Main Session
Sep
28
PQA 04 - Breast Cancer, Patient Reported Outcomes/QoL/Survivorship, Functional Radiation Medicine, Hematologic Malignancies, Palliative Care, and International/Global Oncology
2794 - Spatial and Dosimetric Benefits of FBCT-Based Online Adaptive Radiotherapy for Gastric MALT Lymphoma
Presenter(s)
Xiumei Ma, MD - Department of Radiation Oncology, Ren Ji Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, Shanghai
X. Wang1, X. Xu1, L. Yu2, W. Zhang1, L. Xu1, Z. Zheng2, Y. Wang3, X. Wu3, and X. Ma1; 1Department of Radiation Oncology, Ren Ji Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China, 2Department of Radiation Oncology, Ren Ji Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, Shanghai, China, 3Shanghai United Imaging Healthcare Co. Ltd., Shanghai, China
Purpose/Objective(s):
This study aimed to evaluate the spatial and dosimetric benefits of online adaptive radiotherapy (OART) compared with conventional image-guided radiotherapy (IGRT) for gastric mucosa-associated lymphoid tissue (MALT) lymphoma, using the first ring-gantry linear accelerator with integrated FBCT-guidance.Materials/Methods:
Twelve patients with gastric MALT lymphoma treated with a prescription dose of 30.6 Gy in 17 fractions were retrospectively analyzed. For each fraction, a standard IGRT plan was initially generated. The decision to proceed with OART was made by senior radiation oncologists based on daily pre-treatment setup verification. After anonymization, interfractional spatial variations, including volume changes, centroid motion and the Dice similarity coefficient, were assessed for the clinical target volume (CTV) and planning target volume (PTV). Simultaneously, dosimetric parameters for targets and organs at risk (OARs), including the liver, kidneys and small intestine, were evaluated using established guideline-recommended metrics.Results:
OART demonstrated superior dosimetric outcomes compared with conventional IGRT. For the CTV, OART significantly increased the D95% by 3.24 Gy (30.68 ± 0.38 vs. 27.44 ± 5.95, 95% CI: 2.04 to 4.44, p < 0.001). Additionally, OART improved the V30.6Gy by 11.4% (96.14 ± 12.08 vs. 84.74 ± 15.51, 95% CI: 7.46% to 15.34%, p < 0.001), while maintaining a comparable mean dose. For the PTV, OART reinstated target coverage, achieving a D95% equivalent to the prescription dose and a V30.6Gy of 95.3%. This adjustment effectively addressed the undercoverage observed with IGRT, D95% was (30.62 ± 0.05) Gy vs. (20.37 ± 7.75) Gy (95% CI: 8.60 to 11.89, p < 0.001), and V30.6Gy was 95.3% ± 0.79% vs. 72.39% ± 10.60% (95% CI: 20.65% to 25.16%, p < 0.001). Furthermore, OART reduced high-dose exposure to the colon, duodenum, and small intestine. Spatial analysis indicated substantial interfractional variation, with an average gastric centroid displacement of 18.2 ± 13.2 mm. Such displacement resulted in suboptimal performance of automated deformable registration, as evidenced by a Dice coefficient of 0.755 compared to manual contours. Accordingly, the mean deviation in stomach volume from the planning CT was significantly higher in OART-triggered fractions compared to IGRT-only fractions (23.32% ± 18.13 % vs. 14.62% ± 9.76 %, 95% CI: 4.66% to 12.75%, p < 0.001).Conclusion:
OART for gastric MALT lymphoma effectively reduces interfractional anatomical variations, providing superior target coverage and OARs sparing compared to IGRT. Gastric deformation and displacement represent key triggers for adaptation and highlight the technical feasibility of this method. However, prospective validation is needed to confirm the associated clinical benefit.