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Öğe The dosimetric comparison and evaluation of helical tomotherapy, volumetric-modulated arc radiotherapy (VMAT), step-and-shoot and sliding window radiotherapy techniques in nasopharyngeal carcinoma(Pergamon-Elsevier Science Ltd, 2022) Demir, Hikmettin; Aras, Serhat; Buyukcizmeci, Nihal; Yavuz, Berrin BenliThe 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 tomo-therapy, 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- 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.Öğe Radiation-induced hypothyroidism in patients with breast cancer: a retrospective analysis of 243 cases(Elsevier Science Inc, 2017) Kanyilmaz, Gul; Aktan, Meryem; Koc, Mehmet; Demir, Hikmettin; Demir, Lutfi SaltukThis study aims to estimate the incidence of hypothyroidism (HT) and to evaluate the predictors affecting the development of HT after radiotherapy (RT) for breast cancer, with a focus on radiation dose-volumetric parameters. Between 2009 and 2015, 243 patients undergoing RT for breast cancer were retrospectively analyzed. Free triiodothyronine (FT3), free thyroxin (FT4), and thyrotropin (TSH) were monitored before and after RT. The relation between the doses to thyroid gland (D-mean, D-max, D-min), percentage of thyroid volume receiving > 10 Gy, 20 Gy, 30 Gy, 40 Gy, and 50 Gy (V10 to V50), absolute thyroid volume, and HT were analyzed. The risk of HT according to radiation fields and the other clinic factors were also evaluated. The median follow-up was 41 (range; 6 to 130) months. Sixty-seven percent of the patients received RT to the breast/chest wall and ipsilateral supraclavicular fossa. Of 243 patients, 51 (21%) were diagnosed with HT. The median time to the onset of HT was 27 (range; 5 to 64) months. There were no significant relationships observed between Dmin or V10 to V50 and HT. The surgery type, clinical stage, nodal status, RT field, Dmean, and Dmax were statistically significant predictors for HT in univariate analysis. The Dmean was the only prognostic factor predicting HT in multivariate analysis, and Dmean > 21 Gy was a threshold value for the evolvement of HT. In this study, we present evidence that postoperative irradiation of patients with breast cancer may frequently lead to HT. Patients who have received RT for breast cancer, especially irradiation on the supraclavicular region, may require thyroid function screening after RT. (C) 2017 American Association of Medical Dosimetrists.Öğe Radioprotective effects of melatonin against varying dose rates on radiotherapy-induced salivary gland damage scintigraphy findings(Pergamon-Elsevier Science Ltd, 2022) Aras, Serhat; Can, Uenal; Demir, Hikmettin; Suemer, Engin; Orak, Rahime; Tanzer, Ihsan Oguz; Baydili, Kursad NuriThe 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.Öğe Unplanned irradiation of internal mammary lymph nodes in breast cancer(Springer-Verlag Italia Srl, 2017) Kanyilmaz, Gul; Aktan, Meryem; Koc, Mehmet; Demir, Hikmettin; Demir, Lutfi SaltukTo evaluate the incidental dose to the internal mammary chain (IMC) in patients treated with three-dimensional conformal radiotherapy, to estimate the predictors affecting the magnitude of IMC receiving dose and to determine the predictive role of clinical parameters on survival. Between 2009 and 2015, 348 patients undergoing RT for breast cancer were retrospectively analyzed. All patients underwent our department's routine procedure for breast cancer. The internal mammary lymph nodes were contoured according to Radiation Therapy Oncology Group (RTOG) concensus. Based on each patient's dose-volume histograms, the mean doses (D (mean)) to internal mammary gland were analyzed. Overall survival and disease-free survival were also evaluated. The median follow-up time was 38 (range 3-80) months. The D (mean) to IMC was 32.8 Gy and the dose delivered to IMC showed a greater coverage in modified radical mastectomy (MRM) group compared with breast conserving surgery (34.6 vs 26.7 Gy). The T-stage of tumor and the N-stage of tumor affected the incidental dose to IMC. The tumor size, the number of involved lymph nodes, the percentage of involved lymph nodes, hormonal status, advanced T-stage and advanced N-stage were the prognostic factors that affect survival. The IMC received meaningful incidental irradiation dose when treated with two opposite tangential fields and ipsilateral supraclavicular fossa with a single anterior field. The real effect of incidental dose on survival and the hypothesis about the benefit of incidental irradiation of IMC should be examined in clinical studies.
