Kirschner, Austin N.

Objectives: To summarize the current evidence for radiation therapy (RT) in the prevention and treatment of heterotopic ossification (HO), including patient selection, optimal RT technique, and associated risks. Methods: This multispecialty-led committee includes radiation oncologists, rheumatologists, orthopedic surgeons, and physical medicine/rehabilitation physicians. Using the population, intervention, comparator, outcome, timing and study design (PICOTS) framework, evidence regarding treatment outcomes was assessed using Cochrane and PRISMA methodology. Eligible studies included prospective and retrospective studies published between January 1, 1980, and November 1, 2025, from Embase, Medline, and PubMed databases. Of the 197 articles identified using the search strategy, 83 were selected for inclusion as evidence, including 27 well-designed studies (phase II randomized and phase III), 16 moderately well-designed studies that account for most common biases (matched cohort and phase II studies), 31 studies with design limitations (retrospective reviews), 2 supplemental studies (not useful as primary evidence), and 7 meta-analyses. Additional studies were included to provide context and were not used to guide recommendations. Well-established RAND-UCLA consensus methodology (modified Delphi) was used to rate the appropriateness of the treatment options. Results: The results of this analysis demonstrate that in appropriately selected patients, RT is an effective and safe therapy for prophylaxis of HO formation. Conclusions: This systematic review provides consensus guidelines for the use of RT as prophylaxis of HO based on current peer-reviewed evidence in the literature.

Introduction/Objective: Immune checkpoint inhibitors (ICIs) have limited efficacy in prostate cancer. Radiation therapy (RT) combined with ICIs and PI3K inhibition may enhance anti-tumor immune activity. Methods: RT-induced cytosolic double-stranded DNA (dsDNA) was measured in human and mouse prostate cancer cell lines as the surrogate upstream marker consistent with cGAS–STING engagement. In a syngeneic mouse model for castration-resistant prostate cancer (Myc-CaP in FVB mice), triple therapies were studied: (1) anti-CTLA-4, anti-PD-1, and RT, and (2) PIM kinase inhibitor PIM447, anti-PD-1, and RT. Mass cytometry (CyTOF) was used to measure the tumor-immune profile. Results: The peak induction of cytosolic dsDNA was at an RT dose of 13 Gy. In the mouse model, triple therapy with anti-CTLA-4, anti-PD-1, and RT doubled the median survival compared to monotherapy (32 days vs 11 to 22 days, p<0.006). Triple therapy with the PIM kinase inhibitor PIM447, anti-PD-1, and RT nearly tripled the median survival compared to PIM447 monotherapy (82 days vs 29 days, p=0.002). Mass cytometry analysis revealed that the combination of anti-PD-1 and RT reduced myeloid-derived suppressor cells and tissue-associated macrophages and enhanced CD8+ T-cell infiltration. Discussion: Although prostate cancer is an immunocold entity, RT can trigger immune activation, consistent with engagement of the cGAS–STING signaling pathway (cytosolic dsDNA serving as a surrogate upstream marker). In triple therapy, RT can enhance the efficacy of ICI and PI3K-targeted drug therapy, significantly improving overall survival in a mouse model of CRPC. Conclusions: A combination of RT, ICIs, and PIM kinase inhibition may help overcome immune resistance in prostate cancer. This combination therapy approach supports further preclinical validation and careful clinical evaluation and warrants further clinical investigation to optimize treatment strategies for CRPC.