Purpose: The use of nonsealed radioactive sources can lead to skin contamination due to radiological accidents and staff oversight. This contamination has been shown to contribute considerably to the total skin dose received by nuclear medicine technicians and can easily exceed the limit of 500 mSv/year established by the current regulations. To assess the severity of contamination, it is necessary to estimate the skin dose through the use of suitable skin dose rate conversion factors. To determine the appropriate factors, it is important to study the influence of the contamination area, the epidermal thickness, and the percutaneous absorption on them. Materials and Methods: Monte Carlo simulations using the code PHITS 3.02 were carried out to study and quantify the dosimetry conversion factors of 15 frequently used radionuclides (¹¹C, ¹⁸F, ³⁶Cl, ⁵⁴Mn, ⁶⁰Co, ⁹⁰Sr, ^{99 m}Tc, ¹²³I, ¹³¹I, ¹³⁷Cs, ¹⁵³Sm, ^{177 L}u, ²²³Ra, ²²⁶Ra, and ²⁴¹Am). Results: The absorbed dose to the skin is significantly influenced by epidermal thickness and percutaneous absorptions and can differ by up to two orders of magnitude with respect to the operational magnitude H'(0.07,0°). Conclusions: Skin dosimetry after a contamination incident may be complex because the absorbed dose delivered to the basal layer is influenced by the contamination area, the epidermal thickness, and the percutaneous absorption. Therefore, when an accident occurs, the dose should be quantified taking into account these parameters, especially the epidermal thickness, and the possible percutaneous absorption should be evaluated in cases where the contamination involves a dose approximately equivalent to the established limits.

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Aim: The aim of this study was to compare the Exradin W2 scintillator, PTW microDiamond, IBA Razor Nano, and IBA Razor chamber detectors for small-field dose measurements and validate the measured data against the EGSnrc user code and observe the variation between daisy-chained and direct measurement methods for the above detectors. Materials and Methods: The W2 scintillator, microDiamond, Razor Nano, and Razor chamber detectors were used to measure the in-plane and cross-plane profiles and the output factors (OFs) at 10 cm depth, and 90 source-to-surface distance for 6MV X-rays (Elekta Versa HD). The field sizes ranged from 0.5 cm × 0.5 cm to 5 cm × 5 cm. The BEAMnrc/DOSXYZnrc user codes (EGSnrc) were used to simulate the reference profiles. Gamma analysis was performed to compare the measured and simulated dose distributions. Results: The OFs measured with the W2 scintillator, microDiamond, Razor Nano chamber, Razor chamber, and the calculated Monte Carlo (MC) showed agreement to within 1% for the 3 cm × 3 cm field size. The uncertainty in the MC simulation was observed to be 0.4%. The percent difference in OFs measured using daisy-chained and direct measurement methods was within 0.15%, 0.4%, 1.4%, and 2.4% for microDiamond, W2 scintillator, Nano, and Razor chamber detectors, respectively. Conclusion: The lateral beam profiles and OFs of W2 scintillator, microDiamond, Razor Nano, and Razor chambers exhibit good agreement with the MC simulation within the nominal field sizes. Our results demonstrate that we can achieve considerable time-saving by directly measuring small-field OFs without daisy-chained methods using microDiamond and W2 scintillator. In terms of ease of use, sensitivity, reproducibility, and from a practical standpoint, we recommend microDiamond for small-field dosimetry.

