Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_1_3119 - Whole-Brain Hippocampal-Sparing Treatment Planning on a Novel Jawless Linear Accelerator

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

Whole-Brain Hippocampal-Sparing Treatment Planning on a Novel Jawless Linear Accelerator
R. J. Lalonde, D. E. Heron, and M. S. Huq; UPMC Hillman Cancer Center, Pittsburgh, PA

Purpose/Objective(s): To study the dosimetric performance and treatment efficiency of a novel jawless ring gantry linear accelerator designed for rapid intensity modulated deliveries (IMRT/VMAT) for whole-brain irradiation with hippocampal sparing (NRG protocol CC003).

Materials/Methods: A new jawless ring gantry linear accelerator is now commercially available that uses faster rotation than conventional linacs, a high dose rate 6X-FFF beam, and a fast MLC system for rapid delivery of IMRT/VMAT plans. Beam shaping is currently limited by MLC leaves of 1cm width (28x28cm2 maximum field size at 100cm), and by the lack of the capability to use non-coplanar fields. We compared the performance of this system with a conventional linac with 0.25 cm MLC leaves for a complex protocol for whole brain irradiation with hippocampal sparing. We tested the ability of each system to achieve protocol dose goals and compared time of treatment delivery for 10 patient plans, planned with both 9-field IMRT and 3-arc VMAT delivery.

Results: Results of the dosimetric comparison showed that both systems were capable of achieving all protocol dose goals for targets and organs at risk. Dose coverage to 98% of the PTV volume was significantly lower for the ring gantry linac, averaging 25.74 Gy vs 27.1 Gy for the conventional linac (P= 0.001). Maximum dose to the hippocampus (0.035cc) was not significantly different, averaging 12.65 Gy for the ring gantry linac vs 12.63 Gy for the conventional linac. However, treatment delivery time on the ring gantry linac was significantly reduced by a factor of 1.85 for VMAT plans and 2.19 for IMRT plans.

Conclusion: The new ring gantry accelerator is able to deliver whole brain hippocampal-sparing plans in significantly less time than a conventional linac. Although both systems are able to meet protocol dose goals, the conventional linac plans showed improved target dose coverage.

Author Disclosure: R.J. Lalonde: Chief Scientific Officer; D3 Oncology Solutions. D.E. Heron: No personal compensation; Accuray Exchange in Radiation Oncology. Partnership; Cancer Treatment Services International. Vice Chairman of Clinical Affairs; University of Pittsburgh School of Medicine. Director of Radiation Services; UPMC CancerCenter. M. Huq: Honoraria; Varian Medical Systems. Chair, Therapy Physics Committee (TPC); AAPM. Vice chair, Science Council; American Association of Physicists in Medicine.

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