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1.
PLoS One ; 16(1): e0243554, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-33406084

RESUMO

With COVID-19 N95 shortages, frontline medical personnel are forced to reuse this disposable-but sophisticated-multilayer respirator. Widely used to decontaminate nonporous surfaces, UV-C light has demonstrated germicidal efficacy on porous, non-planar N95 respirators when all surfaces receive ≥1.0 J/cm2 dose. Of utmost importance across disciplines, translation of empirical evidence to implementation relies upon UV-C measurements frequently confounded by radiometer complexities. To enable rigorous on-respirator measurements, we introduce a photochromic indicator dose quantification technique for: (1) UV-C treatment design and (2) in-process UV-C dose validation. While addressing outstanding indicator limitations of qualitative readout and insufficient dynamic range, our methodology establishes that color-changing dosimetry can achieve the necessary accuracy (>90%), uncertainty (<10%), and UV-C specificity (>95%) required for UV-C dose measurements. In a measurement infeasible with radiometers, we observe a striking ~20× dose variation over N95s within one decontamination system. Furthermore, we adapt consumer electronics for accessible quantitative readout and use optical attenuators to extend indicator dynamic range >10× to quantify doses relevant for N95 decontamination. By transforming photochromic indicators into quantitative dosimeters, we illuminate critical considerations for both photochromic indicators themselves and UV-C decontamination processes.


Assuntos
Descontaminação/métodos , Dispositivos de Proteção Respiratória/microbiologia , /prevenção & controle , Relação Dose-Resposta à Radiação , Contaminação de Equipamentos/prevenção & controle , Contaminação de Equipamentos/estatística & dados numéricos , Reutilização de Equipamento/estatística & dados numéricos , Humanos , Indicadores e Reagentes/efeitos da radiação , Radiometria/métodos , Sensibilidade e Especificidade , Raios Ultravioleta , Ventiladores Mecânicos/microbiologia
2.
Sensors (Basel) ; 21(1)2021 Jan 05.
Artigo em Inglês | MEDLINE | ID: mdl-33466275

RESUMO

We have augmented a recently introduced method for noninvasive analysis of skin structure and composition and applied it to monitoring of dynamical processes in traumatic bruises. The approach combines diffuse reflectance spectroscopy in visible spectral range and pulsed photothermal radiometry. Data from both techniques are analyzed simultaneously using a numerical model of light and heat transport in a four-layer model of human skin. Compared to the earlier presented approach, the newly introduced elements include two additional chromophores (ß-carotene and bilirubin), individually adjusted thickness of the papillary dermal layer, and analysis of the bruised site using baseline values assessed from intact skin in its vicinity. Analyses of traumatic bruises in three volunteers over a period of 16 days clearly indicate a gradual, yet substantial increase of the dermal blood content and reduction of its oxygenation level in the first days after injury. This is followed by the emergence of bilirubin and relaxation of all model parameters towards the values characteristic for healthy skin approximately two weeks after the injury. The assessed parameter values and time dependences are consistent with existing literature. Thus, the presented methodology offers a viable approach for objective characterization of the bruise healing process.


Assuntos
Bilirrubina/análise , Contusões/diagnóstico , Contusões/terapia , Tratamento por Radiofrequência Pulsada , Radiometria/métodos , Pele/fisiopatologia , Bilirrubina/metabolismo , Contusões/metabolismo , Feminino , Humanos , Masculino , Oxigênio/sangue , Pele/metabolismo , Espectrofotometria , beta Caroteno
3.
Medicine (Baltimore) ; 99(50): e23574, 2020 Dec 11.
Artigo em Inglês | MEDLINE | ID: mdl-33327317

RESUMO

Hypofractionation for localized prostate cancer treatment is rapidly spreading in the medical community and it is supported by radiobiological evidences (lower α/ß ratio compared with surrounding tissues). Stereotactic body radiation therapy (SBRT) is a technique to administer high doses with great precision, which is commonly performed with CyberKnife (CK) in prostate cancer treatment. Since the CyberKnife (CK) is not available at all radiotherapy center, alternative SBRT techniques are available such as Volumetric Modulated Arc Therapy (VMAT) and Helical Tomotherapy (HT). The aim of the present study was to compare the dosimetric differences between the CK, VMAT, and HT plans for localized prostate cancer treatment.Seventeenpatients have been recruited and replanned using VMAT and HT to this purpose: they received the treatment using the CK with a prescription of 36.25 Gy in 5 fractions; bladder, rectum and penis bulb were considered as organs at risk (OAR). In order to compare the techniques, we considered DVHs, PTV coverage, Conformity Index and new Conformity Index, Homogeneity Index, beam-on time and OARs received dose.The 3 treatments methods showed a comparable coverage of the lesion (PTV 95%: 99.8 ± 0.4% CK; 98.5 ± 0.8% VMAT; 99.4 ±â€Š0.5% HT. P < .05) and good sparing of OARs. Nevertheless, the beam-on time showed a significant difference (37 ±â€Š9 m CK; 7.1 ±â€Š0.3 m VMAT; 17 ±â€Š2 m HT. P < .05).Our results showed that, although CK is the best SBRT technique for prostate cancer treatment, in case this technology is not available, it can be replaced by a similar treatment delivered by VMAT technique. VMAT can be administrated only if it has an appropriate Image Guided Radiation Therapy (IGRT) tracking system.


