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1.
Br J Radiol ; 93(1107): 20190807, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-32003574

RESUMO

After years of lethargy, studies on two non-conventional microstructures in time and space of the beams used in radiation therapy are enjoying a huge revival. The first effect called "FLASH" is based on very high dose-rate irradiation (pulse amplitude ≥106 Gy/s), short beam-on times (≤100 ms) and large single doses (≥10 Gy) as experimental parameters established so far to give biological and potential clinical effects. The second effect relies on the use of arrays of minibeams (e.g., 0.5-1 mm, spaced 1-3.5 mm). Both approaches have been shown to protect healthy tissues as an endpoint that must be clearly specified and could be combined with each other (e.g., minibeams under FLASH conditions). FLASH depends on the presence of oxygen and could proceed from the chemistry of peroxyradicals and a reduced incidence on DNA and membrane damage. Minibeams action could be based on abscopal effects, cell signalling and/or migration of cells between "valleys and hills" present in the non-uniform irradiation field as well as faster repair of vascular damage. Both effects are expected to maintain intact the tumour control probability and might even preserve antitumoural immunological reactions. FLASH in vivo experiments involving Zebrafish, mice, pig and cats have been done with electron beams, while minibeams are an intermediate approach between X-GRID and synchrotron X-ray microbeams radiation. Both have an excellent rationale to converge and be applied with proton beams, combining focusing properties and high dose rates in the beam path of pencil beams, and the inherent advantage of a controlled limited range. A first treatment with electron FLASH (cutaneous lymphoma) has recently been achieved, but clinical trials have neither been presented for FLASH with protons, nor under the minibeam conditions. Better understanding of physical, chemical and biological mechanisms of both effects is essential to optimize the technical developments and devise clinical trials.


Assuntos
Tratamentos com Preservação do Órgão/métodos , Terapia com Prótons/métodos , Animais , Gatos , Proliferação de Células , Dano ao DNA , Reparo do DNA , Fracionamento da Dose de Radiação , Linfoma Cutâneo de Células T/radioterapia , Camundongos , Órgãos em Risco/efeitos da radiação , Oxigênio , Consumo de Oxigênio , Lesões por Radiação/prevenção & controle , Tolerância a Radiação , Radiometria/métodos , Neoplasias Cutâneas/radioterapia , Análise Espaço-Temporal , Suínos , Peixe-Zebra
2.
Int J Radiat Oncol Biol Phys ; 106(2): 440-448, 2020 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-31928642

RESUMO

PURPOSE: Recent studies suggest that ultrahigh-dose-rate, "FLASH," electron radiation therapy (RT) decreases normal tissue damage while maintaining tumor response compared with conventional dose rate RT. Here, we describe a novel RT apparatus that delivers FLASH proton RT (PRT) using double scattered protons with computed tomography guidance and provide the first report of proton FLASH RT-mediated normal tissue radioprotection. METHODS AND MATERIALS: Absolute dose was measured at multiple depths in solid water and validated against an absolute integral charge measurement using a Faraday cup. Real-time dose rate was obtained using a NaI detector to measure prompt gamma rays. The effect of FLASH versus standard dose rate PRT on tumors and normal tissues was measured using pancreatic flank tumors (MH641905) derived from the KPC autochthonous PanCa model in syngeneic C57BL/6J mice with analysis of fibrosis and stem cell repopulation in small intestine after abdominal irradiation. RESULTS: The double scattering and collimation apparatus was dosimetrically validated with dose rates of 78 ± 9 Gy per second and 0.9 ± 0.08 Gy per second for the FLASH and standard PRT. Whole abdominal FLASH PRT at 15 Gy significantly reduced the loss of proliferating cells in intestinal crypts compared with standard PRT. Studies with local intestinal irradiation at 18 Gy revealed a reduction to near baseline levels of intestinal fibrosis for FLASH-PRT compared with standard PRT. Despite this difference, FLASH-PRT did not demonstrate tumor radioprotection in MH641905 pancreatic cancer flank tumors after 12 or 18 Gy irradiation. CONCLUSIONS: We have designed and dosimetrically validated a FLASH-PRT system with accurate control of beam flux on a millisecond time scale and online monitoring of the integral and dose delivery time structure. Using this system, we found that FLASH-PRT decreases acute cell loss and late fibrosis after whole-abdomen and focal intestinal RT, whereas tumor growth inhibition is preserved between the 2 modalities.


