Author: Girish Bal, David J. Carlson, Huixiao Chen, Zhe (Jay) Chen, Emily A. Draeger, Dae Yup Han, Henry S. Park 👨🔬
Affiliation: RefleXion Medical, Department of Therapeutic Radiology, Yale University School of Medicine 🌍
Purpose: This study explores the feasibility, accuracy, and dosimetric performance of hybrid biology-guided radiotherapy (BgRT) combined with image-guided radiotherapy (IGRT) for delivering sequential integrated boost to overlapping target areas. BgRT uses real-time PET signals to guide the targeted radiation. This approach enables delivering targeted patient-specific spatial dose distributions for lesions with heterogenous PET uptake.
Methods: A custom ArcCHECK phantom insert, featuring a spherical target (ball) over a C-shape target was used to simulate heterogeneous 18F-FDG PET uptake. The spherical target was filled with 18F-FDG (tumor-to-background ratio: 20:1). Two planning targets were defined: BGRT_PTV (ball) for Treatment Area 1 (TA1/shrinking-field BgRT boost) and IGRT_PTV (ball + C-shape) for Treatment Area 2 (TA2 /base IGRT area). After functional modeling, the PET/CT image was used to prepare two sequential treatment plans, prescribing 12 Gy to TA1 and 16 Gy to TA2. Beam delivery accuracy was assessed using ArcCheck dosimetry and ion chamber measurements, and treatment plans were compared to assess dosimetric congruence and spatial accuracy.
Results: The clinical system successfully treated the overlapping targets, achieving expected dose painting and boosted dose delivery aligned with the PET signals and plan objectives / constraints. Dosimetric measurements demonstrated excellent agreement with planned doses, with a gamma passing rate of 98.3%, 96.7 %, and 93.7% for criteria of 3%/3mm, 3%/2mm, and 2%/2mm, respectively. In addition, point dose deviation is within 3% (measured vs. calculated).
Conclusion:
This first phantom testing for hybrid IGRT-BgRT demonstrates the feasibility and accuracy of delivering sequential radiation boost to the tumor using PET guided radiotherapy. The approach addresses challenges associated with treating complex heterogenous lesions, providing a novel solution for spatially tailored dose escalation. Further investigations will focus on validating BgRT+IGRT applications in clinical settings and exploring the potential of BgRT multi-target treatment modality for managing overlapping treatment areas in the same session.