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This investigation aimed to optimize gradient positioning for radiochromic film calibration to facilitate a uniform distribution of calibration points. The study investigated the influence of various parameters on gradient dose profiles generated by a physical wedge, assessing their impact on the field's dose dynamic range, a scalar quantity representing the span of absorbed doses. Numerical parameterization of the physical wedge profile was used to visualize and quantify the impact of field size, depth, and energy on the dynamic range of dose gradients. This concept enabled the optimization of the gradient positioning and estimation of the necessary number of exposures for the desired calibration dose range. An optimization algorithm based on histogram bin height minimization was developed and presented. The maximum dynamic range was achieved with a 20 × $\times$ 20 cm 2 $\textrm {cm}^{2}$ field size at 5 cm depth. Optimization of wedge gradient positioning yielded the most uniform dose distribution with 7 exposures for the [1,10] Gy range and 8 exposures for the [1,20] Gy range. Film calibration using gradients centered at 1.6, 3, 3.5, and 7 Gy central axis (CAX), obtained through optimized gradient positioning, was showcased. The presented work demonstrates the potential for an improved film calibration process, with efficient material utilization and enhanced dosimetric accuracy for clinical applications. While the method was described for the use of a physical wedge, the methodology can be easily extended to the use of a more convenient dynamic wedge.

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Reliable calibration is one of the major challenges in using radiochromic films (RCF) for radiation dosimetry. In this study the feasibility of using dose gradients produced by a physical wedge (PW) for RCF calibration was investigated. The aim was to establish an efficient and reproducible method for calibrating RCF using a PW. Film strips were used to capture the wedge dose profile for five different exposures and the acquired scans were processed to generate corresponding net optical density wedge profiles. The proposed method was compared to the benchmark calibration, following the guidelines for precise calibration using uniform dose fields. The results of the benchmark comparison presented in this paper showed that using a single film strip for measuring wedge dose profile is sufficient for estimating a reliable calibration curve within the recorded dose range. Furthermore, the PW calibration can be extrapolated or extended by using multiple gradients for the optimal coverage of the desired calibration dose range. The method outlined in this paper can be readily replicated using the equipment and expertise commonly found in a radiotherapy center. Once the dose profile and central axis attenuation coefficient of the PW are determined, they can serve as a reference for a variety of calibrations using different types and batches of film. This investigation demonstrated that the calibration curves obtained with the presented PW calibration method are within the bounds of the measurement uncertainty evaluated for the conventional uniform dose field calibration method.

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Radiotherapy plays an important role in the multimodal treatment of childhood cancer. Our objective was to provide an analysis of pediatric oncology patients treated with radiotherapy in a national referral institution in Serbia. A retrospective chart review of children treated with radiotherapy between January 2007 and July 2018 was conducted. Of the 806 patients who were identified, 767 formed the basis of this study. CNS tumors (31.2%) were the most common tumors followed by leukemias (17.3%) and bone tumors (14.3%). The most common indication for radiotherapy was in adjuvant setting (69.1%). Anesthesia or sedation was performed on 115 patients. The 5-year and 10-year overall survival rates were 65.7% and 62.1%, respectively. A significant difference in survival in relation to tumor type was seen. The best survival rates were obtained in patients with retinoblastoma, followed by lymphomas and nephroblastoma, while patients with bone sarcomas had the worst survival. The intent of radiotherapy treatment was also a parameter associated with survival. Patients treated with palliative and definitive intent lived shorter than patients treated with prophylactic and adjuvant intent. Our study showed that good treatment outcomes can be achieved in specialized centers with an experienced team of professionals who are dedicated to pediatric oncology.

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OBJECTIVE: This study aimed to evaluate the characteristics of children with primary brain tumors, the effectiveness of treatment modalities, and to detect factors related to the outcome. METHODS: A detailed analysis was performed on a series of 173 pediatric patients treated in a Serbian referral oncology institution between 2007 and 2016, based on their clinical, histological, treatment, and follow-up data. RESULTS: Mean survival time of all children was 94.5months. 2-, 5- and 10-year overall survival probabilities were 68.8%, 59.4%, and 52.8%, respectively. Patients with supratentorial tumors had longer survival than patients with infratentorial tumors and patients with tumors in both compartments (p = 0.011). Children with the unknown histopathology (brainstem glioma) and high-grade glioma had a shorter life than embryonal tumors, ependymoma, and low-grade glioma (p<0.001). Survival of the children who underwent gross total resection was longer than the children in whom lesser degrees of resection were achieved (p = 0.015). The extent of the disease is a very important parameter found to be associated with survival. Patients with no evidence of disease after surgery had a mean survival of 123 months, compared with 82 months in patients with local residual disease and 55 months in patients with disseminated disease (p<0.001). By the univariate analysis, factors predicting poor outcome in our series were the presentation of disease with hormonal abnormalities, tumor location, and the extent of the disease, while the factors predicting a better outcome were age at the time of diagnosis, presentation of the disease with neurological deficit, and type of resection. By the multivariate analysis, the extent of the disease remained as the only strong adverse risk factor for survival (HR 2.06; 95% CI = 1.38-3.07; p<0.001). CONCLUSIONS: With an organized and dedicated multidisciplinary team, the adequate outcomes can be achieved in a middle-income country setting. The presence of local residual disease after surgery and disseminated disease has a strong negative effect on survival.