Assuntos
Órgãos em Risco/efeitos da radiação , Terapia com Prótons/instrumentação , Lesões Experimentais por Radiação/prevenção & controle , Proteção Radiológica/instrumentação , Radioterapia Guiada por Imagem/instrumentação , Abdome/efeitos da radiação , Animais , Proliferação de Células/efeitos da radiação , Desenho de Equipamento/métodos , Estudos de Viabilidade , Feminino , Fibrose , Raios gama , Intestino Delgado/patologia , Intestino Delgado/efeitos da radiação , Camundongos , Camundongos Endogâmicos C57BL , Tratamentos com Preservação do Órgão/instrumentação , Tratamentos com Preservação do Órgão/métodos , Órgãos em Risco/patologia , Neoplasias Pancreáticas/radioterapia , Terapia com Prótons/métodos , Proteção Radiológica/métodos , Radiometria/métodos , Radioterapia Guiada por Imagem/métodos , Espalhamento de Radiação , Células-Tronco/efeitos da radiação , Tomografia Computadorizada por Raios X
3.
Br J Radiol ; 93(1107): 20190332, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-31944824

RESUMO

Proton minibeam therapy (PMBT) is a form of spatially fractionated radiotherapy wherein broad beam radiation is replaced with segmented minibeams-either parallel, planar minibeam arrays generated by a multislit collimator or scanned pencil beams that converge laterally at depth to create a uniform dose layer at the tumor. By doing so, the spatial pattern of entrance dose is considerably modified while still maintaining tumor dose and efficacy. Recent studies using computational modeling, phantom experiments, in vitro and in vivo preclinical models, and early clinical feasibility assessments suggest that unique physical and biological attributes of PMBT can be exploited for future clinical benefit. We outline some of the guiding principle of PMBT in this concise overview of this emerging area of preclinical and clinical research inquiry.


Assuntos
Criatividade , Neoplasias/radioterapia , Terapia com Prótons/métodos , Absorção de Radiação , Algoritmos , Fracionamento da Dose de Radiação , Estudos de Viabilidade , Humanos , Método de Monte Carlo , Tratamentos com Preservação do Órgão , Órgãos em Risco , Radiobiologia , Radiometria
4.
Br J Radiol ; 93(1108): 20190789, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-31971829

RESUMO

OBJECTIVE: Prostate stereotactic ablative radiotherapy (SABR) delivers large doses using a fast dose rate. This amplifies the effect geometric uncertainties have on normal tissue dose. The aim of this study was to determine whether the treatment dose-volume histogram (DVH) agrees with the planned dose to organs at risk (OAR). METHODS: 41 low-intermediate risk prostate cancer patients were treated with SABR using a linac based technique. Dose prescribed was 35 Gy in five fractions delivered on alternate days, planned using volumetric modulated arc therapy (VMAT) with 10X flattening filter free (FFF). On treatment, prostate was matched to fiducial markers on cone beam CT (CBCT). OAR were retrospectively delineated on 205 pre-treatment CBCT images. Daily CBCT contours were overlaid on the planning CT for dosimetric analysis. Verification plan used to evaluate the daily DVH for each structure. The daily doses received by OAR were recorded using the D%. RESULTS: The median rectum and bladder volumes at planning were 67.1 cm3 (interquartile range 56.4-78.2) and 164.4 cm3 (interquartile range 120.3-213.4) respectively. There was no statistically significant difference in median rectal volume at each of the five treatment scans compared to the planning scan (p = 0.99). This was also the case for median bladder volume (p = 0.79). The median dose received by rectum and bladder at each fraction was higher than planned, at the majority of dose levels. For rectum the increase ranged from 0.78-1.64Gy and for bladder 0.14-1.07Gy. The percentage of patients failing for rectum D35% < 18 Gy (p = 0.016), D10% < 28 Gy (p = 0.004), D5% < 32 Gy (p = 0.0001), D1% < 35 Gy (p = 0.0001) and bladder D1% < 35 Gy (p = 0.001) at treatment were all statistically significant. CONCLUSION: In this cohort of prostate SABR patients, we estimate the OAR treatment DVH was higher than planned. This was due to rectal and bladder organ variation. ADVANCES IN KNOWLEDGE: OAR variation in prostate SABR using a FFF technique, may cause the treatment DVH to be higher than planned.


Assuntos
Órgãos em Risco/efeitos da radiação , Neoplasias da Próstata/radioterapia , Radiocirurgia/métodos , Radioterapia de Intensidade Modulada/métodos , Reto/efeitos da radiação , Bexiga Urinária/efeitos da radiação , Idoso , Fracionamento da Dose de Radiação , Humanos , Masculino , Próstata , Radiometria , Planejamento da Radioterapia Assistida por Computador/métodos , Reto/diagnóstico por imagem , Estudos Retrospectivos , Bexiga Urinária/diagnóstico por imagem
5.
Int J Radiat Oncol Biol Phys ; 106(2): 430-439, 2020 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-31678227

