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Hybrid Arc: Combination of IMRT and VMAT Techniques in the Treatment of Prostate Cancer- A Planning Study

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Y Saglam

Y Saglam1,2* , A Bingolbali2, Y Bolukbasi1 , V Alpan1 , U Selek1 , 1) American Hospital-MD Anderson Radiation Treatment Center-Istanbul, Istanbul,Turkey (2) Yildiz Technical University, Istanbul, Turkey


SU-I-GPD-T-292 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Evaluate a potential hybrid radiotherapy approach for prostate cancer patients in comparison to VMAT to increase target dose conformality and organ at risk (OAR) sparing.

Methods: The cohort for this dosimetric planning study included ten consecutive prostate cancer patients treated with double arc VMAT to 78 Gy. New plans per patient were generated on Pinnacle TPS by Hybrid technique combining IMRT (8 step-and-shoot fix fields: 225°, 260°, 295°, 330°, 30°, 65°, 90°, 135°) and VMAT (182°-178° clockwise) with equal weight (50% each).

Results: The Hybrid technique revealed significantly lower rectum (D35 26.66 Gy vs 37.06 Gy, D50 16.88 Gy vs 22.63, etc. p:0.005) and bladder (D35 18.93 Gy vs 24.66 Gy, D50 11.37 Gy vs 15.35, etc. p:0.005) doses compared to VMAT except bladder V80 with a difference of -0.18 Gy. Maximum doses of penile bulb and femoral heads were also lower by the Hybrid technique while mean doses were similar (Penis bulb Max: 44.7 Gy vs 51.7 Gy, p:0.005 and mean 22.1 Gy vs 24.5 Gy, p:0.093, femoral heads Max: 45.54 Gy vs 50.19 Gy p:0.028 and mean 19.37 Gy vs 22.76 Gy). Maximum PTV doses were similar in both techniques, while clinically non significant mean PTV dose difference appeared statistically significant (VMAT 79.95, Hybrid 80.02 Gy, p:0.047). Target dose conformity and the homogeneity were found to be similar. Mean MUs of the Hybrid technique was slightly but significantly higher than double arc VMAT technique (678.7MU vs 776.9 MU, p:0.037); though the hybrid technique ensured lower whole body radiation than double arc VMAT (V5 18.8% vs %22, p:0.008, V10 14.30% vs %17.30, p:0.007).

Conclusion: The hybrid technique appears to combine the advantanges of IMRT and VMAT to seek for a more conformal and homogeneous plans with better OAR sparing in comparison VMAT.

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