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Purpose: The present study aims to investigate the radioprotective effect of melatonin (MEL) against early period brain damage caused by different dose rate beams in the experimental rat model., Materials and Methods: Forty-eight Sprague Dawley rats were randomly divided into six groups; the control, only melatonin, low dose rate-radiotherapy (LDR-RT), high dose rate-radiotherapy (HDR-RT) groups and (LDR-RT) + MEL and (HDR-RT) + MEL radiotherapy plus melatonin groups. Each rat administered melatonin was given a dose of 10 mg/kg through intraperitoneal injection, 15 minutes before radiation exposure. The head and neck region of each rat in only radiotherapy and radiotherapy plus melatonin groups was irradiated with a single dose of 16 Gy in LDR-RT and HDR-RT beams. Rats in all groups were examined for histopathology and biochemistry analysis 10 days after radiotherapy., Results: Comparing the findings for LDR-RT and HDR-RT only radiotherapy groups and the control group, there was a statistically significant difference in histopathological and biochemical parameters, however, melatonin administered in radiotherapy plus melatonin groups contributed improving these parameters ( p  < .05). There was no statistically significant difference between LDR-RT and HDR-RT beams ( p  > .05)., Conclusions: It was concluded that melatonin applied before LDR-RT and HDR-RT radiotherapy protected early period radiotherapy-induced brain damage. The effects of clinically low and high dose beams on the cerebral cortex and cerebellum were investigated histopathologically for the first time. HDR beams can be safely applied in brain radiotherapy. However, more experimental rat and clinical studies are needed to explain the radiobiological uncertainties about the clinic dose rate on different cancerous and healthy tissues.

Radiotherapy plays an important role in the treatment of tumors, and enteritis is a common side effect of this therapy. The aim of present study was to evaluate the protective effect of melatonin and probiotics on radiation-induced intestinal tissue damage in rats. Histopathological, biochemical and microbiological samples were examined.Thirty-two Wistar Albino rats were randomly distributed into four groups: the control group, only radiotherapy (RT) group, radiotherapy plus melatonin (RT + MEL) groups and radiotherapy plus probiotics (RT + PROB) groups. The abdominal-pelvic region of the experimental rat was irradiated with in a single dose of 16 Gy. The melatonin was administered at a single dose of 50 mg/kg through intraperitoneal injection, 15 min before radiation exposure. The probiotic was administered orally every day to the rats for 5 days starting before radiotherapy.There was a statistically significant changes in histopathological (villus atrophy, mitotic activity, apoptotic index, goblet cell swelling, degenerative changes, atypia) and biochemical (oxidant and antioxidant status, IL-1β, IL-6 and TNF- α levels) parameters in the small intestine in the radiotherapy group G2 compared to the G1 control group (p < 0.05). However, a significant decrease was observed with the administration of probiotics and melatonin (p < 0.05). In addition, although positive bacterial growth was detected in the mesenteric lymph node of all rats in the radiotherapy group, there was no statistically significant difference between all groups (p > 0.05).Melatonin and probiotics were found to have a potent radioprotective effect against radiotherapy-induced acute small intestinal tissue damage. However, their superiority over each other was not observed. [ABSTRACT FROM AUTHOR]

AbstractBackgroundMethodsResultsConclusionsRadiotherapy is a widely used treatment method in oncology, applied by delivering high-energy particles or waves to the tumor tissue. Although tumor cells are targeted with radiotherapy, it can cause acute or long-term damage to healthy tissues. Therefore, the preservation of healthy tissues has been an important subject of various scientific researches. Melatonin has been shown to have a radioprotective effect on many tissues and organs such as liver, parotid gland, brain, and testicles. This study aimed to evaluate the protective effect of melatonin against the radiation at various doses and rates administered to the lung tissue of healthy mice.This study was a randomized case-control study conducted with 80 rats comprising 10 groups with eight animals per group. Of the 10 groups, first is the control group, which is not given any melatonin, and second is the group that does not receive RT, which is given only melatonin, and the other eight groups are RT groups, four with melatonin and four without melatonin.There was no statistical difference in terms of histopathological findings in the lung tissue between the second group, which did not receive radiotherapy and received only melatonin, and the control group. Lung damage due to radiotherapy was statistically significantly higher in the groups that did not receive melatonin compared to the groups that received melatonin.This study revealed that melatonin has a protective effect against the cytotoxic damage of RT in rats receiving RT. [ABSTRACT FROM AUTHOR]

