2194 - Dosimetric Evaluation of the Spatial Fractionated Radiotherapy (SFRT) Planning Strategy Combining VMAT and CyberKnife
Presenter(s)
Y. Peng1, K. Yuan1, F. Yang2, H. Guo2, and W. Xianliang3; 1Sichuan Cancer Hospital and Research Institute, University of Electronic Science and Technology of China, Chengdu, China, Chengdu, China, 2Sichuan Cancer Hospital & Institute, Chengdu, China, 3Sichuan Cancer Hospital & Institute, Sichuan Cancer Center, School of Medicine, University of Electronic Science and Technology of China, Radiation Oncology Key Laboratory of Sichuan Province, Chengdu, 610041, China
Purpose/Objective(s): Spatially fractionated radiation therapy (SFRT) delivers a high dose to certain areas within the gross tumor volume (GTV) and reduces the radiation toxicity to normal tissues. For SFRT based on VMAT, due to the limitations of the machine's hardware conditions, both PVDR and ADR are at relatively low values. In contrast, PVDR and ADR can reach relatively good values based on Cyberknife. However, when GTV has a relatively large volume, Cyberknife requires a long treatment time making it unsuitable for clinical treatment. Therefore, we have designed a novel planning strategy that uses the Cyberknife to design a high dose for the lattice points and the VMAT to provide low-dose coverage for GTV. This approach can achieve relatively high PVDR and ADR values and ensure that the treatment time is feasible for clinical treatment.
Materials/Methods: 44 approved SFRT plans (including 31 cases of VMAT and 13 cases of Cyberknife) has been analyzed with the dose distribution and treatment time retrospectively for patient with head/neck tumors with the volumes ranging from 52.04 to 770.82 cc. In addition, a prospective study was carried out on 12 patients with head/neck tumors with the volumes ranging from 66.74 to 583.22 cc. GTV was delineated and used an independently designed automated program to delineate 3-dimensional spherical lattice points employed by hexagonal close-packed arrangement in GTV. The radius of the lattice points ranged from 3.0 to 4.0 mm, spaced center-to-center ranged from 30.0 to 36.0 mm apart, and the distance from the center of the lattice points to the edge of the GTV was greater than 10.0 mm. A new SFRT planning strategy combining VMAT and Cyberknife was adopted by using Cyberknife to design a high dose for the lattice points, and VMAT to provide low-dose coverage for the GTV.
Results: In SFRT plans, each lattice point were disconnected by using 50% of the lattice prescription dose in GTV. Dosimetry analysis was performed on VMAT cases, with PVDR at 2.64 ± 0.23 and ADR at 1.52 ± 0.37. For Cyberknife cases, PVDR could reach 4.62 ± 0.33 and ADR 3.21 ± 0.46. When the tumor volumes greater than 250cc, the treatment time would exceed 60 minutes in Cyberknife and not suitable for clinical treatment. In a prospective study, a novel SFRT planning strategy combining VMAT and Cyberknife was adopted. The treatment time for large-volume tumors could be controlled within 60 minutes with PVDR at 3.57 ± 0.28 and ADR at 2.66 ± 0.32. This strategy could achieve a dose distribution superior to VMAT plans and effectively control the treatment time.
Conclusion: The novel SFRT planning strategy combining VMAT with Cyberknife involves designing the dose at lattice points through Cyberknife and using VMAT to cover the GTV with low doses. This approach enables the maximization of the peak-to-valley dose ratio (PVDR) and ablation ratio (ADR) while minimizing the treatment time for patients and enhances the therapeutic effect of SFRT on large-volume tumors.