Exhibit Hall | Forum 6
Purpose: Treatment tolerability is a significant limitation to treatment of pancreatic cancer with radiotherapy due to close proximity with highly radiosensitive organs at risk and respiratory motion necessitating expanded target margins. Further, pancreatic tumors are difficult to visualize on conventional radiotherapy systems. Surrogates are often used to locate the tumor but are often inconsistent and do not provide linear positional relations throughout the respiratory cycle.
Methods: This work utilizes a retrospective dataset of 45 pancreatic cancer patients treated on an MR-Linac system with cine MRI acquired during every treatment fraction for real-time target tracking. We investigated intra-fraction tumor motion and prediction models from surrogates. Patient specific motion evaluation and prediction models were generated from 225 cine MRI series acquired during treatment. Linear regression and principal component analysis (PCA) based models were used to predict tumor position from abdominal surface anterior-posterior (AP) motion, diaphragm superior-inferior (SI) motion, or a combination of the two to determine tumor position. Models were evaluated using mean squared error (MSE) and mean absolute error (MAE).
Results: Contour analysis showed that pancreatic tumors had an average motion range of 7.4±2.7mm and 14.9±5.8mm in the AP and SI directions, respectively. The PCA model had MSE of 0.6mm² and 1.4mm² for the AP and SI directions, respectively, with both surrogates as inputs for the models. When only the abdomen surrogate was used, MSE was 1.3mm² and 0.4mm² in the AP and SI directions, while it was 0.4mm² and 1.3mm² when the diaphragm surrogate was used.
Conclusion: The models were able to accurately calculate the pancreatic tumor position from diaphragm, abdominal, or a combination of both contours within the standard pancreatic cancer target margin, and the process could be readily applied to other disease sites in the abdominothoracic cavity.
Funding Support, Disclosures, and Conflict of Interest: This research was partially supported by the Alvin J. Siteman Cancer Center through The Foundation for Barnes-Jewish Hospital and the National Cancer Institute (P30 CA091842). Dr. Jin Sung Kim was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2020R1A4A101661911).
IM/TH- MRI in Radiation Therapy: MRI/Linear accelerator combined- IGRT and tracking