We investigated the radioprotective effect of melatonin (MEL) against thyroid gland damage in rats caused by flattening filter (FF) and flattening filter free (FFF) single dose X-ray beams. We used 48 female rats divided into six groups of eight: group 1, untreated control group; group 2, MEL treated group; group 3, FF-low dose rate radiotherapy (FF-LDR) group; group 4, FF-LDR + MEL group; group 5, FFF-high dose rate radiotherapy (FFF-HDR) group; group 6, FFF-HDR + MEL group. Groups 2, 4 and 6 rats were injected intraperitoneally (i.p.) with 10 mg/kg MEL 15 min before exposure to radiation. The head and neck regions of each rat in groups 3 and 5 and groups 4 and 6 were irradiated with 16 Gy at 6 MV X-ray in FF and FFF beam modes. The histopathology of the thyroid gland and salient biochemical parameters were assessed in all rats 10 days after radiotherapy. We found increased inflammation, vacuolization, degradation, swelling and necrosis, and M30 apoptosis and M65 necrosis indicators in groups 3 and 5 compared to group 1; however, we found significant reductions in histopathological and biochemical parameters following application of MEL. MEL treatment before FF-LDR and FFF-HDR radiotherapy minimized thyroid gland injury due to irradiation. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the effects of Modified Batho and Equivalent Tissue-Air Ratio (ETAR) correction-based algorithms on dose distributions in the inhomogeneous media and left-sided breast and lung cancer. Distribution profiles at lateral depth and percentage depth dose (PDD) values were obtained for soft tissue, bone and air rectilinear virtual phantoms in the Eclipse treatment planning system (TPS). In addition, intensity modulated radiotherapy (IMRT) treatment planning technique was applied to 20 patients with left-sided breast and lung cancer diagnosis on computed tomography (CT) sections. The maximum dose, mean dose, D95, Monitor Unit (MU) and segment numbers in planning target volume (PTV) were calculated. Although the effect of correction-based algorithms on (PDD) values and dose distribution profiles in lateral depth were calculated below 1% in soft tissue virtual phantom, dose profiles were obtained as approximately 20% in bone and air media. No statistical differences were observed in dosimetric parameters except for PTVmean and D95 values due to the differences in correction-based algorithms in left-sided breast IMRT treatment planning (p>0.05). However, significant statistical differences were obtained in the values of lung IMRT treatment plans (p<0.05). It was concluded that correction-based algorithms in the different inhomogeneous mediums have a significant effect on the dose values calculated in TPS. [ABSTRACT FROM AUTHOR]

