2310 - Spatially Fractionated Radiation Therapy for Palliation of Large or Deep-Seated Pediatric Tumors
Presenter(s)
B. L. Chau1, B. P. Ziemer1,2, H. R. Han1, L. Lukas3, H. Zhang1, A. J. Olch1,2, and K. Wong2,3; 1Department of Radiation Oncology, University of Southern California, Los Angeles, CA, 2Radiation Oncology Program, Children's Hospital Los Angeles, Los Angeles, CA, 3Department of Radiation Oncology, University of Southern California Keck School of Medicine, Los Angeles, CA
Purpose/Objective(s): Treatment options for massive tumors are limited, as stereotactic body radiation therapy is usually reserved for tumors <5 cm in diameter, and conventional palliative radiation regimens may have limited local control or symptomatic relief. Spatially fractionated radiotherapy (SFRT) is a novel technique that delivers a lattice pattern of small spherical high dose sub-volumes interspersed within a low dose target region. SFRT has shown high rates of clinical response with minimal toxicity in adult bulky tumors, but there is limited data regarding the use of SFRT in the pediatric population.
Materials/Methods: A single institution retrospective review of pediatric patients who received SFRT using lattice volumetric modulated arc therapy for treatment of large, deep-seated tumors between 2022-2026 was performed. Patient and treatment characteristics, and treatment response, including symptom improvement, radiological response, and toxicity data were collected.
Results: There were 31 total tumors treated with palliative SFRT in 17 pediatric and young adult patients, with median age 12.8 years (range 11 months - 23 years). Two patients had stage III disease, and 15 patients had stage IV disease. Median follow-up was 4.0 months and overall survival was 18%. Most patients had sarcomas (70%), with other histologies including neuroblastoma, Wilms tumor, hepatocellular carcinoma, hepatoblastoma, and cholangiocarcinoma (6% each). Treated sites included thorax (39%), abdomen (29%), pelvis (16%), extremity (10%), and face (6%). The median gross tumor volume was 597.6 cc (range 135.8 - 5242.1 cc). SFRT doses ranged from 10 Gy in 1 fraction to 60 Gy in 5 fractions (median 15 Gy in 1 fraction). Conventional external beam radiation therapy was delivered concurrently or sequentially with SFRT in 13 (42%) tumors. SFRT was used for re-irradiation in 11 (35%) tumors, and re-SFRT in 8 (26%) tumors. SFRT was used for upfront treatment in 3 tumors and for treatment of 28 progressive tumors. Of all treated sites, 77% (n=24) had follow-up imaging, of which 48% (n=15) demonstrated a median tumor volume decrease of 191.9 cc (27%) and 29% (n=9) exhibited a median tumor volume increase of 233.2 cc (39%). Five out of nine tumors with volume increase were in one patient with refractory metastatic osteosarcoma, who expired 1.5 months after completion of SFRT. Treatment response was observed in 68% of treated tumors (n=21), including pain relief or improvement in mobility (n=18), gastrointestinal symptom relief (decreased nausea or improved appetite) (n=4), and AFP or bilirubin improvement in two patients. There was one grade 3 adverse event of esophagitis in a patient who received chemotherapy one week prior to SFRT in the thorax.
Conclusion: SFRT may provide safe and effective palliation for pediatric and young adult patients with bulky tumors even in the re-irradiation setting, with a low rate of severe toxicities. Despite the sample size, this study adds to the limited literature of SFRT in the pediatric population.