Hemorrhagic and Cystic Brain Metastases Are Associated With an Increased Risk of Leptomeningeal Dissemination After Surgical Resection and Adjuvant Stereotactic Radiosurgery

BACKGROUND

Brain metastases (BM) treated with surgical resection and focal postoperative radiotherapy have been associated with an increased risk of subsequent leptomeningeal dissemination (LMD). BMs with hemorrhagic and/or cystic features contain less solid components and may therefore be at higher risk for tumor spillage during resection.

OBJECTIVE

To investigate the association between hemorrhagic and cystic BMs treated with surgical resection and stereotactic radiosurgery and the risk of LMD.

METHODS

One hundred thirty-four consecutive patients with a single resected BM treated with adjuvant stereotactic radiosurgery from 2008 to 2016 were identified. Intracranial outcomes including LMD were calculated using the cumulative incidence model with death as a competing risk. Univariable analysis and multivariable analysis were assessed using the Fine & Gray model. Overall survival was analyzed using the Kaplan-Meier method.

RESULTS

Median imaging follow-up was 14.2 mo (range 2.5-132 mo). Hemorrhagic and cystic features were present in 46 (34%) and 32 (24%) patients, respectively. The overall 12- and 24-mo cumulative incidence of LMD with death as a competing risk was 11.0 and 22.4%, respectively. On multivariable analysis, hemorrhagic features (hazard ratio [HR] 2.34, P = .015), cystic features (HR 2.34, P = .013), breast histology (HR 3.23, P = .016), and number of brain metastases >1 (HR 2.09, P = .032) were independently associated with increased risk of LMD.

CONCLUSION

Hemorrhagic and cystic features were independently associated with increased risk for postoperative LMD. Patients with BMs containing these intralesion features may benefit from alternative treatment strategies to mitigate this risk.

Women's Representation in Leadership Positions in Academic Medical Oncology, Radiation Oncology, and Surgical Oncology Programs

IMPORTANCE

Women are underrepresented in medical leadership positions; however, representation of women among academic oncology leadership is unknown.

OBJECTIVES

To evaluate representation of women overall and in leadership positions in academic medical oncology (MO), radiation oncology (RO), and surgical oncology (SO) programs and to examine the association of women leadership with overall faculty representation of women per program.

DESIGN, SETTING, AND PARTICIPANTS

In this cross-sectional study, MO, RO, and SO training program websites were queried from October 2018 through June 2019. All faculty from 265 of 273 accredited MO, RO, and SO training programs (97.1%) were included.

EXPOSURE

Gender.

MAIN OUTCOMES AND MEASURES

Observed proportions of women in leadership positions compared with the expected proportion of overall women faculty in MO, RO, and SO were assessed. Rates of representation of women across each MO, RO, and SO program's faculty based on the presence or absence of a woman in a leadership position were compared.

RESULTS

Of 6030 total faculty, only 2164 (35.9%) were women. Total representation of women among MO, RO, and SO faculty was 37.1% (1563 of 4215), 30.7% (389 of 1269), and 38.8% (212 of 546), respectively. Women composed only 21.7% (30 of 138), 11.7% (11 of 94), and 3.8% (1 of 26) of MO, RO, and SO chair positions, respectively. The observed proportion of women in chair positions was significantly lower than the expected proportion for MO, RO, and SO. In all, 47.9%, 33%, and 18.5% of MO, RO, and SO programs, respectively, had at least 1 woman in a leadership position (program director or chair). Programs with 1 or more women in a leadership position were associated with a higher mean (SD) percentage of women faculty than those without at least 1 woman leader in MO (40.7% [12.5%] vs 33.1% [11.0%]; P < .001) and RO (36.2% [13.3%] vs 23.4% [12.3%]; P < .001) but not SO (40.2% [15.4%] vs 31.4% [16.9%]; P = .29).

CONCLUSIONS AND RELEVANCE

Gender disparity exists in academic MO, RO, and SO faculty, which is magnified at the chair level. Programs in MO and RO with a woman physician in a leadership position were associated with a higher percentage of women faculty, but this was not true for SO. These data will serve as a benchmark to monitor progress toward a more balanced workforce.

Predictors of Lymph Node Involvement by Soft Tissue Sarcoma of the Trunk and Extremity: An Analysis of the National Cancer Database

Background and Objectives

Lymph node metastases (LNM) in soft tissue sarcoma (STS) of the trunk and extremity are rare but are associated with worse survival. Established risk factors for LNM in this group are based on small institutional retrospective reviews. This study identifies the risk factors associated with LNM in otherwise non-metastatic trunk/extremity STS patients using the National Cancer Database (NCDB) and sought out to delineate a high-risk group that may be considered for pathologic nodal evaluation.