The purpose of the present study is to investigate the protective effect of melatonin against early period parotid gland damage, caused by low- and high-dose rate beams in different dose plans, by using experimental rat models. Eighty Sprague Dawley rats were divided into ten randomized groups, each group being different in terms of dose plan and dose rate. Subjects in the control group were given only sodium chloride. Subjects in the melatonin-only group received 10 mg/kg melatonin. The head and neck region of each rat in radiotherapy only and radiotherapy plus melatonin group was irradiated with single dose (SD) and fractional dose (FD) Flattening Filter (FF) and Flattening Filter-Free (FFF) beams. Radiotherapy plus melatonin group subjects were administered 10 mg/kg melatonin 15 min before radiotherapy, radiotherapy only group did not receive melatonin treatment. Ten days after radiotherapy, the parotid gland of rats was examined for histopathological changes and blood samples were collected for biochemical analysis. When radiotherapy only groups and the control group are compared, for both FF, FFF beam modes and single, fractional dose plans, we observed statistically significant difference in histopathology and biochemical parameters due to irradiation. Melatonin administration in radiotherapy plus melatonin groups contributed to conserving these parameters (p < 0.05). In conclusion, melatonin acts as a significant protective agent against early rat parotid gland damage in varying dose plans for both FF and FFF beams. A difference in radiation-induced damage was not observed between FF and FFF beams using in vivo rat model. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the radiobiological effects of Flattening Filter (FF) and Flattening Filter Free (FFF) beams on Malignant Melanoma cancer (MMe Ca) modeled NOD-Prkdc IL2rg tm1 (NSG) mice in vivo, with a specific focus on necrotic and immunofluorescent changes. Thirty-five adult NSG mice models were randomly divided into four groups; MMe Ca, FF with a low dose rate of 400 MU/min (FF-400) and FFF with a high dose rate of 1400 MU/min (FFF-1400), and Control. The NSG mice in FF-400 and FFF-1400 groups (MMe Ca plus RT groups) were irradiated with a single dose of 20 Gy at 400 MU/min and 1400 MU/min. Radiotherapy was administered to NSG mice 20 days after tumor transplantation. The mice were then sacrificed 2 days after radiotherapy for assessment of the necrotic area, cell proliferation and apoptosis. The Ki-67 proliferation index showed a significant increase (p < 0.05) in the MMe Ca group (G1) compared to the FF-400 and FFF-1400 radiotherapy groups (G2 and G3) and the control group (G4), whereas a significant decrease was observed in the radiotherapy groups due to single-dose 20Gy irradiation (p < 0.05). The apoptotic index increased with irradiation in the FF-400 and FFF-1400 radiotherapy groups (p < 0.05). The necrotic area values of FF-400 and FFF-1400 at different dose rates (G2 and G3) increased statistically significantly (p < 0.05) compared to the MMe Ca group (G1). In addition, the Ki-67 cell proliferation, apoptotic index, and necrotic area parameters exhibited statistically significant differences between the FF-400 and FFF-1400 beams (p < 0.05). The FFF-high dose rate beams were found to be more effective on MMe Ca compared to the FF conventional beams (p < 0.05). It was concluded that FF and FFF beams caused significant radiobiological changes in cell proliferation (Ki-67), apoptosis (TUNEL) and necrosis histopathological parameters and the FFF beam was more effective on MMe Ca. • There was significant difference between FF and FFF beams in Ki-67, Apoptosis, Necrosis for MMe Ca. • The FFF-high dose rate beams can be safely applied in MMe Ca radiotherapy. • The clinical dose rate effect may contribute to our radiobiological results in stereotactic cancer radiotherapy. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the radioprotective effect of melatonin by analyzing histopathological changes and serum biochemical levels on experimental rat models exposed to flattening filter (FF) and flattening filter-free (FFF) beam. Forty-eight healthy adult Sprague Dawley rats were randomly divided into six groups. The control (Group 1) was given no treatment, the melatonin (Group 2) was given 10 mg/kg melatonin only, the FF (Group 3) and FFF (Group 5) were given fractionated dose (Total 32 Gy, 5 consecutive days) radiotherapy only, and the FF plus melatonin (Group 4) and FFF plus melatonin (Group 6) were given 10 mg/kg melatonin 15 minutes prior to irradiation. Rats were examined for histopathology and biochemical analysis 10 days after irradiation. When results of FF and FFF radiotherapy only groups are compared to control group, statistically significant difference in histopathological and biochemical parameters are observed; however, melatonin administration in radiotherapy plus melatonin groups improved these parameters (p <.05). In addition, there was no statistically significant difference between FF and FFF beams (p >.05). The effect of low- and high-dose beams on the rat larynx and serum samples were investigated histopathologically and biochemically for the first time. We observed that melatonin supplemented before FF and FFF radiotherapy protected early period radiotherapy-induced laryngeal mucosal damage. Since the radiobiological results of FF and FFF beams are similar, FFF beams can be safely applied in laryngeal irradiation. However, more experimental rat and clinical studies are needed to clarify the radiobiological uncertainy concerning dose rate on cancerous and healthy tissue. [ABSTRACT FROM AUTHOR]

Objective: This study compares standard commercial bolus material (Superflab) to custom prepared silicone dental impression material (CDIM) and play dough material (PDM) with respect to dosimetric properties and applicability by using ion chamber measurement and calculated dose values. Materials and Methods: The CDIM bolus was prepared by mixing dental impression silicone material with enough water to maintain a density of about 1.0 g/cm3. The prepared bolus material is applied on an RW3 solid phantom by covering 10x10 cm2 area with 0.5-1 cm thickness. Ion chamber measurements were performed separately with and without bolus material application. The setup was scanned in CT and the same procedure was repeated in the TPS using the scan data, in which the Pencil Beam Convolution dose calculation algorithm was used. To compare the effect of bolus material on tissue, the Superflab bolus and CDIM bolus were applied with 1 cm of thickness on postmastectomy scar and dose calculations on TPS were performed. Results: After comparison of the dosimetric values for Superflab, CDIM and PDM, we obtained statistically meaningful results between superflab and CDIM. For PDM, the results obtained with TPS and ion chamber measurements indicated that, it is not suitable to use in radiotherapy application due to its material properties. For the simulated skin dose values obtained at five random points on the scar tissue, the comparison of Superflab and CDIM TPS calculation results were not statistically significant. Conclusion: The CDIM is easy to prepare and apply on irregular mastectomy scar tissue and it prevents formation of air gaps in the application surface. Especially for curved anatomical regions such as scar tissue, inclusion of the bolus material in treatment planning protocol will reduce dose uncertainty in application. It is safe to use CDIM as an alternative to Superflab in radiotherapy application, whereas PDM is not useful in clinical practice due to its material properties. [ABSTRACT FROM AUTHOR]

