Variation of 4 MV X-ray dose rate in fractionated irradiation strongly impacts biological endothelial cell response in vitro

Possible association of dose rate and the development of late visual toxicity for patients with intracranial tumours treated with pencil beam scanned proton therapy

BACKGROUND AND PURPOSE

Rare but severe toxicities of the optic apparatus have been observed after treatment of intracranial tumours with proton therapy. Some adverse events have occurred at unusually low dose levels and are thus difficult to understand considering dose metrics only. When transitioning from double scattering to pencil beam scanning, little consideration was given to increased dose rates observed with the latter delivery paradigm. We explored if dose rate related metrics could provide additional predicting factors for the development of late visual toxicities.

MATERIALS AND METHODS

Radiation-induced intracranial visual pathway lesions were delineated on MRI for all index cases. Voxel-wise maximum dose rate (MDR) was calculated for 2 patients with observed optic nerve toxicities (CTCAE grade 3 and 4), and 6 similar control cases. Additionally, linear energy transfer (LET) related dose enhancing metrics were investigated.

RESULTS

For the index cases, which developed toxicities at low dose levels (mean, 50 GyRBE), some dose was delivered at higher instantaneous dose rates. While optic structures of non-toxicity cases were exposed to dose rates of up to 1 to 3.2 GyRBE/s, the pre-chiasmatic optic nerves of the 2 toxicity cases were exposed to dose rates above 3.7 GyRBE/s. LET-related metrics were not substantially different between the index and non-toxicity cases.

CONCLUSIONS

Our observations reveal large variations in instantaneous dose rates experienced by different volumes within our patient cohort, even when considering the same indications and beam arrangement. High dose rate regions are spatially overlapping with the radiation induced toxicity areas in the follow up images. At this point, it is not feasible to establish causality between exposure to high dose rates and the development of late optic apparatus toxicities due to the low incidence of injury.

Detection of radiation-induced senescence by the Debacq-Chainiaux protocol: Improvements and upgrade in the detection of positive events

Senescent cells are blocked in the cell cycle but remain metabolically active. These cells, once engaged in the senescence process, fail to initiate DNA replication. Due to the shortening of telomeres, replicative senescence can be triggered by a DNA damage response. Moreover, cells can also be induced to senesce by DNA damage in response to elevated reactive oxygen species (ROS), activation of oncogenes, cell-cell fusion or after ionizing radiation. There are multiple experimental ways to detect senescent cells directly or indirectly. Senescence-associated cellular traits (SA β-Gal activity, increase in cell volume and lysosome content, appearance of γ-H2AX foci, increase of ROS and oxidative damage adducts, etc.) can be identified by numerous methods of detection (flow cytometry, confocal imaging, in situ staining, etc.). Here, we improved an existing flow cytometry protocol and further developed a new one specifically tailored to ionizing radiation-induced endothelial senescence. Thus, we have upgraded the Debacq-Chainiaux protocol and added improvements in this protocol (i) to better detect positive events (ii) to offer a compatibility to simultaneously analyze various intracellular molecules including phosphorylated signaling proteins and cytokines, whether related or not to senescence processes.

Tissue Reactions and Mechanism in Cardiovascular Diseases Induced by Radiation

The long-term survival rate of cancer patients has been increasing as a result of advances in treatments and precise medical management. The evidence has accumulated that the incidence and mortality of non-cancer diseases have increased along with the increase in survival time and long-term survival rate of cancer patients after radiotherapy. The risk of cardiovascular disease as a radiation late effect of tissue damage reactions is becoming a critical challenge and attracts great concern. Epidemiological research and clinical trials have clearly shown the close association between the development of cardiovascular disease in long-term cancer survivors and radiation exposure. Experimental biological data also strongly supports the above statement. Cardiovascular diseases can occur decades post-irradiation, and from initiation and development to illness, there is a complicated process, including direct and indirect damage of endothelial cells by radiation, acute vasculitis with neutrophil invasion, endothelial dysfunction, altered permeability, tissue reactions, capillary-like network loss, and activation of coagulator mechanisms, fibrosis, and atherosclerosis. We summarize the most recent literature on the tissue reactions and mechanisms that contribute to the development of radiation-induced cardiovascular diseases (RICVD) and provide biological knowledge for building preventative strategies.

Clinical Trial in a Dish for Space Radiation Countermeasure Discovery

NASA aims to return humans to the moon within the next five years and to land humans on Mars in a few decades. Space radiation exposure represents a major challenge to astronauts' health during long-duration missions, as it is linked to increased risks of cancer, cardiovascular dysfunctions, central nervous system (CNS) impairment, and other negative outcomes. Characterization of radiation health effects and developing corresponding countermeasures are high priorities for the preparation of long duration space travel. Due to limitations of animal and cell models, the development of novel physiologically relevant radiation models is needed to better predict these individual risks and bridge gaps between preclinical testing and clinical trials in drug development. "Clinical Trial in a Dish" (CTiD) is now possible with the use of human induced pluripotent stem cells (hiPSCs), offering a powerful tool for drug safety or efficacy testing using patient-specific cell models. Here we review the development and applications of CTiD for space radiation biology and countermeasure studies, focusing on progress made in the past decade.