3024 - Evaluating Breast Radiotherapy Planning with Dynamic Collimator Rotation and Automated Static Angle Port Selection: A Comparative Dosimetric and Physician Analysis
Presenter(s)
E. Hubley1, E. Berlin1, Y. Gao1, B. Koger1, K. P. Risolo Jr1, and K. K. Teo2; 1Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, 2Department of Radiation Oncology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
Purpose/Objective(s): A new treatment planning and delivery solution, VMATp, integrates static-angle modulated ports (STAMPs) and dynamic collimator rotation within arc delivery to combine the dosimetric advantages of static-gantry IMRT and VMAT. STAMPs may be placed manually or automatically. The plan quality of VMATp with manual and automatic STAMP placement was compared to standard VMAT for 14 patients receiving breast or chestwall and regional lymph node treatment on an O-ring linear accelerator.
Materials/Methods: For each patient, a VMAT plan and VMATp plans with manual and automatic STAMP placement were created. 1cm of skin flash was added to all plans. All plans used a multiple isocenter field setup to extend the coverage in the superior-inferior direction. VMAT plans used 1-2 arcs per isocenter. All VMATp plans used 1 arc per isocenter. Two STAMPs were manually placed, approximating each tangent angle, for a total of 4 STAMPS per arc. In the auto-STAMP plans, the optimizer placed 1-3 STAMPs per arc. Dose-volume metrics were recorded for primary and nodal PTVs and organs at risk (OARs). A breast radiation oncologist (RO) performed a blinded review of all plans and ranked the three plans for each patient. A plan preference checklist was provided, including: target coverage, hot spots and dose heterogeneity, heart sparing, lung sparing, contralateral breast sparing, conformality, and a free-text box.
Results:
Heart mean, ipsilateral lung V4Gy, V8Gy, V16Gy, contralateral lung V4Gy, and contralateral breast V3Gy were all significantly reduced in both VMATp plans compared to VMAT. No DVH metrics were significantly different between manual and automatic VMATp plans. There were no significant differences in the PTV coverage between any plans. The RO selected the manual VMATp plan as their preferred plan in 9/14 patients, automatic VMATp for 4 patients, and VMAT for 1 patient. For the patient with VMAT plan preferred, the RO indicated target coverage and conformality were better. Manual VMATp plans were preferred over automatic VMATp in 10/14 cases, with target coverage, lung sparing, and heart sparing as the most common reasons. When automatic VMATp was preferred, lung sparing was the most common reason.Conclusion: VMATp with manual or automatic STAMP placement produced plans with significantly lower OAR doses compared to VMAT. A breast RO preferred VMATp plans over VMAT plans in all but one patient, and more frequently preferred manual STAMP placement over automatic STAMP placement.
| manual VMATp | auto VMATp | VMAT | ||
| PTVp | D95% (%) | 95.7 ± 1.0 | 95.8 ± 1.0 | 94.4 ± 2.1 |
| PTVn | D95% (%) | 95.5 ± 1.4 | 95.3 ± 1.4 | 96.4 ± 2.0 |
| Heart | Dmean | 2.4 ± 0.5 | 2.6 ± 0.6 | 3.5 ± 1.0 |
| Lung_Ipsi | V4Gy (%) | 61.4 ± 13.0 | 66.3 ± 13.1 | 79.8 ± 13.0 |
| Lung_Ipsi | V8Gy (%) | 42.4 ± 11.1 | 43.8 ± 10.3 | 60.0 ± 15.5 |
| Lung_Ipsi | V16Gy (%) | 24.5 ± 7.9 | 24.7 ± 6.8 | 35.4 ± 9.5 |
| Lung_Contra | V4Gy (%) | 18.8 ± 15.2 | 19.3 ± 12.2 | 34.6 ± 15.9 |
| Breast_Contra | V3Gy (%) | 13.8 ± 11.0 | 12.6 ± 9.2 | 28.9 ± 26.3 |