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External beam radiotherapy is a treatment modality that employs high doses for curative or palliative purposes. Safety in such treatments, particularly with high-precision equipment, necessitates strict adherence to quality control protocols to ensure the efficacy of oncological treatments. In this context, chemical dosimeters, particularly the Fricke gel, have emerged as valuable tools for quantitatively analysing absorbed radiation doses. These dosimeters can be applied both as tissue-equivalent phantoms and as radiation detectors in radiotherapy centers. The objective of this study was to evaluate the feasibility of new gelling matrices, comprising common materials such as CMC, GGU, and PVA, for producing ferrous sulphate dosimeters aimed at the relative quantification of radiation dose. A rheological study was conducted for different Fricke gel dosimetric formulations. Initially, the performance of these dosimeters, produced at various gel concentrations, was evaluated in terms of their consistency at room temperature. This was achieved through the straightforward process of humidification the gels with glycerine. These matrices consist of both natural and synthetic polymers that are readily accessible, easy to handle, and can be easily incorporated into the acidic ferrous sulphate solution. Parameters such as the influence of gelling matrix concentration, linearity, and stability were assessed and correlated with those previously investigated for Fricke gel produced with bloom 300 pig skin gelatine (GEL). Ferrous sulphate dosimeters fabricated with sodium carboxymethylcellulose (CMC), guar gum (GGU), and polyvinyl alcohol (PVA) exhibited a coefficient of variation of less than 1% relative to the dose response evaluated in this study. By using readily available and easily manageable materials, it is possible to replicate dosimeters with a favourable dosimetric response for high-dose measurements.

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PET cyclotrons are widely used for producing medical diagnostic radionuclides. The main radionuclide produced in these facilities is the 18F, which is obtained from the [18O (p,n)18F] reaction when 18O-enriched water is bombarded with the proton beams. This work aimed to estimate the radiation source term from the bombardment of an 18O-enriched water target with protons of 16.5 MeV to determine the radiation neutron field around the accelerator.

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BACKGROUND: Gastric cancer is the fourth cancer most common in the world and the second cause of cancer-related deaths. Perioperative chemotherapy may reduce tumor burden and decrease lymph node invasion, improving R0 resections rates. On the other hand, administered before surgery, chemotherapy may cause fibrosis and tissue edema, with potential increase of surgical difficulty and in the number of post-operative complications. Therefore, we aim to investigate the effect of perioperative chemotherapy for tumor burden and metastatic lymph nodes of gastric cancer. METHODS: Retrospective analysis of all patients submitted to perioperative chemotherapy and surgery, between January 2010 and June 2020, which showed lymph node regression and tumor regression (Becker's classification). RESULTS: A total of 112 patients with an average age of 61.9 years were analyzed. About 90.2% completed three cycles of perioperative chemotherapy. Good tumor response to chemotherapy (<10% residual tumor) was achieved in 21.3% of patients. Only three patients obtained a complete pathological response. A median lymph node response of 33.3% was achieved in our series. CONCLUSION: Despite no evident outstanding regression rate was observed, perioperative chemotherapy seems to be useful in obtaining a R0 resection in gastric cancer, even in advanced gastric cancer.

INTRODUCCIÓN: El cáncer de estómago es el cuarto tipo de cáncer más común y la segunda causa de muerte relacionada con el cáncer. La quimioterapia perioperatoria puede reducir la carga tumoral y disminuir la invasión de los ganglios linfáticos. Por otro lado, administrada antes de la cirugía, la quimioterapia puede causar fibrosis y edema tisular, aumentando potencialmente la dificultad quirúrgica y el número de complicaciones posoperatorias. Nuestro objetivo es investigar el efecto de la quimioterapia perioperatoria sobre la carga tumoral y los ganglios metastásicos en el cáncer gástrico. MÉTODOS: Análisis retrospectivo de todos los pacientes sometidos a quimioterapia y cirugía, entre enero de 2010 y junio de 2020. RESULTADOS: Se analizaron 112 pacientes con una edad media de 61.9 años. El 90.2% completó 3 ciclos de quimioterapia perioperatoria. Se logró una buena respuesta tumoral a la quimioterapia (< 10% de tumor residual) en el 21.3% de los pacientes. Tres pacientes lograron una respuesta patológica completa. En nuestra serie se logró una mediana de respuesta de los ganglios linfáticos del 33.3%. CONCLUSIÓN: Aunque no se observó una tasa de regresión manifiesta, la quimioterapia perioperatoria parece ser útil para lograr una resección R0 en el cáncer gástrico, incluso en el cáncer gástrico avanzado.

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PURPOSE: Nanoparticles (NPs) with radioactive atoms incorporated within the structure of the NP or bound to its surface, functionalized with biomolecules are reported as an alternative to low-dose-rate seed-based brachytherapy. In this study, authors report a mathematical dosimetric study on low-dose rate brachytherapy using radioactive NPs. METHOD: Single-cell dosimetry was performed by calculating cellular S-values for spherical cell model using Au-198, Pd-103 and Sm-153 NPs. The cell survival and tumor volume versus time curves were calculated and compared to the experimental studies on radiotherapeutic efficiency of radioactive NPs published in the literature. Finally, the radiotherapeutic efficiency of Au-198, Pd-103 and Sm-153 NPs was tested for variable: administered radioactivity, tumor volume and tumor cell type. RESULT: At the cellular level Sm-153 presented the highest S-value, followed by Pd-103 and Au-198. The calculated cell survival and tumor volume curves match very well with the published experimental results. It was found that Au-198 and Sm-153 can effectively treat highly aggressive, large tumor volumes with low radioactivity. CONCLUSION: The accurate knowledge of uptake rate, washout rate of NPs, radio-sensitivity and tumor repopulation rate is important for the calculation of cell survival curves. Self-absorption of emitted radiation and dose enhancement due to AuNPs must be considered in the calculations. Selection of radionuclide for radioactive NP must consider size of tumor, repopulation rate and radiosensitivity of tumor cells. Au-198 NPs functionalized with Mangiferin are a suitable choice for treating large, radioresistant and rapidly growing tumors.

