West Michigan Cancer Center

298 Background: The phase III FLAME trial demonstrated that in localized prostate cancer, an external beam radiotherapy (EBRT) simultaneous integrated microboost to an MRI-defined dominant intraprostatic lesion improves biochemical control without affecting toxicity and quality of life. Given the complexity required to deliver high microboost doses, we hypothesized that practice patterns are variable in clinical practice. We aimed to characterize microboost utilization and evaluate dosimetric parameters within the statewide Michigan Radiation Oncology Quality Consortium (MROQC). Methods: Men with intermediate or high-risk prostate adenocarcinoma treated with curative intent radiotherapy for intact disease were included. Data was prospectively collected, including T/N-category, Gleason score, prostate-specific antigen, and percent positive biopsy cores. Full DICOM files were available for dosimetric data. Multivariable analyses (MVA) were used to evaluate associations between receipt of microboost, known prognostic factors, and fiducial marker and rectal spacer placement (advanced image guided radiation therapy (IGRT)). Results: From 10/26/20 to 06/26/23, 741 patients across 26 centers were enrolled, 71% (n=528) with intermediate-risk and 29% (n=213) with high-risk disease. Androgen deprivation therapy was planned in 61%. EBRT + whole-gland brachytherapy boost was utilized in 29% (n=217/741) of patients. Of those treated with EBRT (71%, n=524/741), 10% received a microboost (n = 53/524). Brachytherapy boost and microboost were used in 9 and 7 centers, respectively. Most patients received either conventional fractionation or moderate hypofractionation- 11% and 66% in EBRT without microboost and 21% and 60% with microboost, respectively. Microboost treatment was associated with use of a planning MRI (91% vs. 62%, p <0.0001) as well as fiducial marker and rectal spacer placement (76% vs. 45%, p <0.0001). Median prostate planning target volume (PTV) was smaller in microboost patients (127 cc vs. 91 cc, p = 0.002); median boost volume was 21 cc. Median boost dose (D0.1cc) was 117% (IQR 115% – 119%) of the PTV prescription. Microboost patients had significantly higher mean bladder D1cc[%] (105.7% vs. 103.4%, p = 0.002) and numerically lower rectal D1cc[%] (90.7% vs. 94.1%, p = 0.065). On MVA, receipt of microboost was significantly associated with grade group 4 or 5 disease, planning MRI use, and fiducial and rectal spacer use. Conclusions: Within a large, diverse prospective cohort of men with prostate cancer treated in both academic and community settings, a microboost was utilized in 10% of EBRT cases. Microboost use was associated with higher grade group, MRI planning, and advanced IGRT. EBRT microboost is an emerging dose escalation strategy and further studies confirming safety and improved clinically meaningful outcomes may increase uptake in routine practice.

A ccess to high-quality cancer care in the United States remains a challenge in part due to a geographic mismatch between patients with cancers and the oncologic specialists best able to serve them. For example, although the standard of care for patients with gynecologic cancers includes consultation with a subspecialist gynecologic oncologist, [1] [2] [3] [4] approximately 15 million women have geographic barriers to care 5, 6 and are thereby less likely to receive guideline-adherent care and at risk for worse cancer-related survival. 7 Patients with geographic barriers to care may also be less likely to receive high-quality treatment for breast, 8 colon, 9 rectal, 10 esophagogastric, 11 and lung cancers. 12 There is an urgent need to develop communication strategies that allow oncologists to determine which patients might benefit from referral for subspecialty cancer care and to allow subspecialists to guide care remotely when patients are unable or unwilling to travel for cancer care. Virtual consultation between clinicians, without direct patient involvement, has its origins in the common, somewhat informal, "curbside" consultation process. 13 However, this process has become more formalized in multiple settings, including synchronous (i.e., "live") virtual consultation between rural primary care providers and specialists in the University of New Mexico's Project ECHO 14 and asynchronous (i.e., "store-and-forward")

438 Background: Patients (pts) with advanced biliary tract cancers (BTC) have poor prognosis despite systemic chemotherapy and treatment beyond first-line platinum doublet remains largely investigational. The immunomodulatory properties of conventional cytotoxic therapy, particularly in regard to the upregulation of PD-L1 expression rendering tumor cells less sensitive to T cell-mediated lysis, rapid emergence of chemotherapy resistance, and known modest efficacy of single agent anti-PD-1 antibody in BTC provide a rationale for combination chemoimmunotherapy. We conducted a multi-center, phase Ib/II, single-arm study to investigate the role of liposomal-irinotecan, 5FU and LV in combination with nivolumab as second-line therapy in pts with advanced BTC. Methods: Key eligibility criteria include histologically confirmed unresectable or metastatic BTC after progression or intolerance of first-line systemic therapy, measurable disease per RECISTv1.1, ECOG PS 0-1, and absence of autoimmune disease or chronic steroid use. The limited phase Ib portion evaluated 10 pts to determine the recommended phase 2 dose (RP2D) based on the probability of dose-limiting toxicity (DLT) rate <30% during days 1-29. Study treatment included 5FU 2400 mg/m2 over 46 hrs, LV 400 mg/m2, liposomal-irinotecan 70 mg/m2 at dose level 0 along with nivolumab 240 mg every 2 wks for up to 2 yrs in absence of disease progression or unacceptable toxicity. The primary endpoint was median progression-free survival (PFS) rate with an alternative and null hypothesis of 5.0 mo and 2.9 mo (two-sided alpha 0.05, power 80%), respectively. Secondary endpoints included best overall response rate (ORR) per immune related (ir)RECIST, median overall survival (OS), 75th percentile estimates of PFS and OS, and safety. Exploratory objectives include biomarker analysis using include targeted panel exome/transcriptome and immune cell subsets in tissue. Results: 30 eligible pts (60% men, 83% Caucasian) including 10 pts in phase Ib and 20 pts in phase II with a median age of 63.5 yrs (range 36-75) were enrolled across 4 US sites between June 2019 and July 2021. In phase Ib, one pt experienced DLT (grade 3 enterocolitis); RP2D was confirmed at dose level 0. All 30 pts were included in study reported outcomes with a median follow-up time of 10.7 mo. Median PFS was 4.2 mo (95% CI, 1.9-10.2) and failed to reject the null hypothesis. Median OS was 7.5 mo (95% CI, 5.8-21.4). The 75th percentile estimates for PFS and OS are 10.2 mo (95% CI, 5.4-NE) and 21.4 mo (95% CI, 7.8-21.4). ORR estimates and toxicity data are pending and will be presented at the meeting. Conclusions: The observed median PFS is insufficient to reject the null hypothesis. The 75th percentile estimates for PFS and OS are suggestive of prolonged benefit with chemoimmunotherapy in a small fraction of patients with BTC. Clinical trial information: NCT03785873.