In this study, the effects of various bolus materials on dose distributions were compared in electron conformal radiotherapy (ECRT). Superflab, Super Stuff pink wax and Paraffin wax bolus materials are used with 15 MeV electron energy for dosimetric comparison. Additionally, 10 mm thick Super Stuff pink wax bolus and paraffin wax bolus materials were placed on the right eyelid of a patient. Using electron dose calculation algorithm and ion chamber measurements, dosimetric comparisons were made in the Eclipse treatment planning system (TPS). Both for measured and calculated dose, values were acquired 3 times and averaged for each case. Resulting differences are expressed as percentage differences. Dose differences were obtained in measurements with and without using bolus at several locations of the solid phantom, performed by the Roos Ion chamber. Dosimetric differences of 7-7.5% for Superflab, 10-10.5% for paraffin bolus and 13-14% for Super Stuff pink wax bolus are obtained. Besides, when dosimetric comparisons are made in the treatment planning system for cases with and without bolus; Dose differences were calculated to be 2-2.5% for superflab silicon bolus, 3-3.5% for paraffin wax bolus and 5- 6% for Super Stuff pink wax bolus. To increase skin dose in curved anatomical structures in radiotherapy, it is safe to use the paraffin wax bolus material in radiotherapy clinic, as an alternative to Superflab silicon bolus and Super Stuff pink wax bolus materials, due to its low cost and ease of conforming to body surface contours. [ABSTRACT FROM AUTHOR]

The aim of this study is to analyze the effect on histopathological changes and Ki-67 expression levels of Flattening Filter (FF) and Flattening Filter Free (FFF) beams to investigate the radiobiological mechanisms underlying laryngeal cancer (LCa) post-radiotherapy (RT) on mice models. Forty adult NOD SCID gamma (NSG) mice models were randomly divided into four groups; the sham, LCa, FF-RT and FFF-RT groups. The head and neck region of mice in FF-RT and FFF-RT groups (LCa plus RT groups) were irradiated with a single dose of 18 Gy at 400 MU/min and 1400 MU/min. The NSG mice received radiotherapy 30 days after tumor transplantation and sacrificed 2 days after radiotherapy for analysis of histopathology parameters and K-67 expression levels. Comparing the LCa, FF-RT and FFF-RT groups with the sham group, statistically significant differences were observed in histopathological parameters depending on tumor tissue and dose rate (p < 0.05). When the histopathological effects of FF-RT beam on LCa tissue were compared with FFF-RT beam, it was observed that statistically significant differences occurred (p < 0.05). Comparing the LCa group with the sham group, it was observed that the Ki-67 level affected significantly depending on the development of cancer (p < 0.01). It was concluded that FF and FFF beams caused significant changes in the histopathological parameters and Ki-67 expression levels. When the effects of FFF beam on Ki-67 levels, cell nucleus and cytoplasmic findings were compared with FF beam, significant radiobiological differences were observed. • The effect of varying dose rate on laryngeal cancer were investigated for the first time. • There was significant difference between FF and FFF beams in histopathological and Ki-67 parameters. • The high dose rate beams can be safely applied in laryngeal cancer radiotherapy. [ABSTRACT FROM AUTHOR]

