A Comparative Dosimetric Study of Spine SABR Using Two MLC Delivery Systems with Pencil Beam and Monte Carlo Algorithms
J Rahimian1, J Zhang2*, J Vinci3, (1)Kaiser Permanente, Los Angeles, CA, (2) Kaiser Permanente Anaheim Medical Center, CA,(3) Kaiser Permanente, Los Angeles, CA
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PO-GePV-T-411 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: The purpose of this study is to compare two High Definition (HD) and Millennium (MM) MLC Linac dose delivery systems for the treatment of spine SABR using both Pencil Beam (PB) and Monte Carlo (MC) dosimetry algorithms.
Methods: We contoured 3 PTVs at the C-Spine, T-Spine, and L-Spine levels of 4 anonymized patients. We created a total of 48 VMAT plans using both PB and MC dosimetry algorithms with High-Definition MLC (HD) and 120-leaf Millennium MLC 6XFFF beam models. Each plan was optimized to deliver 16Gy in a single fraction using 3 VMAT arcs. The cord and cauda equina were contoured and the dose to these structures was minimized. The treatment plans and the dosimetry algorithms were compared for each PTV and dose delivery system.
Results: There was a statistically significant difference between the MC and PB algorithms for the mean and the maximum dose to the T-spine PTVs using the HD MLC beam (p-values 0.003 and 0.004, respectively). There was no statistically significant difference between the MC and PB dosimetric algorithms for both HD and MM beam models and delivery systems for the VMAT plans to target the C and L-spine. Furthermore, there was no statistically significant difference between the conformity and gradient indices of the HD and MM MLC delivery systems for the spinal lesions. When comparing the mean dose to all 3 PTVs at C, T, and L-spine, there is a statistically significant difference between the PB and MC dosimetry algorithms for both HD and MM MLC delivery systems (p-Values 0.01 and 0.003, respectively).
Conclusion: Compared to MC, the PB overestimated the T-spine tumor dose due to VMAT beams traversing through the soft tissue-lung-bone heterogeneous regions. The conformity and gradient indices of the HD and MM MLC Linac delivery systems are similar when treating spinal lesions due to their larger PTV size. PB overestimates the dose significantly in targets located in heterogeneous areas. Further studies are warranted.
Keywords
Stereotactic Radiosurgery, Monte Carlo, MLC
Taxonomy
Not Applicable / None Entered.
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