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PURPOSE: Within implementation of intensity-modulated radiotherapy (IMRT) in the postoperative irradiation of cervical cancer we evaluated and compared IMRT and three-dimensional conformal radiotherapy (3DCRT) dosimetric parameters for target volumes and organs at risk (OAR). METHODS: We randomized 95 patients with cervical cancer, UICC stage I-III, in groups depending of the type of external beam postoperative radiotherapy. Forty-five patients were treated with IMRT and 50 with 3DCRT. All patients underwent brachytherapy, and according to risk factors some of the patients had concomitant cisplatin chemotherapy. The study was done in a period of three years from December 2015. Analysis of dosimetric parameters for target volume coverage and OARs was performed. RESULTS: IMRT plans showed better conformity compared to 3DCRT plans, represented with homogenity index and conformity index, with higher maximum dose (PTV105 and D2). Both plans achieved adequate planning target volume coverage described with PTV95. Statistically significant difference between groups was found for bladder, rectum and bowel high dose regions: bladder V45 (p=0.000), rectum V40 (p=0.043) and V45 (p=0.000), bowel V45 (p=0.000), and bone marrow dosimetric parameters V20-V45; all were better in IMRT plans. Significant difference was found for volume of patient body normal tissue receiving dose of 20Gy, which was higher in IMRT. CONCLUSION: IMRT is a highly conformal technique. Satisfactory target volume coverage was achieved with both techniques, with better sparing of OARs in the IMRT group. With this technique improvement, we expect better quality of life in cervical cancer patients with good prognosis.

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PURPOSE: The toxicity of postoperative radiotherapy for cervical cancer affects patients' quality of life. We evaluated acute toxicity in postoperative intensity-modulated radiotherapy (IMRT) and three-dimensional conformal radiotherapy (3DCRT) as well as the influence of dosimetric parameters and concomitant chemotherapy. METHODS: A total of 45 patients with early operable cervical cancer underwent postoperative IMRT with 40-45 Gy. The control group of 50 patients was treated with 3DCRT. Brachytherapy and concomitant cisplatin chemotherapy were performed in all patients according to pathologic and histologic findings. The patients were monitored for acute gastrointestinal, urological and hematological toxicity classified according to the RTOG acute radiation morbidity scoring criteria. We also analyzed the influence of dosimetric parameters on acute toxicity. RESULTS: Significant differences were found in overall acute toxicity (p=0.018), acute genitourinary toxicity (p=0.029), anemia (p=0.043) and neutropenia (p=0.027) but not in acute gastrointestinal toxicity between the IMRT and 3DCRT groups. In all patients, regarding chemotherapy administration, differences were found between the chemoradiotherapy and radiotherapy group as far as overall acute toxicity (CHRT vs RT; p=0.011) and hematological toxicity were concerned (p=0.001). Patients with ≥3 cycles of chemotherapy showed increased hematologic toxicity. In the IMRT group according to the administration of chemotherapy (chemoradiotherapy vs radiotherapy), statistically significant difference for leukopenia (p=0.009) was found and in the 3DCRT group for anemia (p=0.021) and neutropenia (p=0.029). According to chemotherapy administration (chemoradiotherapy vs radiotherapy), a statistically significant difference in leukopenia (p=0.009) was found in the IMRT group while in the 3DCRT group the differences were in anemia (p=0.021) and neutropenia (p=0.029). CONCLUSION: IMRT is associated with lower acute toxicity and better dosimetric parameters in organs at risk (OAR) compared to 3DCRT. Higher hematological toxicity occurred when concomitant chemotherapy was performed, regardless of RT technique. Further reduction of toxicity is expected with protocol and technical improvement and research of gene-related toxicity.

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