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Aim: The aim of this study was to measure the dose to planning target and organ at risk (OAR) using Alderson Rando phantom for various treatment techniques in left breast radiotherapy and to estimate the secondary cancer incidence. Materials and Methods: Eleven different combinations of plans containing four techniques (three dimensional conformal radiotherapy, intensity-modulated radiation therapy [IMRT], volumetric modulated arc therapy [VMAT], and combination of 3DCRT and VMAT plans (HYBRID)) were created with 6 MV FF and 6 MV FFF (flattening filter and flattening filter-free) photon energies in phantom. Planned target volume and OAR doses in 23 different locations were measured using optically stimulated luminescence dosimeter (OSLD) and EBT3 films. Assuming the age of exposure as 30 years, lifetime attributable risk (LAR) was estimated based on excess absolute risk (EAR) models outlined in the Biological Effects of Ionizing Radiation VII report. Results: Film showed maximum deviations of 6.15% with IMRT_C_FF plan when compared with treatment planning system (TPS). The maximum percentage difference of 1.7% was found with OSLD measurement when compared with TPS for VMAT_T_FFF plan. EAR estimation was done for all the OARs including target. The LARs for left lung, right lung, and right breast were evaluated. The maximum LAR values of 2.92 ± 0.14 were found for left lung with VMAT_C_FFF plans. Conclusion: This study shows that both OSLD and EBT3 films are suitable for dose measurements using Rando phantom. OSLD shows superior results when compared with films, especially with relatively larger distances. Maximum LAR values were found with VMAT_C_FFF plans. Considering the secondary cancer risk associated with the patients treated in the younger age group, it is suggested that in vivo dose estimation should be a part of treatment quality audit whenever possible.

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Background and Purpose: Radiation therapy of nasopharyngeal carcinomas (NPCs) involves high doses to the target structures which are superficial to the skin surfaces. As a result, the skin toxicities involved are higher and sometimes worsens to such an extent that radiotherapy needs to be interrupted unplanned. This leads to a break in radiation therapy which overall affects the local control and cure rates. The aim of this study is to decrease the skin dose by contouring skin as an organ at risk (OAR) to include in inverse planning calculation. Materials and Methods: Seventy-three cases of nasopharyngeal cancers were planned for 60 Gy to intermediate-risk planning target volume (PTV_{Intermediate)} and 70 Gy to high risk (PTV_High), by three different modes of Intensity-modulated radiation therapy (IMRT)- namely conventional sequential intensity-modulated radiation therapy (S-IMRT PH-I and PH-II), Skin Spared sequential intensity-modulated radiation therapy (SS-IMRT PH-I and PH-II), and Skin Spared simultaneously instantaneous boost intensity-modulated radiation therapy (SS-SIB IMRT). The plans were compared by dose volume histograms and dose statistics to the PTV as well as to the OAR's. For PTV, mean dose (Dmean), maximum dose (Dmax), and minimum dose (Dmin) were compared to check the homogeneity index (HI) while sparing the skin. For other OAR's Dmean, Dmax and dose to to 1 cubic cm was used for comparison. The skin doses to various volumes from volume to receive 5 Gy (V5) to volume to receive 70 Gy (V70) were evaluated and compared between the three techniques. Statistical analysis was done using one away ANOVA on the data editor SPSS Version 26.0 (SPSS Inc., Chicago, Illinois, USA) to evaluate the results. Continuous variables were expressed as mean ± standard deviation, and categorical variables were summarized as frequencies and percentages. Survival analysis was done by Kaplan–Meier Estimator. Results: When the skin was considered as an OAR, the skin volume to receive 5, 10, 15, 20, 30, 40, 50, 60, 70 Gy was reduced by 6.5%, 6.5%, 6%, 11.5%, 7%, 6%, 6%, 5%, 2%, respectively, by SS-IMRT PH-I and II and 2%, 4.05%, 4%, 7%, 5%, 3%, 6%, 5%, 1%, respectively, by SS-SIB IMRT when both the SS techniques were compared with S-IMRT PH-I and II. Volume of skin to receive 20 Gy showed maximum reduction in SS-IMRT PH-I and II. A one-way ANOVA was carried out to find the differences in the skin doses between the three techniques. The skin dose in the two SS techniques, i.e., SS-IMRT PH-I and PH-II and SS-SIB IMRT was found significantly lower than that of IMRT plans without skin as an OAR, i.e., S-IMRT PH-I and PH-II (P = 0.000). The PTV doses were well within the 95%–107% of the prescribed dose (HI) and there were no significant differences in the means of the prescribed dose between the simple and skin spared IMRT techniques. The other OARs doses were also evaluated and there were no significant differences between the means of the doses among the techniques. Conclusions: SS IMRT for NPC has demonstrated reduction in skin dose while using skin as an OAR in the optimization. Moreover, decreased skin dose can decrease the skin related toxicities provided there is no compromise on Target dose coverage and OAR dose. We recommend that skin should be contoured as an OAR for NPC, provided PTV is minimally 3–5 mm beneath skin surface, in order to have a better disease control with lesser toxicities and less unplanned treatment interruptions.

