Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_10_3211 - Dosimetric Analysis of Stereotactic Body Radiation Therapy for Pancreatic Cancer using MR-Guided Tri-60Co Unit, MR-Guided LINAC, and Conventional LINAC Based Plans

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

Dosimetric Analysis of Stereotactic Body Radiation Therapy for Pancreatic Cancer using MR-Guided Tri-60Co Unit, MR-Guided LINAC, and Conventional LINAC Based Plans
S. J. Ramey1, K. R. Padgett2, N. Lamichhane3, H. Neboori Jr4, D. Kwon5, E. A. Mellon6, K. Brown7, M. Duffy8, J. R. Victoria9, N. Dogan2, and L. Portelance2; 1University of Miami; Jackson Health System, Miami, FL, 2Department of Radiation Oncology, University of Miami, Sylvester Comprehensive Cancer Center, Miami, FL, 3University of Maryland Medical Center, Baltimore, MD, 421st Century Oncology, Modesto, CA, 5Department of Statistics, University of Miami Sylvester Comprehensive Cancer Center, Miami, FL, 6Radiation Oncology Department, University of Miami/Sylvester Comprehensive Cancer Center, Miami, FL, 7Department of Radiation Oncology, University of Miami / Sylvester Comprehensive Cancer Center, Miami, FL, 8University of Miami, Miami, FL, 9ViewRay Inc., Cleveland, OH

Purpose/Objective(s): To perform a dosimetric comparison of two MR-guided radiotherapy systems capable of performing on-line adaptive radiotherapy (ART) versus a conventional radiotherapy system for pancreas stereotactic body radiation therapy.

Materials/Methods: Ten cases of patients with pancreatic adenocarcinoma previously treated in our institution were used for this analysis. MR-Cobalt and MR-LINAC "step-and-shoot" intensity-modulated radiation therapy (IMRT) plans were generated and compared to conventional LINAC volumetric modulated arc therapy (VMAT) plans. The prescription dose was 40 Gy in five fractions covering 95% of the planning tumor volume (PTV40) for the 30 plans. The same organs at risk (OARs) dose constraints were used in all plans. Dose volume-based indices were used to compare PTV coverage and OAR sparing.

Results: The PTV40 conformity index (CI) demonstrated higher conformity in both the LINAC- and MR-LINAC plans compared to the MR-Cobalt plans. While there was no difference in mean CI between LINAC and MR-LINAC plans (1.08 in both), there was a large difference between LINAC and MR-Cobalt plans (1.08 vs. 1.52). Overall, 79%, 72%, and 78% of critical structure dosimetric constraints were met with LINAC, MR-Cobalt, and MR-LINAC plans. The MR-Cobalt plans delivered more dose to all OARs when compared to the LINAC plans. In contrast, the doses to the OARs of the MR-LINAC plans were similar to LINAC plans except in two cases—liver mean dose (MR-LINAC—2 .8 Gy versus LINAC—2.1 Gy) and volume of duodenum receiving at least 15 Gy (MR-LINAC—13.2 cubic centimeters [cc] versus LINAC—15.4 cc). Both differences are likely not clinically significant.

Conclusion: This study demonstrates that dosimetrically similar plans were achieved with conventional LINAC VMAT and MR-LINAC "step-and-shoot" while doses to OARs were statistically higher for MR-Cobalt "step-and-shoot" compared to conventional LINAC VMAT plans due to low dose spillage. Given the improved tumor-tracking capabilities of MR-LINAC, further studies should evaluate potential benefits of ART-capable MR-guided LINAC treatment.

Author Disclosure: S.J. Ramey: Travel Expenses; Intellisphere. K.R. Padgett: None. N. Lamichhane: None. H. Neboori: None. D. Kwon: None. E.A. Mellon: None. K. Brown: None. L. Portelance: Cervix Committee; NRG. Dosimetry Advisory Board; BTG.

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TU_10_3211 - Dosimetric Analysis of Stereotactic Body Radiation Therapy for Pancreatic Cancer using MR-Guided Tri-60Co Unit, MR-Guided LINAC, and Conventional LINAC Based Plans



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