Browsing by Author "Demir, Hikmettin"

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Effect of Thermoplastic Mask Hole Diameter on Dose Distribution in the Build-Up Region of Medical Linac
(Elsevier, 2024) Demir, Hikmettin; Gul, Osman Vefa
This study aims to investigate the effect of variations in the hole diameter of unstretched thermoplastic masks offered by a single company on the dose distribution in the build-up region. 2, 2.5, 3 and 4 mm hole diameters masks with the same properties were irradiated with 6 MV X-rays and dose distribution was analyzed according to the open field. Dose measurements were obtained with a parallel plane ionization chamber. All irradiations were repeated for 5 x 5, 8 x 8, 10 x 10 and 15 x 15 cm 2 beam fields. It was observed that the mask had a bolus effect in all measurements. It was observed that this bolus effect varied especially depending on the hole diameter in the mask. In a 10 x 10 cm 2 field, the d max depth without mask was 15 mm, while the d max for masks with 2, 2.5, 3 and 4 mm hole diameters was 11, 12, 13 and 13 mm, respectively. It was observed that the mask hole diameter affected the d max depth. Thermoplastic masks with large hole diameters increase the surface dose less than those with small hole diameters.
Effects of Radiation at Different Dose Rates on Hematologic Parameters in Rats
(Elsevier, 2024) Gul, Osman Vefa; Sengul, Aycan; Demir, Hikmettin
This study aimed to investigate the effects of single and fractionated dose treatment techniques using X-rays at dose rates of 600 and 2400 MU/min on peripheral blood levels in healthy rats. 12-week-old female Wistar albino rats were divided into five groups. Group I was designated as the control group. Groups II and IV received a single dose of 16 Gy and 32 Gy in 5 fractions at a dose rate of 400 MU/min, respectively. Groups III and V received a single dose of 16 Gy and 32 Gy in 5 fractions at a dose rate of 2400 MU/min, respectively. Rats in all radiation groups were exposed to total body radiotherapy. Acute effects of radiation were examined for red blood cells (RBCs), platelets (PLTs), hemoglobin content (Hb), white blood cells (WBCs), lymphocytes (LYM) and granulocytes (GRAN) parameters. A significant difference was observed between the control group and radiation groups for hematologic parameters (p < 0.05). In terms of hematologic parameters, both radiation dose rate and the fraction schedule were found to be effective on these parameters.
Investigation of Skin Dose of Post-Mastectomy Radiation Therapy for the Halcyon and Tomotherapy Treatment Machine: Comparison of Calculation and in Vivo Measurements
(Pergamon-elsevier Science Ltd, 2024) Demir, Hikmettin; Gul, Osman Vefa; Aksu, Telat
In treatments such as post-mastectomy radiation therapy (PMRT) for breast cancer patients, skin doses are of great importance in terms of tumor control and side effects. This dosimetric study aimed to measure the skin dose on the chest wall surface for post-mastectomy radiotherapy with Tomotherapy and Halcyon devices using thermoluminescence dosimetry (TLD) and to evaluate the accuracy of the skin dose calculated by treatment planning systems (TPS). Computed tomography (CT) images of the Alderson Rando phantom were obtained. Treatment plans were created with Tomotherapy and Halycon devices for a total of 50 Gy with a fraction dose of 2 Gy to the target volume. The left chest wall was divided into 9 regions for detailed surface dose assessment. 88 dose measurement points were determined on the left chest wall. The phantom was irradiated separately in Halycon and Tomotherapy devices. In vivo, dose measurements were performed with TLD in both devices. TPS and TLD doses were compared for the left chest wall surface. For skin dose, TLD measurements were lower than the dose estimate by Tomotherapy TPS and higher than the dose estimate by Halycon TPS. In addition, the skin dose measurements showed that the skin dose of the Tomotherapy device was higher than that of the Halycon. It is recommended to consider the distance of the treatment device and the accuracy of the TPS dose calculation in skin dose assessment in PMRT.