Assuntos
Neoplasias da Próstata/radioterapia , Hipofracionamento da Dose de Radiação , Radiocirurgia , Radioterapia de Intensidade Modulada , Humanos , Imagem por Ressonância Magnética , Masculino , Próstata/diagnóstico por imagem , Próstata/patologia , Neoplasias da Próstata/diagnóstico por imagem , Neoplasias da Próstata/patologia , Radiometria/métodos , Radiocirurgia/métodos
4.
Igaku Butsuri ; 40(3): 88-96, 2020.
Artigo em Japonês | MEDLINE | ID: mdl-32999255

RESUMO

The quality assurance (QA) of the output constancy of linear accelerators (linacs) is one of the most basic items for radiation therapy. The necessity and demand of the dosimetric audit is on the rise. We aimed at establishing an on-site dosimetric audit program with a plastic phantom in order to enrich the availability of dosimetric audit in Japan. By this, we developed and evaluated an on-site audit program in multiple institutions in 120 cases for photon and electron standard dosimetry and intensity modulated radiation therapy (IMRT) condition. For photon standard dosimetry, we evaluated the accuracies of institutional measured absorbed dose in 50 cases by this on-site audit program. For the electron standard dosimetry, we evaluated the accuracies of institutional measured absorbed dose in 25 cases. For IMRT condition, we evaluated the accuracies of the institutional calculated dose in radiation treatment planning systems in 45 cases. The agreements of the measured absorbed dose between our audit and the institutions were within±1.1% for photon standard dosimetry. The agreements of the measured absorbed dose between our audit and the institutions were within±2.1% for electron standard dosimetry. The agreements between the measured absorbed dose of our audit and the institutional calculated dose were within±2.1% for IMRT condition. We established an on-site dosimetric audit program with a plastic phantom and this program is suitable with tight criteria similar to criteria required for clinical QA.


Assuntos
Auditoria Médica/métodos , Garantia da Qualidade dos Cuidados de Saúde , Radiometria/métodos , Radioterapia de Intensidade Modulada/métodos , Radioterapia de Intensidade Modulada/normas , Humanos , Japão , Auditoria Médica/normas , Órgãos em Risco , Imagens de Fantasmas , Plásticos , Radiometria/normas , Dosagem Radioterapêutica , Risco , Sensibilidade e Especificidade
5.
Medicine (Baltimore) ; 99(32): e21470, 2020 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-32769880

RESUMO

Esophageal cancer is a common malignant tumor of the digestive system with a high incidence and a poor prognosis. At the present, CT-based radiomics is providing more and more valuable information. However, the heterogeneity of the study and the poor repeatability of the texture feature parameters have limited its wider clinical application. In the present study, we focused on comparing the differences in the texture features of T3 stage esophageal squamous cell carcinoma at different locations and normal esophageal wall, aiming to provide some pieces of useful information for future research on esophageal squamous cell carcinoma.Fifty seven cases with throat CT imaging, including esophageal cancer contrast enhanced CT and conventional CT of healthy control group. The texture characteristics in control group and tumor group among different parts were compared. Using Univariable analysis, we compared the difference and conducted receiver-operator curve analysis to evaluate the performance of tumor grade diagnosis model.53 radiomic features were significantly different in control group and so as 93 features for tumor group. The upper section was the mostly different from the other 2 sections. Run-length matrix (RLM) features in tumor group accounted for the highest proportion, only Surface Volume Ratio was different.There are differences in the texture features of the tube wall in different parts of the esophagus of healthy adults, and this difference is more obvious in pT3 stage esophageal squamous cell carcinoma. In the future radiomics study of esophageal squamous cell carcinoma, we need to pay attention to this to avoid affecting the accuracy of the results.