RESUMO

PURPOSE: To evaluate whether automated knowledge-based planning (KBP) (a) is noninferior to human-driven planning across multiple disease sites and (b) systematically affects dosimetric plan quality and variability. METHODS AND MATERIALS: Clinical KBP automated planning routines were developed for prostate, prostatic fossa, hypofractionated lung, and head and neck. Clinical implementation consisted of independent generation of human-generated and KBP plans (145 cases across all sites), followed by blinded plan selection. Reviewing physicians were prompted to select a single plan; when plan equivalence was volunteered, this scored as KBP selection. Plan selection analysis used a noninferiority framework testing the hypothesis that KBP is not worse than human-driven planning (threshold: lower 95% confidence interval [CI] > 0.45 = noninferiority; > 0.5 = superiority). Target and organ-at-risk metrics were compared by dose differencing: ΔDx = Dx, human-Dx, KBP (2-tailed paired t test, Bonferroni-corrected P < .05 significance threshold). To evaluate the aggregated effect of KBP on planning performance, we examined post-KBP dosimetric parameters against 183 plans generated just before KBP implementation (2-tailed unpaired t test, Bonferroni-corrected P < .05). RESULTS: Across all disease sites, the KBP success rate (physician preferred + equivalent) was noninferior compared with human-driven planning (83 of 145 = 57.2%; range, 49.2%-65.3%) but did not cross the threshold for superiority. The KBP success rate in respective disease sites was superior with head and neck ([22 + 2]/36 = 66.7%; 95% CI, 51%-82%) and noninferior for lung stereotactic body radiation therapy ([21 + 2]/36 = 63.9%; 95% CI, 48%-80%) but did not meet noninferiority criteria with prostate ([16 + 3]/41 = 46.3%; 95% CI, 31%-62%) or prostatic fossa ([17 + 0]/32 = 53.1%; 95% CI, 36%-70%). Prostate, prostatic fossa, and head and neck showed significant differences in KBP-selected plans versus human-selected plans, with KBP generally exhibiting greater organ-at-risk sparing and human plans exhibiting better target homogeneity. Analysis of plan quality pre- and post-KBP showed some reductions in organ doses and quality metric variability in prostate and head and neck. CONCLUSIONS: Fully automated KBP was noninferior to human-driven plan optimization across multiple disease sites. Dosimetric analysis of treatment plans before and after KBP implementation showed a systematic shift to higher plan quality and lower variability with the introduction of KBP.


Assuntos
Protocolos Clínicos , Neoplasias de Cabeça e Pescoço/radioterapia , Gestão do Conhecimento , Neoplasias Pulmonares/radioterapia , Neoplasias da Próstata/radioterapia , Planejamento da Radioterapia Assistida por Computador/métodos , Neoplasias de Cabeça e Pescoço/patologia , Humanos , Bases de Conhecimento , Neoplasias Pulmonares/patologia , Masculino , Tratamentos com Preservação do Órgão/métodos , Órgãos em Risco , Neoplasias da Próstata/patologia , Garantia da Qualidade dos Cuidados de Saúde , Radiometria , Dosagem Radioterapêutica , Planejamento da Radioterapia Assistida por Computador/normas , Equipolência Terapêutica
6.
Int J Radiat Oncol Biol Phys ; 106(2): 243-252, 2020 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-31288053

RESUMO

PURPOSE: A large proportion of preclinical or translational studies using radiation have poor replicability. For a study involving radiation exposure to be replicable, interpretable, and comparable, its experimental methodology must be well reported, particularly in terms of irradiation protocol, including the amount, rate, quality, and geometry of radiation delivery. Here we perform the first large-scale literature review of the current state of reporting of essential experimental physics and dosimetry details in the scientific literature. METHODS AND MATERIALS: For 1758 peer-reviewed articles from 469 journals, we evaluated the reporting of basic experimental physics and dosimetry details recommended by the authoritative National Institute of Standards and Technology symposium. RESULTS: We demonstrate that although some physics and dosimetry parameters, such as dose, source type, and energy, are well reported, the majority are not. Furthermore, highly cited journals and articles are systematically more likely to be lacking experimental details related to the irradiation protocol. CONCLUSIONS: These findings show a crucial deficiency in the reporting of basic experimental details and severely affect the reproducibility and translatability of a large proportion of radiation biology studies.


