Background: CdWO₄ is a scintillator with some unique properties. For example, high density, thermal and chemical stability and so on. Different applications of this scintillator such as X-ray scintillator has been investigated thoroughly so far. However, there is limited number of studies reporting the characteristics of CdWO₄ as an alpha counter. Materials and Methods: The CdWO₄ powder was synthesized by a simple co-precipitation method. Then, the CdWO₄ films with different thicknesses were prepared by spin coating method on glass substrates. The CdWO₄ powder and films were characterized by X-ray diffraction, photoluminescence, scanning electron microscopy, Fourier transformed-infrared spectroscopy, and ion beam induced luminescence. Finally, the response of samples with different thicknesses was measured using a ²⁴¹Am alpha source with 1860 Bq activity. Results: The analyses revealed that the nanocrystalline CdWO₄ with about 30 nm size was successfully synthesized without any impurity. Besides, the CdWO₄ films had the same luminescence emission peak characteristics as CdWO₄ powder had. Conclusion: It was observed that the sample with 2.9 mg/cm² thickness had the best counting efficiency (over 2π geometry) among the others.

Background: The aim of this study was to compare the radiation dose to ipsilateral lung and heart for different radiotherapy (RT) techniques including; two tangential photon beams, electron therapy and combined photon-electron. Materials and Methods: Treatment planning of the mentioned techniques on the CT images of a chest phantom was done using treatment planning system (TiGRT, Lina Tech, China). According to the plans, the phantom was irradiated with 6 MV photon and 10 MeV electron beams of Siemens Primus linac. Radiation dose was also measured using LiF Thermo Luminescence Dosimeter (TLD) which was placed inside 3 mm depth holes of ipsilateral lung and heart on the phantom. Results: The mean (± SD) radiation dose to the ipsilateral lung of the combined photon-electron was 66.12 ± 5.16% of prescribed dose. Whereas for the heart, it was 64.05 ± 2.62%. Mean (± SD) dose of ipsilateral lung and heart for electron irradiation was 54.51 ± 3.88 % and 34.21 ± 3.41%, respectively. The mean (± SD) radiation dose to ipsilateral lung and heart of the tangential was 50.73 ± 3.01 % and 31.36 ± 3.13%, respectively. The mean (± SD) radiation dose to the chest wall-lung interface for electron therapy (72.44 ± 2.01 %) was significantly different in comparison with tangential (65.23± 4.20%; p = 0.045) and combined photon-electron (68.14± 3.53 %; p = 0.032). Conclusion: Tangential beams is more suitable for treating mastectomy patients compared to the other techniques such as electron therapy and combined photon-electron, due to lower radiation dose to patient's ipsilateral lung and heart.

Background: Commissioning tests are recommended before implementing Intensity Modulated Radiation Therapy. This study evaluated five different plans of IMRT mocks for different modulation indices. Materials and Methods: IMRT tests were done in slab phantom for both 6MV and 15 MV photon energies using a 2D array ion chamber dosimeter. Results: The acceptance criteria were based on 3% /3mm. All tests passed the gamma criteria except for the prostate test with 15 MV photon beams and C shape test for both 6 MV and 15 MV energies. The Ratio passing points for Multi target test in 6 MV and 15 MV plans were 93.1% and 91.5%, respectively. The results of the prostate tests with 3%/3mm was 92.3% for 6MV and 91.2% for 15 MV in 4%/4 mm tolerance limit. For Head and Neck test with the same gamma criteria, the percentages of the points were 93.2 and 94 for 6 MV and 15 MV plans, respectively. For C shape tests, the used gamma criteria were 4%/ 4 mm. The ratio passing points were 94.9% and 94.3% for 6MV and 15MV plans, respectively. However, C shape hard test could not pass the gamma criteria of 4%/ 4mm for 6MV. Conclusion: results showed that by increasing the complexity of the IMRT plan, the verification test must be done in a more strict-manner, because a small change in dose delivery can cause a large discrepancy between planned and real dosimetry and may produce hot spots in organs or a cold spot in the target volume.

