Validation of the TOPAS Monte-Carlo Code of the Off-Field Dose of a 6 MV Synergy Linac

The risk of radiation-induced second cancer and the late tissue loss due to Off-field doses in radiotherapy remain a serious concern. Monte Carlo (MC) simulation is currently one of the most accurate methods for calculating these doses. MC simulation model based on the Particle Simulation Tool (TOPAS) has been developed to simulate the off-field dose of an Elekta Synergy linear accelerator (Linac) emitting 6 MV photons. Measurements were taken in a water phantom using an ionization chamber to validate this model. The Percentage Depth Dose (PDD) at the depth of 0.0, 5.0, 10.0 and 15.0 cm from the beam axis for a 10 × 10 cm2 field size was measured and simulated. Off-field dose profiles at the depth of 1.5 (dmax), 5.0 and 10.0 cm for field sizes of 5 × 5, 10 × 10, 15 × 15, and 20 × 20 cm2 respectively were measured and simulated. Comparison of measured and simulated off-field dose values showed a good agreement. The average gamma passing rate of the PDDs and profiles curves for off-field doses were 87.5% and 98.11% respectively. The local dose difference based on the PDD curve between the measured and simulated was less than 6.0 % for all locations. For all field size considered in this study, the average difference between profile curves for off-field dose measured and simulated was 9.1%. PDDs and Profiles curves for off-field dose simulation uncertainties were less than 2.0% and 1.0% respectively. TOPAS-MC simulation model developed is a good representation of our 6 MV Linac Elekta Synergy for assessing off-field dose, which would be the primary cause of some secondary cancers.

Effect of prior malignancy on the prognosis of gastric cancer and somatic mutation

BACKGROUND Cancer survivors have a higher risk of developing secondary cancer,with previous studies showing heterogeneous effects of prior cancer on cancer survivors.AIM To describe the features and clinical significance of a prior malignancy in patients with gastric cancer(GC).METHODS We identified eligible patients from the Surveillance,Epidemiology,and End Results(SEER)database,and compared the clinical features of GC patients with/without prior cancer.Kaplan-Meier curves and Cox analyses were used to assess the prognostic impact of prior cancer on overall survival(OS)and cancerspecific survival(CSS)outcomes.We also validated our results in The Cancer Genome Atlas(TCGA)cohort and compared mutation patterns.RESULTS In the SEER dataset,of the 35492 patients newly diagnosed with GC between 2004 and 2011,4,001(11.3%)had at least one prior cancer,including 576(1.62%)patients with multiple cancers.Patients with a prior cancer history tended to be elderly,with a more localized stage and less positive lymph nodes.The prostate(32%)was the most common initial cancer site.The median interval from initial cancer diagnosis to secondary GC was 68 mo.By using multivariable Cox analyses,we found that a prior cancer history was not significantly associated with OS(hazard ratio[HR]:1.01,95%confidence interval[CI]:0.97–1.05).However,a prior cancer history was significantly associated with better GCspecific survival(HR:0.82,95%CI:0.78–0.85).In TCGA cohort,no significant difference in OS was observed for GC patients with or without prior cancer.Also,no significant differences in somatic mutations were observed between groups.CONCLUSION The prognosis of GC patients with previous diagnosis of cancer was not inferior to that of primary GC patients.

Radiation Induced Bystander Effect: From in Vitro Studies to Clinical Application

In the past 20 years, the classic paradigm in radiobiology recognizing DNA as the main target for the action of radiation has changed. The new paradigm assumes that both targeted and non-targeted effects of radiation determine the final outcome of irradiation. Radiotherapy is one of the main modality treatments of neoplastic diseases with intent to cure, or sometimes to palliate only, thus radiation-induced non-targeted effect, commonly referred to as the radiation-induced bystander effect (RIBE) may have a share in cancer treatment. RIBE is mediated by molecular signaling from radiation targeted cells to their non-irradiated neighbors, and comprises such phenomena as bystander effect, genomic instability, adaptive response and abscopal effect. Whereas first three phenomena may appear both in vitro and in vivo, an abscopal effect is closely related to partial body irradiation and is a systemic effect mediated by immunologic system which synergizes with radiotherapy. From the clinical point of view abscopal effect is particularly interesting due to both its possible valuable contribution to the treatment of metastases, and the potential harmful effects as induction of genetic instability and carcinogenesis. This review summarized the main results of investigations of non-targeted effects coming from in vitro monolayer cultures, 3-dimentional models of tissues, preclinical studies on rodents and clinically observed beneficial abscopal effects with particular emphasis on participation of immunotherapy in the creation of abscopal effects.