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ABFM NEWS - Física Médica Geral
Localized Low-Dose Radiotherapy for Follicular Lymphoma: History, Clinical Results, Mechanisms of Action, and Future Outlooks
The extreme radiosensitivity of indolent lymphomas was reported in the early years of radiotherapy (RT). The efficacy of low-dose total body irradiation (1.5–2 Gy) was particularly demonstrative. Higher doses were considered appropriate for localized disease. The optimal (or conventional) dose of curative RT derived from the early studies was determined to be 30–35 Gy. Nevertheless, in older series addressing the tumoricidal radiation dose in non-Hodgkin|s lymphomas, investigators noted that a significant number of “nodular” lymphomas were controlled with a dose of <22 Gy for >3 years. The idea of reintroducing localized low-dose radiotherapy (LDRT) for indolent non-Hodgkin|s lymphomas came from a clinical observation. The first study showing the high efficacy of LDRT (4 Gy in two fractions of 2 Gy within 3 days) in selected patients with chemoresistant, indolent, non-Hodgkin|s lymphomas was published in 1994. Since this first report, at least eight series of patients treated with localized LDRT have been published, showing a 55% complete response rate in irradiated sites, with a median duration of 15–42 months. How LDRT induces lymphoma cell death remains partly unknown. However, some important advances have recently been reported. Localized LDRT induces an apoptosis of follicular lymphoma cells. This apoptotic cell death elicits an immune response mediated by macrophages and dendritic cells. Follicular lymphoma is probably an ideal model to explore these mechanisms. This review also discusses the future of LDRT for follicular lymphoma. [+ leia mais]
Fonte: International Journal of Radiation Oncology*Biolog
Spectral perturbations from silicon diode detector encapsulation and shielding in photon fields
" Purpose: Silicon diodes are widely used as detectors for relative dose measurements in radiotherapy. The common manufacturing practice is to encapsulate the diodes in plastic for protection and to facilitate mounting in scanning devices. Diodes intended for use in photon fields commonly also have a shield of a high atomic number material (usually tungsten) integrated into the encapsulation to selectively absorb low-energy photons to which silicon diodes would otherwise over-response. However, new response models based on cavity theories and spectra calculations have been proposed for direct correction of the readout from unshielded (e.g., “electron”) diodes used in photon fields. This raises the question whether it is correct to assume that the spectrum in a water phantom at the location of the detector cavity is not perturbed by the detector encapsulation materials. The aim of this work is to investigate the spectral effects of typical encapsulations, including shielding, used for clinical diodes. Methods: The effects of detector encapsulation of an unshielded and a shielded commercial diode on the spectra at the detector cavity location are studied through Monte Carlo simulations with PENELOPE-2005. Variance reduction based on correlated sampling is applied to reduce the CPU time needed for the simulations. Results: The use of correlated sampling is found to be efficient and to not introduce any significant bias to the results. Compared to reference spectra calculated in water, the encapsulation for an unshielded diode is demonstrated to not perturb the spectrum, while a tungsten shielded diode caused not only the desired decrease in low-energy scattered photons but also a large increase of the primary electron fluence. Measurements with a shielded diode in a 6 MV photon beam proved that the shielding does not completely remove the field-size dependence of the detector response caused by the over-response from low-energy photons. Response factors of a properly corrected unshielded diode were shown to give comparable, or better, results than the traditionally used shielded diode. Conclusions: Spectra calculated for photon fields in water can be directly used for modeling the response of unshielded silicon diodes with plastic encapsulations. Unshielded diodes used together with appropriate corrections can replace shielded diodes in photon dose measurements. © 2010 American Association of Physicists in Medicine " [+ leia mais]
Colaborador: Laura Natal
Fonte: Medical Physics
Breast Patient Setup Error Assessment: Comparison of Electronic Portal Image Devices and Cone-Beam Computed Tomography Matching Results
