## 1 Introduction  
About twenty million new cases of malignant diseases were diagnosed in 2022 according to a report of [PERSON] et al. [1] who collected data related to the incidence and mortality of 36 cancers from 185 countries. Colorectal cancer was the third most frequently presented malignancy with more than 1.9 million cases in both males and females [1]. This disease was also the second leading cause of global cancer mortality [1]. It was found that 903,859 people across the world died due to colorectal cancer during 2022 [1]. In the United States of America, the incidence rate decreased by 46% from 1985 to 2019 [2]. The aforementioned decrease can be attributed to the early diagnosis and prevention of colorectal cancer by screening procedures [3].  
One of three colorectal malignancies appears in the rectum, which constitutes the final part of the large intestine ending at the anus [4]. Multimodality treatment, which might involve surgery, chemotherapy, and radiation therapy (RT), may be applied for these patients with rectal malignancies [5, 6]. The multimodality therapeutic approach improves the outcome of rectal cancer patients with respect to that achieved with a surgical approach alone [7]. RT prior to or after surgery has played a major role for decades in the management of early, locally advanced, or metastatic rectal cancer [7, 8]. RT is based on the use of high-energy radiation beams directed toward the site of the tumor. These beams deliver high radiation doses to the tumor site based on short- or long-course treatment [4]. Several RT techniques have been employed in rectal cancer patients. Conventional three-dimensionalconformal RT (3D-CRT) has been considered the standard approach for treating this pelvic tumor [7; 8]. The more advanced intensity modulated RT (IMRT) has gained popularity for the management of malignancies developing in the rectum [9]. Stereotactic body RT should be considered for large tumors or extensive disease [3].  
According to the SEER cancer statistics review [10], the 5-year survival rate for rectal cancer patients was 49.4% in 1975, and it has increased to 65% for patients diagnosed with this malignancy between 2014 and 2020. The respective survival reaches 91.1% for localized disease, and it is 73.7% when there is disease spread to regional lymph nodes [10]. Therapeutic advances have largely contributed to the above-improved survival. Rectal cancer survivors are always concerned about the side effects of the applied anticancer treatments. RT may lead to adverse early or late effects [11]. One of the most serious late effects is the induction of second cancers in irradiated healthy organs and tissues [12; 13; 14]. The time interval between exposure to ionizing radiation and the development of solid malignancies may reach 60 years [11]. Long-term cancer survivors, who previously underwent radiotherapy, are at risk for the presence of a radiation-induced malignancy for decades. The risk of developing radiation-induced secondary malignancies following RT for rectal cancer has been previously discussed in the literature [15; 16]. The above risk exists irrespective of the use of conventional or advanced RT techniques and the applied dose fractionation scheme [17; 18].  
This article reviews the role of external-beam RT in the management of rectal carcinoma and the data related to radiation-induced cancer risk as derived from epidemiological or dosimetric studies. The factors that may influence and restrict the magnitude of this cancer risk are presented.