The diagnostic value of conventional radiography and musculoskeletal ultrasonography in calcium pyrophosphate deposition disease: a systematic literature review and meta-analysis.

OBJECTIVE: To examine and compare the accuracy of conventional radiography (CR) and musculoskeletal ultrasonography (US) in the diagnosis of calcium pyrophosphate (CPP) crystals deposition disease (CPPD). DESIGN: A systematic search of electronic databases (PubMed, Embase, and Cochrane), conference abstracts and reference lists was undertaken. Studies which evaluated the accuracy of CR and/or US in the diagnosis of CPPD, using synovial fluid analysis (SFA), histology or classification criteria as reference tests were included. Subgroup analyses by anatomic site and by reference test were performed. RESULTS: Twenty-six studies were included. Using SFA/histology as reference test, CR and US showed an excellent (CR AUC = 0.889, 95%CI = 0.811-0.967) and an outstanding (US AUC = 0.954, 95%CI = 0.907-1.0) diagnostic accuracy (p < 0.01), respectively. Furthermore, US showed a higher sensitivity (0.85, 95%CI = 0.79-0.90 vs 0.47, 95%CI = 0.40-0.55) and only a little lower specificity (0.87, 95%CI = 0.83-0.91 vs 0.95, 95%CI = 0.92-0.97) than CR. A considerable heterogeneity between the studies was found, with adopted reference test being the main source of heterogeneity. In fact, subgroup analysis showed a significant change in the diagnostic accuracy of CR, but not of US, using Ryan and McCarty criteria or SFA/histology as reference test (CR: AUC = 0.956, 95%CI = 0.925-1.0 vs AUC = 0.889, 95%CI = 0.828-0.950, respectively, p < 0.01) (US: AUC = 0.922, 95%CI = 0.842-1.0 vs AUC = 0.957, 95%CI = 0.865-1.0, respectively, p = 0.08) CONCLUSIONS: Although US is more sensitive and a little less specific than CR for identifying CPP crystals, both these two techniques showed a great diagnostic accuracy and should be regarded as complementary to each other in the diagnostic work-up of patients with CPPD.

[Indications and limits of ablative therapies in prostate cancer]. / Indications et limites actuelles des traitements ablatifs dans le cancer de la prostate.

OBJECTIVE: To perform a state of the art about indications and limits of ablative therapies for localized prostate cancer. METHODS: A review of the scientific literature was performed in Medline database (http://www.ncbi.nlm.nih.gov) and Embase (http://www.embase.com) using different associations of keywords. Publications obtained were selected based on methodology, language and relevance. After selection, 107 articles were analysed. RESULTS: The objective to combine reduction of side effects and oncological control has induced recent development of several ablative therapies. Beyond this heterogeneity, some preferential indications appear: unilateral cancer of low risk (but with significant volume, excluding active surveillance) or intermediate risk (excluding majority of grade 4); treatment targeted the index lesion, by quarter or hemi-ablation, based on biopsy and mpMRI. In addition, indications must considered specific limits of each energy, such as gland volume and tumor localization. CONCLUSION: Based on new imaging and biopsy, ablative therapies will probably increased its role in the future in management of localize prostate cancer. The multiple ongoing trials will certainly be helpful to better define their indications and limits.

Automatic landmark generation for deformable image registration evaluation for 4D CT images of lung.

Deformable image registration (DIR) has become a common tool in medical imaging across both diagnostic and treatment specialties, but the methods used offer varying levels of accuracy. Evaluation of DIR is commonly performed using manually selected landmarks, which is subjective, tedious and time consuming. We propose a semi-automated method that saves time and provides accuracy comparable to manual selection. Three landmarking methods including manual (with two independent observers), scale invariant feature transform (SIFT), and SIFT with manual editing (SIFT-M) were tested on 10 thoracic 4DCT image studies corresponding to the 0% and 50% phases of respiration. Results of each method were evaluated against a gold standard (GS) landmark set comparing both mean and proximal landmark displacements. The proximal method compares the local deformation magnitude between a test landmark pair and the closest GS pair. Statistical analysis was done using an intra class correlation (ICC) between test and GS displacement values. The creation time per landmark pair was 22, 34, 2.3, and 4.3 s for observers 1 and 2, SIFT, and SIFT-M methods respectively. Across 20 lungs from the 10 CT studies, the ICC values between the GS and observer 1 and 2, SIFT, and SIFT-M methods were 0.85, 0.85, 0.84, and 0.82 for mean lung deformation, and 0.97, 0.98, 0.91, and 0.96 for proximal landmark deformation, respectively. SIFT and SIFT-M methods have an accuracy that is comparable to manual methods when tested against a GS landmark set while saving 90% of the time. The number and distribution of landmarks significantly affected the analysis as manifested by the different results for mean deformation and proximal landmark deformation methods. Automatic landmark methods offer a promising alternative to manual landmarking, if the quantity, quality and distribution of landmarks can be optimized for the intended application.

