## 1 Introduction
The frequency with which SSBs occur is much higher than for DSBs, which are more difficult to repair than SSBs because of the severity of the damage. During radiation therapy, DSBs are more favorable as they lead to mutations and cell death. To repair an SSB, the strand that has not been broken is used as a template to repair the DNA. DSBs are repaired through homologous recombination, which is not as direct as both strands are damaged and they are not able to use a template. The repair is achieved by exchanging the genetic material between another DNA molecule that is identical to the damaged DNA [20]. If there are enough strand breaks, cancer cell death will occur. Different cancers require different treatment plans. For example, external beam radiation therapies (EBRTs) that use photon beams are used to treat head and neck cancer while EBRTs that use electron beams are used for superficial cancers such as cutaneous T-cell lymphoma, also known as mycosis fungoides, which requires total skin electron irradiation [21]. Electron therapy has been used as an important treatment method for over 50 years. Emerging research on radiosensitizers has focused on photon beams because of their novelty. However, fewer studies have been conducted on the enhancement of electron therapy when gold nanoparticles are present. Earlier research into Monte Carlo simulations has demonstrated that the presence of a single gold nanoparticle results in dose enhancement [22; 23; 24]. Nonetheless, these investigations do not provide insight into the effects of nanoparticle size of the amount of DNA damage. This study examines the influence of multiple gold nanoparticles, with an equivalent total volume on DNA damage, the magnitude of which is assessed in relation to both SSBs and DSBs. A nanoparticle is a small particle with at least one dimension measuring between 1 and 100 nanometers [15]. They can be made of various materials, such as metals, ceramics, or polymers. Nanoparticles have unique properties due to their size, including a high surface-to-volume ratio, increased reactivity, and unique optical and magnetic properties [9]. In radiation therapy, nanoparticles are used to enhance the effectiveness of radiation treatment. When a nanoparticle is irradiated, it releases secondary electrons that can cause more damage to cancer cells [16; 24]. Additionally, nanoparticles can be designed to accumulate preferentially in cancer cells due to their enhanced permeability and retention, resulting in a higher concentration of the particles in the tumor. This allows for a more targeted and precise delivery of radiation to cancer cells, thereby sparing healthy surrounding tissues [6; 8]. Nanoparticle radiation therapy has shown promise for a variety of cancer types. For example, heavy-atom nanoparticles such as SNPs can be used to enhance the effectiveness of radiation therapy for prostate cancer by improving the distribution of radiation within the tumor and providing dose enhancement [25]. In addition, nanoparticles have been used to deliver radiation therapy directly to lung tumors, improving the effectiveness of treatment and minimizing damage to healthy surrounding tissues [26]. The use of GNPs as a radiosensitizer has been shown to be effective in enhancing the dose for skin lesions when using orthovoltage beams in skin therapy [27].