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Efficiency of Flattening Filter Free Beam in Volumetric Modulated Arc Therapy for LIVER and Lung SBRT Plans

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S Andavar

S Andavar*, V Roshan , A Dhiman , J Singh , Shri Mata Vaishno Devi Narayana Superspeciality Hospital, Jammu, Jammu and Kashmir


SU-I-GPD-T-627 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: The aim of the study was to explore the metrics of Flattening Filter Free beam with combination of Volumetric Modulated Arc Therapy for LIVER and Lung SBRT plans.

Methods: In this study nine suitable CT sets of images were taken from CMS Monaco V 5.11.0. The tumor and critical organs was delineated using the three different phases of CT images. These patients were planned for stereotactic body radiotherapy with the prescription dose of 60Gy in 3 Fractions. For each patient Volumetric Modulated arc stereotactic plans were generated using Elekta Versa HD machine with 6MV photon beam model. The same optimization parameters were used to generate the FFF-VMAT plans. The Stereotactic dosimetric indices such as OAR dose, Maximum dose, prescription isodose coverage, high dose spillage and intermediate spillage were used to evaluate the plan. Other indices such as number of monitor unit and treatment deliver time also evaluated.

Results: For comparison purpose each plans was normalized to cover 99% of the target volume receives a minimum of 90% of the prescription dose.Removal of flattening filter increases the dose rate. Averaged beam on time (BOT) of the FFF-VMAT plans was decreased by 47.7%, which is statistically significant. Difference of the target coverage and OAR sparing between the flattened and unflattened beams were statically insignificant. Stereotactic indices were comparable in both the plans. 6MV flattened beam plans were averagely 3.2% more heterogeneous than unflattened beam.

Conclusion: In terms of treatment time, treatment with small target size and less MLC movement could benefit more from the increased dose rate of the FFF beam. Decreasing the beam on time in stereotactic delivery was valuable in terms of patient comfort and less Intrafraction movement during the treatment delivery.

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