Simulation of an HDR Boost with Stereotactic Proton versus Photon Therapy in Prostate Cancer: A Dosimetric Feasibility Study

Purpose/objectives: To compare the dose escalation potential of stereotactic body proton therapy (SBPT) versus stereotactic body photon therapy (SBXT) using high-dose rate prostate brachytherapy (HDR-B) dose-prescription metrics. Patients and methods: Twenty-five patients previously treated with radiation for prostate cancer were identified and stratified by prostate size (≤ 50cc; n = 13, \u3e 50cc; n = 12). Initial CT simulation scans were re-planned using SBXT and SBPT modalities using a prescription dose of 19Gy in 2 fractions. Target coverage goals were designed to mimic the dose distributions of HDR-B and maximized to the upper limit constraint for the rectum and urethra. Dosimetric parameters between SBPT and SBXT were compared using the signed-rank test and again after stratification for prostate size (≤ 50cm3 and \u3e50cm3) using the Wilcoxon rank test. Results: Prostate volume receiving 100% of the dose (V100) was significantly greater for SBXT (99%) versus SBPT (96%) (P ≤ 0.01), whereas the median V125 (82% vs. 73%, P \u3c 0.01) and V200 (12% vs. 2%, P \u3c 0.01) was significantly greater for SBPT compared to SBXT. Median V150 was 49% for both cohorts (P = 0.92). V125 and V200 were significantly correlated with prostate size. For prostates \u3e 50cm3, V200 was significantly greater with SBPT compared to SBXT (14.5% vs. 1%, P = 0.005), but not for prostates 50cm3 (9% vs 4%, P = 0.11). Median dose to 2cm3 of the bladder neck was significantly lower with SBPT versus SBXT (9.6 Gy vs. 14 Gy, P \u3c 0.01). Conclusion: SBPT and SBXT can be used to simulate an HDR-B boost for locally advanced prostate cancer. SBPT demonstrated greater dose escalation potential than SBXT. These results are relevant for future trial design, particularly in patients with high risk prostate cancer who are not amenable to brachytherapy. Keywords: brachytherapy; prostate cancer; proton therapy; stereotactic radiation therapy

Immunotherapy and radiation therapy for gastrointestinal malignancies: Hope or hype?

Immunotherapy represents the newest pillar in cancer care. Although there are increasing data showing the efficacy of immunotherapy there is a spectrum of response across unselected populations of cancer patients. In fact, response rates can be poor even among patients with immunogenic tumors for reasons that remain poorly understood. A promising clinical strategy to improve outcomes, which is supported by an abundance of preclinical data, is combining immunotherapy with radiation therapy. Here we review the existing evidence and future directions for combining immunotherapy and radiation therapy for patients with gastrointestinal cancers

Emerging Evidence on the Effects of Dietary Factors on the Gut Microbiome in Colorectal Cancer

Dietary factors play an important role in shaping the gut microbiome which, in turn, regulates the molecular events in colonic mucosa. The composition and resulting metabolism of the gut microbiome have been implicated in the development of colorectal cancer (CRC). Diets low in dietary fibers and phytomolecules as well as other lifestyle-related factors may predispose to CRC. Emerging evidence demonstrates that the predominance of microbes, such as Fusobacterium nucleatum, can predispose the colonic mucosa to malignant transformation. Dietary and lifestyle modifications have been demonstrated to restrict the growth of potentially harmful opportunistic organisms. In this study, we aim to present evidence regarding the relationship of dietary factors to the gut microbiome and development of CRC. Keywords: dietary fibers; short chain fatty acid; gut microbiota; colorectal cancer prevention; epigenetic

Consensus Report From the Miami Liver Proton Therapy Conference

An international group of 22 liver cancer experts from 18 institutions met in Miami, Florida to discuss the optimal utilization of proton beam therapy (PBT) for primary and metastatic liver cancer. There was consensus that PBT may be preferred for liver cancer patients expected to have a suboptimal therapeutic ratio from XRT, but that PBT should not be preferred for all patients. Various clinical scenarios demonstrating appropriateness of PBT vs. XRT were reviewed