Methods

The files of 10,731 patients with STS of the trunk/extremity without distant metastasis from 2004 - 2015 were evaluated. Exclusion criteria included neoadjuvant therapy and a lack of pathologic nodal evaluation. Univariate and multivariable logistic regression models were performed to evaluate variables associated with LNM.

Results

Of the total of 10,731 patients, 223 (2.1%) had LNM. On multivariable analysis, LNM was associated with Grade 3 tumors (odds ratio (OR) 15.6, 95% confidence interval (CI) 6.36 - 38.04, p < 0.001) and clear cell/angiosarcoma/rhabdomyosarcoma/epithelioid (CARE) histology (OR 4.72, 95% CI 3.35 - 6.66, p < 0.001), lymphovascular invasion (LVI) (OR 5.86, 95% CI 3.33 - 10.31, p < 0.001, and bone invasion (BI) (OR 2.73, 95% CI 1.32 - 5.61, p = 0.006). Patients with Grade 3 CARE tumors (n = 402) had an 11.9% risk of LNM vs. 1.7% of adults without all these characteristics (p < 0.001). Patients with Grade 3 CARE tumors and either LVI or BI (n = 36) had a 33.3% risk of LNM.

Conclusions

High-grade and CARE histology are associated with LNM in STS. Adult patients with both features have an overall 11.9% risk of LNM and may be considered for pathologic LN assessment, particularly with the presence of LVI or BI.

Does the addition of chemotherapy to neoadjuvant radiotherapy impact survival in high-risk extremity/trunk soft-tissue sarcoma?

BACKGROUND

The role of chemotherapy in extremity/trunk soft-tissue sarcoma (ET-STS) is controversial, even for patients at high risk for distant recurrence and death (those with high-grade tumors ≥5 cm in size). This study examines the impact of integrating chemotherapy with neoadjuvant radiotherapy (RT) on overall survival (OS) for patients with high-risk ET-STS.

METHODS

The National Cancer Data Base was queried for adult patients with high-risk ET-STS who received neoadjuvant RT and limb salvage surgery between 2006 and 2014. Patients were stratified into RT and chemoradiotherapy (CRT) cohorts. OS for the RT and CRT cohorts was analyzed with the Kaplan-Meier method, log-rank tests, and Cox proportional hazards models. Propensity score matching (PSM) analysis was used to account for a potential treatment selection bias between the cohorts.

RESULTS

A total of 884 patients were identified: 639 (72.3%) in the RT cohort and 245 (27.7%) in the CRT cohort. The unadjusted 5-year Kaplan-Meier OS rate was significantly higher in the CRT cohort: 72.0% versus 56.1% (P < .001). Neoadjuvant chemotherapy was associated with improved OS in univariate and multivariable analyses (hazard ratio [HR], 0.57; 95% confidence interval [CI], 0.41-0.78; P < .001). PSM identified 2 evenly matched cohorts of 212 patients each. The 5-year matched Kaplan-Meier OS rates were 69.8% and 55.4% for the CRT and RT cohorts, respectively (P = .002). The addition of neoadjuvant chemotherapy remained prognostic for OS on PSM (HR, 0.56; 95% CI, 0.39-0.83; P = .003).

CONCLUSIONS

The addition of chemotherapy to neoadjuvant RT was associated with improved OS for patients with high-risk ET-STS. In the absence of randomized data evaluating CRT versus RT, these findings warrant further investigation.

Retrospective analysis of safety and efficacy of anti-PD-1 therapy and radiation therapy in advanced melanoma: A bi-institutional study

BACKGROUND AND PURPOSE

Antibodies against programmed cell death protein 1 (PD-1) are standard treatments for advanced melanoma. Palliative radiation therapy (RT) is commonly administered for this disease. Safety and optimal timing for this combination for melanoma has not been established.

MATERIALS AND METHODS

In this retrospective cohort study, records for melanoma patients who received anti-PD-1 therapy at Duke University or Emory University (1/1/2013-12/30/2015) were reviewed. Patients were categorized by receipt of RT and RT timing relative to anti-PD-1.