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Purpose: Many artificial intelligence-based computational procedures are developed to diagnose COVID-19 infection from chest X-ray (CXR) images, as diagnosis by CXR imaging is less time consuming and economically cheap compared to other detection procedures. Due to unavailability of skilled computer professionals and high computer architectural resource, majority of the employed methods are difficult to implement in rural and poor economic settings. Majority of such reports are devoid of codes and ignores related diseases (pneumonia). The absence of codes makes limitation in applying them widely. Hence, validation testing followed by evidence-based medical practice is difficult. The present work was aimed to develop a simple method that requires a less computational expertise and minimal level of computer resource, but with statistical inference. Materials and Methods: A Fast Fourier Transform-based (FFT) method was developed with GNU Octave, a free and open-source platform. This was employed to the images of CXR for further analysis. For statistical inference, two variables, i.e., the highest peak and number of peaks in the FFT distribution plot were considered. Results: The comparison of mean values among different groups (normal, COVID-19, viral, and bacterial pneumonia [BP]) showed statistical significance, especially when compared to normal, except between viral and BP groups. Conclusion: Parametric statistical inference from our result showed high level of significance (P < 0.001). This is comparable to the available artificial intelligence-based methods (where accuracy is about 94%). Developed method is easy, availability with codes, and requires a minimal level of computer resource and can be tested with a small sample size in different demography, and hence, be implemented in a poor socioeconomic setting.

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Accuracy of ionization chamber (IC) to measure the scatter output factor (S_cp) of a linear accelerator (linac) is crucial, especially in small field (<4 cm × 4 cm). The common IC volume of 0.6 cc is not adequate for small-field measurement and not all radiotherapy centers can afford to purchase additional IC due to the additional cost. This study aimed to determine the efficiency of the EGSnrc Monte Carlo (MC) to calculate the S_cp for various field sizes including small field in Elekta Synergy (Agility multileaf collimator) linac. The BEAMnrc and DOSXYZnrc user codes were used to simulate a 6 MV linac model for various field sizes and calculate the radiation dose output in water phantom. The modeled linac treatment head was validated by comparing the percentage depth dose (PDD), beam profile, and beam quality (Tissue Phantom Ratio (TPR)_20,10) with the IC measurement. The validated linac model was simulated to calculate the S_cp consisting of collimator scatter factor (S_c) and phantom scatter factor (S_p). The PDD and beam profile of the simulated field sizes were within a good agreement of ±2% compared with the measured data. The TPR_20,10 value was 0.675 for field size 10 cm × 10 cm. The S_cp, S_c, and S_p simulated values were close to the IC measurement within ±2% difference. The simulation for S_c and S_p in 3 cm × 3 cm field size was calculated to be 0.955 and 0.884, respectively. In conclusion, this study validated the efficiency of the MC simulation as a promising tool for the S_cp calculation including small-field size for linac.

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Aims and Objectives: This study aims to investigate the viability of using RapidPlan (RP) knowledge-based (KB) treatment plans to initiate the new prostate volumetric-modulated arc therapy (VMAT) plans. Materials and Methods: The planning data for 120 prostate VMAT treatment plans were entered into the RP system's database. The database of previous VMAT plans was divided into four model groups for training in the RP system. The models were based on the numbers of 20, 60, and 120 prostate VMAT plans. The model of 120 plans used automated priority and manual priority for the optimization process. The models of 20 and 60 plans used only manual priority for optimization. Each model was validated on 15 cases of new prostate cancer patients by comparing RP model plans against manual clinical plans optimized according to the clinical dose constraints. Results: The RP models can estimate the dose comparable target volume to the manual clinical plan, which evaluated values of Dmax, D95%, D98%, HI, and CI and showed comparable results. For the normal organ doses of the bladder, rectum, penile bulb, and femoral head, all RP models exhibited a comparable or better dose than the manual clinical plan, except for the RP models using the automated priority for the optimization process, which cannot control the rectum dose below the dose constraints. Conclusions: The Varian RP KB planning can produce comparable doses or better doses with the clinical manual in a single optimization, although the RP model uses a minimum requirement of the planning number for the model training. The RP models can enhance the efficacy and quality of plans, which depend on the number of VMAT plans used in RP model training for prostate cancer.