Background: This study aimed to evaluate the dose calculation accuracy of Eclipse^TM treatment planning system (TPS) in a heterogeneous chest phantom with the intensity modulated radiotherapy (IMRT) technique using EBT3 film and Delta4. Materials and Methods: Two IMRT plans (A and B) were prepared for radiotherapy of the heterogeneous chest phantom. Plan A was between the left lung and the surrounding soft tissue and plan B was carried out on the soft tissue. EBT3 film and Delta4 were used for dose measurement in the phantom. Eclipse^TM TPS was also used for dose calculation. Finally, the gamma index values of the TPS with film and TPS with Delta4 were obtained. A 95% passing rate of gamma index with the passing criterion of 3mm/3% and a dose threshold of 20% as the standard criterion was considered in this study. Furthermore, the passing rates of gamma indices of the film and Delta4 were compared with each other via Bland-Altman analysis. Results: The mean passing rate of gamma index with standard passing criterion between the TPS calculations and film measurements was 96.95±0.22%, while it was equal to 97.7±0.56% and 98.45±0.21% between the TPS calculations and 2D and 3D Delta4 measurements, respectively. Additionally, the differences between the passing rates of gamma indices of the film and Delta4 were less than 5%. Conclusion: The findings demonstrate that the accuracy of dose calculations of Eclipse^TM TPS in a heterogeneous chest phantom with the IMRT technique is within the standard passing criterion. Furthermore, it can be concluded that there is a good agreement between the film and Delta4, as IMRT QA devices.

Background: Breast conserving surgery (BCS) followed by radiotherapy (RT) has been widely accepted as the standard treatment in early stages of invasive breast cancer. The standard technique of RT includes whole breast irradiation (WBI). Additional tumor bed boost irradiation has also an important role in the local tumor control. But there are various controversial delivery methods. The aim of the present study was to compare electron and photon boost techniques in terms of heart and lung volume absorbed dose. Materials and Methods: Thirty patients with breast cancer were selected. All patients had undergone BCS and had been treated by WBI and boost irradiation. After delineation of gross tumor volume (GTV) two CT based 3D conformal boost plans by photon and electron were created for each patient. In each plan coverage index (CI), external volume index (EI), conformity index (COIN) and, lung volume absorbed dose (LVAD) and heart volume absorbed dose (HVAD) of at least 2Gy were measured. Statistical analysis was done using SPSS 17. Data were compared using a nonparametric test (Mann-Whitney) and p values <0.05 were considered significant. Results: Photon boost showed statistically significant superior results in terms of mean CI (P=0.002) and COIN (P=0.005). Results of EI revealed no significant difference between two methods (P=0.171). The heart (p=0.01) and lung (P<0.005) volume received 2Gy was lower in photon therapy in comparison with electron therapy. Conclusion: Our results demonstrated that the heart and lung volume absorbed dose is significantly higher in electron boost technique.

Background: Presence of artifacts, caused by dental filling high-Z materials (DFM), on intensity-modulated radiation therapy (IMRT) treatment plan CT images may lead to uncertainty in head and neck calculated dose distributions. Hence, the purpose of this study was to investigate the effects of DFM on the IMRT calculated dose distribution and consequent radiobiological derived outcomes for nasopharyngeal cancer patients. Materials and Methods: IMRT optimization of two groups (15 patients in each) of nasopharyngeal cancer (NPC) patients with (group I) and without (group II) dental amalgam was performed by using the Prowess Panther treatment planning system (TPS). For all the patients, target prescribed dose was 70 Gy to planning target volume. We used 3 sets of treatment plans including; nine fields arrangement (F9E) and two plans of seven fields (namely: F7 and F7E) at different angles. The dose volume histograms (DVHs), monitor units (MUs), Homogeneity index (HI), conformity index (CI), Tumor control probability (TCP) and normal tissue complication probability (NTCP) of main organs at risk (OARs) were analyzed. Results: According to the results, the TCP of PTV70 due to presence of dental filling material was significantly decreased (p=0.031). On the other hand received dose by mandible, left cochlea, both eyes and right optic nerve were considerably different between patients with and without artifacts (p<0.05), whereas mandible showed the maximum differences (up to 315.65 cGy) compared to the other studied OARs. Conclusion: Results Presence of dental artifact in patients with nasopharyngeal carcinoma leads to uncertainty in calculated dose of IMRT treatment plans, especially for mandible as an OAR.

