(P004) A Retrospective Study to Assess Disparities in the Utilization of Intensity-Modulated Radiotherapy (IMRT) and Proton Therapy (PT) in the Treatment of Prostate Cancer (PCa)

Kristina L. Demas, MD, Neha Vapiwala, MD, Stefan Both, PhD, Curtiland Deville, MD; University of Pennsylvania

BACKGROUND: Despite its increase in use, proton therapy (PT) is a relatively limited resource. The purpose of this study was to examine clinical and demographic differences in intensity-modulated radiotherapy (IMRT) and PT utilization for prostate cancer (PCa).

METHODS: All patients with low- and intermediate-risk PCa (n = 350) undergoing definitive RT (2.5 Gy × 28 fractions or 1.8 Gy ×44 fractions) between 2010–2012 at a single institution were divided into IMRT (n = 58) and PT (n = 292) comparison groups. Pretreatment characteristics, including age, race, socioeconomic status (SES) (low vs high, defined as geocoded census tract 20% below or above poverty level, respectively), prostate-specific antigen (PSA), clinical tumor stage, Gleason score, risk group, prostate volume, and patient-reported outcomes, were retrospectively collected. Chi-square and independent sample t-tests were used for analyses.

RESULTS: Of PT patients, 228 (78%), 51 (18%), 4 (1%), and 9 (3%) were white, black, Asian, or other, respectively; 256 patients (88%) had high SES, and 36 (12%) had low SES. Mean age, distance from center, PSA level, prostate volume, International Prostate Symptom Score (IPSS), and International Index of Erectile Function (IIEF) in the PT group were 65 ± 7.1 years, 86 ± 190 miles, 5.6 ± 2.9 ng/mL, 41 ± 18 cc, 8 ± 6, and 19 ± 6, respectively; 142 (49%) patients were low-risk, and 150 (51%) were intermediate-risk. A total of 236 (81%), 46 (16%), and 10 (3%) PT patients were T1c, T2a, and T2b, respectively; 154 (53%) and 138 (47%) patients were Gleason 6 and 7.

In the IMRT group (n = 58), 28 (48%), 24 (42%), 3 (5%), and 3 (5%) patients were white, black, Asian, or other, respectively; 40 (69%) patients had higher SES, and 18 (31%) had low SES. Mean age, distance, PSA, prostate volume, IPSS, and IIEF were 69 ± 8.6, 16 ± 18 miles, 7.4 ± 4.5 ng/mL, 54 ± 40 cc, 8 ± 7, and 14 ± 8, respectively; 142 (49%) were low-risk, and 150 (51%) were intermediate-risk patients. A total of 236 (81%), 46 (16%), and 10 (3%) IMRT patients were T1c, T2a, and T2b, respectively; 154 (53%) and 138 (47%) patients were Gleason 6 and 7.

The cohorts varied in average age (P = .0005), race (P < .0001), SES status (P = .0007), and average miles traveled to the facility (P = .0054)-ie, IMRT patients were older, resided closer, and consisted of more black and low-SES patients. Baseline PSA (P = .0001), Gleason score (P = .0244), prostate volume (P = .0040), and IIEF (P < .001) were significantly increased for IMRT, while risk group, T stage, and IPSS were not (P > .05 for all). Therapeutically, IMRT patients were less likely to receive hypofractionated therapy (P < .0001) and more likely to receive androgen deprivation therapy (P = .0006).

CONCLUSION: Disparities exist in PT utilization compared with IMRT by age, race, and SES and merit further investigation.

Proceedings of the 97th Annual Meeting of the American Radium Society - americanradiumsociety.org