3165 - Biology-Guided Radiation Therapy for Liver Metastases: Patient Eligibility, Treatment Planning, and Treatment Delivery on the 2nd Generation BgRT System
Presenter(s)
P. Wang1, Y. Liu2, S. Sharma3, A. Groll3, T. Yeung3, A. Liu1, and W. T. Watkins1; 1Department of Radiation Oncology, City of Hope National Medical Center, Duarte, CA, 2City of Hope, Duarte, CA, 3RefleXion Medical, Inc., Hayward, CA
Purpose/Objective(s): Biology-guided radiotherapy (BgRT) for liver metastases has the potential to deliver precision dosimetry to Fludeoxyglucose F18 (FDG) avid tumors, reducing geometric uncertainty and controlling dose in the presence of respiratory motion. This study evaluates patient eligibility, treatment plan quality, and verification of treatment delivery on a second generation BgRT treatment planning and delivery system that is currently under development.
Materials/Methods: Twenty-three consecutive patients with liver lesions treated with magnetic resonance-guided radiation therapy were evaluated for BgRT on the new platform. Patients were excluded from BgRT evaluation due to no activity compared to liver background (n=2) and multiple liver lesions (n=9). The remaining 12 patients were anonymized and imported for evaluation. Radiology-reported Standard Uptake Value (SUVmax) and tumor sizes (GTV and PTV) were compared to BgRT-eligibility metrics, including Activity Concentration (AC), Normalized Target Signal (NTS), and Tumor to Background Ratio (TBR). For eligible patients, treatment plans were developed and evaluated including treatment time, conformity indices (CI100, CI50), PTV coverage, and OAR sparing. Selected patient contours were also planned on dosimetric phantoms with patient targets defined from breath hold images and delivered on the prototype system incorporating 20 mm superior-inferior motion.
Results: Radiology diagnostic review showed SUVmax range from 3.10-12.4 with corresponding AC, NTS, and TBR ranges of 1.03-19.79, 0.95-7.00, and 1.18-3.41, respectively. Conversion between SUVmax and AC depends on the target size due to volume-averaging effects, and the ranges of GTV and PTV volumes were 0.7-282.1 cc and 3.00-384.00 cc, respectively. Based on first-generation BgRT thresholds for treatment (AC>5kBq/ml, NTS>2.0), 5/12 (41.6%) patients would be eligible for treatment at diagnostic FDG injection levels (5-10 mCi FDG injection). The second-generation BgRT system has the potential to treat at lower thresholds, allowing for higher eligibility among liver lesions: 10/12 (83.3%) patients had AC>2.7 kBq/ml, and 11/12 (91.7%) had NTS>1.4. Plan quality demonstrated excellent CI100 (1.03-1.22), the ability to spare normal liver, and avoidance of adjacent bowel with treatment times ranging from 11-36 minutes. Treatment delivery was successful in multiple phantoms with patient contours and mimicked patient Positron Emission Tomography (PET) activity. Accounting for motion during delivery, ion chamber and diode array dosimetry produced excellent agreement with no evidence of dosimetric blur.
Conclusion: The second generation BgRT system may provide significant benefits for patients with liver malignancies. The system can accurately deliver plans designed on single-phase images in the presence of respiratory motion across a range of target sizes and activities. Future evaluations will include multi-target liver treatments.