RESULTS

151 patients received anti-PD-1 therapy. Median follow-up was 12.9 months. Patients receiving RT (n = 85) had worse baseline prognostic factors than patients without RT (n = 66). One-year overall survival (OS) was lower for RT patients than patients without RT (66%, 95% CI: 55-77% vs 83%, 95% CI: 73-92%). One-year OS was 61% for patients receiving RT before anti-PD-1 (95% CI: 46-76%), 78% for RT during anti-PD-1 (95% CI: 60-95%), and 58% for RT after anti-PD-1 (95% CI: 26-89%). On Cox regression, OS for patients without RT did not differ significantly from patients receiving RT during anti-PD-1 (HR 1.07, 95% CI: 0.41-2.84) or RT before anti-PD-1 (HR 0.56, 95% CI: 0.21-1.45). RT and anti-PD-1 therapy administered within 6 weeks of each other was well tolerated.

CONCLUSION

RT can be safely administered with anti-PD-1 therapy. Despite worse baseline prognostic characteristics for patients receiving RT, OS was similar for patients receiving concurrent RT with anti-PD-1 therapy compared to patients receiving anti-PD-1 therapy alone.

Does the addition of chemotherapy to neoadjuvant radiotherapy impact survival in high-risk extremity and trunk soft tissue sarcoma?

11054

Background: Large, high-grade extremity/trunk (ET) non-rhabdomyosarcoma soft-tissue sarcoma (STS) is at high risk for distant recurrence and death. The integration of chemotherapy (C) to standard of care neoadjuvant radiotherapy (RT) remains controversial, even for these patients. This study examines the impact of adding C to neoadjuvant RT on overall survival (OS) in high risk ET-STS. Methods: The National Cancer Data Base (NCDB) was queried for patients ≥18 years with high risk (≥5 cm + high grade) non-rhabdomyosarcoma ET-STS (WHO histology) who received neoadjuvant RT and limb sparing surgery from 2006-2014. Patients were next stratified based upon receipt of C (RT and CRT cohorts). Overall survival (OS) for RT vs CRT cohorts was analyzed using the Kaplan-Meier (KM) method, log-rank test, and Cox proportional hazards models. Propensity score-matched analysis (PSM) was employed to account for potential treatment selection bias between cohorts. Results: A total of 848 (71.1%) and 344 (28.9%) patients received RT and CRT, respectively. Patient cohorts were well-balanced except for the CRT cohort having higher rates of treatment in the West (22.1% vs 10.6%) & Midwest (28.3% vs 22.7%), Charlson-Deyo [CD] score 0 vs ≥1 (85.5% vs 79.4%), younger age (≤50) (45.9% vs 21.7%), synovial sarcoma histology (18.9% vs 3.2%), earlier year of diagnosis (2006-2010) (39.5% vs 32.3%), and positive lymphovascular invasion (2.0 vs 1.51%), (p < 0.05 each). The KM 5-year OS was significantly higher in the CRT vs RT cohort: 69.2% vs 58.1% on univariate (p < 0.0001) and multivariate analysis (Hazard Ratio [HR]: 0.66; 95% Confidence Interval [CI]: 0.52-0.85; p = 0.001) even after adjusting for age, race, income, CD score, histology, tumor size, tumor grade, and primary site (lower extremity; upper extremity; trunk). PSM identified evenly matched cohorts of 300 patients each with respect to age, income, CD score, histology, grade, tumor size, and primary site. The addition of neoadjuvant C remained prognostic for OS on PSM (HR: 0.74 [0.56-0.99], p = 0.042). Conclusions: The addition of C to neoadjuvant RT was associated with improved OS in patients with high risk non-rhabdomyosarcoma ET-STS in the NCDB. These hypothesis generating results support prospective evaluation.

It starts at the top: An analysis of female representation in academic medical oncology (MO), radiation oncology (RO), and surgical oncology (SO) program leadership positions

