Dosimetric comparison of magnetic resonance-guided radiation therapy, intensity-modulated proton therapy and volumetric-modulated arc therapy for distal esophageal cancer.

Advances in radiotherapy (RT) technologies permit significant decreases in the dose delivered to organs at risk (OARs) for patients with esophageal cancer (EC). Novel RT modalities such as proton beam therapy (PBT) and magnetic resonance-guided radiotherapy (MRgRT), as well as motion management techniques including breath hold (BH) are expected to further improve the therapeutic ratio. However, to our knowledge, the dosimetric benefits of PBT vs MRgRT vs volumetric-modulated arc therapy (VMAT) have not been directly compared for EC. We performed a retrospective in silico evaluation using the images and datasets of nine distal EC patients who were treated at our institution with a 0.35-Tesla MR linac to 50.4 Gy in 28 fractions in mid-inspiration BH (BH-MRgRT). Comparison free-breathing (FB) intensity-modulated PBT (FB-IMPT) and FB-VMAT plans were retrospectively created using the same prescription dose, target volume coverage goals, and OAR constraints. A 5 mm setup margin was used for all plans. BH-IMPT and BH-VMAT plans were not evaluated as they would not reflect our institutional practice. Planners were blinded to the results of the treatment plans created using different radiation modalities. The primary objective was to compare plan quality, target volume coverage, and OAR doses. All treatment plans met pre-defined target volume coverage and OAR constraints. The median conformity and homogeneity indices between FB-IMPT, BH-MRgRT and FB-VMAT were 1.13, 1.25, and 1.43 (PITV) and 1.04, 1.15, 1.04 (HI), respectively. For FB-IMPT, BH-MRgRT and FB-VMAT the median heart dose metrics were 52.8, 79.3, 146.8 (V30Gy, cc), 35.5, 43.8, 77.5 (V40Gy, cc), 16.9, 16.9, 32.5 (V50Gy, cc) and 6.5, 14.9, 17.3 (mean, Gy), respectively. Lung dose metrics were 8.6, 7.9, 18.5 (V20Gy, %), and 4.3, 6.3, 11.2 (mean, Gy), respectively. The mean liver dose (Gy) was 6.5, 19.6, 22.2 respectively. Both FB-IMPT and BH-MRgRT achieve substantial reductions in heart, lung, and liver dose compared to FB-VMAT. We plan to evaluate dosimetric outcomes across these RT modalities assuming consistent use of BH.

Case-Matched Outcomes of Proton Beam and Intensity-Modulated Radiation Therapy for Localized Prostate Cancer.

Purpose: Although both intensity-modulated radiation therapy (IMRT) and proton beam therapy (PBT) offer effective long-term disease control for localized prostate cancer (PCa), there are limited data directly comparing the 2 modalities. Methods: The data from 334 patients treated with conventionally fractionated (79.2 GyRBE in 44 fractions) PBT or IMRT were retrospectively analyzed. Propensity score matching was used to balance factors associated with biochemical failure-free survival (BFFS). Age, race, and comorbidities (not BFFS associates) remained imbalanced after matching. Univariable and covariate-adjusted multivariable (MVA) Cox regression models were used to determine if modality affected BFFS. Results: Of 334 patients, 176 (52.7%) were included in the matched cohort with exact matching to National Comprehensive Cancer Network (NCCN) risk group. With a median follow-up time of 9.0 years (interquartile range [IQR]: 7.8-10.2 years), long-term BFFS was similar between the IMRT and PBT matched arms with 8-year estimates of 85% (95% CI: 76%-91%) and 91% (95% CI: 82%-96%, P = .39), respectively. On MVA, modality was not significantly associated with BFFS in both the unmatched (hazard ratio [HR] = 0.75, 95% CI: 0.35-1.63, P = .47) and matched (HR = 0.87, 95% CI: 0.33-2.33, P = .78) cohorts. Prostate cancer-specific survival (PCSS) and overall survival (OS) were also similar (P > .05). However, in an unmatched analysis, the PBT arm had significantly fewer incidences of secondary cancers within the irradiated field (0.6%, 95% CI: 0.0%-3.1% versus 4.5%, 95% CI: 1.8%-9.0%, P = .028). Conclusions: Both PBT and IMRT offer excellent long-term disease control for PCa, with no significant differences between the 2 modalities in BFFS, PCSS, and OS in matched patients. In the unmatched cohort, fewer incidences of secondary malignancy were noted in the PBT group; however, owing to overall low incidence of secondary cancer and imbalanced patient characteristics between the 2 groups, these data are strictly hypothesis generating and require further investigation.