The effective dose of different scanning protocols using the Sirona GALILEOS(®) comfort CBCT scanner.

OBJECTIVES: To determine the effective dose and CT dose index (CTDI) for a range of imaging protocols using the Sirona GALILEOS(®) Comfort CBCT scanner (Sirona Dental Systems GmbH, Bensheim, Germany). METHODS: Calibrated optically stimulated luminescence dosemeters were placed at 26 sites in the head and neck of a modified RANDO(®) phantom (The Phantom Laboratory, Greenwich, NY). Effective dose was calculated for 12 different scanning protocols. CTDI measurements were also performed to determine the dose-length product (DLP) and the ratio of effective dose to DLP for each scanning protocol. RESULTS: The effective dose for a full maxillomandibular scan at 42 mAs was 102 ± 1 µSv and remained unchanged with varying contrast and resolution settings. This compares with 71 µSv for a maxillary scan and 76 µSv for a mandibular scan with identical milliampere-seconds (mAs) at high contrast and resolution settings. CONCLUSIONS: Changes to mAs and beam collimation have a significant influence on effective dose. Effective dose and DLP vary linearly with mAs. A collimated maxillary or mandibular scan decreases effective dose by approximately 29% and 24%, respectively, as compared with a full maxillomandibular scan. Changes to contrast and resolution settings have little influence on effective dose. This study provides data for setting individualized patient exposure protocols to minimize patient dose from ionizing radiation used for diagnostic or treatment planning tasks in dentistry.

Hematopoiesis in the equine fetal liver suggests immune preparedness.

We investigated how the equine fetus prepares its pre-immune humoral repertoire for an imminent exposure to pathogens in the neonatal period, particularly how the primary hematopoietic organs are equipped to support B cell hematopoiesis and immunoglobulin (Ig) diversity. We demonstrated that the liver and the bone marrow at approximately 100 days of gestation (DG) are active sites of hematopoiesis based on the expression of signature messenger RNA (mRNA) (c-KIT, CD34, IL7R, CXCL12, IRF8, PU.1, PAX5, NOTCH1, GATA1, CEBPA) and protein markers (CD34, CD19, IgM, CD3, CD4, CD5, CD8, CD11b, CD172A) of hematopoietic development and leukocyte differentiation molecules, respectively. To verify Ig diversity achieved during the production of B cells, V(D)J segments were sequenced in primary lymphoid organs of the equine fetus and adult horse, revealing that similar heavy chain VDJ segments and CDR3 lengths were most frequently used independent of life stage. In contrast, different lambda light chain segments were predominant in equine fetal compared to adult stage, and surprisingly, the fetus had less restricted use of variable gene segments to construct the lambda chain. Fetal Igs also contained elements of sequence diversity, albeit to a smaller degree than that of the adult horse. Our data suggest that the B cells produced in the liver and bone marrow of the equine fetus generate a wide repertoire of pre-immune Igs for protection, and the more diverse use of different lambda variable gene segments in fetal life may provide the neonate an opportunity to respond to a wider range of antigens at birth.

