3377 - Spatially Fractionated Radiation Therapy (SFRT) Based on Multimodal Imaging: A Promising Salvage Treatment Strategy for Metastatic and Refractory Cancer Patients

Y. X. Guo¹, Z. Dai², and J. Jin³; ¹Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen, China, ²National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital,Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen, ShenZhen, Guangdong, China, ³Department of Radiation Oncology, National Cancer Center / National Clinical Research Center for Cancer / Cancer Hospital & Shenzhen Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen, China

Purpose/Objective(s): SFRT delivers non-uniform doses to the entire tumor, resulting in three biological effects (bystander, abscopal, and cohort effects), vascular damage and immune response. Previous studies have reported high local control rates under GRID and Lattice therapy. In this study, we have applied Lattice and Stereotactic Central Ablative Radiation Therapy (SCART) based on multimodal imaging to evaluate the short-term efficacy and acute toxicity. Materials/

Methods: Patients with stage IV and active progression after at least two lines of therapy were eligible for this study. Patients were reexamined by at least one type of imaging as following: ultrasound, CT, MRI, and PET/CT before and after SFRT. Target delineation is as follows: 1) Lattice, the pellets were 1-cm at 3-cm intervals; 2) SCART, each slice was reduced in diameter up to 24%. The location of the targets were the degree of enhancement the tumor bed based on CT imaging, as well as considering the metabolism of FDG/PSMA PET/CT. Both recent efficacy and safety were evaluated.

Results: Since June 2023, a total of 16 patients have received SFRT, 11 cases received SCART radiotherapy and 5 patients received lattice radiotherapy, including 13 males and 3 females, median age 60 years. Twelve patients had multiple metastases and four had single metastatic lesion. The median maximum diameter and volume of tumors were 10.5cm and 264.75cc, respectively. Apart from three patients on treatment, one died with progression and one interrupted because of persistent fever, there were 8 patients(72.7%) with imaging done within six months after SFRT. Of the 8 patients, partial response was confirmed in five(62.5%) and three(37.5%) showed stable disease, representing a response rate of 100%. Moreover, there were no adverse events of CTCAE Grade 2 or higher, with 3 cases Grade 1 increased levels of transaminase.
Conclusion: SFRT is an effective and safety salvage treatment strategy for advanced and refractory patients. With the application of multimodal imaging and artificial intelligence (radiomics and radiogenomics), it is a promising choice for radiation oncologist. Further investigation and cohort control study are warranted.