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Dosimetric Evaluation On the Reduction of Rib Dose in Stereotactic Body Radiation Therapy (SBRT) of Peripheral Lung Tumors Proximal to Chest Wall Using Field-In-Field (FiF) Technique and Monte Carlo Based Calculation Algorithm

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E Sam Jeyakumar

E Sam Jeyakumar1*, N Demez2 , F Wang3 , R Badkul4 , (1) Christian Medical College, Vellore, Tamil Nadu, (2) University of Kansas Hospital, Overland Park, KS, (3) Univ of Kansas, Kansas City, KS, (4) University of Kansas Hospital, Kansas City, KS


SU-F-FS2-2 (Sunday, July 30, 2017) 2:05 PM - 3:00 PM Room: Four Seasons 2

Purpose: To evaluate 3D-conformal FiF treatment planning technique for reduction of rib doses in SBRT of peripheral lung tumors proximal to chest wall computed by Monte Carlo based XVMC algorithm following RTOG-0915 guidelines.

Methods: 10 SBRT lung patients were treated with 50 Gy in 5 fractions using hybrid 3D-conformal technique (non-FIF) with two non-coplanar conformal arcs and 3 to 5 conformal beams on Varian Novalis-TX using 6 MV photons and HD-MLC. Brainlab-iplan treatment planning system using Monte Carlo algorithm was utilized for planning. FiF treatment plans were retrospectively planned for all 10 patients while keeping the same PTV coverage with the intention to reduce rib doses as compared to non-FiF plans. Rib doses of 0.5cc (D0.5), 1.0cc (D1), 2.0cc (D2), 5cc (D5) and 30 Gy volume (V30) were analysed.

Results: The average rib doses D0.5, D1, D2 and D5 were 51.72±4.37 Gy (range, 42.6 – 56.8 Gy), 49.38±6.42 Gy (range, 36.0 – 57.1 Gy), 46.20±7.8 Gy (range, 29.3 – 53.7) and 37.84±9.64 Gy (range, 19.3 – 49.1) respectively for FiF plans compared to 55.27±4.99 Gy (range, 46.9 – 63.7 Gy), 52.92±6.58 Gy (range, 40.3 – 63.6 Gy), 49.77±8.34 Gy (range, 33.3 – 60.6 Gy) and 41±10.21 Gy (range, 21.5 – 54.1) respectively for non-FiF reference plans. Rib doses were reduced for FiF plans, D0.5 by 6.4%, D1 by 6.7%, D2 by 7.2% and D5 by 7.7% as compared to non-FiF reference plans. Ribs average V30 was also reduced by 14.8% for FiF plans.

Conclusion: Overall doses to ribs were reduced using FiF technique in SBRT of peripheral lung tumors. This study shows that FiF 3D-conformal technique with Monte Carlo based calculations can be successfully utilized to reduce the chest wall toxicity, where PTVs are proximal or extending into the chest wall, without using complex IMRT or VMAT techniques.

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