Assuntos
Física , Radiobiologia , Radiometria , Reprodutibilidade dos Testes , Bibliometria , Pesquisa Biomédica/estatística & dados numéricos , Congressos como Assunto , Humanos , Fator de Impacto de Revistas , Exposição à Radiação , Dosagem Radioterapêutica , Padrões de Referência , Fatores de Tempo , Pesquisa Médica Translacional/estatística & dados numéricos
7.
Tumori ; 106(1): 39-46, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31451102

RESUMO

BACKGROUND: We evaluated the prognostic role of gross tumor volumes (GTVs) of primary tumor and positive lymph nodes on overall survival (OS) and progression-free survival (PFS) in locally advanced unresectable sinonasal cancer (SNC) treated with definitive intensity-modulated radiotherapy (IMRT) with or without chemotherapy. METHODS: Primary tumor GTV (GTV-T), pathologic neck nodes GTV (GTV-N), and positive retropharyngeal nodes GTV (GTV-RPN) of 34 patients with epithelial nonglandular SNC receiving IMRT with or without chemotherapy were retrospectively measured. The GTV variables were analyzed in relation with OS and PFS. Survival curves were estimated using the Kaplan-Meier method and compared with the log-rank test. We also estimated the crude cumulative incidence of locoregional relapses only. The optimal volume cutoff value was determined using an outcome-oriented method among the observed values. RESULTS: GTV-T was significantly associated with decreased OS (P=0.003) and PFS (P=0.003). Moreover, patients with disease total volumes (GTV) smaller than 149.44 cm³ had better OS and PFS than patients with higher volumes (P<0.0001 for both). Neck nodal metastasis impacted on OS and PFS (P=0.030 and P=0.033, respectively), but GTV-N did not (P=0.961; P=0.958). Retropharyngeal nodes metastasis was not associated with prognosis (OS: P=0.400; PFS: P=0.104). When GTV-RPN was added to GTV-N (GTV-TN), a relation with PFS (P=0.041) and a trend toward significance for OS (P=0.075) were found. CONCLUSIONS: Our results show that tumor volume is a powerful predictor of outcome in SNC. This could be useful to identify patients with worse prognosis deserving different treatment strategies.


Assuntos
Neoplasias dos Seios Paranasais/mortalidade , Neoplasias dos Seios Paranasais/patologia , Neoplasias Faríngeas/mortalidade , Neoplasias Faríngeas/patologia , Adulto , Idoso , Idoso de 80 Anos ou mais , Protocolos de Quimioterapia Combinada Antineoplásica/efeitos adversos , Protocolos de Quimioterapia Combinada Antineoplásica/uso terapêutico , Terapia Combinada , Feminino , Humanos , Metástase Linfática , Masculino , Pessoa de Meia-Idade , Estadiamento de Neoplasias , Neoplasias dos Seios Paranasais/terapia , Neoplasias Faríngeas/terapia , Prognóstico , Modelos de Riscos Proporcionais , Radiometria , Dosagem Radioterapêutica , Radioterapia de Intensidade Modulada/efeitos adversos , Radioterapia de Intensidade Modulada/métodos , Estudos Retrospectivos , Análise de Sobrevida , Resultado do Tratamento , Carga Tumoral
8.
Br J Radiol ; 93(1107): 20190598, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-31782941

RESUMO

OBJECTIVES: To describe the measurements and to present the results of the beam commissioning and the beam model validation of a compact, gantry-mounted, spot scanning proton accelerator system with dynamic layer-by-layer field collimation. METHODS: We performed measurements of depth dose distributions in water, spot and scanned field size in air at different positions from the isocenter plane, spot position over the 20 × 20 cm2 scanned area, beam monitor calibration in terms of absorbed dose to water and specific field collimation measurements at different gantry angles to commission the system. To validate the beam model in the treatment planning system (TPS), we measured spot profiles in water at different depths, absolute dose in water of single energy layers of different field sizes and inversely optimised spread-out Bragg peaks (SOBP) under normal and oblique beam incidence, field size and penumbra in water of SOBPs, and patient treatment specific quality assurance in homogeneous and heterogeneous phantoms. RESULTS: Energy range, spot size, spot position and dose output were consistent at all gantry angles with 0.3 mm, 0.4 mm, 0.6 mm and 0.5% maximum deviations, respectively. Uncollimated spot size (one sigma) in air with an air-gap of 10 cm ranged from 4.1 to 16.4 mm covering a range from 32.2 to 1.9 cm in water, respectively. Absolute dose measurements were within 3% when comparing TPS and experimental data. Gamma pass rates >98% and >96% at 3%/3 mm were obtained when performing 2D dose measurements in homogeneous and in heterogeneous media, respectively. Leaf position was within ±1 mm at all gantry angles and nozzle positions. CONCLUSIONS: Beam characterisation and machine commissioning results, and the exhaustive end-to-end tests performed to assess the proper functionality of the system, confirm that it is safe and accurate to treat patients. ADVANCES IN KNOWLEDGE: This is the first paper addressing the beam commissioning and the beam validation of a compact, gantry-mounted, pencil beam scanning proton accelerator system with dynamic layer-by-layer multileaf collimation.