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The effects of low energy electrons in biological tissues have proved to lead to severe damages at the cellular and sub-cellular level. It is due to an increase in the relative biological effectiveness (RBE) of these electrons with a decrease in their penetration range. That is, lower the range higher will be its RBE.Therefore, accurate determination of low energy electron range becomes a key issue for radiation dosimetry. This work reports on in-water electron tracks evaluated at low kinetic energy (1-50 keV) using isotropic mono-energetic point source approach suitably implemented by different general-purpose Monte Carlo codes. For this aim, simulations were performed using PENELOPE, EGSnrc, MCNP6, FLUKA and Geant4-DNA Monte Carlo codes to obtain the particle range, R,R90,R50. Finally, evaluation of dose point kernel (DPK), as used for internal dosimetry, was carried out as an application example. Scaled dose point kernels (sDPK) were estimated for a range of mono-energetic low energy electron sources. The non-negligible differences among the calculated sDPK using different codes were obtained for energy electrons up to 5 keV. It was also observed that differences of in-water range for low-energy electrons, due to the different general-purpose Monte Carlo codes, affected the DPKs used for dosimetry by convolution approach. Finally, the 3D dosimetry was found to be almost not affected at macroscopic clinical scale, whereas non-negligible differences appeared at the microscopic level. Hence, a thorough validation of the used sDPKs have to be performed before they could be used in applications to derive any conclusions.

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This study reports the comparison between two dose calculation algorithms, Acuros XB 13.5 (AXB) and Analytical Anisotropic Algorithm (AAA) against Monte Carlo (MC) simulations for 3D-Conformal Radiation Therapy (3D-CRT) using a female pelvic rando phantom. 3D-CRT treatment plans were generated on the CT images of rando phantom using AXB and AAA with Source to Axis Distance (SAD) technique. Doses obtained using two algorithms and MC results were compared using MATLAB based software CERR. In house MATLAB code was developed to calculate the gamma dose distribution comparison in terms of dose difference (DD) and distance to agreement distribution (DTA). The results showed that the Dmean in the PTV TOTAL (PTV) volume for AXB and AAA was equal to the mean dose calculated by MC simulations. The gamma passing rates for AXB were more accurate in comparison to AAA with reference to MC for PTV, Bladder and Femoral Heads region. After analysing the dose comparison specially for the PTV, femoral heads, also the analysis of dose volume histogram (DVH) and gamma dose distribution comparison for PTV, femoral heads and bladder, it can be concluded that AXB is more accurate in comparison to AAA. It can be said that AXB is well suited for dose calculation in clinical setup when compared to MC calculations.

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OBJECTIVE: The aim of this work was to simulate a 6MV conventional breast 3D conformational radiation therapy (3D-CRT) with physical wedges (50 Gy/25#) in the left breast, calculate the mean absorbed dose in the body organs using robust models and computational tools and estimate the secondary cancer-incidence risk to the Brazilian population. METHODS: The VW female phantom was used in the simulations. Planning target volume (PTV) was defined in the left breast. The 6MV parallel-opposed fields breast-radiotherapy (RT) protocol was simulated with MCNPx code. The absorbed doses were evaluated in all the organs. The secondary cancer-incidence risk induced by radiotherapy was calculated for different age groups according to the BEIR VII methodology. RESULTS: RT quality indexes indicated that the protocol was properly simulated. Significant absorbed dose values in red bone marrow, RBM (0.8 Gy) and stomach (0.6 Gy) were observed. The contralateral breast presented the highest risk of incidence of a secondary cancer followed by leukaemia, lung and stomach. The risk of a secondary cancer-incidence by breast-RT, for the Brazilian population, ranged between 2.2-1.7% and 0.6-0.4%. CONCLUSION: RBM and stomach, usually not considered as OAR, presented high second cancer incidence risks of 0.5-0.3% and 0.4-0.1%, respectively. This study may be helpful for breast-RT risk/benefit assessment. Advances in knowledge: MCNPX-dosimetry was able to provide the scatter radiation and dose for all body organs in conventional breast-RT. It was found a relevant risk up to 2.2% of induced-cancer from breast-RT, considering the whole thorax organs and Brazilian cancer-incidence.

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ABSTRACT The aim of this study was to create and test a new mice 3D-voxel phantom named DM_BRA for mice and human first-estimation radiopharmaceutical dosimetry. Previously, the article reviews the state-of-art in animal model development. Images from Digimouse CT database were used in the segmentation and on the generation of the voxelized phantom. Simulations for validation of the DM_BRA model was performed at 0.015, 0.1, 0.5, 1 and 4 MeV photons with heart-source. Specific Absorbed Fractions (SAF) data were compared with literature data. The organ masses of DM_BRA correlated well with existing models based on the same dataset; however, few small organ masses hold significant variations. The SAF data in most simulated cases were statistically equal to a significant level of 0.01 to the reference data.

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The Laboratory of Internal Dosimetry of the Center for Development of Nuclear Technology (LDI/CDTN) is responsible for routine internal monitoring of occupationally exposed individuals. The determination of photon emitting radionuclides in the human body requires calibration of the detector in specific counting geometries. The calibration process uses physical phantoms containing certified activities of the radionuclides of interest. The objective of this work was to obtain calibration efficiency curves of the Whole Body Counter in operation at the LDI/CDTN using a BOMAB physical phantom and Monte Carlo simulations.

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