Investigation of the Effect of Bolus on Skin Dose in Breast Cancer Treatment With Tomotherapy and Linac Radiotherapy Devices
(Pergamon-elsevier Science Ltd, 2024) Gul, Osman Vefa; Demir, Hikmettin; Basaran, Hamit; Kanyilmaz, Gul
In postmastectomy radiation therapy (PMRT), it is important that the chest wall skin is included in the target volume and receives an adequate dose. This study aims to investigate the effect of bolus on skin dose in breast cancer treatment with Tomotherapy and LINAC radiotherapy devices and to examine the accuracy of the surface dose calculated by treatment planning system (TPS) with thermoluminescence dosimetry (TLD). Female Alderson Rando Phantom's chest wall is virtually divided into 9 regions. Computed tomography (CT) images of the phantom were obtained with a section thickness of 3 mm. Two plans, with and without bolus, were created for each of the helical tomotherapy (HT), intensity -modulated radiotherapy (IMRT) and field -in -field (FiF) techniques. A bolus thickness of 0.5 cm was used for all bolus plans. Doses calculated from TPSs were obtained for 88 predetermined points on the chest wall. After irradiation, doses measured with TLDs were obtained. The effect of bolus use on the chest wall surface was examined. The increase in surface dose due to bolus use was 50.35%, 55.35% and 68.56% for HT, IMRT and FiF techniques in TPS, respectively. This increase in TLD measurements was 58.18%, 30.90% and 46.31% for HT, IMRT and FiF techniques, respectively. The best agreement between TPS and TLD doses for bolus and non -bolus plans was found in the HT technique. The difference between TPS and TLD doses decreased within the three treatment techniques due to bolus use. Since the chest wall skin cannot receive the required dose in IMRT and FiF techniques, bolus use is recommended until acute skin reactions occur. There is no need to use a bolus for the HT technique.
Investigation of the Effect of Calibration Curves Obtained From Different Computed Tomography Devices on the Dose Distribution of Tomotherapy Plans
(Wolters Kluwer Medknow Publications, 2024) Demir, Hikmettin; Gul, Osman Vefa; Kanyilmaz, Gul
Purpose: This study investigated the effect of Hounsfield units (HU)-relative electron density (RED) calibration curves obtained with devices from three different Computed Tomography (CT) manufacturers on dose distribution in Accuray Precision planning of patients with lung cancer. Methods: All CT data required for treatment planning system (TPS) were obtained using the Tomotherapy "cheese" phantom. HU RED calibration curves were created with images obtained from Siemens Somatom, GE Optima, and Toshiba Aquilion devices. The obtained calibration curve was extrapolated. CT images of lung cancer patients were acquired on a single device and treatment plans were created. The existing plans were recalculated using three calibration curves and the effect of the HU RED calibration curve on dose distribution was analyzed. Results: The results showed that different CTs did not produce significant dose differences in organ doses and PTV for Accuray TPS. Conclusions: Based on clinical judgment, images from different CT devices can be used in treatment planning.
Investigation of the Effects of Gamma Radiation and Y2o3 on the Elastic Properties of Al2024 Composites by Ultrasonic Method
(Pergamon-elsevier Science Ltd, 2025) Demir, Hikmettin; Atas, Mehmet Sahin; Oral, Imran
In this study, the effect of Y2O3 contribution and gamma-irradiation on the elastic properties of pure Al2024 and Al2024/Y2O3 composites was precisely investigated with the help of determined density and ultrasonic wave velocities. Ultrasonic longitudinal and shear wave velocity measurements of the samples were performed at room temperature using the ultrasonic pulse-echo method at 20 and 5 MHz frequencies, respectively. X-ray diffraction analysis and scanning electron microscopy examined the microstructural properties and phase characterizations of metal matrix composite (MMC) samples. A gamma cell type Co-60 source was used to irradiate MMC samples in the air at room temperature. The absorbed dose rate was measured to be approximately 1.5 kGy/h, and the total delivered dose was 50 kGy. According to the findings obtained from the research, the contribution of Y2O3 to pure Al 2024 at 0.5, 1, and 5 wt% ratios and exposure to gamma rays of 50 kGy caused a decrease in V-L, L, K, and mu values and a significant increase in rho, V-S, G, HV, H, and E values. The highest Young's modulus values compared with pure Al2024 were obtained in both unirradiated and irradiated Al2024/0.5Y(2)O(3) composites.