National practice patterns of proton versus photon therapy in the treatment of adult patients with primary brain tumors in the United States

Figures & data

Figure 1. Final patient population with exclusion criteria.

Figure 2. Percentage of reported primary brain tumor proton cases out of all external beam radiation therapy (EBRT) cases of each diagnosis year.

Table 1. Patient characteristics by modality.

Predictor	Level	Modality		p value
		Photon (n = 72,635)	Proton (n = 438)
Age^a		59 [49–68]	45.5 [31–60]	<.001
Distance from residence to reporting facility (miles)^a		11.9 [5.2–27.4]	16.7 [7.8–39.1]	<.001
Tumor size (millimeters)^a		43 [31–56]	44 [32–55]	.794
Sex	Female	30,425 (41.9%)	202 (46.1%)	.074
	Male	42,210 (58.1%)	236 (53.9%)
Race	Black	4202 (5.8%)	17 (3.9%)	.003
	White	65,661 (90.4%)	392 (89.5%)
	Other	2772 (3.8%)	29 (6.6%)
Insurance	Private	39,278 (54.8%)	300 (69%)	<.001
	Medicaid/other non-Medicare government	6656 (9.3%)	44 (10.1%)
	Medicare	22,786 (31.8%)	74 (17%)
	Uninsured	2929 (4.1%)	17 (3.9%)
Income Quartile	Less than $38,000	9891 (13.9%)	42 (9.8%)	<.001
	$38,000–$47,999	16,100 (22.7%)	66 (15.3%)
	$48,000–$62,999	19,948 (28.1%)	106 (24.7%)
	$63,000+	25,139 (35.4%)	216 (50.2%)
Charlson–Deyo Score	0	55,703 (76.7%)	382 (87.2%)	<.001
	1	10,716 (14.8%)	42 (9.6%)
	2	6216 (8.6%)	14 (3.2%)
Facility type	Academic	35,062 (54.9%)	192 (74.1%)	<.001
	Community	28,779 (45.1%)	67 (25.9%)
Urban rural	Metro	57,777 (85.5%)	390 (94%)	<.001
	Rural	1311 (1.9%)	1 (0.2%)
	Urban	8464 (12.5%)	24 (5.8%)
Facility location	Northeast	14,252 (22.3%)	65 (25.1%)	<.001
	Midwest	17,854 (28%)	40 (15.4%)
	South	20,160 (31.6%)	48 (18.5%)
	West	11,575 (18.1%)	106 (40.9%)
Primary site	Brainstem	1378 (1.9%)	31 (7.1%)	<.001
	Cerebellum	1221 (1.7%)	33 (7.5%)
	Frontal	20,695 (28.5%)	133 (30.4%)
	Occipital	2645 (3.6%)	15 (3.4%)
	Other	19,554 (26.9%)	94 (21.5%)
	Parietal	10,470 (14.4%)	42 (9.6%)
	Temporal	16,672 (23%)	90 (20.6%)
Percentage of persons in zip code without high school diploma	Less than 7%	20,156 (28.3%)	160 (37.1%)	.001
	13%–20.9%	16,923 (23.8%)	97 (22.6%)
	7%–12.9%	24,197 (34%)	122 (28.4%)
	21% or more	9844 (13.8%)	51 (11.9%)
Histology	Glioblastoma	51,828 (71.4%)	142 (32.4%)	<.001
	Oligodendroglioma	3237 (4.5%)	48 (11%)
	Anaplastic ODG	1597 (2.2%)	16 (3.7%)
	ODG NOS	1640 (2.3%)	32 (7.3%)
	Astrocytoma/mixed glioma	15,534 (21.4%)	181 (41.3%)
	Mixed glioma (OA/AOA)	2490 (3.4%)	37 (8.4%)
	Glioma NOS	1769 (2.4%)	28 (6.4%)
	Astrocytoma NOS	3813 (5.2%)	55 (1.3%)
	Anaplastic Astrocytoma	6,384 (8.8%)	55 (1.3%)
	Fibrillary Astrocytoma	1194 (1.6%)	6 (1.4%)
	Medulloblastoma/PNET	993 (1.4%)	39 (8.9%)
	Ependymoma	845 (1.2%)	24 (5.5%)
	Pilocytic astrocytoma	198 (0.3%)	4 (0.9)
Year of diagnosis	2009 or earlier	35,644 (49.1%)	124 (28.3%)	<.001
	2010–2014	36,991 (50.9%)	314 (71.7%)

^a The median and [first quartile–third quartile] were reported. The non-parametric Wilcoxon sum-rank test for comparisons. Italicized values represent subsets of histology.

ODG: oligodendroglioma; NOS: not otherwise specified; OA: Oligoastrocytoma; AOA: anaplastic oligoastrocytoma; PNET: primitive neuroendocrine tumor. Significant p values are in bold.

Table 2. Univariate logistics regression analysis of factors predictive of proton therapy utilization.