10520

Background: Female underrepresentation in academic medicine leadership is well-documented; however, oncology specific data are scarce. This study evaluates female leadership representation in academic medical oncology (MO), radiation oncology (RO) and surgical oncology (SO) programs. Furthermore, we examine the impact of female leadership on overall female faculty representation. Methods: A total of 264 (96%) Accreditation Council for Graduate Medical Education actively accredited MO [144 of 153], RO [93 of 94] and SO [27 of 27] training programs were included. The gender of overall faculty and those in leadership positions (program director and departmental chair/division chief) of each program was determined using hospital websites from 10/01/18 to 01/27/19. The chi-squared goodness-of-fit test was used to examine whether the observed proportion of females in leadership positions deviates significantly from the expected proportion based on the actual proportion of overall female faculty in MO, RO and SO. Two-sample t-tests were used to compare rates of female faculty representation across each program based on the presence/absence of female in a leadership position for MO, RO and SO. Results: Female faculty representation in MO, RO and SO was 37.1% (1,554/4,191), 30.7% (389/1,269) and 38.8% (212/546), respectively. Female representation in leadership positions was 31.5% (82/260), 17.4% (31/178) and 11.1% (5/45), respectively. The observed proportion of females in leadership positions was significantly lower than the expected proportion of females in leadership positions for RO (17.4% vs. 30.7%, p = .0001) and SO (11.1% vs. 38.8%, p = .0001), and demonstrated a trend towards significance for MO (31.5% vs. 37.1%, p = .063). 47.9%, 33% and 18.5% of MO, RO and SO programs had ≥1 female in a leadership position, respectively. Programs that had a female in a leadership position had a higher mean percentage of overall female faculty than those that did not: 41.0% vs 35.0% (p = .0006), 36.0% vs 26.0% (p = .0002) and 39.0% vs 32.0% (p = .348) for MO, RO and SO, respectively. Conclusions: Gender disparity exists in academic MO, RO and SO faculty and is magnified at the leadership level. Programs with a female physician in a leadership position are associated with a higher percentage of female faculty.

Safety and Efficacy of Palbociclib and Radiation Therapy in Patients With Metastatic Breast Cancer: Initial Results of a Novel Combination

Purpose

Palbociclib is a selective cyclin-dependent kinase 4/6 inhibitor approved for metastatic ER+/HER2- breast cancer. Preclinical evidence suggests a possible synergistic effect of palbociclib when combined with radiation therapy (RT); however, the toxicity of this pairing is unknown. We report preliminary results on the use of this combination.

Methods and Materials

Records of patients treated with palbociclib at our institution from 2015 to 2018 were retrospectively reviewed. Patients who received RT for symptomatic metastases concurrently or within 14 days of palbociclib were included. Local treatment effect was assessed by clinical examination and subsequent computed tomography/magnetic resonance imaging. Toxicity was graded based on Common Terminology Criteria for Adverse Events version 5.0.

Results

A total of 16 women received palliative RT in close temporal proximity to palbociclib administration. Four patients received palbociclib before RT (25.0%), 5 concurrently (31.3%), and 7 after RT (43.8%). The median interval from closest palbociclib use to RT was 5 days (range, 0-14). The following sites were irradiated in decreasing order of frequency: bone (11 axial skeleton [9 vertebra and 2 other]; 4 pelvis; 3 extremity), brain (4: 3 whole brain RT and 1 stereotactic radiosurgery), and mediastinum (1). The median and mean follow-up time is 14.7 and 17.6 months (range, 1.7-38.2). Pain relief was achieved in all patients. No radiographic local failure was noted in the 13 patients with evaluable follow-up imaging. Leukopenia, neutropenia, and thrombocytopenia were seen in 4 (25.0%), 5 (31.3%), and 1 (6.3%) patient before RT. After RT, 5 (31.3%), 1 (6.3%), and 3 (18.8%) patients were leukopenic, neutropenic, and thrombocytopenic, respectively. All but 2 (grade 2) hematologic toxicities were grade 1. No acute or late grade 2+ cutaneous, neurologic, or gastrointestinal toxicities were noted. Toxicity results did not differ based on disease site, palbociclib-RT temporal association, or irradiated site.

Conclusions

The use of RT in patients receiving palbociclib resulted in minimal grade 2 and no grade 3+ toxicities. This preliminary work suggests that symptomatic patients receiving palbociclib may be safely irradiated.

Abstract PD8-12: Safety and efficacy of palbociclib and radiotherapy in metastatic breast cancer patients: Initial results of a novel combination

Purpose: Palbociclib is a selective CDK4/6 inhibitor approved for the treatment of metastatic ER+/HER2- breast cancer. Inhibition of CDK4/6 prevents cell cycle progression from G1 to the more radioresistant S phase, raising the possibility of an enhanced therapeutic effect if combined with radiotherapy (RT). Despite this potential benefit, clinicians seldom use this combination due to fear that RT may exacerbate palbociclib toxicity, particularly leukopenia. Our aim is to report the preliminary results of patients with metastatic breast cancer who received RT while receiving palbociclib.