"Purpose To quantify the differences in setup errors measured with the cone-beam computed tomography (CBCT) and electronic portal image devices (EPID) in breast cancer patients. Methods and Materials Repeat CBCT scan were acquired for routine offline setup verification in 20 breast cancer patients. During the CBCT imaging fractions, EPID images of the treatment beams were recorded. Registrations of the bony anatomy for CBCT to planning CT and EPID to digitally reconstructed-radiographs (DRRs) were compared. In addition, similar measurements of an anthropomorphic thorax phantom were acquired. Bland-Altman and linear regression analysis were performed for clinical and phantom registrations. Systematic and random setup errors were quantified for CBCT and EPID-driven correction protocols in the EPID coordinate system (U, V), with V parallel to the cranial-caudal axis and U perpendicular to V and the central beam axis. Results Bland-Altman analysis of clinical EPID and CBCT registrations yielded 4 to 6-mm limits of agreement, indicating that both methods were not compatible. The EPID-based setup errors were smaller than the CBCT-based setup errors. Phantom measurements showed that CBCT accurately measures setup error whereas EPID underestimates setup errors in the cranial–caudal direction. In the clinical measurements, the residual bony anatomy setup errors after offline CBCT-based corrections were ΣU = 1.4 mm, ΣV = 1.7 mm, and σU = 2.6 mm, σV = 3.1 mm. Residual setup errors of EPID driven corrections corrected for underestimation were estimated at ΣU = 2.2mm, ΣV = 3.3 mm, and σU = 2.9 mm, σV = 2.9 mm. Conclusion EPID registration underestimated the actual bony anatomy setup error in breast cancer patients by 20% to 50%. Using CBCT decreased setup uncertainties significantly. Author Keywords: Setup verification; Electronic portal image device (EPID); Cone-beam computed tomography (CBCT); Image-guided radiotherapy (IGRT); Breast cancer " [+ leia mais]
Fonte: Int. Journal of Radiation Oncology Biology and Phy
“SABER”: A new software tool for radiotherapy treatment plan evaluation
"Purpose: Both spatial and biological information are necessary in order to perform true optimization of a treatment plan and for predicting clinical outcome. The goal of this work is to develop an enhanced treatment plan evaluation tool which incorporates biological parameters and retains spatial dose information. Methods: A software system is developed which provides biological plan evaluation with a novel combination of features. It incorporates hyper-radiosensitivity using the induced-repair model and applies the new concept of dose convolution filter (DCF) to simulate dose wash-out effects due to cell migration, bystander effect, and/or tissue motion during treatment. Further, the concept of spatial DVH (sDVH) is introduced to evaluate and potentially optimize the spatial dose distribution in the target volume. Finally, generalized equivalent uniform dose is derived from both the physical dose distribution (gEUD) and the distribution of equivalent dose in 2 Gy fractions (gEUD2) and the software provides three separate models for calculation of tumor control probability (TCP), normal tissue complication probability (NTCP), and probability of uncomplicated tumor control (P+). TCP, NTCP, and P+ are provided as a function of prescribed dose and multivariable TCP, NTCP, and P+ plots are provided to illustrate the dependence on individual parameters used to calculate these quantities. Ten plans from two clinical treatment sites are selected to test the three calculation models provided by this software. Results: By retaining both spatial and biological information about the dose distribution, the software is able to distinguish features of radiotherapy treatment plans not discernible using commercial systems. Plans that have similar DVHs may have different spatial and biological characteristics and the application of novel tools such as sDVH and DCF within the software may substantially change the apparent plan quality or predicted plan metrics such as TCP and NTCP. For the cases examined, both the calculation method and the application of DCF can change the ranking order of competing plans. The voxel-by-voxel TCP model makes it feasible to incorporate spatial variations of clonogen densities (n), radiosensitivities (SF2), and fractionation sensitivities (α/β) as those data become available. Conclusions: The new software incorporates both spatial and biological information into the treatment planning process. The application of multiple methods for the incorporation of biological and spatial information has demonstrated that the order of application of biological models can change the order of plan ranking. Thus, the results of plan evaluation and optimization are dependent not only on the models used but also on the order in which they are applied. This software can help the planner choose more biologically optimal treatment plans and potentially predict treatment outcome more accurately. " [+ leia mais]
Fonte: Medical Physics
Low molecular weight heat shock protein HSP27 is a prognostic indicator in rectal cancer but not colon cancer
