Room: AAPM ePoster Library
Purpose: MRI-ART and RO-IMPT encompass two of the most sophisticated treatment modalities currently available in radiation therapy. RO-IMPT benefit from the ability to create highly conformal plans and minimize dose to organs at risk (OARs) while MRI-ART allows for daily adjustments fractions using high fidelity imaging. Limited studies have been completed that directly compare the two modalities.
Methods: A simulated MRI-ART treatment course was created from a previously treated MR-guided SBRT patient. Electron density information and contours from a pretreatment CT scan were deformably registered to daily MRIs. GTV and OAR volumes were recontoured and each fraction independently optimized to the preference of an attending physician. The dose data from all fractions were deformably accumulated back onto the pretreatment CT. A single RO-IMPT plan was created on the pretreatment CT. The proton fluence of this plan was projected on the daily deformed CT scans and the resultant daily dose distributions were deformably accumulated back onto the pretreatment CT. The adaptive photon plans were then compared against the proton plan.
Results: Over the entire treatment course, the MRI-ART was adjusted to prioritize sparing of the stomach, this resulted in the 50 Gy prescription dose being delivered to only 57% of the GTV. The RO-IMPT plan was able to cover 81% of the GTV and provided OAR sparing to the duodenum (Dmax 0.05 vs. 22.35 Gy), large bowel (Dmax 21.6 vs. 30.4 Gy), and uninvolved liver (V21Gy 47 vs. 183 cc). Without daily adaptations RO-IMPT was less sparing to the stomach that MRI-ART (Dmax 56.0 vs. 39.2 Gy).
Conclusion: The RO-IMPT plan was capable of maintaining high GTV coverage while minimizing dose to most OARs despite interfractional anatomy changes. However, without the ability to adaptively replan, sparring of the stomach was not possible when it encroached near the GTV.
Funding Support, Disclosures, and Conflict of Interest: Dr. Portelance received an honorarium from Viewray inc. for a talk delivered in 2019. None of the other authors of this manuscript have any conflicts of interest to report.
Not Applicable / None Entered.