Assuntos
Ciclotrons , Terapia com Prótons/instrumentação , Absorção de Radiação , Ar , Calibragem , Certificação , Desenho de Equipamento , Humanos , Países Baixos , Imagens de Fantasmas , Terapia com Prótons/métodos , Radiometria/métodos , Reprodutibilidade dos Testes , Água
10.
Int J Radiat Biol ; 96(1): 22-34, 2020 01.
Artigo em Inglês | MEDLINE | ID: mdl-30605362

RESUMO

Purpose: In a significant nuclear event, hundreds of thousands of individuals will require rapid triage for absorbed radiation to ensure effective medical treatment and efficient use of medical resources. We are developing a rapid screening method to assess whether an individual received an absorbed dose of ≥2 Gy based on the analysis of a specific panel of blood proteins in a fingerstick blood sample.Materials and methods: We studied a data set of 1051 human blood samples obtained from radiotherapy patients, normal healthy individuals, and several special population groups. We compared the findings in humans with those from irradiation studies in non-human primates (NHPs).Results: We identified a panel of three protein biomarkers, salivary alpha amylase (AMY1), Flt3 ligand (FLT3L), and monocyte chemotactic protein 1 (MCP1), which are upregulated in human patients receiving fractionated doses of total body irradiation (TBI) therapy as a treatment for cancer. These proteins exhibited a similar radiation response in NHPs after single acute or fractionated doses of ionizing radiation.Conclusion: Our work provides confidence in this biomarker panel for biodosimetry triage using fingerstick blood samples and in the use of NHPs as a model for irradiated humans.


Assuntos
Proteínas Sanguíneas/análise , Radiometria/métodos , Triagem/métodos , Adolescente , Adulto , Idoso , Animais , Biomarcadores/sangue , Criança , Feminino , Humanos , Imunoensaio , Macaca mulatta , Masculino , Pessoa de Meia-Idade , Adulto Jovem
11.
Int J Radiat Biol ; 96(1): 35-46, 2020 01.
Artigo em Inglês | MEDLINE | ID: mdl-30394814

RESUMO

Purpose: There is a need to rapidly triage individuals for absorbed radiation dose following a significant nuclear event. Since most exposed individuals will not have physical dosimeters, we are developing a method to assess exposure dose based on the analysis of a specific panel of blood proteins that can be easily obtained from a fingerstick blood sample.Materials and methods: In three large non-human primate (NHP) studies, animals were exposed to single acute total body doses of x-ray or gamma radiation. A total of 895 blood samples were obtained at baseline and for 7 days after exposure, to evaluate the temporal progression of markers in each of 10 animals (5M/5F) in six dose groups receiving 0-10 Gy. We used tandem mass spectrometry and immunoassay techniques to identify radiation-responsive proteins in blood plasma samples.Results: A blood protein biomarker panel was developed based on analysis of blood plasma samples obtained from several irradiation studies in NHPs that aimed to simulate acute radiation injury in humans from a nuclear exposure event. Panels of several subsets of proteins were shown to accurately classify plasma samples into two exposure groups either above or below a critical dose threshold with sensitivities and specificities exceeding 90%.Conclusion: This study lays the groundwork for developing a radiation biodosimetry triage tool. Our results in NHPs must be compared with those in human patients undergoing radiotherapy to determine if the biomarker panel proteins exhibit a similar radiation response and allow adequate classification power in humans.


Assuntos
Proteínas Sanguíneas/análise , Sistemas Automatizados de Assistência Junto ao Leito , Radiometria/métodos , Animais , Biomarcadores/análise , Testes Hematológicos , Imunoensaio , Macaca mulatta , Fatores de Tempo
12.
Int J Radiat Biol ; 96(1): 57-66, 2020 01.
Artigo em Inglês | MEDLINE | ID: mdl-30507310

RESUMO

PURPOSE: We introduce and evaluate a high throughput biodosimetry test system (REDI-Dx) suitable for testing of thousands of potential radiation victims following a mass scale nuclear event caused by detonation of a nuclear device or a nuclear accident, as part of an overall strategy for effective medical management of the crisis. MATERIALS AND METHODS: The performance of a high throughput biodosimetry test was evaluated by collecting samples of both non-irradiated presumed healthy donors as well as irradiated subjects collected as part of either cancer treatment regimens or banked from previous studies. The test measures the gene expression of a set of radiation responsive genes based on the DxDirect® genomic platform. The potential diagnostic accuracy of REDI-Dx was evaluated as a predictor of actual dose of radiation. While the REDI-Dx test has been calibrated to provide a quantitative measure of actual absorbed dose, we compared the performance of the REDI-Dx test (sensitivity and specificity) as a qualitative result at the most commonly applied thresholds 2.0 Gy and 6.0 Gy. RESULTS: The test demonstrated high specificity and lack of effect of medical conditions. Using receiver operating characteristic (ROC) curve analysis, REDI-Dx was shown to be a good predictor of actual dose for determining treatment category based on either 2.0 or 6.0 Gy, with a 98.5% sensitivity and 90% specificity for 2.0 Gy, and 92% sensitivity and 84% specificity for 6.0 Gy. Results were reproducible between clinical laboratories with an SD of 0.2 Gy for samples ≤2.0 Gy and a CV of 10.3% for samples from 2.0 to 10.0 Gy. CONCLUSIONS: Use of a biodosimetry test, like REDI-Dx test system would provide valuable information that would improve the ability to assign patients to the correct treatment category when combined with currently available biodosimetry tools, as compared to the use of existing tools alone. The REDI-Dx biodosimetry test system is for investigational use only in the U.S.A. The performance characteristics of this product have not been established.