Atención de la urgencia en salud mental: modalidades de demanda y tipos de abordaje en el hospital municipal San Vicente de Paul de Chascomús / Urgent attention in mental health service: different ways of demand and types of approach in hospital San Vicente de Paul hospital in Chascomús

INTRODUCCIÓN La urgencia en Salud Mental forma parte de las demandas cotidianas en los efectores de Salud Pública. En Argentina, aún son escasos los hospitales que cuentan con dispositivos de salud mental que atienden específicamente la urgencia, aunque se reciben esas demandas y se les da algún tipo de respuesta. OBJETIVOS Indagar qué tipo de demandas incluyen los profesionales dentro del campo de la urgencia en salud mental y qué tipo de respuestas de atención reciben esas demandas en el Hospital Municipal de Chascomús, que no cuenta con profesionales de Salud Mental en la guardia general. MÉTODOS Se utilizó una metodología de corte cualitativo para un estudio exploratorio. Se realizaron 10 entrevistas semiestructuradas a profesionales y enfermeros de distintos sectores del hospital para la obtención de datos, y se llevó a cabo una lectura de material documentado (historias clínicas). RESULTADOS Entre las demandas más frecuentes ligadas a la urgencia en Salud Mental, se identificaron las siguientes crisis de angustia acompañadas o no por "intentos de autoeliminación", descompensaciones psicóticas y abuso sexual infantil. Según los entrevistados, este tipo de presentaciones ha aumentado en los últimos 20 años. Los profesionales cuentan con mecanismos de selección de aquellas demandas que merecen atención, vinculados a diferentes concepciones teóricas (modelo médico hegemónico / salud mental). DISCUSIÓN Los tipos de abordaje se dividen en dos grandes grupos de prácticas coexistentes las que legitiman el padecimiento psíquico y las que no. Las primeras logran alojar la urgencia en el ámbito institucional; las segundas operan bajo diferentes modalidades, rechazando este tipo de demandas o derivando. En el primer caso se percibe una respuesta más favorable que en el segundo. No obstante, los profesionales consignan un índice importante de no legitimación de las urgencias en salud mental.

Abordaje del padecimiento psíquico: perspectiva de los profesionales y trabajadores de los equipos de salud del hospital Alejandro Korn / Approach to psychical suffering: professional and worker´s perspective of health team in Alejandro Korn hospital

INTRODUCCIÓN Dentro de la problemática general vinculada a la evaluación de los servicios de atención de Salud Mental, la perspectiva de los profesionales, trabajadores, usuarios y familiares constituye un pilar fundamental. Se cuenta con un antecedente de investigación en el Hospital Dr. Alejandro Korn, que se centró en la evaluación de los servicios desde la perspectiva de los usuarios y pudo establecer que hay dispositivos versátiles y no versátiles con respecto a la consideración de la singularidad de los usuarios en el abordaje. OBJETIVOS Complementar el estudio realizado con anterioridad, tomando como referencia el punto de vista de los profesionales y trabajadores. MÉTODOS Se utilizó una metodología de corte cualitativo para un estudio exploratorio, que implementó entrevistas semiestructuradas para la obtención de datos. La muestra estuvo conformada por profesionales y trabajadores con una antigüedad de 3 a 35 años en la institución, a quienes se les preguntó por aquellos elementos de los servicios que consideraban favorables o desfavorables en el abordaje del padecimiento psíquico. RESULTADOS Los profesionales y trabajadores lograron establecer con claridad los aspectos eficaces e ineficaces de los servicios de Salud Mental en el abordaje del padecimiento psíquico. Repartieron esos aspectos en dos lógicas antinómicas, la de los dispositivos versátiles y la de los dispositivos no versátiles, estableciendo una correlación con lo obtenido en el estudio de usuarios. DISCUSIÓN Los resultados abren perspectivas de estudio vinculadas a cómo incluir la lógica de los dispositivos versátiles en los servicios de Salud Mental.

Sci-Thur PM: YIS - 04: Forcing lateral electron disequilibrium to spare lung tissue: A novel technique for SBRT of small lung tumours.