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Purpose: To study the impact of different optimization methods in dealing with metallic hip implant using intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) techniques. Materials and Methods: A cohort of 16 patients having metallic implants was selected for the study. Three sets of IMRT and VMAT plans were generated. Set 1 IMRT (IM_Base), VMAT (VM_Base) without any restrictions on beam entry and exit, set 2 (IM_ENT and VM_ENT) optimizer restricts the beam entry and set 3 (IM_EXT+ENT), neither entry nor exit doses were allowed toward the metallic implant. Results: There was no significant difference in target (D_95%) and organ-at-risk doses between IM_Base and IM_ENT. There were significant (P = 0.002) improvements in planning target volume (PTV) V_95% and homogeneity from IM_EXT+ENT to IM_ENT. There was no significant difference in plan quality between VM_Base and VM_ENT. There were significant (P = 0.005) improvements in PTV, V_95%, homogeneity from VM_EXT+ENT to VM_ENT. V_40Gy, V_30Gy for bladder, rectum, bowel, and bowel maximum dose decreases significantly (P < 0.005) in IM_ENT compared to IM_EXT+ENT, but not significant for VMAT plans. Similarly, there was a significant decrease in dose spill outside target (P < 0.05) comparing 40%, 50%, 60%, and 70% dose spills for IM_ENT compared to IM_EXT+ENT, but variations among VMAT plans are insignificant. VMAT plans were always superior to IMRT plans for the same optimization methods. Conclusion: The best approach is to plan hip prosthesis cases with blocked entry of radiation beam for IMRT and VMAT. The VMAT plans had more volumetric coverage, fewer hotspots, and lesser heterogeneity.

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Introduction/: As per the recommendations of the American Association of Physicists in Medicine Task Group 43, Monte Carlo (MC) investigators should reproduce previously published dose distributions whenever new features of the code are explored. The purpose of the present study is to benchmark the TG-43 dosimetric parameters calculated using the new MC user-code egs_brachy of EGSnrc code system for three different radionuclides ¹⁹²Ir, ¹⁶⁹Yb, and ¹²⁵I which represent high-, intermediate-, and low-energy sources, respectively. Materials and Methods: Brachytherapy sources investigated in this study are high-dose rate (HDR) ¹⁹²Ir VariSource (Model VS2000), ¹⁶⁹Yb HDR (Model 4140), and ¹²⁵I -low-dose-rate (LDR) (Model OcuProsta). The TG-43 dosimetric parameters such as air-kerma strength, S_k, dose rate constant, Λ, radial dose function, g(r) and anisotropy function, F(r,θ) and two-dimensional (2D) absorbed dose rate data (along-away table) are calculated in a cylindrical water phantom of mass density 0.998 g/cm³ using the MC code egs_brachy. Dimensions of phantom considered for ¹⁹²Ir VS2000 and ¹⁶⁹Yb sources are 80 cm diameter ×80 cm height, whereas for ¹²⁵I OcuProsta source, 30 cm diameter ×30 cm height cylindrical water phantom is considered for MC calculations. Results: The dosimetric parameters calculated using egs_brachy are compared against the values published in the literature. The calculated values of dose rate constants from this study agree with the published values within statistical uncertainties for all investigated sources. Good agreement is found between the egs_brachy calculated radial dose functions, g(r), anisotropy functions, and 2D dose rate data with the published values (within 2%) for the same phantom dimensions. For ¹⁹²Ir VS2000 source, difference of about 28% is observed in g(r) value at 18 cm from the source which is due to differences in the phantom dimensions. Conclusion: The study validates TG-43 dose parameters calculated using egs_brachy for ¹⁹²Ir, ¹⁶⁹Yb, and ¹²⁵I brachytherapy sources with the values published in the literature.