Background: Due to the small size of the beamlets in IMRT (intensity modulated radiotherapy), physical penumbra is one of the important dosimetric parameters and small changes in the penumbra have a notable impact on the results. The physical penumbra width is defined as the lateral distance between two specified isodose curves at a specified depth of phantom. In this study, after demonstrating the inconsistency of conventional physical penumbra definition for non-uniform MLC (multileaf collimator) fields, two new dosimetric parameters proposed that are suitable for MLC fields. Materials and Methods: Physical penumbra evaluation was obtained using IAEA (international atomic energy agency) phase space data for a Varian IX and EGS (electron gamma shower)nrc Monte Carlo code package.  These measurements have been performed in water phantom at an SSD of 100 cm and a depth of 5 cm. Results: With conventional definition, physical penumbra width for all MLC setups on right and left sides of isodose curves (parallel to X and Y axes) are not equal.  With a novel beam penumbra parametrization, the effect of MLC setup is taken into consideration. Conclusion: The conventional definition of physical penumbra for non-uniform MLC setups is not comprehensive. For such cases, surface penumbra and uniformity index parameters are demonstrated to be more suitable and indicative of the field non-uniformity. It is also shown that for an idle treatment planning system, the uniformity index approaches unity.

Background: Bismuth composites are new and non-lead shields that are capable of breast dose reduction while preserving image quality. In this study, different percentages of Bismuth were used in designing and constructing polymer composites as breast shields in chest CT.  Materials and Methods: Micro particles of Bismuth with a ratio of 1% to 15% in Silicone matrix with two thicknesses were used as Bismuth Silicone composite (BSC) shield. The female chest phantom and standard chest CT exposure factors were used. Dosimetry was performed by thermo luminescent dosimeters. The image quality was evaluated with two methods. Statistical analyses were performed by Kruskal-Wallis and Mann-Whitney tests using SPSS 16. Results: The application of 1% and 15% BSC shields reduced the breast dose to 14.9% and 62.2%, respectively. Increases in image noise in BSC was observed 2.33% (P=0.439) for breast and from 7.13% (p=0.513) for mediastinum areas, depending on the type of shields. Conclusion: The Application of Bismuth shields with Silicone composite and changing of the Bismuth percentages in composite and thickness are effective factors on the breast dose reduction significantly that can reduce the risk of breast cancer when engaged in Chest CT.

Background: Photoneutrons are produced during the radiotherapy treatment, when high energy X rays interacts with structures of the head of the linear accelerator (linac). The present day TPS are not taking into account the photo-neutron dose and the biological effects associated with it. The late induction of cancer and recurrence of the disease in old cancer patients are being frequently reported. Materials and Methods: Patients undergoing radiotherapy treatment with 15 MV X rays from a Siemens Primus Plus linear accelerator was considered for the study. In the present work, photoneutron spectrum from the linac head is measured using CR 39 SSNTD and the corresponding dose is calculated using Geant4. The composite photoneutron spectrum from the linac head and the corresponding dose was calculated using the kerma evaluation method in a human equivalent tissue phantom. The repeated calculation outcomes and the covariance error analysis in the nuclear data give consistency and an accuracy of 2 % in the results. Results: The result shows that significant amount of photoneutron dose was deposited during radiotherapy treatment when high energy X rays are used. The photoneutron production from the patient itself is yet another major issue which will cause out off field dose. Conclusion: This work gives importance in considering the photoneutron dose during radiotherapy planning and protection. This extra dose might be a factor that contributes to the induction of cancer and also to the recurrence of cancer to previously cured patients.