S. Acklin1, J. Raffi2, Y. Kim3, D. N. Ayala-Peacock4, S. J. Stephens5, O. I. Craciunescu6, and J. P. Chino5; 1Department of Radiation Oncology, University of Arkansas for Medical Sciences, Little Rock, NC, 2Duke University Medical Center, Durham, NC, 3Duke, Durham, NC, 4Vanderbilt University Medical Center, Nashville, TN, 5Department of Radiation Oncology, Duke University Medical Center, Durham, NC, 6Duke University Medical Center, Department of Radiation Oncology, Durham, NC
Purpose/Objective(s): A hybrid brachytherapy (BT) approach consisting of a combined intracavitary (IC)/interstitial (IS) implant is often used in patients with bulky or asymmetric primary tumors of the cervix to improve target coverage and limit organ at risk (OAR) doses compared to an IC applicator alone. However, its role in patients with non-bulky primary tumors is not yet defined. Here we report the differences in dosimetry between hybrid BT and IC plans in patients with non-bulky cervical tumors. Materials/
Methods: We retrospectively identified patients with cervical cancer or medically inoperable endometrial cancer who underwent BT including IS needles and had a high-risk clinical target volume (HRCTV) measuring less than 35 cm2. The BT plan was reoptimized without IS needles, and the cumulative D90 and D98 for the HRCTV and D2cc for the bladder, rectum, sigmoid, bowel, and vagina were estimated and compared to the original dosimetry. Planning aims and limits for prescribed dose were used as defined in EMBRACE-II as well as planning aim for vagina D2cc of < 100 Gy EQD23. Statistical significance was evaluated with Wilcoxon signed-rank test. Results: 35 patients were included with an average HRCTV volume of 18.38 cm2. In IC alone plans, significant differences were seen in HRCTV D90, bladder D2cc, rectum D2cc, and vagina D2cc EQD2 doses. Fewer plans met proposed planning aims for HRCTV D90 (4 versus 10) and HRCTV D98 (32 versus 33). Median HRCTV D90 decreased (88.8Gy versus 85.5Gy, p<0.001) while bladder D2cc (71.90Gy versus 71.91Gy, p=0.041) and rectum D2cc (53.50Gy versus 55.13Gy, p=0.015) increased. More IC alone plans exceeded the proposed limits for prescribed dose for bladder (2 versus 1) while no plans exceeded limits for prescribed dose for rectum. Vagina D2cc significantly decreased (81.89Gy versus 85.05Gy, p=0.017). No significant differences were seen in median HRCTV D98, sigmoid D2cc, and bowel D2cc EQD2 doses. Conclusion: The addition of IS needles for non-bulky cervical tumors significantly increases HRCTV D90 and allows for more plans to meet planning aims while maintaining or improving OAR doses except for vagina dose.