Predictor	Class	Odds ratio	95% odds ratio Confidence limits		p value
			Lower CL	Upper CL
Age	Continuous	0.95	0.95	0.96	<.001
Distance from residence to reporting facility (miles)	Continuous	1.00	1.00	1.00	<.001
Tumor size (millimeters)	Continuous	1.00	1.00	1.00	.261
Sex	Female	Ref
	Male	0.84	0.70	1.02	.073
Race	Black	Ref
	White	1.44	0.89	2.32	.500
	Other	2.56	1.41	4.63	.001
Insurance	Private	Ref
	Medicaid/other non-Medicare government	0.87	0.63	1.19	.190
	Medicare	0.43	0.33	0.55	<.001
	Uninsured	0.76	0.47	1.24	.816
Income quartile (2 level)	Less than $63,000	Ref
	$63,000+	1.84	1.53	2.23	<.001
Charlson–Deyo score	2	Ref
	0	3.05	1.79	5.19	<.001
	1	1.74	0.95	3.19	.989
Facility type	Academic	Ref
	Community	0.43	0.32	0.56	<.001
Urban/rural	Urban	Ref
	Rural	0.27	0.04	1.99	.083
	Metro	2.38	1.58	3.60	.003
Facility location	Northeast	Ref
	Midwest	0.49	0.33	0.73	<.001
	South	0.52	0.36	0.76	<.001
	West	2.01	1.47	2.74	<.001
Primary site (4 levels)	Others	Ref
	Frontal	0.92	0.73	1.16	.088
	Parietal	0.56	0.41	0.81	.007
	Temporal	0.77	0.60	1.00	.718
Percentage of persons in zip code without high school diploma	21% or more	Ref
	Less than 7%	1.53	1.12	2.10	<.001
	7%–12.9%	0.97	0.70	1.35	.067
	13%–20.9%	1.10	0.79	1.55	.787
Histology	Astrocytoma/mixed glioma	Ref
	Oligodendroglioma	1.27	0.92	1.75	.997
	Glioblastoma	0.23	0.18	0.29	<.001
	Ependymoma	2.44	1.58	3.75	.001
	Medulloblastoma/ PNET	3.37	2.37	4.79	<.001
	Pilocytic astrocytoma	1.73	0.64	4.72	.467
Histology (3 levels)	Others	Ref
	Glioblastoma	0.12	0.10	0.16	<.001
	Astrocytoma/mixed glioma	0.53	0.42	0.68	<.001
Year of diagnosis	2009 or earlier	Ref
	2010–2014	2.43	1.98	3.00	<.001

Significant p values are in bold.

Table 3. Multivariate logistics regression analysis of factors predictive of proton therapy utilization.

Predictor	Level	Odds ratio	95% Odd ratio Confidence limits		p value
			Lower CL	Upper CL
Age		0.99	0.98	1.00	.041
Percentage of persons in zip code without high school diploma	7%–12.9%	Ref
	Less than 7%	1.17	0.83	1.63	.460
	13%–20.9%	1.69	1.17	2.43	.021
	21% or more	1.37	0.87	2.15	.666
Income quartile (2 levels)	Less than $63,000	Ref
	$63,000+	1.57	1.13	2.16	.007
Facility type	Academic	Ref
	Community	0.45	0.34	0.60	<.001
Facility location	Northeast	Ref
	Midwest	0.54	0.36	0.80	<.001
	South	0.57	0.39	0.83	<.001
	West	2.09	1.52	2.88	<.001
Year of diagnosis	2009 or earlier	Ref
	2010–2014	1.69	1.30	2.19	.003
Charlson–Deyo score	2	Ref
	0	2.27	1.16	4.44	.018
	1	1.97	0.94	4.13	.279
Histology (3 levels)	Glioblastoma	Ref
	Astrocytoma/mixed glioma	3.01	2.27	3.98	.007
	Others	4.27	2.96	6.15	<.001

Significant p values are in bold.

Figure 3. Percentage of reported primary brain tumor proton cases out of all external beam radiation therapy (EBRT) cases of each diagnosis year by region. Northeast (CT, MA, ME, NH, RI, VT, NJ, NY and PA); South (DC, DE, FL, GA, MD, NC, SC, VA, WV, AL, KY, MS, TN, AR, LA, OK and TX); Midwest (IL, IN, MI, OH, WI, IA, KS, MN, MO, ND, NE and SD); West (AZ, CO, ID, MT, NM, NV, UT, WY, AK, CA, HI, OR and WA).

Figure 4. Percentage of reported glioblastoma proton cases out of all external beam radiation therapy (EBRT) cases of each diagnosis year.

Figure 5. Percentage of reported glioblastoma proton cases out of all external beam radiation therapy (EBRT) cases of each diagnosis year by region. Northeast (CT, MA, ME, NH, RI, VT, NJ, NY and PA); South (DC, DE, FL, GA, MD, NC, SC, VA, WV, AL, KY, MS, TN, AR, LA, OK and TX); Midwest (IL, IN, MI, OH, WI, IA, KS, MN, MO, ND, NE and SD); West (AZ, CO, ID, MT, NM, NV, UT, WY, AK, CA, HI, OR and WA).