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Monte Carlo Versus Ray-Tracing for Treatment Planning Involving CNS Tumors On the MultiPlan System for CyberKnife Radiosurgery

R Teboh Forbang

R Teboh Forbang1*, (1) John Hopkins University, Baltimore, MD


SU-E-T-587 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

MultiPlan, the treatment planning system for the CyberKnife Robotic Radiosurgery system offers two approaches to dose computation, namely Ray-Tracing (RT), the default technique and Monte Carlo (MC), an option. RT is deterministic, however it accounts for primary heterogeneity only. MC on the other hand has an uncertainty associated with the calculation results. The advantage is that in addition, it accounts for heterogeneity effects on the scattered dose. Not all sites will benefit from MC. The goal of this work was to focus on central nervous system (CNS) tumors and compare dosimetrically, treatment plans computed with RT versus MC.

Treatment plans were computed using both RT and MC for sites covering (a) the brain (b) C-spine (c) upper T-spine (d) lower T-spine (e) L-spine and (f) sacrum. RT was first used to compute clinically valid treatment plans. Then the same treatment parameters, monitor units, beam weights, etc., were used in the MC algorithm to compute the dose distribution. The plans were then compared for tumor coverage to illustrate the difference if any. All MC calculations were performed at a 1% uncertainty.

Using the RT technique, the tumor coverage for the brain, C-spine (C3-C7), upper T-spine (T4-T6), lower T-spine (T10), L-spine (L2) and sacrum were 96.8%, 93.1%, 97.2%, 87.3%, 91.1%, and 95.3%. The corresponding tumor coverage based on the MC approach was 98.2%, 95.3%, 87.55%, 88.2%, 92.5%, and 95.3%. It should be noted that the acceptable planning target coverage for our clinical practice is >95%. The coverage can be compromised for spine tumors to spare normal tissues such as the spinal cord.

For treatment planning involving the CNS, RT and MC appear to be similar for most sites but for the T-spine area where most of the beams traverse lung tissue. In this case, MC is highly recommended.

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