"Objective There are currently no biomarkers in routine clinical use for determining prognosis in rectal cancer. In a preliminary proteomic study, variation in the levels of heat shock protein 27 (HSP27) in colorectal cancer samples was observed. The expression of HSP27 in a cohort of 404 patients with colorectal cancer with a predominantly poor prognosis was characterised and an investigation was undertaken of whether the differences were related to clinical outcome. HSP27 levels in diagnostic rectal biopsies were compared with matched surgical samples to determine whether changes in expression occurred in the time between biopsy and surgery and to investigate whether preoperative radiotherapy affected expression. Finally, the relationship between HSP27 expression and outcome was examined in an independent cohort of 315 patients with a predominantly good prognosis. Methods HSP27 levels were determined using combined two-dimensional gel electrophoresis and tandem mass spectrometry (12 cases) and by immunohistochemistry using tissue microarrays of colorectal cancers sampled at surgery and 80 diagnostic rectal biopsies. Results HSP27 overexpression was strongly associated with poor cancer-specific survival in rectal cancer (n=205, p=0.0063) but not colon cancer (n=199, p=0.7385) in the cohort with a poor prognosis. Multivariate Cox regression confirmed nodal metastases (p=0.0001) and HSP27 expression (p=0.0233) as independent markers of survival in rectal cancer. HSP27 levels remained unchanged in the majority of cases (65/80, 81%) between diagnostic biopsies and matched surgical samples, regardless of whether patients had undergone preoperative radiotherapy. In the cohort with a good prognosis the association between HSP27 and survival was not observed in patients with either rectal (n=115; p=0.308) or colon cancer (n=200; p=0.713). Conclusion In a large cohort of patients with a poor prognosis, HSP27 is an independent marker of poor outcome in rectal cancer; its expression is not altered by neoadjuvant radiotherapy. This finding requires validation in an independent similar cohort of patients with rectal cancer. HSP27 levels merit evaluation as a stratification factor for treatment of rectal cancer. " [+ leia mais]
Fonte: GUT An Int. J. of Gastroenterology and Hepatology
A radiotherapy planning study of RapidArc, intensity modulated radiotherapy, three-dimensional conformal radiotherapy, and parallel opposed beams in t
"Abstract BACKGROUND: This planning study compared RapidArc, fixed-field IMRT (cIMRT), 3D conformal radiotherapy (3D-CRT), and a parallel-opposed pair (POP) for children with retroperitoneal tumors. PROCEDURE: Plans were generated in eight patients to treat the PTV (dose range 19.8-45 Gy) while limiting kidney and liver doses. In selected patients, vertebral body (VB) dose heterogeneity was minimized. Cumulative DVH parameters, monitor units (MU), and treatment times were compared for the four techniques using the Wilcoxon matched pairs test. RESULTS: RapidArc and cIMRT covered target volumes more conformally than 3D-CRT and POP (P = 0.012). There was no difference in the ability to meet kidney dose constraints. A significantly lower volume of the liver received 12 Gy with cIMRT or RapidArc compared with 3D-CRT (P = 0.028). Where VB was included in PTV, VB dose homogeneity was generally within 94-104% of the prescription dose. Time to deliver a single fraction with RapidArc, POP, 3D-CRT, and cIMRT was 1.25 ± 0.01, 1.38 ± 0.10, 2.6 ± 0.45, and 4.02 ± 1.12 min, respectively (P = 0.012). Monitor units for a single fraction with POP, 3D-CRT, RapidArc, and cIMRT were 203 ± 26, 235 ± 32, 325 ± 71, and 665 ± 215, respectively (P < 0.05). CONCLUSIONS: POP resulted in favorable MU, treatment time and dosimetry but had poor conformality. 3D-CRT was more conformal but had higher MU and treatment time. RapidArc and cIMRT were generally no better dosimetrically than conformal techniques. RapidArc was dosimetrically very similar to cIMRT, but resulted in a major reduction in time and MU used to deliver the radiation. Pediatr Blood Cancer. " [+ leia mais]
Fonte: Pediatric Blood & Cancer
Large volume unresectable locally advanced non-small cell lung cancer: acute toxicity and initial outcome results with Rapid Arc
