2930 - Beyond Conventional Palliation: Outcomes of Spatially Fractionated Radiation Therapy (SFRT) In the Era of Prolonged Metastatic Survival
Presenter(s)
E. R. Zhang-Velten1, M. L. Tao1, J. P. Schiff2, J. C. Ye1, A. Lim1, H. Matani1, D. C. Ling1, A. A. Garsa Jr1, K. Wong1, E. L. Chang1, H. Zhang1, S. Balik1, Z. Xu2, B. P. Ziemer1, and L. Lukas1; 1Department of Radiation Oncology, University of Southern California Keck School of Medicine, Los Angeles, CA, 2Department of Radiation Oncology, Keck School of Medicine, University of Southern California, Los Angeles, CA
Purpose/Objective(s): Bulky advanced tumors are a challenge to treat with palliative radiotherapy due to hypoxia, a higher initial number of clonogens, and overlap with critical normal organs. Spatially fractionated radiation therapy (SFRT), an emerging technique, addresses these challenges via the methodical distribution of highly heterogeneous ablative dose “vertices” interspersed within tumor. We report oncologic and toxicity outcomes of SFRT patients treated in a single academic radiation oncology network.
Materials/Methods: After IRB approval, we retrospectively identified 29 patients (20 males, 9 females) who received palliative SFRT at our institution. 17 patients (59%) received single-fraction SFRT with 3 Gy to gross tumor volume (GTV) and 15 Gy to the vertices, while 12 patients (41%) received 5-fraction SFRT with 20 Gy to GTV and 66.7 Gy to the high-dose vertices. SFRT was planned with a 6X-FFF VMAT technique. Response of primary tumors was measured by contouring the GTV on subsequent follow-up imaging. Toxicities were graded according to CTCAE.
Results: Median age and performance status was 71 and ECOG 1 at SFRT. Patients received a median of 3 prior lines of systemic therapy, and 12 patients (41%) received prior radiation to the local site. Median GTV size was 368.3 cc. (IQR 205.8 cc – 903.4 cc). Most patients (21, 72.4%) presented with pain. 24 of 29 patients (83%) had follow up, median 7 months. Only 3 patients (12%) did not experience improvement of symptoms. 21 (84%) patients received subsequent systemic therapy. Of the 22 patients who had post-SFRT diagnostic imaging, objective response rate was 72.7%, with median GTV volume decrease of 54.4% at last imaging evaluation. The most common acute toxicity was fatigue (24%). 13 patients (52%) had no acute toxicities. There was one grade 3+ toxicity observed as fistula between neobladder and pre-existing anorectal fistula, possibly due to either tumor progression or radiation treatment.
Conclusion: Oncologic advances have enabled patients with metastatic disease to live longer, and SFRT is a novel option which was well-tolerated and provided a favorable objective response rate of 72.7% in our patients with limited alternatives for palliation. Larger prospective studies are needed to refine patient selection and guide clinical guidelines for SFRT.