Gynecological Cancer

PV QA 4 - Poster Viewing Q&A 4

TU_14_3452 - Dosimetric Analysis of Rectum and Mesorectum in 3D Conformal RT and IMRT for Intact Cervical Cancer

Tuesday, October 23
2:45 PM - 4:15 PM
Location: Innovation Hub, Exhibit Hall 3

Dosimetric Analysis of Rectum and Mesorectum in 3D Conformal RT and IMRT for Intact Cervical Cancer
F. Cordero1, A. P. Dalton1, R. A. Popple2, and R. Y. Kim1; 1University of Alabama at Birmingham, Birmingham, AL, 2University of Alabama at Birmingham Department of Radiation Oncology, Birmingham, AL

Purpose/Objective(s): Advanced imaging modalities have identified mesorectal nodal metastasis as a risk in locally advanced cervical cancer. Although controversial, recent contouring guidelines for IMRT recommend inclusion of mesorectum in high-risk patients. This study is to evaluate how much rectum and mesorectum receives the prescription dose for conventional 3D conformal RT (3D-CRT) and IMRT. Materials/Methods: Twenty previously irradiated intact cervical cancer were identified (Stage I: 10, Stage II: 4, Stage III: 6). The planning target volume was constructed by adding 2.0 cm margin to the gross tumor and uterus, 1.5 cm to the vagina, and 0.7 cm to the common, external and internal iliac, obturators and pre-sacral pelvic lymph nodes. The mesorectum was comprised of the portion of the rectum extending from the caudal aspect to where the sigmoid could be first visualized in the axial plane on CT scan. For 3D-CRT planning, a 4-field box was designed with appropriate dosimetric margin and the plan normalized such that 88-93% of the PTV received the prescription dose. For IMRT, a seven-field plan was optimized for conformity only and normalized so that the 100% of the dose matched the same volume covered in the 3D-CRT plan. The beam energy was 15 MV and the prescription dose was 45Gy. Rectum and mesorectum dose-volume histograms were compared between 3D-CRT and IMRT. Results: The mean mesorectal and rectal volumes were 117cm3 (60.6 - 237 cm3) and 71cm3 (33 – 163 cm3) respectively. The mean volume of rectum receiving at least 95% of the prescription was 93.0 % (79.9 – 100%) and 82.2% (44.9 – 99.9%) for 3D-CRT and IMRT, respectively. The mean volume of mesorectum receiving at least 95% of the prescription was 90.7% (78.6 – 99.7%) and 78.8% (48.2 – 99.4%) for 3D-CRT and IMRT, respectively. Larger rectum volumes were observed to have a larger volume covered by prescription dose as a trend with either modality. Conclusion: When treating with either conventional 3D or IMRT, the mean rectal volume receive most of the prescription dose. Therefore, it is likely that inclusion of entire mesorectum within target volume would be tolerated and can be considered for patients with high-risk for mesorectal nodal metastasis.
Author Disclosure: F. Cordero: None. A.P. Dalton: None. R.A. Popple: Research Grant; Varian Medical Systems. Honoraria; Varian Medical Systems. Travel Expenses; Varian Medical Systems. Patent/License Fees/Copyright; University of Alabama at Birmingham. R.Y. Kim: None.

Francisco Cordero, MD

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