Stereotactic body radiation therapy(SBRT), a technique that uses tightly conformed Megavoltage(MV) x-ray fields, improves local control of lung cancer. However, small MV x-ray fields can cause lateral electron disequilibrium(LED), which reduces the dose within lung. These effects are difficult to predict and are presently a cause of alarm for the radiotherapy community. Previously, we developed The Relative Depth Dose Factor(RDDF), which is an indicator of the extent of LED (RDDF < 1). We propose a positive application of LED for lung sparing in SBRT: LED can be exploited to irradiate a small tumor while greatly reducing the dose in surrounding lung tissue. The Monte Carlo code, DOSXYZnrc, was employed to calculate dose within a cylindrical lung phantom. The phantom's diameter and height were set to 25 cm, and consisted of water and lung (density = 0.25g/cm3 ) shells surrounding a small water tumor (volume = 0.8 cm3 ). Two 180° 6MV arcs were focused onto the tumor with field sizes of 1×1cm2 (RDDF∼0.5) and 3×3cm2 (RDDF∼1). Analyzing dose results, the 1×1cm2 arc reduced dose within lung and water tissues by 70% and 80% compared to the 3×3cm2 arc. Although, central tumor dose was also reduced by 15% using the 1×1cm2 arc, these reductions can be offset by escalating the prescription dose appropriately. Using the RDDF as a guideline, it's possible to design a SBRT treatment plan that reduces lung dose while maintaining relatively high tumor dose levels. Clinical application requires an accurate dose algorithm and may lower SBRT dose-induced toxicity levels in patients.

Sci-Fri PM: Delivery - 02: CT image guidance strategies for dose-adaptive IMRT of the prostate.

On-line CT imaging in the radiotherapy room has become the norm for targeted intensity-modulated radiotherapy (IMRT), enabling precise adjustments of the daily patient setup based on soft tissue visualization. Corrections for plasticity of the anatomy and dose deformation are within technological reach but will require more on-line resources. We have developed a computer model that allows exploration of "what if" scenarios for assessing the benefits of Image Guidance strategies in terms of the multi-fraction dose distribution and DVH metrics (Target D95 and rectum V70). In this work we report on changes in anatomy and resultant dose distribution as observed in 35 daily megavoltage CT (MVCT) scans of the pelvis during prostate therapy for 13 patients. Our goal is to assess the effectiveness and efficiency of various adaptive strategies involving imaging schedule with and without dose re-planning of 5-field IMRT with 18 MV x-rays. Our research questions are: To what extent do radiation dose distributions delivered to individual patients (in vivo) diverge from the planned dose distributions (in silico)? Is there a robust schedule of CT image guidance, with or without dose re-planning that will mitigate discrepancies? For prostate IMRT, we conclude that image guidance schedule can be relaxed when generous GTV margins (10/7mm) are used. Tighter margins (isotropic 5 mm) reduce the dose to the rectum as expected. However, daily re-planning may be required to maintain adequate target coverage as planned when tighter margins are used.

Sci-Fri PM: Delivery - 11: Accuracy considerations in modern radiation oncology: An update.

The most recent reviews of accuracy requirements in radiation oncology were published in the 1990s, primarily in an era that was transitioning from 2-D to 3-D conformal radiation therapy (CRT). Since then, the technology associated with radiation oncology has changed dramatically. The combination of various forms of imaging for radiation therapy planning, treatment planning software, dose delivery technology including 4-D considerations as well as in-room daily image guidance has resulted in new perspectives on accuracy considerations. The underlying hypothesis for the use of these advanced technologies is that loco-regional control of cancer remains a significant barrier to cancer cure for many common cancers and that better dose distributions will translate into better outcomes. However, further clinical gain using these new technologies may be limited by single or compounded uncertainties associated with the entire treatment process. Thus, it is important to understand what factors should be considered in determining accuracy requirements as well as the realistic expectations of uncertainties that exist within the total treatment process. The need for accuracy is based on clinical requirements such as the steepness of dose-response curves, inherent heterogeneity in patient response to treatment, and the level of accuracy that is practically achievable. Statements on accuracy are dependent on the technology used and the reality of what is practically achievable and necessary. This review highlights some of the major differences between accuracy requirements as determined in the 2-D RT and 3-D CRT era versus the modern era of intensity modulated, image-guided, 4-D radiation therapy.

The cardinal role of the phospholipase A(2)/cyclooxygenase-2/prostaglandin E synthase/prostaglandin E(2) (PCPP) axis in inflammostasis.