Assuntos
Neoplasias Esofágicas/diagnóstico por imagem , Carcinoma de Células Escamosas do Esôfago/diagnóstico por imagem , Radiometria/estatística & dados numéricos , Tomografia Computadorizada por Raios X/estatística & dados numéricos , Idoso , Estudos de Casos e Controles , Meios de Contraste , Neoplasias Esofágicas/patologia , Carcinoma de Células Escamosas do Esôfago/patologia , Esôfago/diagnóstico por imagem , Esôfago/patologia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Estadiamento de Neoplasias , Valor Preditivo dos Testes , Curva ROC , Radiometria/métodos , Reprodutibilidade dos Testes , Estudos Retrospectivos , Sensibilidade e Especificidade , Tomografia Computadorizada por Raios X/métodos
6.
J Cancer Res Ther ; 16(3): 485-493, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32719255

RESUMO

Purpose: In this study, it is aimed to compare three different radiotherapy treatment planning techniques in terms of critical organ scoring index (COSI), two different conformity index (CI), tumor control probability (TCP), and normal tissue complication probability (NTCP) calculations in early (T1) glottic larynx carcinoma (T1GL). Furthermore, it is aimed to investigate these parameters compliance with dose-volume histograms (DVH) parameters. Materials and Methods: Ten T1GL patients were immobilized in a supine position with a head and neck thermoplastic mask. Treatment plans were created with opposed lateral fields (OLAFs) and intensity-modulated radiation therapy (IMRT) techniques with a total dose of 66 Gy in 33 fraction with 2 Gy/day. IMRT fields were selected as five fields (5IMRT) and seven fields (7IMRT). Dosimetric evaluation of three different treatment plans for T1GL carcinoma was performed in two consequential steps. First step was the assessment of planning target volume (PTV), all organs at risks (OARs), and normal tissue (NT) dose calculations according to given dose constraint directions and comparing the plans via DVH. In the second step, for PTV, the compatibility of DVH data with CIs-TCP was investigated where COSI-NTCP was compared with DVH for OARs. The DVH data were considered as reference in all evaluations. Results: The CIRTOG mean values were significantly closer to 1 with IMRT plans when compared to OLAF plans (P = 0.005). The CIPADDICK mean values revealed that OLAF plans were significantly worse than IMRT plans (P = 0.005). No statistically significant difference was found between all three plans in terms of homogeneity index mean values (P = 0.076). The calculated mean TCP values were significantly better for 7IMRT plans when compared to OLAF and 5IMRT plans (P = 0.007 and P = 0.017, respectively). Both NTCP and COSI evaluations, which is compatible with DVH, significantly favored OLAF plan for spinal cord and 7IMRT for thyroid gland. The COSI evaluations, which are compatible with DVH, significantly favored 7IMRT plan for carotid arteries and 5IMRT plan for NT. Conclusion: Our results demonstrated that CIPADDICK-TCP calculations for PTV and COSI-NTCP calculations for OARs were compatible with DVH in T1 GL plans. Therefore, we suggest such parameters as valuable tools for choosing the feasible one among multiple plans and even with different treatment machines.


Assuntos
Algoritmos , Glote/efeitos da radiação , Neoplasias Laríngeas/radioterapia , Laringe/efeitos da radiação , Órgãos em Risco/efeitos da radiação , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia de Intensidade Modulada/métodos , Glote/patologia , Humanos , Neoplasias Laríngeas/patologia , Laringe/patologia , Radiometria/métodos , Dosagem Radioterapêutica
7.
J Cancer Res Ther ; 16(3): 508-512, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32719258

RESUMO

Purpose: The study aimed to compare the radiobiological and dosimetric parameters between sequential boost (SEQB) and simultaneous integrated boost (SIB) treatment regimen using intensity-modulated arc therapy technique in locally advanced head-and-neck cancer (LAHNC) patients. Materials and Methods: A total of 24 previously untreated LAHNC patients were randomized into SIB (n= 11) and SEQB (n = 13) arms. The planning computed tomography data set was transferred to the treatment planning system. All the target volumes and organ at risk volumes were delineated. Single plan for SIB group and three plans (three phases) were generated for SEQB group of patients. Radiobiological and dosimetric parameters were compared. Results: The BED10(planned) value for high-risk (HR) planning target volume (PTV) was same in both groups, whereas for intermediate-risk (IR) PTV and low-risk (LR) PTV, the values were higher in SEQB arm than SIB arm. The V95 values were 100% for all the target volumes in both arms of patients. The average D100 value for gross target volume, HR PTV, and IR PTV was higher in SEQB arm than that in the SIB arm. The average D100 value for LR PTV was higher in the SIB arm compared to that of the SEQB arm. The BED10(achieved) was calculated using D100 values of target volumes. The difference of BED10(achieved) values between SEQB arm and SIB arm further increased than the BED10(planned) values for all target volumes. The maximum doses for spinal cord, spinal cord planning risk volume, and brain stem were within the tolerance dose in both groups of patients. The left and right parotid glands sparing was comparable in both groups of patients. Average integral dose was higher in the SIB group than SEQB group. The average total monitor unit per fraction was higher in the SEQB arm than that in the SIB arm. Conclusion: SIB regimen may be considered as more logical and efficient over SEQB regimen in the treatment of LAHNC with comparable radiobiological and dosimetric parameters.


