2611 - Stereotactic Radiation Therapy to Extracranial Sites of Symptomatic vs. Asymptomatic Metastatic Disease

E. M. Steele¹, T. Joshi², R. Darawsheh³, M. M. Payne², J. W. Shumway⁴, S. Sud¹, A. A. Weiner¹, and C. Shen¹; ¹Department of Radiation Oncology, University of North Carolina, Chapel Hill, NC, ²University of North Carolina, Chapel Hill, NC, ³University of North Carolina School of Medicine, Chapel Hill, NC, ⁴El Camino Hospital, Mountain View, CA

Purpose/Objective(s): Utilization of stereotactic body radiation therapy (SBRT) has evolved over the past decade to increasingly include sites of metastasis. Recent evidence demonstrates the possible benefit of prophylactic radiation to asymptomatic bone metastases which has the potential to expand the utilization of this technique. In the interest of designing prospective trials evaluating prophylactic SBRT to sites of metastatic disease, the current study aims to compare trends in the utilization of SBRT to sites of symptomatic versus asymptomatic metastatic disease. Materials/

Methods: Patients who received SBRT to extracranial sites of metastatic cancer between 2014-22 were identified and these medical records were reviewed to build a database of demographic, disease, and treatment details. Descriptive statistics were performed. SBRT events were separated into two groups: those directed to asymptomatic vs symptomatic sites of disease. Chi-square, Fisher’s exact test, and t-test were used to compare these two groups. Kaplan-Meier survival analysis was conducted and log rank test was performed to compare the survival distributions between groups.
Results: 267 patients with 366 SBRT treatments were identified. 304 and 62 treatments were directed to asymptomatic vs symptomatic sites respectively. Overall characteristics and those among the two groups are shown in Table 1. The median overall survival after SBRT to asymptomatic versus symptomatic sites was 37.0 (95% CI, 26.6 to 47.4) months versus 17.0 (95% CI, 2.0 to 32.0) months respectively (p = 0.018).
Conclusion: SBRT for metastatic cancers is predominantly employed to sites of asymptomatic disease, but even among symptomatic sites, SBRT is most often utilized when the patient has a limited number of progressing lesions although seemingly closer to the time of death. These results provide context in understanding the current utilization of SBRT as future studies look to employ this technique ever earlier in a patient’s metastatic disease course, including for prophylaxis, such as in the setting of high-risk bone metastases.

Table 1: Characteristics associated with SBRT treatments

Variable	Group	Asymptomatic n = 304 (%)	Symptomatic n = 62 (%)	Total N = 366	Sig (p)
Age (mean, years)	–	63.2	58.7	62.5	0.008
Sex	Male	194 (64%)	28 (45%)	222 (61%)	0.006
	Female	110 (36%)	34 (55%)	144 (39%)
Lines of Therapy Before SBRT	0-1	220 (72%)	55 (89%)	275 (75%)	0.007
	=2	84 (28%)	7 (11%)	91 (25%)
Progressing Lesions	=3	282 (93%)	45 (73%)	327 (89%)	<0.001
	=4	22 (7%)	17 (27%)	39 (11%)
Date	<2018	111 (37%)	31 (50%)	142 (39%)	0.047
	2018+	193 (63%))	31 (50%)	224 (61%)
Site	Spine	64 (21%)	46 (74%)	110 (30%)	<0.001
	Non-spine bone	59 (19%)	14 (23%)	73 (20%)
	Liver	39 (13%)	0 (0%)	39 (11%)
	Lung	92 (30%)	1 (1.6%)	93 (25%)
	Other	50 (16%)	1 (1.6%)	51 (14%)
Histology	NSCLC	34 (11%)	7 (11%)	41 (11%)	<0.001
	Breast	24 (8%)	21 (34%)	45 (12%)
	Prostate	45 (15%)	4 (7%)	49 (13%)
	Colorectal	59 (19%)	3 (5%)	62 (17%)
	Melanoma	16 (5%)	4 (7%)	20 (6%)
	Renal Cell Carcinoma	54 (18%)	15 (24%)	69 (19%)
	Other	72 (24%)	8 (13%)	80 (22%)