Room: AAPM ePoster Library
Purpose: To quantify the clinically achieved improvements in daily delivered dose distributions when performing MR-linac guided online adaptive radiotherapy.
Methods: Seventy-two fractions of online adaptive MR-guided radiotherapy was performed clinically for 35 human subjects accrued to an IRB-approved clinical trial. Online adaptation was performed when the predicted dose distribution for the anatomy segmented on the daily volumetric MR scan (Plan-P) failed to meet the treatment planning objectives established in the initial plan (Plan-INT). In those situations, an online adaptive plan was created and delivered (Plan-ART). Radiation dose distributions from all three plans were compared for the planning target volume (PTV) and multiple organs-at-risk (OAR): bowel, kidneys, duodenum, spinal cord, sigmoid, stomach, rectum, esophagus, chest wall, liver, lung, heart, proximal bronchial tree. The subjects were treated with the treatment plan that best met the treatment planning objectives.
Results: Online adaptation was indicated for at least one fraction, and on average nearly half the fractions, for 80% of patients in this study. Within the adapted fractions (N=72), the indication for adaptation was inadequate PTV coverage (64% occurrence) and/or excessive OAR doses (84% occurrence). The most common OAR to exceed dose-constraints were within the gastrointestinal (duodenum & bowel), due to their mobility with respect to the PTV. When compared to Plan-INT, the volume of at least one OAR receiving its dose-constraint increased for Plan-P twofold (65% occurrence) and fivefold (51% occurrence). Consequently, these fractions were clinically delivered using Plan-ART. The Plan-ART fractions increased PTV coverage (V100, 51% occurrence) and reduced the OAR volume exceeding its dose constraint (76% & 48% occurrence) when compared to Plan-P and Plan-INT, respectively.
Conclusion: Online adaptation was frequently indicated, both for reduced PTV coverage and increased OAR doses. Daily delivered dose distributions using MR-linac guided online adaptive radiotherapy more frequently achieved the physicians stated treatment planning objectives.
Funding Support, Disclosures, and Conflict of Interest: Drs. Bayouth and Mittauer report honorarium and travel expenses by ViewRay Inc., and co-founders of MR Guidance, LLC.