Tehran University Medical Journal

---

Discovery of x-ray and using of it for medical imaging have produced tremendous outcomes for diagnosis and treatment of diseases. More than 10 million diagnostic radiological procedures and 100,000 nuclear medicine exams are being performed daily around the world. According to the national commission on radiological protection and measurements (NCRP)-report 160, medical x-ray is contribute to approximately 95% of all radiological examinations that is responsible for 74% of the collective dose to the US population. Despite of unique benefits of ionizing radiations, in the field of radiation protection, they are associated with potential risks such as cancer and genetically abnormalities. The cancer risk attributable to diagnostic radiology is estimated about 0.6% to 3%. It is estimated that the radiation dose from diagnostic x-ray procedures are annually responsible for 7,587 and 5,695 cases of radiation induced cancer in the population of Japan and US, respectively. Although the radiation dose associated with most radiological procedures are very low, but rapid increasing use of radiography procedures during two past decades have been concerned due to the cancer risk associated with ionizing radiations. On the base of linear no-threshold (LNT) model of dose-response curve, any level of exposure is dangerous. Deoxyribonucleic acid (DNA) is the main target of ionizing radiation. For radiological exposure with low dose, the stochastic effects such as genetic damages and leukemia are concerned. According to the recommendations of the radiation protection regulatory organizations, radiological procedure must be done with respect to social and economic factors in which exposure of patient and population kept as low as reasonable and achievable. Hence, prescription of a radiological test is acceptable only when its advantages are higher than its damages. Optimizing the different parameters such as: collimating the primary beam field to the area of diagnostic interest, exposure conditions (high kVp and low mAs), projections, exposure time and shielding can reduce the patients' exposure besides the saving of image quality. Following the radiation protection guidelines can considerably decrease the exposure risks.

---

Background: To date, different kinds of treatment methods have been proposed for radiotherapy of cancer patients. Choosing the kind of treatment method affects the quality of the patient's treatment. This study aims to investigate the effect of the number of radiation treatment sessions on the dose received by the patient and the distribution of tumor dose and dose received by organs at risk in breast cancer radiation therapy. These results help us to select the appropriate treatment schedules for the treatment of left breast patients.
Methods: This prospective cross-sectional study was performed on the treatment plans of 35 patients with left breast cancer who referred to Isfahan Milad Hospital between July 2019 and April 2020. They were candidates for left breast radiation therapy. Also, these patients had no history of surgery or chemotherapy, and no supraclavicular or axillary lymph nodes were involved. Patients were treated with a conventional fraction regimen (CF) or hypofractionated (HF) treatment schedule. Different dosimetry parameters for the target and organ at risks such as conformity index, homogeneity index and mean dose were obtained from the dose-volume histogram plot. Finally, the results of both plans were compared with each other.

Results: The data obtained from this study indicate a decrease in the average dose of all organs in the hypo fractionated regimens compared to conventional plans. The differences between two plans were statistically significant for tumor, lung, and skin (P=0.0). Moreover, the maximum dose for the skin was also reduced when hypofractionated regimens were used. However, the values of the homogeneity index and conformity index of tumor in the two methods did not show a significant difference (P were 0.99 and 0.86, respectively). Conclusion: In general, the results of the current study indicate that the hypofractionated regimen leads to a reduction in dosimetric factors compared to conventional fraction plans. It seems that this method can be used as an alternative treatment plan for breast cancer radiation therapy due to the reduced duration of the treatment period.

 

---

Prostate cancer is the most common and second leading cause of death among men in the world. Nowadays, radiotherapy has been known as one of the most affecting methods for prostate cancer treatment. Nevertheless, radiotherapy is accompanied by the concern of developing secondary cancers by the scattered radiation to the neighbor  organs at risk. Several studies have shown that secondary cancers after the radiotherapy of prostate cancer treatment, occur in tissues such as the bladder and rectum which have been exposed to direct or indirect radiations. Therefore, this review study aimed to evaluate the influencing factors for developing secondary cancers after the radiotherapy of prostate cancer. To access the previously validated published studies, Persian and English keywords such as prostate cancer, secondary cancers, radiotherapy and organs at risk have been searched in ISID, Google Scholar, Science Direct, PubMed, and World Health Organization, between 1997 and 2021. Totally 246 pieces of literature have been selected which finally, by ignoring the similar and overlapping studies, only 40 studies were reviewed. In the present study, the most affecting factors for developing secondary malignancies including the anatomical status changes, dose variations, smoking and the impact of the various treatment techniques, have been studied. The results of the reviewed studies showed a reduction of secondary cancer risks with performing the modern modalities such as proton therapy to treat prostate cancer. Moreover, organ movements and anatomical status changes which vary from one patient to others, have been reported to make a significant difference in the relative risk of secondary cancers. It has been shown that smoking may increase the risk of secondary cancers after the radiotherapy of prostate cancer, so radiotherapy and smoking may cause genetic mutations. Despite the advantages of radiotherapy for prostate cancer treatment, developing secondary cancers after the radiotherapy should not be ignored. Assessments of the affecting factors for secondary cancers after the radiotherapy of prostate cancer require social and comprehensive studies which can result in an accurate modality with fewer side effects.

---

Background: In prostate cancer radiotherapy, due to the proximity of the prostate to the rectum, it can be affected by high radiation doses. It has been reported that about 70% of secondary cancers after prostate cancer radiotherapy occur in the bladder and rectum, which are exposed to direct radiation. Since prostate cancer radiotherapy may be accompanied by side effects, the aim of this study is to investigate the risk of secondary cancers after the radiotherapy of prostate cancer inside the outfield organs.
Methods: The dose volume histogram data relevant to 39 patients with prostate cancer (who were treated with 3-dimensional conformal radiotherapy technique in 2022 in Tehran) were extracted, and the uniform absorbed dose inside the sensitive tissues was calculated according to the gEUD concept. Then, the risks of secondary malignancies following prostate cancer radiotherapy were calculated using the model introduced by the BEIR report. Accordingly, the lifetime attributable risk values (LAR) were estimated based on the desired organs and patient age at exposure time through the calculation of Excess relative risk (ERR) and Excess absolute risk (EAR) values.