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Treatment Plan Comparison of Normal Tissue Objective Vs. Customised Stereotactic Radiosurgery Normal Tissue Objective for Multiple Target Radiosurgery

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P Houston

P Houston*, S Smith , NHS Greater Glasgow and Clyde


SU-I-GPD-T-564 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To evaluate the effects of Normal Tissue Objective(NTO) and Stereotactic Radiosurgery Normal Tissue Objective(SRSNTO) in radiotherapy treatment planning to reduce dose to normal brain whilst maintaining PTV coverage.

Methods: Twenty patients with multiple cranial metastases, treated in a single fraction, were planned using the Eclipse Treatment Planning System [Varian Medical Systems]. NTO and SRSNTO were compared as means of controlling dose. Plans included 5 non-coplanar arcs with a single isocentre placed at the centre of mass of the target. Plans were optimized using standard objectives with both NTO and SRSNTO. Plans were also calculated with no upper constraint on target dose.

Results: PTV coverage was comparable amongst the techniques. D2% to PTV increased by 1% when planning with SRSNTO compared to NTO. SRSNTO with no upper objectives results in increased D2% by 13% compared to with standard objectives.V12Gy to brain was not significantly different (p = 0.1) between NTO and SRSNTO but was significantly reduced (p = 0.01) with SRSNTO with no upper objectives. Mean dose to brain was significantly reduced when optimized with SRSNTO (p = 0.01). Plans optimized with SRSNTO and no upper objectives saw a further decrease in mean dose to brain (p=0.01).V4Gy to brain was reduced by an average of 38cc (range 5cc-259cc) representing an average 28.7% reduction when planning with SRSNTO compared to NTO (p = 0.01). SRSNTO with no upper objectives resulted in a further significant decrease of V4Gy to brain (p=0.01).OAR doses were not significantly changed when planning with NTO or SRSNTO.

Conclusion: Multiple target radiosurgery planning with SRSNTO can result in significantly decreased dose to normal brain with no reduction in PTV coverage. SRSNTO optimised with no upper objectives and no OAR constraints offers an uncomplicated planning solution to reduce brain dose further with little optimizer interaction.

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