Radiation Therapy for Relapsed or Refractory Diffuse Large B-Cell Lymphoma: What Is the Right Regimen for Palliation?

Purpose: To report objective response rates (ORR), time to local failure (TTLF), and overall survival (OS) among patients with relapsed or refractory diffuse large B-cell lymphoma after salvage- or palliative-intent radiation therapy (RT) and to investigate whether outcomes differed with conventional versus hypofractionated (≥2.5 Gy/fraction) RT. Methods and Materials: A single-institution observational cohort study was performed for patients who completed a course of RT for relapsed or refractory diffuse large B-cell lymphoma between January 1, 2008, and April 1, 2020. Predictors of ORR, TTLF, and OS were calculated using univariable and multivariable regression models. The Kaplan-Meier method was used to estimate TTLF and OS, and log-rank analysis was used to compare outcomes. Equivalent dose in 2 Gy fractions (EQD2) was calculated using an α/ß of 10. Results: One-hundred and sixty-nine patients were treated with 205 RT courses (73 [36%] salvage, 132 [64%] palliative), and hypofractionated RT was used in 100 RT courses (49%). Median RT dose was 30 Gy (range, 8-60 Gy). ORR was 60% for the total cohort (53% and 69% for palliative and salvage cohorts, respectively). Over a median follow-up time of 4 months, median OS in all patients was 5 months (3 and 22 months for palliative and salvage cohorts, respectively). No statistically significant differences in ORR, TTLF, and OS were observed with hypofractionation compared with conventional fractionation. EQD2 ≥35 Gy was associated with improved ORR (odds ratio, 3.79 [1.19-12.03]; P = .024) and prolonged TTLF (0.39 [0.18-0.87]; P = .022), while double-hit receptor status (8.18 [1.08-62.05]; P = .042), cell of origin (3.87 [1.17-8.74]; P = .0012), and bulky disease (≥7.5 cm; 2.12 [1.18-3.81]; P = .012) were associated with inferior TTLF. In the palliative-only cohort, a low-dose regimen of 8 Gy in 2 fractions was associated with similar ORR compared with other fractionation schema but trended towards inferior TTLF (P = .36). Conclusions: Hypofractionation is not associated with differences in disease outcomes for patients with relapsed or refractory diffuse large B-cell lymphoma, while higher RT dose (EQD2 ≥35 Gy) may improve ORR and TTLF. Future work is warranted to elucidate the ideal dose and fractionation schema for such patients who will likely also undergo novel systemic agents and cellular therapies.

Dosimetric Results for Adjuvant Proton Radiation Therapy of HPV-Associated Oropharynx Cancer.

Purpose: One significant advantage of proton therapy is its ability to improve normal tissue sparing and toxicity mitigation, which is relevant in the treatment of oropharyngeal squamous cell carcinoma (OPSCC). Here, we report our institutional experience and dosimetric results with adjuvant proton radiation therapy (PRT) versus intensity-modulated radiotherapy (IMRT) for Human Papilloma Virus (HPV)-associated OPSCC. Materials and Methods: This was a retrospective, single institutional study of all patients treated with adjuvant PRT for HPV-associated OPSCC from 2015 to 2019. Each patient had a treatment-approved equivalent IMRT plan to serve as a reference. Endpoints included dosimetric outcomes to the organs at risk (OARs), local regional control (LRC), progression-free survival (PFS), and overall survival (OS). Descriptive statistics, a 2-tailed paired t test for dosimetric comparisons, and the Kaplan-Meier method for disease outcomes were used. Results: Fifty-three patients were identified. Doses delivered to OARs compared favorably for PRT versus IMRT, particularly for the pharyngeal constrictors, esophagus, larynx, oral cavity, and submandibular and parotid glands. The achieved normal tissue sparing did not negatively impact disease outcomes, with 2-year LRC, PFS, and OS of 97.0%, 90.3%, and 97.5%, respectively. Conclusion: Our study suggests that meaningful normal tissue sparing in the postoperative setting is achievable with PRT, without impacting disease outcomes.

Long-term Clinical Outcomes in Favorable Risk Prostate Cancer Patients Receiving Proton Beam Therapy.

