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    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 Benli
    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 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.
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    Dosimetric Comparison of Three-Dimensional Conformal Radiotherapy (3D-CRT) and Intensity Modulated Radiotherapy Techniques (IMRT) with Radiotherapy Dose Simulations For Left-Sided Mastectomy Patients
    (Galenos Publ House, 2019) Aras, Serhat; Ikizceli, Turkan; Aktan, Meryem
    Objective: To compare 3-dimensional conformal radiotherapy (3D-CRT) and intensity modulated radiotherapy (IMRT) techniques on the target tissue and critical organ doses in terms of dosimetry, during treatment planning of patient's post-mastectomy radiotherapy (PMRT) to the left chest wall. Materials and Methods: Twenty breast cancer patients with left-sided post-mastectomy have selected for PMRT both 3D-CRT and IMRT techniques. Dosimetric calculation of dose simulation in Eclipse treatment planning system have been performed. Organs at risk with the maximum dose, minimum dose, mean. dose, D95, conformity and homogeneity indexes and total monitor unit for the Planning Target Volume were compared in terms of the critical organ doses. Results: There was no significant difference between the two treatment planning techniques in terms of maximum, minimum, mean dose and heterogeneity index (p>0.05). At low doses, the dose received at the heart was significantly lower with the 3D-CRT technique, but there was no significant difference between the two techniques at the maximum and average doses in the high dose regions. Conclusion: For PMRT to the left chest wall, IMRT significantly improves the conformity of plan and reduce the high-dose volumes of ipsilateral lung and heart compared to 3D-CRT, but 3D-CRT is superior in terms of low-dose volume.
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    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 Nuri
    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.