The process of inflammation is regulated in part by bioactive lipids of which prostaglandins/eicosanoids form an important class. We provide evidence that the phospholipase A(2)/cyclooxygenase-2/prostaglandin E synthase/prostaglandin E(2) (PCPP) axis is positioned at the core of a natural regulatory circuit controlling the initiation, magnitude, duration, and resolution of the inflammatory response. During the inflammatory phase, proinflammatory cytokine, chemokine and matrix destructive metalloprotease expression levels are moderated by the PCPP axis through the modulation of signaling pathways that control proinflammatory gene expression at transcriptional, post-transcriptional, and translational levels. The PCPP axis also contributes to the activation of lipid mediator class switching; this highly coordinated process results in the biosynthesis of lipoxins and resolvins that promote inflammatory resolution through a variety of cellular and molecular mechanisms. The PCPP axis activity is autoregulated by way of a positive feedback circuit involving PGE(2)-mediated, p38 MAPK-dependent stabilization of COX-2 mRNA and COX-2 catalytic potentiation via its limited proteolytic cleavage (e.g., Ca(2+)-activated calpains). In conclusion, through its fine temporal modulation of multiple signaling cassettes via EP1-EP4 GPCRs, PGE(2) influences the onset, course, magnitude, and duration of the inflammatory response and functions as a key feedback regulator of the cellular and molecular processes controlling inflammation.

Evaluation of inter-fraction prostate motion using kilovoltage cone beam computed tomography during radiotherapy.

AIMS: The success of delivering the prescribed radiation dose to the prostate while sparing adjacent sensitive tissues is largely dependent on the ability to accurately target the prostate during treatment. Kilovoltage cone beam computed tomography (CBCT) imaging can be used to monitor and compensate for inter-fraction prostate motion, but this procedure increases treatment session time and adds incidental radiation dose to the patient. We carried out a retrospective study of CBCT data to evaluate the systematic and random correction shifts of the prostate with respect to bones and external marks. MATERIALS AND METHODS: A total of 449 daily CBCT studies from 17 patients undergoing intensity-modulated radiotherapy (IMRT) for localised prostate cancer were analysed. The difference between patient set-up correction shifts applied by radiation therapists (via matching prostate position in CBCT and planning computed tomography) and shifts obtained by matching bony anatomy in the same studies was used as a measure of the daily inter-fraction internal prostate motion. RESULTS: The average systematic and random shifts in prostate positions, calculated over all fractions versus only 10 fractions, were not found to be significantly different. DISCUSSION: The measured prostate shifts with respect to bony anatomy and external marks after the first 10 imaging sessions were shown to provide adequate predictive power for defining patient-specific margins in future fractions without a need for ongoing computed tomography imaging. Different options for CBCT imaging schedule are proposed that will reduce the treatment session time and imaging dose to radiotherapy patients while ensuring appropriate prostate cover and normal tissue sparing.

Effect of lateral target motion on image registration accuracy in CT-guided helical tomotherapy: a phantom study.

Optimisation of imaging modes for kilovoltage CT (kVCT) used for treatment planning and megavoltage CT (MVCT) image guidance used in ungated helical tomotherapy was investigated for laterally moving targets. Computed tomography images of the QUASAR Respiratory Motion Phantom were acquired without target motion and for lateral motion of the target, with 2-cm peak-to-peak amplitude and a period of 4 s. Reference kVCT images were obtained using a 16-slice CT scanner in standard fast helical CT mode, untagged average CT mode and various post-processed 4D-CT modes (0% phase, average and maximum intensity projection). Three sets of MVCT images with different inter-slice spacings of were obtained on a Hi-Art tomotherapy system with the phantom displaced by a known offset position. Eight radiation therapists performed co-registration of MVCT obtained with 2-, 4- and 6-mm slice spacing and kVCT studies independently for all 15 CT imaging combinations. In the investigated case, the untagged average kVCT and 4-mm slice spacing for the MVCT yielded more accurate registration in the transverse plane. The average residual uncertainty of this combination of imaging procedures was 0.61 +/- 0.16 mm in the longitudinal direction, 0.45 +/- 0.14 mm in the anterior-posterior direction and insignificant in the lateral direction. Manual registration of MVCT-kVCT study pairs is necessary to account for a target in significant lateral motion with respect to bony structures.

[Endoscopic approaches to the orbit]. / Les abords endoscopiques de l'orbite.

