Comparison of Monte Carlo and Pencil Beam Algorithms in Brain Dose Calculations for Stereotactic Radiosurgery of Multiple Brain Metastases
H Jiang*, R Badkul, N Demez, D Johnson, D Soultan, D Craft, University of Kansas Medical Center, Kansas City,KS
Presentations
PO-GePV-T-384 (Sunday, 7/25/2021) [Eastern Time (GMT-4)]
Purpose: In stereotactic radiosurgery, dose to brain tissue is a major factor for necrosis. When multiple brain tumors are present, it is more challenging for accurate brain dose calculations because the brain dose might be the sum of scattered low doses from individual tumor treatments. This retrospective study compared brain doses calculated with Pencil Beam(PB) and Monte Carlo(MC) algorithms for SRS patients with multiple brain metastases.
Methods: Fifteen previously treated patients with number of brain tumors ranging from 7 to 14 were selected. Tumor volume varied from 0.1 to several cc. Treatment planning system was Brainlab iPlan. Each tumor was planned individually with 3 to 4 conformal dynamic arcs, with the isocenter located at the PTV center. Prescription dose was up to 24Gy, dependent on PTV volume. In this study, all these plans originally calculated with PB algorithm were re-calculated with MC algorithm. All arc parameters were kept the same, so that the sole difference in calculations was the algorithm. The data collected for comparison was the 12Gy volume (V12) to brain tissue, which is a common element in evaluating brain radionecrosis.
Results: Differences in brain V12 were discovered. MC usually presented higher V12 than PB. However, the difference varied from case to case. V12 was almost identical for a few cases. For some other cases, the difference reached near 4%. The percentage difference in V12 was not associated with either total PTV volume or number of PTVs. The cause of V12 variation would require further investigations. Even at 4%, the change in V12 might not be significant enough clinically to justify the adoption the MC algorithm.
Conclusion: Even though noticeable difference in brain V12 was discovered between the algorithms, the difference may not be significant enough to revise dose calculation algorithms. PB algorithm is accurate enough for most cases.
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