Assuntos
Neoplasias de Cabeça e Pescoço/radioterapia , Recidiva Local de Neoplasia/radioterapia , Planejamento de Assistência ao Paciente/normas , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia de Intensidade Modulada/métodos , Tomografia Computadorizada por Raios X/métodos , Terapia Combinada , Neoplasias de Cabeça e Pescoço/diagnóstico por imagem , Neoplasias de Cabeça e Pescoço/patologia , Humanos , Pessoa de Meia-Idade , Recidiva Local de Neoplasia/diagnóstico por imagem , Recidiva Local de Neoplasia/patologia , Estadiamento de Neoplasias , Radiometria/métodos , Dosagem Radioterapêutica , Eficiência Biológica Relativa , Resultado do Tratamento
8.
J Cancer Res Ther ; 16(3): 594-599, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32719273

RESUMO

Introduction: Radiation therapy is commonly used in the treatment of head and neck cancer in both the definitive and postoperative settings. Proton therapy, due to its intrinsic physical properties, has the ability to reduce the integral dose delivered to the patients while maintaining highly conformal target coverage. Materials and Methods: .A literature search was performed on scientific databases, and Preferred Reporting Items for Meta-Analyses guidelines were followed to compute results. Only original studies were selected. Selected studies were used to extract some proposed data for comparison, dosimetry, site, complications, and survival. Results: Proton beam therapy technology can be used against the conventional radiotherapy and shows satisfactory results. Yet conventional therapy is not less advantageous considering the amount of work available for any cross interpretations. Conclusion: Comparative preplanning could be beneficial considering multiple therapies for ruling out the best treatment outcomes that could be expected.


Assuntos
Neoplasias de Cabeça e Pescoço/radioterapia , Terapia com Prótons/métodos , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia Conformacional/métodos , Radioterapia de Intensidade Modulada/métodos , Neoplasias de Cabeça e Pescoço/patologia , Implementação de Plano de Saúde , Humanos , Radiometria/métodos , Dosagem Radioterapêutica , Resultado do Tratamento
9.
Photodiagnosis Photodyn Ther ; 31: 101914, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32645436

RESUMO

BACKGROUND: Actinic keratosis (AK) affects one quarter of over 60  year olds in Europe with the risk of transforming into invasive squamous cell carcinoma. Daylight photodynamic therapy (dPDT) is an effective and patient preferred treatment that uses sunlight to clear AK. Currently, there is no standardised method for measuring the light received during treatment. METHODS: SmartPDT® is a smartphone-based application and web-portal, developed by siHealth Ltd, enabling remote delivery of dPDT. It uses satellite imagery and computational algorithms to provide real-time determination of exposure to PpIX-effective solar radiation ("light dose"). The application also provides forecast of expected radiant exposures for 24- and 48-hs prior to the treatment period. Validation of the real-time and forecasted radiant exposure algorithms was performed against direct ground-based measurement under all weather conditions in Chilton, UK. RESULTS: Agreement between direct ground measurements and satellite-determined radiant exposure for 2-h treatment was excellent at -0.1 % ± 5.1 % (mean ±â€¯standard deviation). There was also excellent agreement between weather forecasted radiant exposure and ground measurement, 1.8 % ± 17.7 % at 24-hs and 1.6 % ± 25.2 % at 48-hs. Relative Root Mean Square of the Error (RMSEr) demonstrated that agreement improved as time to treatment reduced (RMSEr = 22.5 % (48 -hs), 11.2 % (24-hs), 5.2 % (real-time)). CONCLUSION: Agreement between satellite-determined, weather-forecasted and ground-measured radiant exposure was better than any existing published literature for dPDT. The SmartPDT® application and web-portal has excellent potential to assist with remote delivery of dPDT, an important factor in reducing risk in an elderly patient population during the Covid-19 pandemic.


Assuntos
Infecções por Coronavirus/tratamento farmacológico , Ceratose Actínica/tratamento farmacológico , Fotoquimioterapia/métodos , Pneumonia Viral/tratamento farmacológico , Radiometria/métodos , Smartphone/estatística & dados numéricos , Idoso , Ritmo Circadiano , Infecções por Coronavirus/epidemiologia , Feminino , Humanos , Ceratose Actínica/diagnóstico , Masculino , Pandemias , Pneumonia Viral/epidemiologia , Medição de Risco , Luz Solar , Resultado do Tratamento , Reino Unido
10.
J Appl Clin Med Phys ; 21(9): 259-265, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32652862

