SU-E-T-85: A Systematic Analysis of Mono-Isocentric Techniques for the Treatment of Multiple Metastasis

Authors


Abstract

Purpose:

In this planning study, we compared two mono-isocentric techniques for the treatment of multiple brain metastasis. We hypothesize that, dynamic conformal arc delivery produces significantly more efficient plans of similar quality when compared to volumetric modulated arc therapy (VMAT).

Methods:

Recently published clinical data demonstrated a benefit in treating multiple brain metastasis (more than four mets) with SRS. A number of publications showed the feasibility of planning such patients with VMAT. In our study, we planned ten SRS patients with three to eight brain metastasis. The Varian eclipse system used four arcs with a VMAT optimized delivery whereas the Brainlab multiple elements software (MME) selected between 3 and 7 optimized arcs to deliver the prescribed dose using a hybrid conformal arc technique (non-IMRT).

Results:

We have found that both planning systems achieved the goal to deliver the prescribed dose to the 99.5% of the tumor volume. The tumor doses ranged from 18 to 24Gy, following the RTOG criteria, with most tumors receiving 24Gy. The VMAT and MME plans had varying maximum doses for each tumor and were on average at least 132% of the prescribed dose. We found that once the segmentation and the plan objectives were specified the MME plan was the fastest to compute (less than 3min) whereas the VMAT took on average an hour to calculate with the AAA engine and 15 minutes with the Acuros engine (dose grid resolution of 1mm).

Conclusion:

Patients with multiple brain metastasis can be treated very efficiently using a mono-isocentric non-IMRT delivery technique. Whereas VMAT produces equivalent plans, it takes longer to both compute and deliver with the added complexity of IMRT delivery.

UTHSCSA, division of medical physics has a research grant with Brainlab

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