PV QA 3 - Poster Viewing Q&A 3
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.
The asset you are trying to access is locked. Please enter your access key to unlock.