RESUMO

The SARS-CoV-2 coronavirus pandemic has spread around the world including the United States. New York State has been hardest hit by the virus with over 380 000 citizens with confirmed COVID-19, the illness associated with the SARS-CoV-2 virus. At our institution, the medical physics and dosimetry group developed a pandemic preparedness plan to ensure continued operation of our service. Actions taken included launching remote access to clinical systems for all dosimetrists and physicists, establishing lines of communication among staff members, and altering coverage schedules to limit on-site presence and decrease risk of infection. The preparedness plan was activated March 23, 2020, and data were collected on treatment planning and chart checking efficiency for 6 weeks. External beam patient load decreased by 25% during the COVID-19 crisis, and special procedures were almost entirely eliminated excepting urgent stereotactic radiosurgery or brachytherapy. Efficiency of treatment planning and chart checking was slightly better than a comparable 6-week interval in 2019. This is most likely due to decreased patient load: Fewer plans to generate and more physicists available for checking without special procedure coverage. Physicists and dosimetrists completed a survey about their experience during the crisis and responded positively about the preparedness plan and their altered work arrangements, though technical problems and connectivity issues made the transition to remote work difficult. Overall, the medical physics and dosimetry group successfully maintained high-quality, efficient care while minimizing risk to the staff by minimizing on-site presence. Currently, the number of COVID-19 cases in our area is decreasing, but the preparedness plan has demonstrated efficacy, and we will be ready to activate the plan should COVID-19 return or an unknown virus manifest in the future.


Assuntos
Betacoronavirus/isolamento & purificação , Defesa Civil/organização & administração , Infecções por Coronavirus/epidemiologia , Física Sanitária/organização & administração , Pneumonia Viral/epidemiologia , Guias de Prática Clínica como Assunto/normas , Garantia da Qualidade dos Cuidados de Saúde , Radiometria/métodos , Defesa Civil/normas , Infecções por Coronavirus/terapia , Infecções por Coronavirus/virologia , Física Sanitária/normas , Humanos , Pandemias , Pneumonia Viral/terapia , Pneumonia Viral/virologia , Fatores de Risco , Estados Unidos/epidemiologia
11.
Phys Med Biol ; 65(16): 16TR01, 2020 08 31.
Artigo em Inglês | MEDLINE | ID: mdl-32604077

RESUMO

Semiconductor dosimeters are ubiquitous in modern external-beam radiation therapy. They possess key features. The response, electronically available in real time, is stable and linear with absorbed dose for given irradiation conditions; the radiation-sensitive volume can be rather small in size, while retaining mechanical strength and high sensitivity. We describe three common semiconductor dosimeters: diodes, metal-oxide-semiconductor field-effect transistors and diamonds. We discuss in detail their operation principles and applications in modern external-beam radiation therapy, primarily with megavoltage photon beams. We also explore their use in proton and heavy ion therapy, and in experimental radiotherapy techniques such as synchrotron-based micro-beam radiation therapy.


Assuntos
Dosímetros de Radiação/normas , Radiometria/métodos , Radiometria/normas , Planejamento da Radioterapia Assistida por Computador/normas , Semicondutores , Síncrotrons/normas , Humanos , Dosagem Radioterapêutica , Planejamento da Radioterapia Assistida por Computador/métodos , Síncrotrons/instrumentação
12.
Phys Med Biol ; 65(19): 195006, 2020 09 22.
Artigo em Inglês | MEDLINE | ID: mdl-32503026

RESUMO

The 1990 code of practice (COP), produced by the IPSM (now the Institute of Physics and Engineering in Medicine, IPEM) and the UK National Physical Laboratory (NPL), gave instructions for determining absorbed dose to water for megavoltage photon (MV) radiotherapy beams (Lillicrap et al 1990). The simplicity and clarity of the 1990 COP led to widespread uptake and high levels of consistency in external dosimetry audits. An addendum was published in 2014 to include the non-conventional conditions in Tomotherapy units. However, the 1990 COP lacked detailed recommendations for calibration conditions, and the corresponding nomenclature, to account for modern treatment units with different reference fields, including small fields as described in IAEA TRS483 (International Atomic Energy Agency (IAEA) 2017, Vienna). This updated COP recommends the irradiation geometries, the choice of ionisation chambers, appropriate correction factors and the derivation of absorbed dose to water calibration coefficients, for carrying out reference dosimetry measurements on MV external beam radiotherapy machines. It also includes worked examples of application to different conditions. The strengths of the 1990 COP are retained: recommending the NPL2611 chamber type as secondary standard; the use of tissue phantom ratio (TPR) as the beam quality specifier; and NPL-provided direct calibration coefficients for the user's chamber in a range of beam qualities similar to those in clinical use. In addition, the formalism is now extended to units that cannot achieve the standard reference field size of 10 cm × 10 cm, and recommendations are given for measuring dose in non-reference conditions. This COP is designed around the service that NPL provides and thus it does not require the range of different options presented in TRS483, such as generic correction factors for beam quality. This approach results in a significantly simpler, more concise and easier to follow protocol.