Purpose: Long-term data regarding the disease control outcomes of proton beam therapy (PBT) for patients with favorable risk intact prostate cancer (PC) are limited. Herein, we report our institution's long-term disease control outcomes in PC patients with clinically localized disease who received PBT as primary treatment. Methods: One hundred sixty-six favorable risk PC patients who received definitive PBT to the prostate gland at our institution from 2010 to 2012 were retrospectively assessed. The outcomes studied were biochemical failure-free survival (BFFS), biochemical failure, local failure, regional failure, distant failure, PC-specific survival, and overall survival. Patterns of failure were also analyzed. Multivariate Cox proportional hazards modeling was used to estimate independent predictors of BFFS. Results: The median length of follow-up was 8.3 years (range, 1.2-10.5 years). The majority of patients had low-risk disease (58%, n = 96), with a median age of 64 years at the onset of treatment. Of 166 treated men, 13 (7.8%), 8 (4.8%), 2 (1.2%) patient(s) experienced biochemical failure, local failure, regional failure, respectively. Regional failure was seen in an obturator lymph node in 1 patient and the external iliac lymph nodes in the other. None of the patients experienced distant failure. There were 5 (3.0%) deaths, none of which were due to PC. The 5- and 8-year BFFS rate were 97% and 92%, respectively. None of the clinical disease characteristics or treatment-related factors assessed were associated with BFFS on multivariate Cox proportional hazards modeling (all P > .05). Conclusion: Disease control rates reported in our assessment of PBT were similar to those reported in previous clinically localized intact PC analyses, which used intensity-modulated radiotherapy, three-dimensional conformal radiotherapy, or radical prostatectomy as definitive therapy. In addition, BFFS rates were similar, if not improved, to previous PBT studies.

Tubarial salivary gland sparing with proton therapy.

The recently identified bilateral macroscopic tubarial salivary glands present a potential opportunity for further toxicity mitigation for patients receiving head and neck radiotherapy. Here, we show superior dosimetric sparing of the tubarial salivary glands with proton radiation therapy (PRT) compared to intensity-modulated radiotherapy (IMRT) for patients treated postoperatively for human papillomavirus (HPV)-associated oropharyngeal squamous cell carcinoma (OPSCC). This was a retrospective, single institutional study of all patients treated with adjuvant PRT for HPV-associated OPSCC from 2015 to 2019. Each patient had a treatment-approved, equivalent IMRT plan to serve as a reference. The main end point was dose delivered to the tubarial salivary glands by modality, assessed via a 2-tailed, paired t-test. We also report disease outcomes for the entire cohort, via the Kaplan-Meier method. Sixty-four patients were identified. The mean RT dose to the tubarial salivary glands was 23.6 Gy (95% confidence interval (CI) 21.7 to 25.5) and 30.4 Gy (28.6 to 32.2) for PRT and IMRT plans (p < 0.0001), respectively. With a median follow-up of 25.2 months, the two-year locoregional control, progression-free survival and overall survival were 97.8% (95% CI 85.6% to 99.7%), 94.1% (82.8% to 98.1%) and 98.1% (87.4% to 99.7%), respectively. Our study suggests that meaningful normal tissue sparing of the recently identified tubarial salivary glands is achievable with PRT. The apparent gains with PRT did not impact disease outcomes, with only 1 observed locoregional recurrence (0 local, 1 regional). Further studies are warranted to explore the impact of the improved dosimetric sparing of the tubarial salivary glands conveyed by PRT on patient toxicity and quality of life.

Radiomic Phenotypes for Improving Early Prediction of Survival in Stage III Non-Small Cell Lung Cancer Adenocarcinoma after Chemoradiation.

We evaluate radiomic phenotypes derived from CT scans as early predictors of overall survival (OS) after chemoradiation in stage III primary lung adenocarcinoma. We retrospectively analyzed 110 thoracic CT scans acquired between April 2012-October 2018. Patients received a median radiation dose of 66.6 Gy at 1.8 Gy/fraction delivered with proton (55.5%) and photon (44.5%) beam treatment, as well as concurrent chemotherapy (89%) with carboplatin-based (55.5%) and cisplatin-based (36.4%) doublets. A total of 56 death events were recorded. Using manual tumor segmentations, 107 radiomic features were extracted. Feature harmonization using ComBat was performed to mitigate image heterogeneity due to the presence or lack of intravenous contrast material and variability in CT scanner vendors. A binary radiomic phenotype to predict OS was derived through the unsupervised hierarchical clustering of the first principal components explaining 85% of the variance of the radiomic features. C-scores and likelihood ratio tests (LRT) were used to compare the performance of a baseline Cox model based on ECOG status and age, with a model integrating the radiomic phenotype with such clinical predictors. The model integrating the radiomic phenotype (C-score = 0.69, 95% CI = (0.62, 0.77)) significantly improved (p<0.005) upon the baseline model (C-score = 0.65, CI = (0.57, 0.73)). Our results suggest that harmonized radiomic phenotypes can significantly improve OS prediction in stage III NSCLC after chemoradiation.

