Presenter(s)
O. Dawood1, D. S. Mohan2, M. D. Patel1, J. Moreno1, A. Mikaeilian1, R. Khan1, J. Friedman1, L. Johnson3, and M. G. Skinner1; 1Kaiser Permanente, South San Francisco, CA, 2Kaiser Permanente Medical Group, South San Francisco, CA, 3Varian Advanced Oncology Solutions, Newton Highlands, MA
Purpose/Objective(s): Recent work in the ACCEL trial has demonstrated that a non-coplanar, IMRT field arrangement can achieve dosimetrically superior plans in Accelerated Partial Breast Irradiation (APBI) compared to other major phase III clinical trials using 3D-conformal or IMRT techniques, while maintaining equally favorable patient outcomes. However, a non-coplanar IMRT technique increases the risk of gantry-patient collision and treatment complexity. RapidArc Dynamic (RAD) is a new treatment technique that combines static IMRT beams (STAMPs) and volumetric modulated arc therapy (VMAT) into a single, hybrid treatment field, offering the opportunity to realize more efficient delivery without compromising plan quality. This study compared RAD and ACCEL technique APBI plans to assess the potential benefits of this new technology.
Materials/Methods: A total of 38 plans were compared for 19 breast patients (10 left-sided, 9 right-sided). A RAD technique using one partial arc and 3–4 STAMPs was developed. All patients received 26–27 Gy in 5 fractions, with deep inspiration breath-hold (DIBH) used for left-sided treatments. RAD and IMRT plans were generated for each patient using the target delineation and dose constraints from the ACCEL trial. All dose calculations were done using Eclipse 18.1, Acuros dose algorithm (0.2 cm grid size), and planned for a TrueBeam with Millennium MLC.
Results:
The dosimetry averages are listed in Table 1. The RAD treatment plans achieved improved dose conformality in the ipsilateral breast and lung. The heart, contralateral breast, and thyroid dose metrics were essentially equivalent between the two techniques. In addition, average treatment time for RAD plans from beam-on to beam-off was 2.6 min (range:1.4-6.0 min), including breathing breaks for DIBH treatments. In a cohort of 14 prior IMRT patients using ACCEL, the average time was 5.3 min (range: 3.6-7.0 min), including couch rotations between each treatment field. This demonstrates a potential treatment time reduction by 50% with RAD.Conclusion: The RAD technique provides a simpler, faster treatment option, particularly beneficial for patients treated during DIBH. It is a worthy option for APBI and warrants further investigation for additional applications.
| Constraint | Minor variation | Average: IMRT plans | Average: RAD plans | IMRTavg - RADavg | Standard deviation |
| Ipsilateral breast | |||||
| <50% to receive >50% of Rx | 50-60% | 6.9% | 4.7% | 2.3% | 3.5% |
| <25% to receive >95% of Rx | 25-35% | 35.6% | 30.8% | 4.8% | 6.8% |
| Ipsilateral lung | |||||
| <20% to receive >10% of Rx | 20-25% | 15.8% | 12.1% | 3.6% | 5.5% |
| <10% to receive >30% of Rx | 10-13% | 4% | 2.6% | 1.4% | 1.6% |
| Heart (R breast) | |||||
| <5% to receive >5% of Rx | 5-8% | 0% | 0.1% | -0.1% | 0.1% |
| Heart (L breast) | |||||
| <5% to receive >10% of Rx | 15% (lower inner quadrant) | 0.1% | 0% | 0.10% | 0.1% |
| Contralateral breast | |||||
| <3% to receive >3% of Rx | 0% | 0.2% | -0.2% | 0.5% | |
| Thyroid gland | |||||
| <1 cc to receive >3% of Rx | 0 cc | 0 cc | 0 cc | 0.2 cc | |
| Table 1. Averages from IMRT and RAD plans following ACCEL trial dose constraints | |||||