2272 - Manage Intra-Fractional Motions in Cervical Cancer Online Adaptive Radiation Therapy Using Personalized Anisotropic Margin
Presenter(s)
Q. Guo1, H. Xiao1,2, Q. Wu1, J. Liu1, X. Yan1, J. Ma1, J. Chen1, L. Zhang1, Z. Zhang3, Y. Yin4, P. Xie5, and Y. Cui6; 1Department of Radiation Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, Shandong, China, 2Shandong Provincial Key Medical and Health Laboratory of Pediatric Cancer Precision Radiotherapy (Shandong Cancer Hospital), Jinan, Shandong, China, 3Department of Radiation Oncology, Peking University Shenzhen Hospital, Shenzhen, China, 4Department of Radiation Oncology Physics and Technology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China, 5Department of Gynecologic Radiation Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, Shandong, China, 6Department of Radiation Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China
Purpose/Objective(s): Although online adaptive radiation therapy (ART) has shown great effectiveness in planning target volumes (PTV) reduction and clinical target volume (CTV) coverage improvement, it requires long on-couch time for plan re-optimization and intra-fractional motions may increase. This study aims to develop a personalized anisotropic margin strategy to address intra-fractional motion in cervical cancer online ART.
Materials/Methods: This study included 196 online ART sessions of 7 patients, and each session included two iterative cone-beam computed tomography (iCBCT) scans: iCBCT1 shows CTVs after positioning (CTV1) and iCBCT2 shows them prior to beam delivery (CTV2). The CTV motions between them in the first 5 fractions of each patient determined the separate personalized anisotropic margins for the uterus (CTVu) and the remaining CTV (CTV-CTVu). Oncologists retrospectively contour the CTVs and organs at risk (OARs) on iCBCT2 to ensure the structures match the doses on the synthetic CT (sCT) derived from it. The proposed margins were compared with 5 mm isotropic margins, both geometrically and dosimetrically. In the geometrical comparison, PTV volumes, CTV coverages, and doses to organs at risk (OARs) in the reference plans were assessed. In the dosimetric comparison, the sixth to the tenth fractions of each patient were re-treated with different margins on an emulator, and the doses deposited in the sCT were compared.
Results: The table below shows the personalized anisotropic margin values for CTVu and CTV-CTVu (presented in the order of anterior, posterior, left, right, superior, and inferior directions) and the corresponding CTV2 coverages in the geometric and dosimetric evaluations. The margins show clear anisotropy, and major motions happened at the uterus. CTV2 coverage was maintained at 99.05 ± 0.29 % in the geometric evaluation and 98.45 ± 0.88 % in the dosimetric evaluation, respectively. The proposed margins reduced PTV volumes by 16% (p<0.001). V30 of small intestines decreased from 30.4 ± 16.5 % to 26.2 ± 14.5 % (p<0.05), V40 of bladders decreased from 37.7 ± 7.5 % to 35.3 ± 7.7 % (p<0.001), and V40 of rectums decreased from 36.5 ± 4.8 % to 33.4 ± 5.1 % (p<0.05).
Conclusion: The proposed personalized anisotropic margin strategy significantly reduced the PTV volumes and the damage to healthy tissues while maintaining adequate CTV coverage, which may facilitate the clinical implementation of online ART and maximize the benefits for cervical cancer patients.
Abstract 2272 - Table 1| Patient No. | MCTV-CTVu(mm) | MCTVu(mm) | CTV2 Coverage (Geometric) (%) | CTV2 Coverage (Dosimetric) (%) |
| 1 | 1,1,1,2,6,5 | 14,1,14,14,14,1 | 98.82 ± 0.87 | 99.46 ± 0.65 |
| 2 | 1,1,1,1,5,4 | 1,1,1,1,1,1 | 99.01 ± 0.33 | 97.42 ± 0.95 |
| 3 | 1,1,1,1,9,2 | 16,1,16,10,23,1 | 99.46 ± 0.21 | 97.84 ± 1.38 |
| 4 | 1,1,2,4,9,8 | 6,10,10,13,13,1 | 99.50 ± 0.43 | 99.78 ± 0.07 |
| 5 | 1,1,1,2,3,4 | 5,1,5,1,7,3 | 98.74 ± 1.49 | 97.44 ± 0.72 |
| 6 | 1,1,1,1,5,5 | 2,11,10,9,13,10 | 99.01 ± 0.44 | 98.44 ± 0.74 |
| 7 | 1,1,1,1,2,2 | 6,7,7,6,11,9 | 98.81 ± 0.49 | 98.80 ± 0.52 |
| Total | / | / | 99.05 ± 0.29 | 98.45 ± 0.87 |