Assuntos
Calibragem/normas , Imagens de Fantasmas , Fótons/uso terapêutico , Radiometria/métodos , Radiometria/normas , Radioterapia de Alta Energia/normas , Humanos , Agências Internacionais , Dosagem Radioterapêutica , Água
13.
Gulf J Oncolog ; 1(33): 45-50, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-32476649

RESUMO

AIM: To evaluate and compare the dosimetric parameters between volumetric modulated arc therapy (VMAT) and Intensity modulated radiotherapy (IMRT) in head and neck cancers (HNCs). MATERIAL AND METHODS: A total of 30 patients newly diagnosed with Head and Neck cancers planned for radiotherapy were enrolled in the study. Two plans were made for each patient, one VMAT plan with two complete arcs (one clockwise and another counter clockwise ranging from 181° to 179° (clockwise) and 179° to 181° (counter clockwise) and other seven field IMRT dynamic Plan with beam angles at 0°, 50°, 100°,150°, 210°, 260°, 310°. All plans were generated with 6 MV photons. Optimization and calculations were done in Varian Eclipse planning system. RESULTS: VMAT plan achieved a better Conformity Index 95% with value of 1.016 ± 0.014 compared to 1.033±0.012 in IMRT. D2%, D5%, D50% were higher in VMAT compared to IMRT. Homogeneity Index was higher for the plans in IMRT with value of 0.035 ± 0.003 compared to 0.058 ± 0.008 with VMAT. The dose to the surrounding organs-at-risk (OARs) are better in VMAT and in particular for brainstem and spinal cord (statistically significant). The monitor units were significantly lower with VMAT (610±70) compared to IMRT (1079± 149). CONCLUSION: VMAT achieved acceptable planning target volume coverage with high conformity to the primary tumor and better sparing effect on organs-at-risk particularly spinal cord and brain stem. Statistically significant reduction in monitor units was achieved in VMAT than in IMRT. VMAT should be preferred wherever feasible with due consideration to cost and availability.


Assuntos
Neoplasias de Cabeça e Pescoço/radioterapia , Radiometria/métodos , Radioterapia de Intensidade Modulada/métodos , Feminino , Humanos , Masculino
15.
PLoS One ; 15(4): e0232008, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32330192

RESUMO

BACKGROUND: Accurate radiation dose estimates are critical for determining eligibility for therapies by timely triaging of exposed individuals after large-scale radiation events. However, the universal assessment of a large population subjected to a nuclear spill incident or detonation is not feasible. Even with high-throughput dosimetry analysis, test volumes far exceed the capacities of first responders to measure radiation exposures directly, or to acquire and process samples for follow-on biodosimetry testing. AIM: To significantly reduce data acquisition and processing requirements for triaging of treatment-eligible exposures in population-scale radiation incidents. METHODS: Physical radiation plumes modelled nuclear detonation scenarios of simulated exposures at 22 US locations. Models assumed only location of the epicenter and historical, prevailing wind directions/speeds. The spatial boundaries of graduated radiation exposures were determined by targeted, multistep geostatistical analysis of small population samples. Initially, locations proximate to these sites were randomly sampled (generally 0.1% of population). Empirical Bayesian kriging established radiation dose contour levels circumscribing these sites. Densification of each plume identified critical locations for additional sampling. After repeated kriging and densification, overlapping grids between each pair of contours of successive plumes were compared based on their diagonal Bray-Curtis distances and root-mean-square deviations, which provided criteria (<10% difference) to discontinue sampling. RESULTS/CONCLUSIONS: We modeled 30 scenarios, including 22 urban/high-density and 2 rural/low-density scenarios under various weather conditions. Multiple (3-10) rounds of sampling and kriging were required for the dosimetry maps to converge, requiring between 58 and 347 samples for different scenarios. On average, 70±10% of locations where populations are expected to receive an exposure ≥2Gy were identified. Under sub-optimal sampling conditions, the number of iterations and samples were increased, and accuracy was reduced. Geostatistical mapping limits the number of required dose assessments, the time required, and radiation exposure to first responders. Geostatistical analysis will expedite triaging of acute radiation exposure in population-scale nuclear events.