Assuntos
Seleção de Pacientes , Lesões por Radiação/terapia , Liberação Nociva de Radioativos , Relação Dose-Resposta à Radiação , Humanos , Linfócitos/efeitos da radiação , Lesões por Radiação/complicações , Lesões por Radiação/etiologia , Radiometria , Vômito/complicações
13.
Br J Radiol ; 93(1106): 20190535, 2020 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-31846347

RESUMO

OBJECTIVES: Radiotherapy plan quality may vary considerably depending on planner's experience and time constraints. The variability in treatment plans can be assessed by calculating the difference between achieved and the optimal dose distribution. The achieved treatment plans may still be suboptimal if there is further scope to reduce organs-at-risk doses without compromising target coverage and deliverability. This study aims to develop a knowledge-based planning (KBP) model to reduce variability of volumetric modulated arc therapy (VMAT) lung plans by predicting minimum achievable lung volume-dose metrics. METHODS: Dosimetric and geometric data collected from 40 retrospective plans were used to develop KBP models aiming to predict the minimum achievable lung dose metrics via calculating the ratio of the residual lung volume to the total lung volume. Model accuracy was verified by replanning 40 plans. Plan complexity metrics were calculated using locally developed script and their effect on treatment delivery was assessed via measurement. RESULTS: The use of KBP resulted in significant reduction in plan variability in all three studied dosimetric parameters V5, V20 and mean lung dose by 4.9% (p = 0.007, 10.8 to 5.9%), 1.3% (p = 0.038, 4.0 to 2.7%) and 0.9 Gy (p = 0.012, 2.5 to 1.6Gy), respectively. It also increased lung sparing without compromising the overall plan quality. The accuracy of the model was proven as clinically acceptable. Plan complexity increased compared to original plans; however, the implication on delivery errors was clinically insignificant as demonstrated by plan verification measurements. CONCLUSION: Our in-house model for VMAT lung plans led to a significant reduction in plan variability with concurrent decrease in lung dose. Our study also demonstrated that treatment delivery verifications are important prior to clinical implementation of KBP models. ADVANCES IN KNOWLEDGE: In-house KBP models can predict minimum achievable lung dose-volume constraints for advance-stage lung cancer patients treated with VMAT. The study demonstrates that plan complexity could increase and should be assessed prior to clinical implementation.


Assuntos
Neoplasias Pulmonares/radioterapia , Radioterapia de Intensidade Modulada/métodos , Humanos , Bases de Conhecimento , Modelos Biológicos , Órgãos em Risco , Radiometria , Dosagem Radioterapêutica , Planejamento da Radioterapia Assistida por Computador/métodos , Estudos Retrospectivos
14.
Bioelectromagnetics ; 41(1): 3-20, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31854006

RESUMO

Wireless wearable and implantable devices are continuing to grow in popularity, and as this growth occurs, so too does the need to consider the safety of such devices. Wearable and implantable devices require the transmitting and receiving of electromagnetic waves near and through the body, which at high enough exposure levels may damage proximate tissues. The specific absorption rate (SAR) is the quantity commonly used to enumerate exposure levels, and various national and international organizations have defined regulations limiting exposure to ensure safe operation. In this paper, we comprehensively review dosimetric studies reported in the literature up to the year 2019 for wearables and implants. We discuss antenna designs for wearables and implants as they relate to SAR values and field and thermal distributions in tissue, present designs that have made steps to reduce SAR, and then review SAR considerations as they relate to applied devices. As compared with previous review papers, this paper is the first review to focus on dosimetry aspects relative to wearable and implantable devices. Bioelectromagnetics. 2020;41:3-20 © 2019 The Authors. Bioelectromagnetics published by Wiley Periodicals, Inc.