The aim of this study was to dosimetrically compare treatment plans prepared with volumetric-modulated arc radiotherapy (VMAT), tomotherapy, step-and-shoot and sliding radiotherapy techniques in nasopharyngeal cancer (NPC) and to evaluate the superiority of different techniques in routine clinical practice. Treatment plans obtained by VMAT, tomotherapy, step and shoot and sliding window techniques were evaluated for twenty NPC patients. Different treatment plans were prepared by using the simultaneous integrated boost (SIB) technique in 35 fractions of 70Gy to primary planning target volume and 56Gy to elective lymph nodes. While NPC treatment plans were obtained in four different radiotherapy techniques, 95% of the target volumes were provided with defined dose coverage and critical organs received the lowest possible dose. In addition to the doses received by target tissues and critical organs, dose delivered time, monitor unit (MU), dose homogeneity (HI) and conformity (CI) index were compared for different radiotherapy techniques. The D 95 dose coverage and lowest maximum dose values (Dmax) are better achieved in the tomotherapy technique for primary tumor and elective lymph node target volumes. However, the lowest dose coverage is obtained in the step-and-shoot technique (p < 0.05). Although the highest MU value was calculated in tomotherapy, the lowest delivered time was also achieved in the VMAT technique. It was observed that different radiotherapy techniques had advantages and disadvantages compared to each other at certain dose-volume constraints (D max , D min , D mean , D 1 , and V 30) for organs at risk. Although the tomotherapy technique was better in target volume dose coverage, it was observed that other techniques had superiority over each other in terms of protection of organs at risk and dosimetric parameters for NPC patients. • The different radiotherapy techniques should be decided on a patient-by-patient basis. • The dosimetric parameters are important in nasopharyngeal cancer radiotherapy. • The radiotherapy techniques have advantages over each other. [ABSTRACT FROM AUTHOR]

The aim of present study was to evaluate the acute radioprotective effect of melatonin against radiotherapy-induced rat salivary gland damage by applying salivary gland scintigraphy imaging technique in varying dose rates. Forty-eight Sprague Dawley rats were randomly distributed into six group: the control group, only melatonin (MEL) group, flattening filter (FF-RT) and flattening filter free (FFF-RT) only radiotherapy groups and radiotherapy plus melatonin groups, (FF-RT)+Mel and (FFF-RT)+Mel. The head and neck region of experimental rat was irradiated with in a single fraction of a 16 Gy in FF and FFF modes. Melatonin was administered at a single dose of 10 mg/kg through intraperitoneal injection, 15 min before radiation exposure. The assessment of salivary gland function was performed using gamma scintigraphy prodecure before and after radiotherapy. Statistically significant difference in target-to-background (T/B) ratio, between the only melatonin and control groups were not observed (p = 0.981). However, when acute effects of irradiation are considered after radiotherapy, salivary gland T/B ratios was a significant difference (p < 0.001). In the only radiotherapy groups applied considering in the FF and FFF options no statistically significant difference was observed in the salivary gland T/B ratio FF-RT group compared to the FFF-RT group (p = 0.999). The T/B ratio between the radiotherapy plus melatonin groups for FF-RT and FFF-RT beam was significantly higher in the compared to the only radiotherapy (p < 0.05). In conclusion, our findings suggest that melatonin is a radioprotective agent for treatment of low and high dose rate against acute salivary gland damage during radiotherapy of head and neck cancer. • The effect of FF and FFF beams on rat salivary gland were studied for the first time. • There was no significantly radiobiological difference between FF and FFF modes. • The melatonin was significantly protected salivary glands against radiation toxicity. • The ionizing radiation caused to salivary glands dysfunctions.. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate whether Flattening Filter (FF) and Flattening Filter Free (FFF) beams cause any difference on rat peripheral blood levels in a single dose (SD) and fractioned dose (FD) plans. Forty Sprague Dawley rats were randomly divided into five groups. No action was taken on the subjects in the control group (Group 1). FF-SD (Group 2) and FF-FD (Group 4) subjects received radiotherapy at 400 MU/min in SD 16 Gy and 5-day consecutive FD 32 Gy, respectively. FFF-SD (Group 3) and FFF-FD (Group 5) subjects received radiotherapy at 1400 MU/min in SD 16 Gy and 5-day consecutive FD 32 Gy, respectively. Blood samples were collected 24 h after radiotherapy. The levels of white blood cells (WBC), granulocytes (GRAN%), red blood cells (RBCs), lymphocytes (LYM%), hemoglobin (HGB) and platelets (PLT) were analyzed. In SD and FD plans, the levels of hematological parameters except for PLT level due to FF and FFF beams decreased statistically significant when compared with the control group (p < 0.05), but it was observed that the values of these parameters decreased less in the FD plans. In addition, when the effects of FF and FFF beams on peripheral blood cells were compared, a statistically significant difference was observed (p < 0.05). It was shown that FF and FFF beams significantly decrease hematological parameter levels in SD and FD plans. In addition, it was concluded that FFF beams were more dominant when we compared the effects of FF and FFF beams on peripheral blood cells. • The effect of FF and FFF beams on peripheral blood cell were investigated for the first time. • FF and FFF beams were reduced significantly hematological parameter levels. • There was significant difference between FF and FFF beams. [ABSTRACT FROM AUTHOR]

