Dose measurements in a thorax phantom at 3DCRT breast radiation therapy.

BACKGROUND: The anthropomorphic and anthropometric phantom developed by the research group NRI (Núcleo de Radiações Ionizantes) can reproduce the effects of the interactions of radiation occurring in the human body. The whole internal radiation transport phenomena can be depicted by film dosimeters in breast RT. Our goal was to provide a dosimetric comparison of a radiation therapy (RT) plan in a 4MV 3D-conformal RT (4MV-3DCR T) and experimental data measured in a breast phantom. MATERIALS AND METHODS: The RT modality was two parallel opposing fields for the left breast with a prescribed dose of 2.0 Gy in 25 fractions. The therapy planning system (TPS) was performed on CA T3D software. The dose readings at points of interest (POI) pre-established in TPS were recorded. An anthropometric thorax-phantom with removal breast was used. EBT2 radiochromic films were inserted into the ipisilateral breast, contralateral breast, lungs, heart and skin. The irradiation was carried out on 4/80 Varian linear accelerator at 4MV. RESULTS: The mean dose at the OAR's presented statistically significant differences (p < 0.001) of 34.24%, 37.96% and 63.47% for ipsilateral lung, contralateral lung, and heart, respectively. The films placed at the skin-surface interface in the ipsilateral breast also showed statistically significant differences (p < 0.001) of 16.43%, -10.16%, -14.79% and 15.67% in the four quadrants, respectively. In contrast, the PTV dosimeters, representative of the left breast volume, encompassed by the electronic equilibrium, presented a non-significant difference with TPS, p = 0.20 and p = 0.90. CONCLUSION: There was a non-significant difference of doses in PTV with electronic equilibrium; although no match is achieved outside electronic equilibrium.

Estudo da razão contraste-ruído em sistema CR para mamografia utilizando diferentes tensões de pico e combinações alvo/filtro / Contrast to noise-ratio study in CR system for mammography using different peak voltages and target/filter combinations

Introdução: a mamografia é o exame padrão ouro para o diagnóstico de patologias mamárias, permitindo o rastreamento e o diagnóstico precoce do câncer de mama. Em 2015, foi elaborado pela European Federation of Organizations for Medical Physics (EFOMP) um protocolo internacional para testes de controle de qualidade em equipamentos. Objetivo: o objetivo foi avaliar a qualidade da imagem mamográfica de um sistema de radiografia computadorizada (CR) para mamografia, por meio do teste de razão contraste-ruído (CNR) e CNR relativa (CNRrel), com tensões, combinações alvo/filtro e espessuras diferentes. Metodologia: a metodologia seguiu o protocolo EFOMP, utilização de mamógrafo com detector de imagem CR e placas de polimetilmetacrilato (PMMA). Os fatores de exposição foram de 25, 28 e 32 kV, com seleção do mA.s de acordo com espessura das placas de PMMA. As combinações alvo/filtro foram de Mo/Mo, Mo/Rh e W/Rh. Resultados: concluiu-se que quanto menor a tensão, maior a CNR. Assim, as tensões de 25 kV a 28 kV apresentaram maior qualidade em nível de contraste da imagem, indicadas para mamas de menor densidade. Dessa forma, as espessuras menores das placas de PMMA geraram maior contraste na imagem, o que foi apresentado também nos resultados da CNRrel. A combinação de Mo/Mo, recomendada para mamas de menor densidade, também gerou maior contraste em relação aos outros alvos/filtros, reiterado no teste de CNRrel. Todos os valores de CNRrel medidos mostraram-se dentro dos valores limites esperados. Conclusão: pode-se observar com este estudo que mesmo diante de tensões e combinações alvo/filtro diferentes, a resposta da CNR foi proporcional à espessura do objeto irradiado para mamografia com sistema CR.