Assuntos
Radiometria/instrumentação , Tecnologia sem Fio/instrumentação , Campos Eletromagnéticos , Humanos , Músculo Esquelético/efeitos da radiação , Próteses e Implantes , Exposição à Radiação/análise , Temperatura Ambiente , Dispositivos Eletrônicos Vestíveis
15.
Int J Radiat Oncol Biol Phys ; 106(1): 206-215, 2020 01 01.
Artigo em Inglês | MEDLINE | ID: mdl-31627178

RESUMO

PURPOSE: The current magnetic resonance imaging-computed tomography (MRI-CT) fusion-based workflow for postimplant dosimetry of low-dose-rate (LDR) prostate brachytherapy takes advantage of the superior soft tissue contrast of MRI, but still relies on CT for seed visualization and detection. Recently an MR-only workflow has been proposed that employs standard MR sequences and visualizes conventional implanted seed with positive contrast solely through MR postprocessing. In this work, the novel MR-only based workflow is compared with the clinical CT-MRI fusion approach. METHODS AND MATERIALS: Twenty-four prostate patients with a total of 1775 implanted LDR seeds were scanned using a 3-dimensional multiecho gradient echo sequence on a 3 Tesla MR scanner within 30 days after implantation. Quantitative susceptibility mapping was used for seed visualization. Seeds were automatically segmented and localized on the quantitative susceptibility mapping using convolutional neural network and k-means clustering, respectively. To assess the MR-only seed localization error, CT and MR-derived seed positions were coregistered, and ultimately, the resulting dose-volume histograms were compared. RESULTS: The MR-based seed visualization, segmentation, and localization generated comparable results to the CT-MR registration approach. The accuracy of the MRI-only based seed identification was 99.1%. After a rigid registration between the MR and CT-derived seed centroids, the average localization error was 0.8 ± 0.8 mm. The average prostate D90, V100, V150, and V200 for MRI-only and CT-MR fusion based dosimetry were 114.3 ± 12.5% versus 113.9 ± 11.9%, 95.1 ± 3.7% versus 95.3 ± 3.8%, 54.5 ± 14.5% versus 55.0 ± 13.2% and 22.9 ± 6.8% versus 23.2 ± 6.7%, respectively. No significant differences were observed in 3-dimensional seed positions and dosimetric parameters between MR-only and CT-MR fusion-based workflows (P > 0.2). CONCLUSIONS: The MRI-only LDR postimplant dosimetry is feasible and has very good potential to eliminate the need for CT-based seed identification.


Assuntos
Braquiterapia/métodos , Imagem por Ressonância Magnética , Imagem Multimodal/métodos , Neoplasias da Próstata/diagnóstico por imagem , Neoplasias da Próstata/radioterapia , Tomografia Computadorizada por Raios X , Fluxo de Trabalho , Algoritmos , Braquiterapia/instrumentação , Estudos de Viabilidade , Gases , Humanos , Radioisótopos do Iodo/administração & dosagem , Masculino , Neoplasias da Próstata/patologia , Radiometria/métodos , Reto/diagnóstico por imagem , Fatores de Tempo
16.
Br J Radiol ; 93(1107): 20190469, 2020 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-31860338

RESUMO

Proton arc therapy (PAT) has been proposed as a possible evolution for proton therapy. This commentary uses dosimetric and cancer risk evaluations from earlier studies to compare PAT with intensity modulated proton therapy. It is concluded that, although PAT may not produce better physical dose distributions than intensity modulated proton therapy, the radiobiological considerations associated with particular PAT techniques could offer the possibility of an increased therapeutic index.


Assuntos
Terapia com Prótons/métodos , Radioterapia de Intensidade Modulada/métodos , Índice Terapêutico , Humanos , Neoplasias Pulmonares/radioterapia , Órgãos em Risco/efeitos da radiação , Hipofracionamento da Dose de Radiação , Radiobiologia , Radiometria/métodos , Dosagem Radioterapêutica , Eficiência Biológica Relativa , Incerteza
17.
Br J Radiol ; 93(1107): 20190412, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-31868525

RESUMO

Proton therapy has shown dosimetric advantages over conventional radiation therapy using photons. Although the integral dose for patients treated with proton therapy is low, concerns were raised about late effects like secondary cancer caused by dose depositions far away from the treated area. This is especially true for neutrons and therefore the stray dose contribution from neutrons in proton therapy is still being investigated. The higher biological effectiveness of neutrons compared to photons is the main cause of these concerns. The gold-standard in neutron dosimetry is measurements, but performing neutron measurements is challenging. Different approaches have been taken to overcome these difficulties, for instance with newly developed neutron detectors. Monte Carlo simulations is another common technique to assess the dose from secondary neutrons. Measurements and simulations are used to develop analytical models for fast neutron dose estimations. This article tries to summarize the developments in the different aspects of neutron dose in proton therapy since 2017. In general, low neutron doses have been reported, especially in active proton therapy. Although the published biological effectiveness of neutrons relative to photons regarding cancer induction is higher, it is unlikely that the neutron dose has a large impact on the second cancer risk of proton therapy patients.


