2359 - The Feasibility of Using Daily Online CT Image Evaluation as an Indication to Trigger Adaptive Radiation Therapy for Esophageal Cancer

Y. Liu¹, Y. Zhu², M. Chen¹, H. Jiang³, Z. Mo⁴, H. Li⁴, L. Jia⁵, Y. Peng⁶, and X. Deng⁷; ¹State Key Laboratory of Oncology in South China, Guangdong Provincial Clinical Research Center for Cancer, Department of Radiation Oncology, Sun Yat-sen University Cancer Center, Guangzhou, Guangdong, China, ²State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou 510060, P. R. China, Guangzhou, China, ³Sun Yat-Sen University Cancer Center, Guangzhou, Guangdong, China, ⁴Shenzhen United Imaging Research Institute of Innovative Medical Equipment, Shenzhen, China, ⁵Shenzhen United Imaging Research Institute of Innovative Medical Equipment, Shenzhen, Guangdong, China, ⁶Department of Radiation Oncology, Sun Yat-Sen University Cancer Center, Guangzhou, China, ⁷Department of Radiation Oncology, Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangdong Key Laboratory of Nasopharyngeal Carcinoma Diagnosis and Therapy, Guangzhou, China

Purpose/Objective(s): To assess the dose variation of target volume and organs at risk (OARs) during treatment course and their relationship with the anatomical changes in intensity-modulated radiation therapy for esophageal carcinoma, and the feasibility of using the online CT image as a trigger indication for adaptive radiation therapy (ART). Materials/

Methods: Eight patients with esophageal cancer underwent intensity-modulated radiation therapy were included in the study. All patients were treated with a CT-linac (uRT506c, United Imaging, China) and had online CT scans before each treatment fraction. The daily CT images were then evaluated by two radiation oncologists, based on indicators such as tumor shrinkage, migration, and edema. When the esophageal tumor on the daily CT image deviates from the planned target volume (PTV), an adaptive process was considered to be triggered and the replanning was conducted according to the contours on the daily CT (Adaptive-plan). Meanwhile, a so called IGRT-plan was recalculated on the shifted daily CT image by registered the daily CT with the original plan CT images. Difference in dose distribution of the Adaptive-Plan and the IGRT-plan were then compared to evaluate the effectiveness of ART.
Results: In the Adaptive-Plan, the dose of 98% volume (D98%) and the volume covered by 100% prescription dose (V100%) of the gross tumor volume (GTV) were significantly increased compared to the IGRT-plan (4533.09 cGy vs. 4390.60 cGy and 99.62% vs. 95.06%, respectively), indicating an enhanced dose coverage of the target. The maximum dose delivered to the GTV in the Adaptive-plan was reduced by an average of 69.47 cGy compared to the IGRT-plan, with a noted decrement from 4901.66 cGy to 4832.19 cGy, shown a better dose uniformity in the target volume. Furthermore, the Adaptive-plan resulted in decreased doses to the organs-at-risks (OARs), indicating better organ sparing. For instance, the mean dose to the heart was significantly lowered by 155.09 cGy (from 1257.68 cGy to 1102.59 cGy), and the maximum dose to the spinal cord was diminished by 116.80 cGy (from 3047.58 cGy to 2930.78 cGy).
Conclusion: This study show that it is feasible to use daily CT assessment of GTV deviation as an indication for triggering ART for esophageal cancer. Anatomical geometry guided ART with these indications can provide better dose coverage to the target area of radiotherapy, and better sparing of normal tissues and organs. Further investigation in a larger cohort is warranted to corroborate these preliminary findings and to optimize ART protocols.