Osman Vefa Gul

Objective: The present study aims to compare field-in-field (FIF) radiation therapy, static intensity-modulated radiation therapy (S-IMRT), and dynamic static intensity-modulated radiation therapy (D-IMRT) techniques concerning dosimetric benefits for the treatment of pancreatic cancers. Materials and Methods: Sixteen pancreatic cancer patients who had undergone radiotherapy were selected for this study FIF, D-IMRT and S-IMRT plans were compared with respect to the planning target volume (PTV) and organs at risk (OARs). All plans were designed to cover 95% of the dose in the target. Also, homogeneity index (HI), conformity index (CI) and the monitor unit counts (MUs) were evaluated for all plans. Paired sample t-test was used for statistical analyses. Results: The CI and HI for D-IMRT and S-IMRT plans showed significant positive results than FIF plans. S-IMRT resulted in significantly reduced bilateral kidney V10 and V20 doses relative to FIF and D-IMRT plans (p

Objectives: The increasing use of CT in feline medicine necessitates the optimization of radiation protocols to adhere to the ALARA (as low as reasonably achievable) principle. This prospective study aimed to evaluate the impact of patient positioning (dorsoventral (DV) vs ventrodorsal (VD)) on radiation doses absorbed by the ocular lenses and thyroid gland during feline cranial CT. Methods: A total of 70 cats were divided into two equal groups (DV: n = 35, VD: n = 35). Radiation doses were measured using thermoluminescent dosimeters (TLD-100) placed at the anatomical projections of the target organs. Results: Although no statistically significant difference was observed in ocular lens doses between the groups ( P >0.05), VD positioning resulted in a 24.4% reduction in mean radiation dose absorbed by the thyroid gland compared with the DV position (1.33 ± 0.17 mGy vs 1.76 ± 0.35 mGy, respectively; P = 4.97 ×10 ^–9 ). This reduction is attributed to the “natural shielding” effect provided by the dorsal axial skeleton and epaxial muscles in the VD position. Conclusions and relevance: VD positioning offers a significant dosimetric advantage for protecting the thyroid gland without requiring additional equipment or compromising diagnostic quality. Adopting the VD position as a routine standard in feline cranial CT is recommended to minimize radiation exposure to the thyroid gland.

Aim: The purpose of this study is to compare plans for bladder cancer using field-in-field (FIF), intensity modulated radiotherapy (IMRT) and simultaneous integrated boost (SIB) technique.Method: FIF, IMRT and SIB treatment plans were created using tomography images of 20 patients diagnosed with bladder cancer. Two separate planning target volume (PTV) were defined for each patient: PTV1 and PTV2. For the FIF and IMRT plans, PTV1 and PTV2 received treatment doses of 50.4 Gray (Gy) and 60 Gy in 33 fractions, respectively. In 28 daily fractions, the SIB method was used in which different doses were delivered simultaneously in the target volumes. In the SIB technique, the daily treatment dose was determined as 2.14 Gy. The plans were compared in terms of PTV, organs at risk (OARs) such as rectum, bowel, femoral heads, homogeneity index (HI), conformity index (CI) and monitor unit values (MU).Results: All plans were designed to cover 95% of the dose in the target volume. The CI for SIB plans showed significantly favourable results compared to FIF and IMRT plans. The V45 and V30 doses for the rectum in the SIB plans were statistically significantly lower compared to the FIF (p<0.05). The biologically effective doses (BED) values of rectum V30 were found to be 57.01±11.94 in SIB plans and 56.37±10.95 in IMRT plans. MU counts were significantly lower in FIF plans (p<0.05).Conclusion: The SIB technique demonstrated better sparing of critical organs compared with FIF and IMRT in bladder radiotherapy. BED analysis, however, indicated higher doses with SIB. Overall, SIB appears to be a feasible option for appropriate patients, provided that dose to critical organs is carefully monitored.