Assuntos
Neoplasias Induzidas por Radiação/etiologia , Segunda Neoplasia Primária/etiologia , Nêutrons/efeitos adversos , Terapia com Prótons/métodos , Humanos , Método de Monte Carlo , Fótons/uso terapêutico , Terapia com Prótons/efeitos adversos , Radiometria/instrumentação , Radiometria/métodos , Dosagem Radioterapêutica , Eficiência Biológica Relativa
18.
J Environ Radioact ; 211: 106075, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31627053

RESUMO

This paper discusses the development, comparison, and application of three anatomically representative computational phantoms for the grass species Andropogon virginicus, an indigenous grass species in the Southeastern United States. Specifically, the phantoms developed in this work are: (1) a stylized phantom where plant organs (roots or shoots) are represented by simple geometric shapes, (2) a voxel phantom developed from micro-CT imagery of a plant specimen, and (3) a hybrid phantom resulting from the refinement of (2) by use of non-uniform rational basis spline (NURBS) surfaces. For each computational phantom, Monte Carlo dosimetric modeling was utilized to determine whole-organism and organ specific dose coefficients (DC) associated with external and internal exposure to 99Tc, 137Cs, 237Np, and 238U for A. virginicus. Model DCs were compared to each other and to current values for the ICRP reference wild grass in order to determine if noteworthy differences resulted from the utilization of more anatomically realistic phantom geometry. Modeled internal DCs were comparable with ICRP values. However, modeled external DCs were more variable with respect to ICRP values; this is proposed to be primarily due to differences in organism and source geometry definitions. Overall, the three anatomical phantoms were reasonably consistent. Some noticeable differences in internal DCs were observed between the stylized model and the voxel or hybrid models for external DCs for shoots and for cases of crossfire between plant organs. Additionally, uptake data from previous hydroponic (HP) experiments was applied in conjunction with hybrid model DCs to determine dose rates to the plant from individual radionuclides as an example of practical application. Although the models within are applied to a small-scale, hypothetical scenario as proof-of-principle, the potential, real-world utility of such complex dosimetric models for non-human biota is discussed, and a fit-for purpose approach for application of these models is proposed.


Assuntos
Andropogon , Radioisótopos de Césio , Método de Monte Carlo , Netúnio , Imagens de Fantasmas , Poaceae , Monitoramento de Radiação , Radiometria , Urânio
19.
Eur Radiol ; 30(1): 487-500, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31359122

RESUMO

PURPOSE: To assess the dose performance in terms of image quality of filtered back projection (FBP) and two generations of iterative reconstruction (IR) algorithms developed by the most common CT vendors. MATERIALS AND METHODS: We used four CT systems equipped with a hybrid/statistical IR (H/SIR) and a full/partial/advanced model-based IR (MBIR) algorithms. Acquisitions were performed on an ACR phantom at five dose levels. Raw data were reconstructed using a standard soft tissue kernel for FBP and one iterative level of the two IR algorithm generations. The noise power spectrum (NPS) and the task-based transfer function (TTF) were computed. A detectability index (d') was computed to model the detection task of a large mass in the liver (large feature; 120 HU and 25-mm diameter) and a small calcification (small feature; 500 HU and 1.5-mm diameter). RESULTS: With H/SIR, the highest values of d' for both features were found for Siemens, then for Canon and the lowest values for Philips and GE. For the large feature, potential dose reductions with MBIR compared with H/SIR were - 35% for GE, - 62% for Philips, and - 13% for Siemens; for the small feature, corresponding reductions were - 45%, - 78%, and - 14%, respectively. With the Canon system, a potential dose reduction of - 32% was observed only for the small feature with MBIR compared with the H/SIR algorithm. For the large feature, the dose increased by 100%. CONCLUSION: This multivendor comparison of several versions of IR algorithms allowed to compare the different evolution within each vendor. The use of d' is highly adapted and robust for an optimization process. KEY POINTS: • The performance of four CT systems was evaluated by using imQuest software to assess noise characteristic, spatial resolution, and lesion detection. • Two task functions were defined to model the detection task of a large mass in the liver and a small calcification. • The advantage of task-based image quality assessment for radiologists is that it does not include only complicated metrics, but also clinically meaningful image quality.


Assuntos
Interpretação de Imagem Radiográfica Assistida por Computador/métodos , Tomografia Computadorizada por Raios X/métodos , Algoritmos , Calcinose/diagnóstico por imagem , Humanos , Hepatopatias/diagnóstico por imagem , Neoplasias Hepáticas/diagnóstico por imagem , Imagens de Fantasmas , Garantia da Qualidade dos Cuidados de Saúde/métodos , Doses de Radiação , Interpretação de Imagem Radiográfica Assistida por Computador/normas , Radiometria/métodos , Cintilografia , Software , Tomografia Computadorizada por Raios X/normas
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