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Background: Surface/skin dose measurement is one of the most challenging tasks for clinical dosimetry in radiotherapy and comparison with almost all the commercially available treatment planning systems (TPSs) brings a significant variation with the measured dose. Aims and Objectives: In the current study, doses calculated from the TPS in the near-surface region for conformal plans (both three-dimensional conformal radiotherapy [3DCRT] and intensity-modulated radiotherapy [IMRT]) of 35 breast cancer patients were evaluated and compared with the doses measured with Markus chamber. Materials and Methods: The computed tomography (CT) images of a solid water slab phantom with a Markus chamber (at different depths ranging from 1 mm to 5 mm from the surface) were taken and imported into the TPS. All the conformal treatment plans made in TPS were executed on a linear accelerator and dose agreements between TPS calculated and chamber measured doses were analysed. Results: Results showed that this TPS underestimated the calculated doses in the superficial region by up to 26% and 21%, respectively, with respect to mean and maximum dose values obtained within the effective volume of the chamber used. Conclusion: The uncertainty of doses in the superficial region should be kept in mind when evaluating treatment plans for superficial tumours in TPS.

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Aims: Calculation of the absorbed dose in human organs is one of the first steps for developing new radiopharmaceuticals. The aim of this study is to estimate the human absorbed dose of a newly developed ⁶⁸Ga-NODAGA-RGD-BBN radiolabeled compound. Materials and Methods: ⁶⁸Ga-NODAGA-RGD-BBN was prepared by varying different parameters at optimized conditions. The stability of the radiolabeled peptide in phosphate-buffered saline (PBS) and in human serum was evaluated for 120 min. Afterward, the biodistribution of the complex was assessed in normal and tumor-bearing mice, at least for 120 min postinjection. Finally, the human absorbed dose of ⁶⁸Ga-NODAGA-RGD-BBN was estimated based on mice data using Radiation Dose Assessment Resource and Spark method. Results: ⁶⁸Ga-NODAGA-RGD-BBN was produced with radiochemical purity of more than 98% (high-performance liquid chromatography/ radio thin layer chromatography (RTLC)) with high stability in PBS buffer and in human serum at least for 2 h. The complex demonstrated high uptake in gastrin-releasing peptide receptor-expressing tumors compared to other nontarget organs. Furthermore, the dose assessment for the complex showed that the kidneys receive the highest absorbed dose in comparison with other organs. Conclusion: The result of this study showed that 68Ga-NODAGA-RGD-BBN is an effective and radiolabeled ligand for tumor detection, however more studies are still needed.

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Introduction: The quality of images obtained from the nuclear medicine imaging systems depends on different factors. One of the most important of these factors is the geometrical and physical characteristics of collimator used for imaging with a given radioisotope. Aims and Objectives: The aim of this study is to investigate the contribution of different components of collimator response for determining the most suitable parallel-hole collimator for the different radioisotope energies used in nuclear medicine imaging. Materials and Methods: In this study, the SIMIND Monte Carlo simulation program is used to determine the contribution of geometrical, penetrating and scattered response components of four hexagonal parallel-hole collimators including low-energy high-resolution (LEHR), low-energy general-purpose (LEGP), medium-energy general-purpose (MEGP), and high-energy general-purpose (HEGP) collimators, for 12 different energies used in nuclear medicine imaging. Results: According to the simulation results, the use of both the LEHR and LEGP collimators leads to a geometrical component above 60% for energies between 69 and 171 keV. On the other hand, for energies between 185 and 245 keV, the MEGP collimator and for energy of 364 keV, the HEGP collimator gives the geometrical components above 70% and 60%, respectively, while for energy of 511 keV, the geometrical response of all four collimators is below 20%. Conclusion: The results of this study show that for two low-energy single-photopeak radioisotopes, Tc-99m and I-123, the LEHR and LEGP collimators, and for high-energy single-photopeak radioisotope, I-131, the HEGP collimator are most suitable collimators. For dual-photopeak In-111 radioisotope and triple-photopeak Ga-67 radioisotope, the MEGP and HEGP collimators and for triple-photopeak Tl-201 radioisotopes, the LEHR and LEGP collimators are proposed as most suitable collimators.

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