Assuntos
Exposição à Radiação/análise , Radiometria/métodos , Teorema de Bayes , Humanos , Modelos Teóricos , Exposição Ocupacional/análise , Doses de Radiação , Análise Espacial , Triagem , Tempo (Meteorologia)
16.
Phys Med Biol ; 65(11): 115002, 2020 06 05.
Artigo em Inglês | MEDLINE | ID: mdl-32235075

RESUMO

Respiratory-gated radiotherapy treatments of lung tumors reduce the irradiated normal tissue volume and potentially lower the risk of side effects. However, in clinical routine, the gating signal is usually derived from external markers or other surrogate signals and may not always correlate well with the actual tumor position. This study uses the kV-imaging system of a LINAC in combination with a multiple template matching algorithm for markerless real-time detection of the tumor position in a dynamic anthropomorphic porcine lung phantom. The tumor was realized by a small container filled with polymer dosimetry gel, the so-called gel tumor. A full end-to-end test for a gated treatment was performed and the geometric and dosimetric accuracy was validated. The accuracy of the tumor detection algorithm in SI- direction was found to be [Formula: see text] mm and the gel tumor was automatically detected in 98 out of 100 images. The measured 3D dose distribution showed a uniform coverage of the gel tumor and comparison with the treatment plan revealed a high 3D [Formula: see text]-passing rate of [Formula: see text] ([Formula: see text]). The simulated treatment confirmed the employed margin sizes for residual motion within the gating window and serves as an end-to-end test for a gated treatment based on a markerless fluoroscopic real-time tumor detection.


Assuntos
Fluoroscopia/métodos , Neoplasias Pulmonares/radioterapia , Planejamento da Radioterapia Assistida por Computador/métodos , Estudos de Viabilidade , Humanos , Neoplasias Pulmonares/diagnóstico por imagem , Movimento (Física) , Aceleradores de Partículas , Imagens de Fantasmas , Radiometria/métodos
17.
Phys Med Biol ; 65(11): 115003, 2020 06 05.
Artigo em Inglês | MEDLINE | ID: mdl-32235080

RESUMO

The ion recombination is examined in parallel-plate ionization chambers in scanning proton beams at the Danish Centre for Particle Therapy and the Skandion Clinic. The recombination correction factor k s is investigated for clinically relevant energies between 70 MeV and 244 MeV for dose rates below 400 Gy min-1 in air. The Boutillon formalism is used to separate the initial and general recombination. The general recombination is compared to predictions from the numerical recombination code IonTracks and the initial recombination to the Jaffé theory. k s is furthermore calculated with the two-voltage method (TVM) and extrapolation approaches, in particular the recently proposed three-voltage (3VL) method. The TVM is in agreement with the Boutillon method and IonTracks for dose rates above 100 Gy min-1. However, the TVM calculated k s is closer related to the Jaffé theory for initial recombination for lower dose rate, indicating a limited application in scanning light ion beams. The 3VL is in turn found to generally be in agreement with Boutillon's method. The recombination is mapped as a function of the dose rate and proton energy at the two centres using the Boutillon formalism: the initial recombination parameter was found to be A = (0.10 ± 0.01) V at DCPT and A = (0.22 ± 0.13) V at Skandion, which is in better agreement with the Jaffé theory for initial recombination than previously reported values. The general recombination parameter was estimated to [Formula: see text] and [Formula: see text]. Furthermore, the numerical algorithm IonTracks is demonstrated to correctly predict the initial recombination at low dose rates and the general recombination at high dose rates.


Assuntos
Terapia com Prótons/métodos , Planejamento da Radioterapia Assistida por Computador/métodos , Algoritmos , Radiometria/métodos , Cintilografia/métodos
18.
Radiat Res ; 193(6): 531-542, 2020 06 01.
Artigo em Inglês | MEDLINE | ID: mdl-32315249

RESUMO

We report the generation of dose point kernels for clinically-relevant radionuclide beta decays and monoenergetic electrons in various tissues to understand the impact of tissue type on dose point kernels. Currently available voxel-wise dosimetry approaches using dose point kernels ignore tissue composition and density heterogeneities. Therefore, the study on the impact of tissue type on dose point kernels is warranted. Simulations were performed using the GATE Monte Carlo toolkit, which encapsulates GEANT4 libraries. Dose point kernels were simulated in phantoms of water, compact bone, lung, adipose tissue, blood and red marrow for radionuclides 90Y, 188Re, 32P, 89Sr, 186Re, 153Sm and 177Lu and monoenergetic electrons (0.015-10 MeV). All simulations were performed by assuming an isotropic point source of electrons at the center of a homogeneous spherical phantom. Tissue-specific differences between kernels were investigated by normalizing kernels for effective pathlength. Transport of 20 million particles was found to provide sufficient statistical precision in all simulated kernels. The simulated dose point kernels demonstrate excellent agreement with other Monte Carlo packages. Deviation from kernels reported in the literature did not exceed a 10% global difference, which is consistent with the variability among published results. There are no significant differences between the dose point kernel in water and kernels in other tissues that have been scaled to account for density; however, tissue density predictably demonstrated itself to be a significant variable in dose point kernel distribution.