During the last decade, the use of endoscopic endonasal approaches to the pituitary has increased considerably. The endoscopic endonasal and transantral approaches offer a minimally invasive alternative to the classic transcranial or transconjunctival approaches to the medial aspect of the orbit. The medial wall of the orbit, the orbital apex, and the optic canal can be exposed through a middle meatal antrostomy, an anterior and posterior ethmoidectomy, and a sphenoidotomy. The inferomedial wall of the orbit can be also perfectly visualized through a sublabial antrostomy or an inferior meatal antrostomy. Several reports have described the use of an endoscopic approach for the resection or the biopsy of lesions located on the medial extraconal aspect of the orbit and orbital apex. However, the resection of intraconal lesions is still limited by inadequate instrumentation. Other indications for the endoscopic approach to the orbit are the decompression of the orbit for Graves' ophthalmopathy and traumatic optic neuropathy. However, the optimal management of traumatic optic neuropathy remains very controversial. Endoscopic endonasal decompression of the optic nerve in case of tumor compression could be a more valid indication in combination with radiation therapy. Finally, the endoscopic transantral treatment of blowout fracture of the floor of the orbit is an interesting option that avoids the eyelid or conjunctive incision of traditional approaches. The collaboration between the neurosurgeon and the ENT surgeon is mandatory and reduces the morbidity of the approach. Progress in instrumentation and optical devices will certainly make this approach promising for intraconal tumor of the orbit.

Schedule for CT image guidance in treating prostate cancer with helical tomotherapy.

The aim of this study was to determine the effect of reducing the number of image guidance sessions and patient-specific target margins on the dose distribution in the treatment of prostate cancer with helical tomotherapy. 20 patients with prostate cancer who were treated with helical tomotherapy using daily megavoltage CT (MVCT) imaging before treatment served as the study population. The average geometric shifts applied for set-up corrections, as a result of co-registration of MVCT and planning kilovoltage CT studies over an increasing number of image guidance sessions, were determined. Simulation of the consequences of various imaging scenarios on the dose distribution was performed for two patients with different patterns of interfraction changes in anatomy. Our analysis of the daily set-up correction shifts for 20 prostate cancer patients suggests that the use of four fractions would result in a population average shift that was within 1 mm of the average obtained from the data accumulated over all daily MVCT sessions. Simulation of a scenario in which imaging sessions are performed at a reduced frequency and the planning target volume margin is adapted provided significantly better sparing of organs at risk, with acceptable reproducibility of dose delivery to the clinical target volume. Our results indicate that four MVCT sessions on helical tomotherapy are sufficient to provide information for the creation of personalised target margins and the establishment of the new reference position that accounts for the systematic error. This simplified approach reduces overall treatment session time and decreases the imaging dose to the patient.

[Endoscopy versus microsurgery: results in a consecutive series of nonfunctioning pituitary adenomas]. / Résultats comparés de la chirurgie endoscopique et de la microchirurgie dans une série consécutive de macroadénomes hypophysaires non fonctionnels.

Microsurgical removal of nonfunctioning pituitary adenomas (NFPAs) is often subtotal. Removing the blind spots as viewed through the microscope, endoscopic surgery may improve the quality of removal. Our purpose was to compare the results of the two techniques in a series of NFPA patients operated on by a single surgeon. Thirty-six patients with newly diagnosed NFPAs were operated on using a purely endoscopic procedure and 29 with a microsurgical technique. All patients were explored pre- and postoperatively (at 3 and 6 months and then every 12 months) by endocrine assays, ophthalmologic exam, and 3D MRI. The endocrine and ophthalmologic results as well as the quality of resection and the complications from the two techniques were compared. The follow-up duration and the mean tumor volume (higher in the microsurgical group) were the only differences observed between the two groups. Tumor height and the invasion of the cavernous sinus were not different. All patients with preoperative visual impairment in the endoscopic group improved, whereas in the microsurgical group 90.9% improved, 4.5% were stabilized, and 4.5% worsened (p=ns). Regarding anterior pituitary functions, 42.8% of the patients improved in the endoscopic group, 45.7% remained stable, and 11.4% worsened compared to, respectively, 31, 44,8, and 24.1% in the microsurgical group (p=ns). Gross total removal was achieved in 86.1% for the endoscopic group and in only 65.5% for the microsurgical group (p=0.075). Morbidity was similar in the two groups. This retrospective series showed that endoscopic surgery compared to microsurgery increases the quality of NFPA removal with similar morbidity.

Consistency check of planned adaptive option on helical tomotherapy.