Safety of cyclin-dependent kinase4/6 inhibitor combined with palliative radiotherapy in patients with metastatic breast cancer.

INTRODUCTION: Cyclin-dependent kinase (CDK)4/6 inhibitor is a first-line therapy for metastatic ER+/HER2-breast cancer. However, there are limited data on safety of combined radiotherapy (RT) and CDK4/6 inhibition. METHODS: We conducted a retrospective study of women with metastatic breast cancer who received palliative RT within 14 days of CDK4/6 inhibitor use. The primary endpoint was toxicity per Common Terminology Criteria for Adverse Events v5. Secondary endpoints were pain response and local control based on clinical assessment and imaging. RESULTS: Thirty patients underwent 36 RT courses with palbociclib (n = 34 courses, 94.4%) or abemaciclib (n = 2, 5.6%). RT was delivered before, concurrently or after CDK4/6 inhibitors in 7 (19.4%), 8 (22.2%), and 21 (58.3%) of cases with median 3.5 days from RT to closest CDK4/6 inhibitor administration. Median RT dose was 30Gy (range 8-40.05Gy). Treated sites included brain (n = 5, 11.6%), spine (n = 19, 44.2%), pelvis (n = 9, 20.9%), other bony sites (n = 6, 14.0%) and others (n = 4, 9.3%). No acute grade ≥3 non-hematologic toxicity occurred. No increased hematologic toxicity was attributable to RT with grade 3 hematologic toxicities rates 16.7%, 0%, and 6.7% before, during, and 2 weeks after RT completion. All but one patient (29/30) achieved symptom relief. Local control rates were 94.4%, 91.7% at 6 and 12 months. CONCLUSIONS: The use of RT within 2 weeks of CDK4/6 inhibitors had low acceptable toxicity and high efficacy, suggesting that it is safe for palliation of metastatic breast cancer.

Definitive tumor directed therapy confers a survival advantage for metachronous oligometastatic HPV-associated oropharyngeal cancer following trans-oral robotic surgery.

OBJECTIVES: To assess the prognostic significance of oligometastatic versus polymetastatic disease in human papillomavirus (HPV)-associated oropharyngeal squamous cell carcinoma (OPSCC), and to evaluate the impact of definitive tumor directed therapy on the survival outcomes for patients with oligometastatic disease when compared to systemic therapy. MATERIALS AND METHODS: This was a retrospective observational cohort study of patients with HPV-associated OPSCC who developed distant metachronous metastatic disease after undergoing initial primary surgical management from 2008 to 2017. We classified patients based on the extent of metastatic disease [Oligometastatic (≤5 metastases) and polymetastatic (>5 metastases)], and the initial treatment of metastatic disease [definitive tumor directed therapy (all metastases treated with surgery or radiotherapy) versus upfront systemic therapy]. RESULTS: Among 676 patients undergoing primary surgical management for HPV-associated OPSCC, 39 patients (5.8%) developed metastases after a median follow-up of 29.6 months (range 4.5-127.0). Of the 34 metastatic patients who met study criteria, 26 (76.5%) were oligometastatic and 8 (23.5%) were polymetastatic. Oligometastatic patients had improved median overall survival (OS) compared to polymetastatic patients (47.9 vs. 22.7 months, p = 0.036). For oligometastatic patients, definitive tumor directed therapy was associated with an improved median progression free survival (not reached vs 6.13 months, p = 0.001) and median OS (not reached vs 40.7 months, p = 0.004). CONCLUSION: In a cohort of patients surgically treated for HPV-associated OPSCC, metachronous metastatic disease was uncommon and, in most cases, considered oligometastatic. Oligometastasis portends a favorable prognosis and definitive tumor directed therapy may be associated with improved overall survival in these patients. Future multi-institutional efforts are warranted to further demonstrate the impact of definitive tumor directed therapy on disease outcomes.

