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Improving Normal Brain Sparing with Increasing Number of Arc Beams for Volume Modulated Arc Beam Radiosurgery of Multiple Brain Metastases

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S Hossain

S Hossain1*, K Hildebrand1 , S Ahmad1 , D Larson2 , A Sahgal3 , L Ma2 , (1) University of Oklahoma Health Science Center, Oklahoma City, OK, (2) University of California San Francisco, San Francisco, California, (3) University of Toronto, Toronto, Ontario


SU-E-T-568 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Intensity modulated arc beams have been newly reported for treating multiple brain metastases. The purpose of this study was to determine the variations in the normal brain doses with increasing number of arc beams for multiple brain metastases treatments via the TrueBeam Rapidarc system (Varian Oncology, Palo Alto, CA).

Methods: A patient case with 12 metastatic brain lesions previously treated on the Leksell Gamma Knife Perfexion (GK) was used for the study. All lesions and organs at risk were contoured by a senior radiation oncologist and treatment plans for a subset of 3, 6, 9 and all 12 targets were developed for the TrueBeam Rapidarc system via 3 to 7 intensity modulated arc-beams with each target covered by at least 99% of the prescribed dose of 20 Gy. The peripheral normal brain isodose volumes as well as the total beam-on time were analyzed with increasing number of arc beams for these targets.

Results: All intensisty modulated arc-beam plans produced efficient treatment delivery with the beam-on time averaging 0.6-1.5 min per lesion at an output of 1200 MU/min. With increasing number of arc beams, the peripheral normal brain isodose volumes such as the 12-Gy isodose line enclosed normal brain tissue volumes were on average decreased by 6%, 11%, 18%, and 28% for the 3-, 6-, 9-, 12-target treatment plans respectively. The lowest normal brain isodose volumes were consistently found for the 7-arc treatment plans for all the cases.

Conclusion: With nearly identical beam-on times, the peripheral normal brain dose was notably decreased when the total number of intensity modulated arc beams was increased when treating multiple brain metastases.

Funding Support, Disclosures, and Conflict of Interest: Dr Sahgal and Dr Ma are currently serving on the board of international society of stereotactic radiosurgery.

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