"Background To report acute toxicity, initial outcome results and planning therapeutic parameters in radiation treatment of advanced lung cancer (stage III) with volumetric modulated arcs using RapidArc (RA). Methods Twenty-four consecutive patients were treated with RA. All showed locally advanced non-small cell lung cancer with stage IIIA-IIIB and with large volumes (GTV:299+/-175cm3, PTV:818+/-206cm3). Dose prescription was 66Gy in 33 fractions to mean PTV. Delivery was performed with two partial arcs with a 6MV photon beam. Results From a dosimetric point of view, RA allowed us to respect most planning objectives on target volumes and organs at risk. In particular: for GTV D1%=105.6+/-1.7%, D99%=96.7+/-1.8%, D5%-D95%=6.3+/-1.4%; contra-lateral lung mean dose resulted in 13.7+/-3.9Gy, for spinal cord D1%=39.5+/-4.0Gy, for heart V45Gy=9.0+/-7.0Gy, for esophagus D1%=67.4+/-2.2Gy. Delivery time was 133+/-7s. At three months partial remission >50% was observed in 56% of patients. Acute toxicities at 3 months showed 91% with grade 1 and 9% with grade 2 esophageal toxicity; 18% presented grade 1 and 9% with grade 2 pneumonia; no grade 3 acute toxicity was observed. The short follow-up does not allow assessment of local control and progression free survival. Conclusions RA proved to be a safe and advantageous treatment modality for NSCLC with large volumes. Long term observation of patients is needed to assess outcome and late toxicity. " [+ leia mais]
Fonte: Radiation Oncology
Proteção Radiológica
Fonte: SEPR
"Optimizing non-Pb radiation shielding materials using bilayers"
"Purpose: The objective of this study was to demonstrate that the weight of non-Pb radiation shielding materials can be minimized by structuring the material as a bilayer composed of different metal-powder-embedded elastomer layers. " [+ leia mais]
Colaborador: Érika Yumi Watanabe
Fonte: Medical Physics
Adult Reference Computational Phantoms
This report describes the development and intended use of the computational phantoms [+ leia mais]
Colaborador: Laura Natal Rodrigues
Fonte: ICRP
Literature - Radiation Protection of Patients
Radiation Protection of Patients [+ leia mais]
Colaborador: Laura Natal Rodrigues
Fonte: IAEA
Radiation Protection of Patients [+ leia mais]
Colaborador: Laura Natal Rodrigues
Fonte: IAEA
Initial investigation on the use of MR spectroscopy and micro-MRI of GAFCHROMIC® EBT radiotherapy film.
This article presents an initial investigation of the efficacy of using 1H MRS and micro-MRI as analysis techniques for irradiated GAFCHROMIC EBT® radiotherapy films. [+ leia mais]
Colaborador: Laura Natal Rodrigues.
Fonte: Medical Physics.
Reliable Domestic & Global Supplier of Molybdenum-99 (Mo-99) and Switch from Highly Enriched Uranium (HEU) to Low-Enriched Uranium (LEU) to Produce...
Reliable Domestic & Global Supplier of Molybdenum-99 (Mo-99) and Switch from Highly Enriched Uranium (HEU) to Low-Enriched Uranium (LEU) to Produce Mo-99. A White Paper by a Coalition of Professional Organizations, 10 July 2009. [+ leia mais]
Colaborador: Laura Natal Rodrigues.
Fonte: AAPM.
Monte Carlo dose mapping on deforming anatomy.
This paper proposes a Monte Carlo-based energy and mass congruent mapping (EMCM) method to calculate the dose on deforming anatomy. Different from dose interpolation methods, EMCM separately maps each voxel|s deposited energy and mass from a source image to a reference image with a displacement vector field (DVF) generated by deformable image registration (DIR). [+ leia mais]
Colaborador: Camila Pessoa de Sales.
Fonte: Physics in Medicine and Biology.
The estimation of 3D SAR distributions in the human head from mobile phone compliance testing data for epidemiological studies.
A worldwide epidemiological study called |INTERPHONE| has been conducted to estimate the hypothetical relationship between brain tumors and mobile phone use. In this study, we proposed a method to estimate 3D distribution of the specific absorption rate (SAR) in the human head due to mobile phone use to provide the exposure gradient for epidemiological studies. [+ leia mais]
Colaborador: Camila Pessoa de Sales.
Fonte: Physics in Medicine and Biology.
IOMP Science Committee Bibliographic database: Radiation Safety.
A set of references has been developed by the IOMP Science Committee covering the medical physics aspect of radiation therapy, medical imaging, nuclear medicine, and radiation safety. [+ leia mais]
Colaborador: Laura Natal Rodrigues.
Fonte: IOMP.
EMITEL: Encyclopaedia of Medical Physics and Mutilingual Dictionary of Terms.
EMITEL is product of an EU project including: King’s College London (Contractor and Coordinator) and King’s College Hospital (UK), University of Lund and Lund University Hospital (Sweden), University of Florence (Italy), AM Studio (Software company, Bulgaria) and the International Organization for Medical Physics (IOMP). [+ leia mais]
Colaborador: Laura Natal Rodrigues.
Fonte: IOMP.
Clasificación de las fuentes radiactivas.
Guía de seguridad No. RS-G-1.9. [+ leia mais]
Colaborador: Laura Natal Rodrigues.
Fonte: AIEA.
Managing Human Resources in the field of nuclear energy.
"The nuclear field, comprising industry, government authorities, regulators, R&D organizations and educational institutions, relies heavily on a specialized, highly trained and motivated workforce for its sustainability." [+ leia mais]
Colaborador: Laura Natal Rodrigues.
Fonte: AIEA.
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