The purpose of the present study was to investigate the acute period radioprotective effect of melatonin (Mel) against radiation-iömnduced tissue damage in thyroid gland of rats using thyroid gland scintigraphy imaging. Forty-eight Sprague Dawley female rats were divided into six groups; the control group, melatonin treatment group, low dose rate (LDR-RT), high dose rate (HDR-RT) only radiotherapy groups and radiotherapy plus melatonin groups, (LDR-RT) + Mel and (HDR-RT) + Mel. The head and neck region of each rat was irradiated with single dose of 16 Gy at 6 MV X-ray in FF and FFF beam mode. Melatonin was administered at a single dose of 10 mg/kg through intraperitoneal injection, 15 min prior to radiation exposure. Functional evaluation of the thyroid glands were made using scintigraphy imaging before and after radiotherapy. Statistically significant difference was not observed in thyroid gland to background ratio (T/B) for all experimental rat groups before exposure (p = 0.379). However, when acute effects of irradiation are considered after radiotherapy T/B ratio showed a significant difference (p < 0.001). In the radiotherapy only groups, for both FF and FFF modes, statistically significant difference was not observed in the T/B ratio of LDR-RT group compared to HDR-RT group (p = 0.946). In the radiotherapy plus melatonin groups, both FF and FFF modes, statistically significant difference was also observed in the T/B ratio of LDR-RT group compared to HDR-RT group (p < 0.05). We showed that melatonin administered before radiotherapy provided significant protective effect against acute rat thyroid gland dysfunction caused by single dose LDR-RT and HDR-RT. • The melatonin was shown radioprotective effect in thyroid gland. • The radiotherapy caused thyroid gland dysfunction. • The effect of FF and FFF beam on rat thyroid gland was shown for the first time. • There was no radiobiological difference between FF and FFF beam. [ABSTRACT FROM AUTHOR]

This study aimed to explore the radioprotective effect of melatonin against acute testicular injury caused by low- and high-dose-rate radiotherapy in rats. A total of 40 12-week-old adult male rats were divided into 5 groups (n = 8). Group 1 comprised control rats who were not subjected to any procedures. A single dose of 8 Gy (Gy) radiotherapy was administered to the abdominopelvic regions of Group 2 (low-dose rate radiotherapy (LDRR) group) and Group 4 (high-dose rate radiotherapy (HDRR) group) rats at dose rates of 400 MU/min and 1400 MU/min, respectively. A single dose of 8 Gy radiotherapy was administered to Group 3 (low-dose rate radiotherapy + melatonin (LDRR + MEL) group) and Group 5 (high-dose rate radiotherapy + melatonin (HDRR + MEL) group) rats at dose rates of 400 MU/min and 1400 MU/min, respectively. Following this, 50 mg/kg/intraperitoneal melatonin was given to the rats 15 min before radiotherapy. The subjects were sacrificed 48 h after radiotherapy. Histological, immunohistochemical, immunofluorescence, and biochemical analyses of testicular tissue samples were performed. As a result of comparing the FF and FFF radiotherapy groups with the control group, a statistically significant difference was observed in histopathological, biochemical, immunohistochemical and immunofluorescent parameters (p < 0.001). An improvement in these parameters was observed in the groups where melatonin was applied along with radiotherapy (p < 0.001). Additionally, no statistically significant difference was found between FF and FFF dose rates (p > 0.05). No significant difference was observed between these low- and high-dose rates of radiotherapy in terms of testicular damage and the effect of melatonin. Further, melatonin may be useful in preventing testicular damage caused by low- and high-dose rate radiotherapy. • No difference was found between the damages caused by FF and FFF dose rates in rat testicular tissue. • Melatonin administration increased ZO-1 and LECTIN expression in testicular tissue damaged by radiotherapy. • Melatonin administration decreases the OSI value increased by radiotherapy in rat testis. • Melatonin administration decreased the apoptotic index increased by radiotherapy in rat testis. • Melatonin may be a safe antioxidant that can be applied to prevent radiotherapy-induced testicular injury. [ABSTRACT FROM AUTHOR]