The efficacy and safety of definitive concurrent chemoradiotherapy for non-operable esophageal cancer.

OBJECTIVE: To report outcomes and toxicity in patients who received definitive concurrent chemoradiation (DCCRT) for non-operable esophageal cancer (EC) in the modern era, and to identify markers of overall and disease-free survival (OS/DFS). METHODS: We conducted a retrospective cohort study of patients with unresectable EC who received DCCRT at our institution between 1/2008 and 1/2019. Descriptive statistics were used to report disease-control outcomes and CTCAE v4.0-5.0 toxicities. Univariable and multivariable Cox regression, and stepwise regression were used to identify associations with survival. RESULTS: At a median follow-up of 19.5 months, 130 patients with adenocarcinoma (AC) (62%) or squamous cell carcinoma (SCC) (38%) were evaluable (Stage II-III: 92%). Patients received carboplatin/paclitaxel (75%) or fluorouracil-based (25%) concurrent chemotherapy. Median total RT dose was 50.4 Gy (range, 44.7-71.4 Gy) delivered in 28 fractions (24-35). Locoregional and distant recurrence occurred in 30% and 35% of AC, and 24% and 33% of SCC, respectively. Median OS and DFS were 22.9 and 10.7 months in AC, and 25.7 and 20.2 months in SCC, respectively. On stepwise regression, tumor stage, feeding tube during DCCRT, and change in primary tumor PET/CT SUVmax were significantly associated with OS and DFS. Most severe toxicities were acute grade 4 hematologic cytopenia (6%) and radiation dermatitis (1%). Most common acute grade 3 toxicities were hematologic cytopenia (35%), dysphagia (23%), and anorexia (19%). CONCLUSIONS: Treatment of non-operable EC with DCCRT has acceptable toxicity and can provide multi-year disease control for some patients, even in AC. Continued follow-up and investigation in large studies would be useful.

18F-Fluciclovine PET/CT in Therapeutic Decision Making for Prostate Cancer: A Large Single-Center Practice-Based Analysis.

METHODS: We carried out a retrospective cohort study of patients with BR after primary treatment of PC who received imaging with 18F-fluciclovine PET/CT at our institution between January 2010 and January 2019. PET/CT results were compared with biopsy, conventional imaging results, and/or response to PC therapy. 18F-Fluciclovine PET/CT performance statistics and effects on treatment planning were calculated. RESULTS: A total of 328 patients with a median age of 71 years (range, 47-90 years) and median serum prostate-specific antigen level of 1.6 ng/mL (0.02-186.7 ng/mL) were included. Three hundred thirty-six 18F-fluciclovine PET/CT scans were analyzed and classified as positive (65%), negative (25%), or equivocal (10%) based on radiology reports. Sensitivity was 93% (95% confidence interval, 86%-96%) and specificity was 63% (95% confidence interval, 45%-77%). Of patients with known management recommendations post-PET/CT, scan results changed or influenced pre-PET/CT management plans in 73%, and 58% of recommendations involved treatment modality decisions. Overall, 82% of patients' actual management was concordant with post-PET/CT recommendations. Of evaluable patients, 116 (35%) had some form of post-PET radiotherapy included in their care plans, with 95% receiving radiotherapy at a PET-avid target. CONCLUSIONS: In the largest single-institutional cohort to date, 18F-fluciclovine PET/CT showed value in the workup of PC in the setting of BR, with noteworthy influence over clinical management decisions. Further studies are needed to evaluate whether PET/CT-based changes in management are associated with improved outcomes.

Comparative Analysis of 5-Year Clinical Outcomes and Patterns of Failure of Proton Beam Therapy Versus Intensity Modulated Radiation therapy for Prostate Cancer in the Postoperative Setting.

