# Neural Network Ensemble to Detect Dicentric Chromosomes in Metaphase Images
## 1 Introduction  
Human beings are exposed to both natural and man-made sources of ionizing radiation (IR). Natural sources of IR include cosmic radiation and consumables with trace amounts of radioactivity and radon, a decay product of uranium found in water and soil at varyingconcentrations. IR is used for multiple applications, including the sterilization of certain food items, medical appliances, medical diagnostic imaging, and radiotherapy for cancer. IR causes a wide spectrum of DNA lesions: single-strand break (SSB), double-strand break (DSB), base damage, mutations and DNA-protein cross-links, with their induction depending on radiation dose, dose rate and radiation quality. Among these lesions, a DSB is the most critical lesion which, when not repaired or mis-repaired, can lead to either cell death or chromosome aberrations depending on the severity of exposure. Besides these lesions, IR can also trigger the generation of reactive oxygen species (ROS) through the hydrolysis of water and ROS generation. Oxidized DNA base lesions can lead to cytotoxic and genotoxic effects. Some of the man-made sources include medical diagnostic exposures and IR treatment of various illnesses such as cancer. Additionally, nuclear power plant accidents such as Chernobyl and Fukushima Daiichi [1; 2; 3] could potentially expose several hundreds and thousands of people to substantial doses of IR. IR exposure leads to an array of health effects, ranging from an early onset of acute radiation syndrome (ARS, hematopoietic syndrome, gastrointestinal syndrome, cerebrovascular syndrome, and cutaneous syndrome) to delayed effects of tissue degeneration and cancer. These early and delayed health effects are broadly classified into two groups: (I) deterministic effects and (II) stochastic effects. While tissue reactions like cataracts, skin reddening and ARS manifest only after exceeding a threshold dose (deterministic effects), gene mutations and cancer occur randomly without a threshold, but with the probability of incidence increasing with exposure dose (stochastic effects). Human exposure to 3.5-4 Gy of photons (X-rays and gamma rays) is expected to result in a mortality of 50% of the exposed population within 30 days (LD50/30) without any medical intervention. Therefore, the timely assessment of absorbed radiation dose is critical for saving human lives. Furthermore, estimating absorbed radiation dose assumes even greater importance in the case of large-scale accidents, where prioritizing the exposed population aids in the effective utilization of available medical resources. In addition, DNA is a highly radiation-sensitive molecule. This molecule contains information to encode all proteins in the organism, and alterations in this molecule can be fatal. Both radiation itself and the free radicals generated by radiation cause adverse effects on DNA [4]: disruption of the nitrogenous bases (scission, modification or dimerization of nitrogen bases) and DNA strand breakage (which can occur on a single strand or on both strands). In some cases, damage to double-stranded DNA can be reflected at the chromosomal level. The cellular machinery has mechanisms to counteract such DNA damage to ensure the correct transmission of genetic information to daughter cells [5]. However, it may sometimes fail. If two chromosomes fragment because of ionizing radiation at some point prior to replication, ideally, the repair mechanisms fuse each fragment with its corresponding chromosome. However, if both chromosomes are in close proximity to each other, a failure in the repair process can also occur and the fragments do not fuse with their original chromosome; instead, the fragmented chromosomes fuse with each other, and the fragments join together. This results in two types of chromosomes: those derived from the union of fragmented chromosomes, with two centromeres (dicentric chromosomes), and those derived from the fusion of fragments, without centromeres (acentric chromosomes).