Sep 29

SS 30 - Radiation and Cancer Physics 4: Novel Treatment Techniques and Early Clinical Experience

274 - First-in-Human Dual Modality Radiotherapy Treatment in a Single Plan Using Biology-Guided Radiotherapy: A Case Report

05:10pm - 05:20pm PT

Room 154

Presenter(s)

Henry Park, MD, MPH - Yale University, New Haven, CT

H. S. M. Park¹, H. Chen¹, E. Draeger¹, L. Tressel¹, J. J. Kim¹, K. L. Johung¹, M. R. Young¹, K. A. Al Feghali², D. de Jong², Z. Chen¹, and D. J. Carlson¹; ¹Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, CT, ²RefleXion Medical, Inc., Hayward, CA

Purpose/Objective(s): Biology-guided radiotherapy (BgRT) is an innovative radiotherapy technique that utilizes PET emissions from a tumor to dynamically guide beam delivery in real time. Recent technological advancements have enabled the integration of BgRT with stereotactic body radiotherapy (SBRT) to treat multiple lesions within a single plan or through multiple concurrent plans, a strategy known as multi-target treatment (MTT). We report the first clinical case incorporating both BgRT and SBRT within a single treatment plan for lung and kidney metastases, highlighting the associated technical and clinical considerations.

Materials/Methods:

In August 2024, a patient with an oligoprogressive ultra-central right lung metastasis of thymic origin, measuring 3.8 cm, was assessed for eligibility for biology-guided radiotherapy (BgRT). The criteria included a tumor size between 2–5 cm, an SUVmax greater than 6, and a location at least 2 cm away from FDG-avid critical structures. During this evaluation, an additional 2.4 cm oligoprogressive lesion in the left kidney was incidentally detected. The treatment plan consisted of delivering 40 Gy in five fractions, with BgRT targeting the lung lesion and stereotactic body radiotherapy (SBRT) directed at the kidney lesion. For BgRT, the planning target volume (PTV) was established by applying a 5 mm margin around the gross tumor volume (GTV) as identified on a single-phase (50%) 4D scan. A single treatment plan was optimized to cover both targets simultaneously.To ensure precise BgRT delivery, each fraction and the initial PET modeling scan were preceded by a 15 mCi FDG injection, followed by a PET prescan conducted 60 minutes post-injection to confirm sufficient FDG activity. The BgRT target was treated first, followed by SBRT for the kidney lesion.

Results: The multi-target treatment (MTT) was delivered successfully with high conformity. Synthetic PET imaging showed the lung tumor met BgRT criteria (AC =5 kBq/ml, NTS =2.7), confirmed on the functional PET scan. FDG dose remained within 2% uncertainty, with consistent uptake time (60±3 min), AC =15 kBq/ml, and NTS =7 despite tumor shrinkage. Target coverage stayed at 100%, meeting all dose constraints. Average treatment time per fraction was 36 min 9 sec for BgRT and 16 min 8 sec for SBRT.

Conclusion: This first successful multimodality MTT case marks a significant step in assessing BgRT’s reliability for multi-target treatment. With expanding BgRT indications, this approach could be adapted to different tumor sites and tailored to patient needs.