PURPOSE: Although proton beam therapy (PBT) is a rapidly expanding modality to treat prostate cancer compared with intensity modulated radiation therapy (IMRT), data comparing disease control outcomes and patterns of failure in the postprostatectomy setting remain substantially limited. METHODS AND MATERIALS: All patients who underwent postoperative IMRT or PBT to the prostate bed only at a single institution were included (2009-2017). Endpoints included biochemical failure (BF; using institutional and recent cooperative group trial definitions), local failure (LF), regional failure (RF), distant failure (DF), and all-cause mortality. A case-matched cohort analysis was performed using 3-to-1 nearest-neighbor matching; multivariable Cox proportional hazards modeling (MVA) estimated hazard ratios for disease-related outcomes by treatment modality. RESULTS: Of 295 men, 260 were matched (n = 65 PBT, 195 IMRT); after matching, only age at diagnosis (P < .01) significantly differed between cohorts. At a median follow-up of 59 months, BF (institution-defined), LF, RF, DF, and mortality rates were 45% (n = 29), 2% (n = 1), 9% (n = 6), 9% (n = 6), and 2% (n = 1) for PBT, and 41% (n = 80), 3% (n = 5), 7% (n = 13), 9% (n = 18), and 5% (n = 9) for IMRT (all P > .05). RT modality was not significantly associated with BF on MVA using institutional or cooperative group definitions (all P > .05), nor with LF (P = .82), RF (P = .11), DF (P = .36), or all-cause mortality (P = .69). Patterns of failure were qualitatively similar between cohorts (DF: bone, retroperitoneal nodes, lung). CONCLUSIONS: In this single institution, case-matched analysis, PBT yielded similar long-term disease-related outcomes and patterns of failure to IMRT in the postprostatectomy setting.

Quantitation and predictors of short-term mortality following extrapleural pneumonectomy, pleurectomy/decortication, and nonoperative management for malignant pleural mesothelioma.

BACKGROUND: For malignant pleural mesothelioma (MPM), the benefit of resection, as well as the optimal surgical technique, remain controversial. In efforts to better refine patient selection, this retrospective observational cohort study queried the National Cancer Database in an effort to quantify and evaluate predictors of 30- and 90-day mortality between extrapleural pneumonectomy (EPP) and pleurectomy/decortication (P/D), as well as nonoperative management. METHODS: After applying selection criteria, cumulative incidences of mortality by treatment paradigm were graphed for the unadjusted and propensity-matched populations, as well as for six a priori age-based intervals (≤60, 61-65, 66-70, 71-75, 76-80, and ≥81 years). The interaction between age and hazard ratio (HR) for mortality between treatment paradigms was also graphed. Cox multivariable analysis ascertained factors independently associated with 30- and 90-day mortality. RESULTS: Of 10,723 patients, 2,125 (19.8%) received resection (n=438 EPP, n=1,687 P/D) and 8,598 (80.2%) underwent nonoperative management. The unadjusted 30/90-day mortality for EPP, P/D, and all operated cases was 3.0%/8.0%, 5.4%/14.1%, and 4.9%/12.8%, respectively. There were no short-term mortality differences between EPP and P/D following propensity-matching, within each age interval, or between age subgroups on interaction testing (P>0.05 for all). Nonoperative patients had a crude 30- and 90-day mortality of 9.9% and 24.6%, respectively. Several variables were identified as predictors of short-term mortality, notably patient age (HR 1.022, P<0.001), Charlson-Deyo comorbidity index (HR 1.882, P<0.001), receipt of treatment at high-volume centers (HR 0.834, P=0.032) and induction chemotherapy (HR 1.735, P=0.025), among others. The patient (yearly) incremental increase in age conferred 2.0% (30 day) and 2.2% (90 day) increased risk of mortality (P<0.001). CONCLUSIONS: Quantitative estimates of age-associated 30- and 90-day mortality of EPP and P/D should be considered when potentially operable patients are counseled regarding the risks and benefits of resection.

Initial Clinical Experience Treating Patients With Lung Cancer on a 6MV-Flattening-Filter-Free O-Ring Linear Accelerator.

Introduction Modern technologies, like intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT), have improved the therapeutic ratio of thoracic radiotherapy (TRT) for lung cancer (LC). Halcyon™ (Varian Medical Systems, Palo Alto, CA, USA), a novel 6MV-flattening-filter-free O-ring linear accelerator (6X-FFF ORL), was designed to deliver IMRT and VMAT with greater speed than a C-arm linac. Herein, we report our initial clinical experience treating patients with LC on this linac. Methods All patients who received TRT for LC on the 6X-FFF ORL at our institution were retrospectively identified. Patients' clinicopathologic data, radiotherapy details, early disease-control and toxicity outcomes, dosimetric data, couch corrections, and treatment times are reported. Results Between 10/2018-12/2019, 30 consecutive patients (median age 66 years, range 54-94 years) received definitive or post-operative TRT for LC (median 66 Gy/33 fractions; range 5-70 Gy/2-37 fractions) following four-dimensional computed tomography (CT) simulation (97%) using daily kilovoltage KV cone-beam CT (CBCT) (100%) on a 6X-FFF ORL for non-small cell LC (84%) or small cell LC (16%), with 53% receiving VMAT, 43% receiving static-field IMRT, and 77% receiving concurrent systemic therapy. All plans were approved through institutional peer review. The average three-dimensional vector couch correction based on CBCT guidance was 0.90 ± 0.50 cm. The average beam-on and beam on plus CBCT times were 1.7 ± 1.1 min, and 5.0 ± 3.2 min, respectively. Grade 3 dyspnea and fatigue occurred in 3% and 3% of patients, respectively. There were no grade ≥4 toxicities. Conclusion In this first clinical report of TRT for LC on a 6X-FFF ORL, daily CBCT-guided treatment was fast and safe with respect to dosimetry and clinical outcomes. Thus, use of this linac for TRT may increase LC patient throughput without a detriment in radiotherapy quality.

