## 1 Introduction  
Over the course of past centuries, cancer has affected many people. With over 100 types, it continues to be one of the leading causes of death worldwide. In 2020, there was an estimated 18.1 million cases [1]. This is about 0.225 percent of the entire population. A Canadian study released in 2021 predicted that 1 in 4 people will die from cancer [2]. In the United States of America alone, it is estimated there will be about 1.8 million new cases of cancer a year, and 600,000 will die from it. With the progress of healthcare and treatment, the projected number of cancer survivors will increase by 5.3 million by 2030 [3]. While the number of cancer survivors is increasing, there continues to be an anticipated increase in the number of cancer diagnoses and deaths [4]. Cancer can be treated by one or more treatments such as surgery, chemotherapy, or radiation therapy. Given the different types of cancer, there are many factors to consider when creating a treatment plan. Radiation therapy is a common and effective treatment that can be used as the primary treatment or in combination with other forms of treatments. It is estimated that about half of cancer patients will receive treatment involving radiation therapy [5]. Radiation therapy is a form of treatment where cancer cells or tumors are irradiated by an ionizing radiation source such as X-rays, electrons, or protons. In hospitals, patients are irradiated using a linear accelerator (LINAC). The LINACs head rotates around the patient to irradiate the tumor to avoid unnecessary damage to healthy tissue. The energy deposited kills the cancer cells by damaging their deoxyribonucleic acid (DNA),which leads to cell death or tumor shrinkage. The main goal of cancer treatment is to kill cancer cells without compromising the surrounding healthy tissue. Because of the effects of radiation on cells, minimizing the damage to normal cells has become important in medical physics research, and radiosensitizers have been shown to be effective in minimizing the damage done to healthy tissue. Radiosensitizers are chemical or pharmaceutical agents that increase cancer cell death through the production of free radicals and secondary electrons [6; 7; 8]. Radiosensitizer candidates that exhibit a high biocompatibility with cancer cells and are non-toxic to healthy cells are considered favorable [9; 10]. Compared to other traditionally used agents, gold has a low biological toxicity. GNPs deposit preferentially at tumor sites due to their enhanced permeability and retention or enhanced permeability and retention effect. The tumor vasculature system is leaky and has a low permeability to normal vasculature [11]. Furthermore, GNPs can be used as an imaging contrast [12; 13], and using gold as a contrast agent has shown that it exhibits high X-ray attenuation [14]. Another characteristic that makes a favorable candidate is an agent with a high atomic number. During radiation therapy, the target is irradiated, and the radiation particle interacts with molecules in cells such as water and undergoes Compton scattering, during which there is a loss of energy in the conversion into an electron and a scattered photon. The scattered photon has lower energy relative to the recoiling electron, resulting in the electron being ejected from the atom [15; 16]. When the radiation particle interacts with a molecule with a high atomic number, such as gold (\(Z=79\)), there is a larger total absorption cross-section. Gold's total absorption cross-section is 100 times greater than for water, so it is more effective in absorbing photon energy [17; 18; 19]. The production of secondary electrons is important for causing indirect damage to cancer cell DNA. Two types of DNA damage can occur: single-strand breaks (SSBs) and double-strand breaks (DSBs). SSBs occur when one DNA strand breaks, and DSBs occur when both strands break simultaneously. One nucleotide sequence is broken in an SSB while a DSB results in two broken nucleotide sequences, and a disturbed or broken sugar-phosphate backbone.