Purpose: In MRgRT, the patients receiving radiation are positioned with arm(s)-up in order to improve the target conformality using lateral beams which may cause them discomfort due to prolonging treatment. In this study, we evaluated the treatment planning quality between the arm(s)-up and arms-down position for liver and pancreatic cancer patients. In addition, we proposed a single structure constraint for some organs at risk to improve the dose optimization process.
Methods: We studied clinical plans for ten cancer patients; five with liver and five with pancreatic tumor treated in 0.35 MRgRT with arm(s)-up position. The same treatment plans were utilized to generate plans with arms-down position by re-optimizing the target doses. For the arms-down plan, the treatment beams were set by avoiding the arms on both sides in order to remove the substantial dose deposition. The dose constraints of some organs at risk such as stomach, small bowel, large bowel, and duodenum were removed and placed as a single structure to reduce the complexity of penalty functions for OAR.
Results: The average target dose coverage for PTV_OPT remains consistent between clinical arm(s)-up; 98.13% and 95.34% and arms-down plan; 98.51% and 97. 61% for both liver and pancreatic cancer patients, respectively. In regard to OAR, the average dose in arms-down; 0.6 cc and 1.66 cc is significantly lower than arm(s)-up; 0.17 cc and 0.91 cc for liver and pancreatic patients respectively. Both arm(s)-up and arms-down patients received the required target dose constraints whereas OARS for pancreatic patients with arm(s)-up position received higher dose constraints than the required amount.
Conclusion: The arms-down approach provided stable and reproducible plans compared to clinical arm(s)-up plans for both liver and pancreatic patients. Treating in arms-down position is expected to increase patient comfort and to provide clinical team convenience with a higher degree of OAR sparing.
Image-guided Therapy, MRI, Radiation Therapy
Not Applicable / None Entered.