Initial Clinical Experience Treating Patients With Gynecologic Cancers on a 6MV Flattening Filter Free O-Ring Linear Accelerator.

PURPOSE: Radiation therapy (RT) is commonly used in the treatment of gynecologic cancers. Intensity-modulated RT (IMRT) has been shown to reduce gastrointestinal toxicity compared with 2-dimensional and 3-dimensional RT modalities. We report the initial clinical experience using IMRT for gynecologic cancers with a novel 6MV flattening filter free O-ring linear accelerator (6X-FFF ORL). METHODS AND MATERIALS: We retrospectively identified consecutive women with uterine or cervical cancer who received pelvic RT on Halcyon (Varian Medical Systems, Palo Alto, CA), a novel 6X-FFF ORL. We report their clinicopathologic data, RT details, early disease-control outcomes, acute toxicities, dose-volume histogram data, couch corrections, and treatment times. RESULTS: Seventeen women received RT on a 6X-FFF ORL for uterine cancer (76%) or cervical cancer (24%) between January 2017 and September 2019. RT was delivered postoperatively (82%) or to intact disease (18%), to a median dose of 50.4 Gy (range, 19.8-55.0 Gy) in 25 fractions (range, 11-28), with 12% receiving extended-field RT and 65% receiving chemotherapy. Target and organ-at-risk constraints were met in all plans. The 3-dimensional vector couch correction average was 0.90 ± 0.37 cm. The mean beam-on time was 2.9 ± 0.4 min and mean treatment time, from imaging start to beam-off, was 3.6 ± 0.4 min. Grade 2 fatigue, anorexia, diarrhea, bloating, and nausea occurred in 41%, 12%, 12%, 6%, and 6% of patients, respectively. There were no grade ≥3 toxicities. CONCLUSIONS: In the initial clinical report of pelvic RT for gynecologic cancers using a 6X-FFF ORL, the linac showed versatility in treatment; comparability to flattening-filtered IMRT for early disease-control, toxicity, and dosimetry; and treatment speed that compared favorably to IMRT on a C-arm gantry. Accordingly, a 6X-FFF ORL may increase throughput or reduce day length in departments with high gynecologic cancer volumes, without compromising clinical outcomes.

Initial clinical experience treating patients with palliative radiotherapy for malignant pleural mesothelioma on the HalcyonTM linear accelerator.

BACKGROUND: Radiation therapy (RT) can provide effective symptomatic palliation in patients with malignant pleural mesothelioma (MPM). Advances in RT technology, including intensity-modulated RT (IMRT) and volumetric-modulated arc therapy (VMAT), have improved treatment conformality, potentially improving the therapeutic ratio of RT. A novel 6-MV flattening-filter-free O-ring linear accelerator, HalcyonTM (Varian Medical Systems, Palo Alto, CA, USA), was built to provide such advanced therapies, while possibly reducing treatment time. Here, we report the initial clinical experience using HalcyonTM to deliver palliative RT for patients with MPM. METHODS: We retrospectively assessed consecutive patients with MPM who received thoracic RT on HalcyonTM. Their electronic medical records were reviewed for clinical, RT planning, treatment timing, and image-guidance RT (IGRT) data. RESULTS: Four patients with metastatic MPM received palliative RT on HalcyonTM between 1/2017-1/2020 for severe pain (50%), dysphagia (25%), or dyspnea (25%). Targets included a combination of pleura, chest wall, lung, hilum, and mediastinum, with patient-specific dose and fractionation regimens ranging from 20-45 Gy in 5-15 fractions, and 75% of patients receiving concurrent systemic therapy. Pre-specified target and organ-at-risk constraints were met for nearly all plans. At a median follow-up of 2.2 months (range, 1.6-7.1 months), all patients experienced either improved (75%) or stable (25%) tumor-related symptoms following palliative RT. The mean 3D vector couch correction was 0.67±0.15 cm. The mean beam-on, treatment (beam-on plus cone-beam computed tomography times), and approximated total room usage times were 1.6±0.2, 1.8±0.2, and 9.8±0.2 min, respectively. Grade 2 fatigue and cough occurred in 25% and 25% of patients, and no patients experienced Grade ≥3 toxicity. CONCLUSIONS: In this initial clinical experience treating patients with palliative RT for MPM on HalcyonTM, treatment provided symptom palliation and local control across multiple palliative scenarios, with minimal toxicity, acceptable dosimetry, and setup corrections and treatment times that compared favorably with other published experiences of MPM RT. Palliative RT on HalcyonTM can provide patients with MPM quick and safe tumor-related symptom relief, even in a frail, elderly population.