Methods: We retrospectively reviewed records of all patients who were treated with palbociclib at our institution from 2015-2018. Patients who received RT for symptomatic metastases concurrently or within 14 days of last drug administration were included in our analysis. Local treatment effect was assessed by clinical exam and subsequent CT or MRI imaging, if applicable. Toxicity was graded based on CTCAE v5.0.

Results: A total of 16 females received palliative RT in association with palbociclib. The median age of the treated patients was 59.6 (range 33.3-91.0) years. The median time of closest palbociclib use to RT administration was 5 (range 0-14) days.

The following sites were treated in order of frequency: bone (10-axial skeleton [8-vertebra]; 1-ilium), brain (4: 3-WBRT & 1-SRS), and mediastinum (1). RT dose/fractionation for bone was 30 Gy/10 fxn (7), 35 Gy/14 fxn (2), 37.5 Gy/15 fxn (1), and 18 Gy/1 fxn (1). WBRT dose/fractionation was 30 Gy/10 fxn for all patients. SRS brain dose was 25 Gy/5 fxn. The patient treated to the mediastinum received 36 Gy/18 fxn.

At most recent follow-up, 12 patients are still living. The median time from RT to last known follow-up or death is 10.3 (range 1.7-29.6) months. Pain relief was achieved in 15 of 16 (93.8%) patients. No radiographic local failure was noted in the 13 patients with evaluable follow-up imaging.

The combination of RT and palbociclib was well-tolerated. Grade 1 fatigue, dermatitis, and nausea was noted in 5, 3, and 1 patient, respectively. One patient with WBRT developed Grade 1 headache. Six of 16 patients were leukopenic prior to RT initiation. Following RT, 7 patients were observed to have a drop in WBC count, of which 2 dropped into the leukopenic range. Only a total of 5 patients were leukopenic following RT, of which 3 were leukopenic before receiving RT. No acute or late Grade 2 or higher cutaneous, neurological, gastrointestinal, or hematologic toxicities were noted.

Conclusions: The use of RT in patients receiving palbociclib resulted in minimal Grade 1 and no Grade 2+ toxicities, including leukopenia. This treatment can be used safely in symptomatic patients without discontinuation of systemic therapy. Further larger prospective studies with longer follow-up are needed to confirm these results.

Citation Format: Chowdhary M, Sen N, Chowdhary A, Usha L, Cobleigh M, Patel KR, Wang D, Barry PN, Rao RD. Safety and efficacy of palbociclib and radiotherapy in metastatic breast cancer patients: Initial results of a novel combination [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr PD8-12.

Abstract P3-12-19: Withdrawn

This abstract was withdrawn by the authors.

Citation Format: Chowdhary M, Lee A, Gao S, Barry PN, Diaz R, Decker RH, Wilson LD, Evans SB, Moran MS, Knowlton CA, Patel KR. Withdrawn [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-12-19.

Is Proton Therapy a "Pro" for Breast Cancer? A Comparison of Proton vs. Non-proton Radiotherapy Using the National Cancer Database

Background: Limited data exists demonstrating the clinical benefit of proton radiotherapy (PRT) in breast cancer. Using the National Cancer Database, we evaluated predictors associated with PRT use for patients with breast cancer. An exploratory analysis also investigates the impact of PRT on overall survival (OS).

Methods: Patients with non-metastatic breast cancer treated with adjuvant radiotherapy from 2004 to 2014 were identified. Patients were stratified based on receipt of PRT or non-PRT (i.e., photons ± electrons). A logistic regression model was used to determine predictors for PRT utilization. For OS, Multivariable analysis (MVA) was performed using Cox proportional hazard model.

Results: A total of 724,492 patients were identified: 871 received PRT and 723,621 received non-PRT. 58.3% of the PRT patients were group stage 0–1. Median follow-up time was 62.2 months. On multivariate logistic analysis, the following factors were found to be significant for receipt of PRT (all p < 0.05): academic facility (odds ratio [OR] = 2.50), South (OR = 2.01) and West location (OR = 12.43), left-sided (OR = 1.21), ER-positive (OR = 1.59), and mastectomy (OR = 1.47); pT2-T4 disease predicted for decrease use (OR = 0.79). PRT was not associated with OS on MVA for all patients: Hazard Ratio: 0.85, p = 0.168. PRT remained not significant on MVA after stratifying for subsets likely associated with higher heart radiation doses, including: left-sided (p = 0.140), inner-quadrant (p = 0.173), mastectomy (p = 0.095), node positivity (p = 0.680), N2-N3 disease (p = 0.880), and lymph node irradiation (LNI) (p = 0.767).

