Room: Exhibit Hall
Purpose: To explore tangential VMAT planning technique consisting of multiple short arcs using AutoPlan on Pinnacle for left breast radiotherapy.
Methods: Ten left-sided breast cancer patients with gated CT scans were randomly chosen from our patient database for this study. Structures of left breast tissue (PTV), heart, left-lung, right-breast and right-lung are delineated. Tangential VMAT plans consist of 4-6 partial arcs with gantry rotating from 300-0 degrees (IEC) for medial beams, 110-170 degrees for lateral beams with collimator angels of 5 or 355. Jaws are manually preset similar to 3DCRT tangential beams to minimize doses to heart and left-lung. Treatment plans were optimized using AutoPlan module in Pinnacle (Pinnacle Version 9.10, Philips Radiation Oncology Systems). Prescription dose of 45Gy/25fx is chosen to cover at least 95% of planed PTV volumes. 3DCRT and IMRT plans are also generated for comparison purposes.
Results: Tangential VMAT provides better dose homogeneity to the treated volume. Compared to the 3DCRT and IMRT techniques, all VMAT plans offer better heart and left-lung dose sparing; the mean heart doses were 5.85Gy (3DCRT), 3.60Gy (IMRT) and 1.95Gy (VMAT), the mean left-lung doses were 9.27Gy (3DCRT), 6.25Gy (IMRT) and 3.69Gy (VMAT ). The right-lung mean doses were 0.28Gy (3DCRT), 0.20Gy ( IMRT) and 0.14Gy (VMAT). The right-breast mean doses were 0.28Gy (3DCRT), 0.22Gy (IMRT) and 0.10Gy (VMAT). Delivery time of each VMAT beams was tested on our treatment machine Varian 21iX. Each VMAT beam could be delivered within 21 seconds.
Conclusion: Multiple-short-arc tangential VMAT auto-plan achieved comparable or better dose distributions while minimizing doses to right-lung and right-breast compared to 3DCRT and tangential IMRT. Pinnacle Auto Plan could be helpful to achieve better left-lung and heart sparing. The short beam delivery time might potentially be used for deep breath hold breast treatments, where more heart sparing is desirable.