Multi-institutional retrospective review of stereotactic radiosurgery for brain metastasis in patients with small cell lung cancer without prior brain-directed radiotherapy.

Introduction: Patients with small cell lung cancer (SCLC) brain metastasis (BM) typically receive whole brain radiotherapy (WBRT) as data regarding upfront radiosurgery (SRS) in this setting are sparse. Methods: Patients receiving SRS for SCLC BM without prior brain radiation were identified at three U.S. institutions. Overall survival (OS), freedom from intracranial progression (FFIP), freedom from WBRT (FFWBRT), and freedom from neurologic death (FFND) were determined from time of SRS. Results: Thirty-three patients were included with a median of 2 BM (IQR 1-6). Median OS and FFIP were 6.7 and 5.8 months, respectively. Median FFIP for patients with ≤2 versus >2 BM was 7.1 versus 3.6 months, p=0.0303. Eight patients received salvage WBRT and the 6-month FFWBRT and FFND were 87.8%. and 90.1%, respectively. Conclusions: Most SCLC patients with BM who received upfront SRS avoided WBRT and neurologic death, suggesting that SRS may be an option in select patients.

18F-Fluciclovine Uptake in Acute Appendicitis.

An 85-year-old man with biochemical recurrence of prostate cancer after prostatectomy was imaged with F-fluciclovine PET/CT. Images incidentally revealed F-fluciclovine uptake in a dilated appendix with associated fat stranding, suggestive of acute appendicitis. The patient was then questioned about abdominal symptoms, and he reported severe right lower quadrant pain. He then underwent laparoscopic appendectomy with pathology confirming acute appendicitis.

Gender-based Disparities in Receipt of Care and Survival in Malignant Pleural Mesothelioma.

BACKGROUND: Despite accounting for a minority of malignant pleural mesothelioma (MPM) diagnoses, females may experience differential survival relative to males. It is unclear if there are gender-based differences in receipt of treatment or disease-related outcomes for patients with MPM. We therefore utilized the National Cancer Database (NCDB) to assess patterns-of-care and overall survival (OS) among patients with MPM by gender. MATERIALS AND METHODS: Patients with histologically confirmed MPM treated from 2004 to 2013 were identified from the NCDB. The association between female gender and OS was assessed using multivariable Cox proportional hazards models with propensity score matching. Patterns-of-care were assessed using multivariable logistic regression. The overall treatment effect was tested in subsets of patients by treatment strategy, histology, and clinical stage. RESULTS: A total of 18,799 patients were identified, of whom 14,728 (78%) were male and 4071 (22%) were female. Females were statistically more likely to present at a younger age, with fewer comorbidities, and with epithelioid histology. Despite these favorable prognostic features, women were less likely to receive surgery (P ≤ .001) or chemotherapy (P ≤ .001) compared with males. On multivariable analysis, female gender was associated with improved OS (hazard ratio, 0.83; 95% confidence interval, 0.80-0.86; P ≤ .001). Gender-based survival differences were seen across all stages, but only among patients with epithelioid (P ≤ .001) and not biphasic (P = .17) or sarcomatoid (P = 1.00) histology. CONCLUSIONS: Surgery and chemotherapy are disproportionately underutilized in female patients with MPM. Despite this concerning disparity, female gender is independently associated with improved survival relative to males. Further research to understand factors that lead to gender disparities in MPM is warranted.