Assuntos
Método de Monte Carlo , Radiometria/métodos , Elétrons , Humanos , Especificidade de Órgãos , Imagens de Fantasmas , Radioisótopos/uso terapêutico
19.
Phys Med Biol ; 65(9): 095003, 2020 05 04.
Artigo em Inglês | MEDLINE | ID: mdl-32143198

RESUMO

Previous work has shown that PRESAGE® can be used successfully to perform 3D dosimetric measurements of complex radiotherapy treatments. However, measurements near the sample edges are known to be difficult to achieve. This is an issue when the doses at air-material interfaces are of interest, for example when investigating the electron return effect (ERE) present in treatments delivered by magnetic resonance (MR)-linac systems. To study this effect, a set of 3.5 cm-diameter cylindrical PRESAGE® samples was uniformly irradiated with multiple dose fractions, using either a conventional linac or an MR-linac. The samples were imaged between fractions using an optical-CT, to read out the corresponding accumulated doses. A calibration between TPS-predicted dose and optical-CT pixel value was determined for individual dosimeters as a function of radial distance from the axis of rotation. This data was used to develop a correction that was applied to four additional samples of PRESAGE® of the same formulation, irradiated with 3D-CRT and IMRT treatment plans, to recover significantly improved 3D measurements of dose. An alternative strategy was also tested, in which the outer surface of the sample was physically removed prior to irradiation. Results show that for the formulation studied here, PRESAGE® samples have a central region that responds uniformly and an edge region of 6-7 mm where there is gradual increase in dosimeter response, rising to an over-response of 24%-36% at the outer boundary. This non-uniform dose response increases in both extent and magnitude over time. Both mitigation strategies investigated were successful. In our four exemplar studies, we show how discrepancies at edges are reduced from 13%-37% of the maximum dose to between 2 and 8%. Quantitative analysis shows that the 3D gamma passing rates rise from 90.4, 69.3, 63.7 and 43.6% to 97.3, 99.9, 96.7 and 98.9% respectively.


Assuntos
Imageamento Tridimensional/instrumentação , Neoplasias Pulmonares/radioterapia , Aceleradores de Partículas/instrumentação , Imagens de Fantasmas , Radiometria/instrumentação , Planejamento da Radioterapia Assistida por Computador/métodos , Calibragem , Raios gama , Humanos , Imageamento Tridimensional/métodos , Radiometria/métodos , Dosagem Radioterapêutica , Radioterapia Conformacional/métodos
20.
Phys Med Biol ; 65(9): 095002, 2020 04 28.
Artigo em Inglês | MEDLINE | ID: mdl-32143207

RESUMO

In-room imaging is a prerequisite for adaptive proton therapy. The use of onboard cone-beam computed tomography (CBCT) imaging, which is routinely acquired for patient position verification, can enable daily dose reconstructions and plan adaptation decisions. Image quality deficiencies though, hamper dose calculation accuracy and make corrections of CBCTs a necessity. This study compared three methods to correct CBCTs and create synthetic CTs that are suitable for proton dose calculations. CBCTs, planning CTs and repeated CTs (rCT) from 33 H&N cancer patients were used to compare a deep convolutional neural network (DCNN), deformable image registration (DIR) and an analytical image-based correction method (AIC) for synthetic CT (sCT) generation. Image quality of sCTs was evaluated by comparison with a same-day rCT, using mean absolute error (MAE), mean error (ME), Dice similarity coefficient (DSC), structural non-uniformity (SNU) and signal/contrast-to-noise ratios (SNR/CNR) as metrics. Dosimetric accuracy was investigated in an intracranial setting by performing gamma analysis and calculating range shifts. Neural network-based sCTs resulted in the lowest MAE and ME (37/2 HU) and the highest DSC (0.96). While DIR and AIC generated images with a MAE of 44/77 HU, a ME of -8/1 HU and a DSC of 0.94/0.90. Gamma and range shift analysis showed almost no dosimetric difference between DCNN and DIR based sCTs. The lower image quality of AIC based sCTs affected dosimetric accuracy and resulted in lower pass ratios and higher range shifts. Patient-specific differences highlighted the advantages and disadvantages of each method. For the set of patients, the DCNN created synthetic CTs with the highest image quality. Accurate proton dose calculations were achieved by both DCNN and DIR based sCTs. The AIC method resulted in lower image quality and dose calculation accuracy was reduced compared to the other methods.


Assuntos
Tomografia Computadorizada de Feixe Cônico/métodos , Neoplasias de Cabeça e Pescoço/radioterapia , Processamento de Imagem Assistida por Computador/métodos , Redes Neurais de Computação , Terapia com Prótons/métodos , Radiometria/métodos , Planejamento da Radioterapia Assistida por Computador/métodos , Adulto , Idoso , Idoso de 80 Anos ou mais , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Dosagem Radioterapêutica
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