Introduction: mammography is a gold standard radiological examination for the diagnosis of breast pathologies, allowing screening and early diagnosis of breast cancer. In 2015, researchers from the European Federation of Organizations for Medical Physics (EFOMP) prepared a protocol used internationally for quality control tests on equipment. Objective: the aim was to evaluate the quality of mammographic image of a computerized radiography system (CR) for mammography upon the contrast to noise-ratio (CNR) test and relative CNR (CNRrel), with peak voltages, target/filter combinations and different thicknesses. Methodology: the methodology followed the EFOMP protocol, use of a mammograph with CR image detector and polymethyl methacrylate (PMMA) plates. The exposure factors were 25, 28 and 32 kV, with selection of the mA.s according to the thickness of the PMMA plates. The target/filter combinations used were Mo/Mo, Mo/Rh, W/Rh. Results: it was concluded that the lower the peak voltage, the higher the CNR. Thus, the voltages from 25 kV to 28 kV presented higher quality in the contrast level of the image, indicated for lower density breasts. In this way, the smaller thicknesses of PMMA plates generated greater contrast in the image, also presented in the CNRrel results. The Mo/Mo combination, recommended for lower density breasts, also generated greater contrast in relation to the other targets/ filters, reiterated in the CNRrel results. All measured CNRrel values were within the expected relative CNR limits. Conclusion: it can be observed with this study that even in the face of different peak voltages and target/filter combinations, the CNR response was proportional to the thickness of the irradiated object for mammography with CR system.

Dosimetric intercomparison of permanent Ho-166 seed's implants and HDR Ir-192 brachytherapy in breast cancer.

AIM: To provide a comparative dosimetric analysis of permanent implants of Ho(166)-seeds and temporary HDR Ir(192)-brachytherapy through computational simulation. BACKGROUND: Brachytherapy with Ir(192)-HDR or LDR based on temporary wires or permanent radioactive seed implants can be used as dose reinforcement for breast radiation therapy. Permanent breast implants have not been a practical clinical routine; although, I(125) and Pd(103)-seeds have already been reported. Biodegradable Ho(166)-ceramic-seeds have been addressed recently. MATERIAL AND METHODS: Simulations of implants of nine Ho(166)-seeds and equivalent with HDR Ir(192)-brachytherapy were elaborated in MCNP5, shaped in a computational multivoxel simulator which reproduced a female thorax phantom. Spatial dose rate distributions and dose-volume histograms were generated. Protocol's analysis involving exposure time, seed's activities and dose were performed. RESULTS: Permanent Ho(166)-seed implants presented a maximum dose rate per unit of contained activity (MDR) of 1.1601 µGy h(-1) Bq(-1); and, a normalized MDR in standard points (8 mm, equidistant to 03-seeds - SP1, 10 mm - SP2) of 1.0% (SP1) and 0.5% (SP2), respectively. Ir(192)-brachytherapy presented MDR of 4.3945 × 10(-3) µGy h(-1) Bq(-1); and, 30% (SP1), and 20% (SP2). Therefore, seed's implant activities of 333 MBq (Ho(166)) and 259 GBq (Ir(192)) produced prescribed doses of 58 Gy (SP1; 5d) and 56 Gy (SP1, 5 fractions, 6 min), respectively. CONCLUSIONS: Breast Ho(166)-implants of 37-111 MBq are attractive due to the high dose rate near 6-10 mm from seeds, equivalent to Ir(192)-brachytherapy of 259 GBq (3 fractions, 6 min) providing similar dose in standard points at a week; however, with spatial dose distribution better confined. The seed positioning can be adjusted for controlling the breast tumor, in stages I and II, in flat and deep tumors, without any breast volumetric limitation.

Experimental dosimetry in conformal breast teletherapy compared with the planning system.

The objective of this study was to compare and analyse the absorbed dose profiles from the conformal radiotherapy planning and experimental dosimetry taken in a breast anthropomorphic and anthropometric phantom. Conformal radiotherapy planning was elaborated in the Treatment Planning System (TPS). EBT2 Gafchromic radiochromic films were applied as dosimeters, positioned internally and superficially in the breast phantom. The standard radiation protocol was applied in the breast phantom. The films were digitalised, and their responses were analysed in RGB. The optical densities were processed, reproducing the spatial dose distribution.

Radiological response of ceramic and polymeric devices for breast brachytherapy.

In the present study, the radiological visibility of ceramic and polymeric devices implanted in breast phantom was investigated for future applications in brachytherapy. The main goal was to determine the radiological viability of ceramic and polymeric devices in vitro by performing simple radiological diagnostic methods such as conventional X-ray analysis and mammography due to its easy access to the population. The radiological response of ceramic and polymeric devices implanted in breast phantom was determined using conventional X-ray, mammography and CT analysis.