We investigated dosimetrically lymphopenia concerning radiotherapy (RT) in patients receiving pelvic RT due to locally advanced prostate cancer (LAPCA). A total of 195 patients with lymph node-positive LAPCA were retrospectively evaluated and included in this single-center study. The relationship among absolute lymphocyte count (ALC), treatment modality, clinical stage, RT dose, and existence of pre-RT and post-RT lymphopenia (Grade≥2) was evaluated. Dependent McNemar analyses revealed significant relationship in pre-RT and post-RT (p<0.001). Of those with Grade<2, 108 (56.5%) developed Grade≥2 post-RT lymphopenia (p<0.001). V20-whole pelvic bone marrow (WPBM) (p=0.036), V30-WPBM (p=0.025), and V50-WPBM (p=0.008) values were significantly higher in Grade≥2 lymphopenia group. Also, V5-lumbo-sacral BM (LSBM) (p=0.013), V10-LSBM (p=0.041), V20-LSBM (p=0.015), and V30-LSBM (p=0.007) values were significant in Grade≥2 lymphopenia group. However, V30-lower-pelvis BM (LPBM) (p=0.024) and V50-LPBM (p<0.001) values were significant in Grade≥2 lymphopenia group. ROC analysis showed a significant effect on the development of Grade≥2 lymphopenia post-RT. Pre-RT baseline ALC values were associated with the development of Grade≥2 lymphopenia at a cut-off value of ≤1805 (p<0.001). Additionally, cut-off values of ≥76.1% for V20-WPBM (p=0.036), ≥47.3% for V30-WPBM (p=0.021), ≥7.3% for V50-WPBM (p=0.008), ≥68.5% for V30-WPBM (p=0.007), ≥41.2% for V30-LPBM (p=0.023), and ≥4.3% for V50-LPBM (p=0.001) were associated with development of Grade≥2 lymphopenia. Among all dosimetric parameters, V50-LPBM emerged as the strongest predictor of Grade ≥2 lymphopenia after RT. In clinical evaluations, no significant difference was seen in OS or PFS between Grades ≥2 and <2 groups (OS: p=0.194; PFS: p=0.489). This study demonstrated the clinical importance of pre-RT hematologic status and BM dosimetry, demonstrating that low pre-RT ALC and V50-LPBM values were the most significant predictors of Grade ≥2 lymphopenia after PNRT. These findings highlight importance of considering BM as an organ at risk and considering appropriate BM-sparing strategies in PNRT planning.

The aim of this study was to quantitatively evaluate out-of-field (peripheral) doses in electron beam radiotherapy, to compare experimental measurements with treatment planning system (TPS) calculations and Monte Carlo (MC) simulations, and to discuss their clinical relevance. Peripheral dose measurements were performed in a water phantom using a Roos parallel-plate ionization chamber for 6, 9, 12, and 15 MeV electron beams delivered by a Varian linear accelerator with various applicator sizes. Under identical conditions, dose distributions were recalculated with the Eclipse TPS using the General Gaussian Pencil Beam (GGPB) algorithm and with Geant4/GATE MC simulations. The dependence of peripheral dose on energy, applicator size, and distance from the field edge was assessed. Experimental data showed that peripheral doses increased with both beam energy and applicator size, while decreasing with greater depth and distance from the field border. TPS calculations consistently underestimated peripheral doses, with discrepancies up to 30% at higher energies and near-field regions. By contrast, MC simulations demonstrated excellent agreement with measurements across all energies and field sizes, with differences typically within 1–2%. The results demonstrate that the GGPB algorithm tested in this study substantially underestimates out-of-field doses. Experimental dosimetry and validated MC simulations are essential for comprehensive dose evaluation, particularly for estimating secondary cancer risks, protecting adjacent critical organs, and ensuring the safety of implantable devices. The integration of GPU-accelerated Monte Carlo algorithms and AI-based prediction models into clinical workflows may further improve the accuracy and efficiency of peripheral dose calculations, ultimately enhancing patient safety.

In radiotherapy (RT), the dose given to the organs at risk (OAR) is as important as the dose received by the tumor. FF (Flattening Filtered) and FFF (Flattening Filter Free) treatment techniques used in RT offer different advantages in terms of their effects on target and critical organs. Treatment duration varies depending on the number of monitor units (MU) delivered per unit time. The aim of this study was to investigate biochemically and histopathologically the damage in healthy laryngeal tissue exposed to 600 MU/min FF and 2400 MU/min FF ionizing radiation under different fractionation protocols. Also to investigate the radioprotective effect of melatonin against the radiological damage. The 78 rats included in the study were divided into 10 groups. Control and melatonin-only groups did not receive RT. The other 8 groups received FF and FFF ionizing radiation in different dose fractions. Half of the radiation group received melatonin 15 min before RT. No histological and biochemical differences were observed in the control and MLT only groups. Radiobiological damage was statistically significantly lower in the RT+MLT group compared to the RT only group. It has been observed that melatonin has a protective effect against tissue damage caused by radiation exposure in healthy laryngeal tissue.

Brain computed tomography (CT) is commonly performed in pediatric patients; however, radiation exposure to radiosensitive organs such as the lens and thyroid remains a major concern. This prospective study investigated the impact of gantry tilt on organ doses using thermoluminescent dosemeters. A total of 67 pediatric patients undergoing brain CT were divided into four age groups: 0–18 months, 18 months–5 y, 5–10 y, and 10–17 y. In vivo lens and thyroid doses were measured with and without gantry tilt, and their correlation with volume CT dose index (CTDIvol) was assessed. Significant positive correlations were observed between CTDIvol and both lens and thyroid doses. With gantry tilt, mean lens doses were 2.19–5.73 mGy and thyroid doses 0.68–0.99 mGy, compared with 10.89–29.30 mGy and 1.29–3.72 mGy, respectively, without tilt. Gantry tilt parallel to the supraorbital–meatal baseline substantially reduced organ doses, particularly to the lens, and should be considered as a practical optimisation technique in pediatric neuroimaging.