Conclusions: Receipt of PRT was associated with left-sided, ER+ tumors, mastectomy, South and West location, and academic facilities, but not higher group stages or LNI. PRT was not associated with OS, including in subsets likely at risk for higher heart doses. Further studies are required to determine non-OS benefits of PRT. In the interim, given the high cost of protons, only well-selected patients should receive PRT unless enrolled on a clinical trial.

The Impact of Graduates' Job Preferences on the Current Radiation Oncology Job Market

PURPOSE

To examine the role of radiation oncology (RO) graduates' application patterns and personal preferences in current labor concerns.

METHODS AND MATERIALS

An anonymous, voluntary survey was distributed to 665 domestic RO graduates from 2013 to 2017. Questions assessed graduates' regional (Northeast [NE]; Midwest [MW]; South [SO]; West [WT]) job type and population size preferences. Top regional choice was compared across other categorical and numerical variables using the χ² test and analysis of variance, respectively.

RESULTS

Complete responses were obtained from 299 (45.0% response rate) participants: 82 (27.4%), 74 (24.7%), 85 (28.4%), and 58 (19.4%) graduated from NE, MW, SO, and WT programs. The most to least commonly applied regions were SO (69.2%), MW (55.9%), and then NE/WT (55.2% each). The first and last regional choices were the WT (29.4%) and MW (15.7%), respectively. The most and least common application and top choice preferences were consistent in terms of city size: >500,000 (86.0% and 64.5%, respectively) and <100,001 (26.1% and 7.0%, respectively). The majority of applicants applied to both academic and nonacademic positions (60.9%), with top job type choice being equally split. The majority of respondents independently received a job offer in their preferred region (75.3%), city population size (72.6%) or job type (81.9%). Additionally, 52.5% received a job offer that included all three preferences. Those who underwent residency training (44.3% vs 62.0%-83.6%, P < .001) or medical schooling (50.7% vs 56.3%-75.6%, P < .001) or grew up in the MW (60.8% vs 70.0%-74.7%, P < .001) were least likely to choose this region as their top regional choice compared with other regions.

CONCLUSIONS

The MW and jobs in smaller cities are less appealing to RO graduates, even if they receive training in the MW, which may contribute to current job market concerns. Nonetheless, the majority of respondents received a job offer in the region, population size, and job type of their top choice. Assessing prospective candidates' city size and geographic preferences and prioritizing applicants who are compatible with positions may help address potential job market discrepancies.

Proton vs. Photon Radiation Therapy for Primary Gliomas: An Analysis of the National Cancer Data Base

Background: To investigate the impact of proton radiotherapy (PBT) on overall survival (OS) and evaluate PBT usage trends for patients with gliomas in the National Cancer Data Base (NCDB).

Methods: Patients with a diagnosis of World Health Organization (WHO) Grade I-IV glioma treated with definitive radiation therapy (RT) between the years of 2004–13 were identified. Patients were stratified based on WHO Grade and photon radiotherapy (XRT) vs. PBT. Univariate (UVA) and multivariable analysis (MVA) with OS were performed by Cox proportional hazards model and log-rank tests. Propensity score (PS) weighting was utilized to account for differences in patient characteristics and to minimize selection bias.

Results: There were a total of 49,405 patients treated with XRT and 170 patients treated with PBT. Median follow-up time was 62.1 months. On MVA, the following factors were associated with receipt of PBT (all p < 0.05): WHO Grade I-II gliomas, treatment at an academic/research program, west geographic facility location, and surgical resection. After PS weighting, all patients treated with PBT were found to have superior median and 5 year survival than patients treated with XRT: 45.9 vs. 29.7 months (p = 0.009) and 46.1 vs. 35.5% (p = 0.0160), respectively.

Conclusions: PBT is associated with improved OS compared to XRT for patients with gliomas. This finding warrants verification in the randomized trial setting in order to account for potential patient imbalances not adequately captured by the NCDB, such as tumor molecular characteristics and patient performance status.

Importance of the Study: This is the first study that compares the outcomes of patients treated with photon based radiotherapy vs. proton based radiotherapy for patients with gliomas. In this retrospective analysis, the results demonstrate that proton therapy is associated with improved outcomes which support ongoing prospective, randomized clinical trials comparing the two modalities in patients with gliomas.