensus guidelines. We hypothesized that patients with large tumors would benefit from the addition of BT to EBRT. Materials/Methods: We utilized data from the Surveillance, Epidemi- ology, and End Results (SEER) program of the US National Cancer Institute from January 1, 1983 to December 31, 2009. Inclusion criteria were women with non-metastatic cervical carcinoma diagnosed in 1983- Scientific Abstract 2665; Table Percent difference between 2 OAR dose integration techniques Case Rectum D2cc Rectum D0.1cc Bladder D2cc Bladder D0.1cc 1 -1.7% -13.3% -2.9% -18.4% 2 -1.8% -1.1% -2.8% -19.5% 3 -5.8% -12.1% -3.1% -14.4% 4 -3.0% -8.1% 0.9% -9.4% 5 0.1% -6.3% 1.4% -12.5% 6 -1.4% -5.6% -8.0% -5.3% Average -2.3% -7.7% -2.4% -13.3% Std Dev 2.0% 4.5% 3.4% 5.4% International Journal of Radiation Oncology  Biology  Physics S474