This study aims to evaluate a new Planned Adaptive software (TomoTherapy Inc., Madison, WI) of the helical tomotherapy system by retrospective verification and adaptive re-planning of radiation treatment. Four patients with different disease sites (brain, nasal cavity, lungs, prostate) were planned in duplicate using the diagnostic planning kVCT data set and MVCT studies of the first treatment fraction with the same optimization parameters for both plan types. The dosimetric characteristics of minimum, maximum, and mean dose to the targets as well as to organs at risk were compared. Both sets of plans were used for calculation of dose distributions in a water-equivalent phantom. Corresponding measurements of these plans in phantom were carried out with the use of radiographic film and ion chamber. In the case of the lung and prostate cancer patients, changes in dosimetric parameters compared to data generated with the kVCT study alone were less than 2%. Certain changes for the nasal cavity and brain cancer patients were greater than 2%, but they were explained in part by anatomy changes that occurred during the time between kVCT and MVCT studies. The Planned Adaptive software allows for adaptive radiotherapy planning using the MVCT studies obtained by the helical tomotherapy imaging system.

Fundamental x-ray interaction limits in diagnostic imaging detectors: spatial resolution.

The practice of diagnostic x-ray imaging has been transformed with the emergence of digital detector technology. Although digital systems offer many practical advantages over conventional film-based systems, their spatial resolution performance can be a limitation. The authors present a Monte Carlo study to determine fundamental resolution limits caused by x-ray interactions in four converter materials: Amorphous silicon (a-Si), amorphous selenium, cesium iodide, and lead iodide. The "x-ray interaction" modulation transfer function (MTF) was determined for each material and compared in terms of the 50% MTF spatial frequency and Wagner's effective aperture for incident photon energies between 10 and 150 keV and various converter thicknesses. Several conclusions can be drawn from their Monte Carlo study. (i) In low-Z (a-Si) converters, reabsorption of Compton scatter x rays limits spatial resolution with a sharp MTF drop at very low spatial frequencies (< 0.3 cycles/mm), especially above 60 keV; while in high-Z materials, reabsorption of characteristic x rays plays a dominant role, resulting in a mid-frequency (1-5 cycles/mm) MTF drop. (ii) Coherent scatter plays a minor role in the x-ray interaction MTF. (iii) The spread of energy due to secondary electron (e.g., photoelectrons) transport is significant only at very high spatial frequencies. (iv) Unlike the spread of optical light in phosphors, the spread of absorbed energy from x-ray interactions does not significantly degrade spatial resolution as converter thickness is increased. (v) The effective aperture results reported here represent fundamental spatial resolution limits of the materials tested and serve as target benchmarks for the design and development of future digital x-ray detectors.

Fundamental x-ray interaction limits in diagnostic imaging detectors: frequency-dependent Swank noise.

A frequency-dependent x-ray Swank factor based on the "x-ray interaction" modulation transfer function and normalized noise power spectrum is determined from a Monte Carlo analysis. This factor was calculated in four converter materials: amorphous silicon (a-Si), amorphous selenium (a-Se), cesium iodide (CsI), and lead iodide (PbI2) for incident photon energies between 10 and 150 keV and various converter thicknesses. When scaled by the quantum efficiency, the x-ray Swank factor describes the best possible detective quantum efficiency (DQE) a detector can have. As such, this x-ray interaction DQE provides a target performance benchmark. It is expressed as a function of (Fourier-based) spatial frequency and takes into consideration signal and noise correlations introduced by reabsorption of Compton scatter and photoelectric characteristic emissions. It is shown that the x-ray Swank factor is largely insensitive to converter thickness for quantum efficiency values greater than 0.5. Thus, while most of the tabulated values correspond to thick converters with a quantum efficiency of 0.99, they are appropriate to use for many detectors in current use. A simple expression for the x-ray interaction DQE of digital detectors (including noise aliasing) is derived in terms of the quantum efficiency, x-ray Swank factor, detector element size, and fill factor. Good agreement is shown with DQE curves published by other investigators for each converter material, and the conditions required to achieve this ideal performance are discussed. For high-resolution imaging applications, the x-ray Swank factor indicates: (i) a-Si should only be used at low-energy (e.g., mammography); (ii) a-Se has the most promise for any application below 100 keV; and (iii) while quantum efficiency may be increased at energies just above the K edge in CsI and PbI2, this benefit is offset by a substantial drop in the x-ray Swank factor, particularly at high spatial frequencies.