Table of contents

Historically, medical devices to image either anatomical structure or functional processes have developed along somewhat independent paths. The recognition that combining images from different modalities can nevertheless offer significant diagnostic advantages gave rise to sophisticated software techniques to coregister structure and function. Recently, alternatives to retrospective software-based fusion have become available through instrumentation that combines two imaging modalities within a single device, an approach that has since been termed hardware fusion. As a result, following their recent introduction into the clinic, combined PET/CT and SPECT/CT devices are now playing an increasingly important role in the diagnosis and staging of human disease. Recently, although limited to the brain, the first clinical MR scanner with a PET insert, a technically-challenging design, has been undergoing evaluation. This review will follow the development of multimodality instrumentation for clinical use from conception to present-day technology and assess the status and future potential for such devices.

Accurate daily patient localization is becoming increasingly important in external-beam radiotherapy (RT). Mega-voltage cone-beam computed tomography (MV-CBCT) utilizing a therapy beam and an on-board electronic portal imager can be used to localize tumor volumes and verify the patient's position prior to treatment. MV-CBCT produces a static volumetric image and therefore can only account for inter-fractional changes. In this work, the feasibility of using the MV-CBCT raw data as a fluoroscopic series of portal images to monitor tumor changes due to e.g. respiratory motion was investigated. A method was developed to read and convert the CB raw data into a cine. To improve the contrast-to-noise ratio on the MV-CB projection data, image post-processing with filtering techniques was investigated. Volumes of interest from the planning CT were projected onto the MV-cine. Because of the small exposure and the varying thickness of the patient depending on the projection angle, soft-tissue contrast was limited. Tumor visibility as a function of tumor size and projection angle was studied. The method was well suited in the upper chest, where motion of the tumor as well as of the diaphragm could be clearly seen. In the cases of patients with non-small cell lung cancer with medium or large tumor masses, we verified that the tumor mass was always located within the PTV despite respiratory motion. However for small tumors the method is less applicable, because the visibility of those targets becomes marginal. Evaluation of motion in non-superior–inferior directions might also be limited for small tumor masses. Viewing MV-CBCT data in a cine mode adds to the utility of MV-CBCT for verification of tumor motion and for deriving individualized treatment margins.

In this paper, we develop a method of forming pharmacokinetic-rate images of indocyanine green (ICG) and apply our method to in vivo data obtained from three patients with breast tumors. To form pharmacokinetic-rate images, we first obtain a sequence of ICG concentration images using the differential diffuse optical tomography technique. We next employ a two-compartment model composed of plasma, and extracellular–extravascular space (EES), and estimate the pharmacokinetic rates and concentrations in each compartment using the extended Kalman filtering framework. The pharmacokinetic-rate images of the three patient show that the rates from the tumor region and outside the tumor region are statistically different. Additionally, the ICG concentrations in plasma, and the EES compartments are higher around the tumor region agreeing with the hypothesis that around the tumor region ICG may act as a diffusible extravascular flow in compromised capillary of cancer vessels. Our study indicates that the pharmacokinetic-rate images may provide superior information than single set of pharmacokinetic rates estimated from the entire breast tissue for breast cancer diagnosis.

The purpose of this work was the understanding of microbeam radiation therapy at the ESRF in order to find the best compromise between curing of tumors and sparing of normal tissues, to obtain a better understanding of survival curves and to report its efficiency. This method uses synchrotron-generated x-ray microbeams. Rats were implanted with 9L gliosarcomas and the tumors were diagnosed by MRI. They were irradiated 14 days after implantation by arrays of 25 µm wide microbeams in unidirectional mode, with a skin entrance dose of 625 Gy. The effect of using 200 or 100 µm center-to-center spacing between the microbeams was compared. The median survival time (post-implantation) was 40 and 67 days at 200 and 100 µm spacing, respectively. However, 72% of rats irradiated at 100 µm spacing showed abnormal clinical signs and weight patterns, whereas only 12% of rats were affected at 200 µm spacing. In parallel, histological lesions of the normal brain were found in the 100 µm series only. Although the increase in lifespan was equal to 273% and 102% for the 100 and 200 µm series, respectively, the 200 µm spacing protocol provides a better sparing of healthy tissue and may prove useful in combination with other radiation modalities or additional drugs.

Glioblastoma multiforma (GBM) is one of the most aggressive tumors of the central nervous system. It can be represented by two components: a proliferative component with a mass effect on brain structures and an invasive component. GBM has a distinct pattern of spread showing a preferential growth in the white fiber direction for the invasive component. By using the architecture of white matter fibers, we propose a new model to simulate the growth of GBM. This architecture is estimated by diffusion tensor imaging in order to determine the preferred direction for the diffusion component. It is then coupled with a mechanical component. To set up our growth model, we make a brain atlas including brain structures with a distinct response to tumor aggressiveness, white fiber diffusion tensor information and elasticity. In this atlas, we introduce a virtual GBM with a mechanical component coupled with a diffusion component. These two components are complementary, and can be tuned independently. Then, we tune the parameter set of our model with an MRI patient. We have compared simulated growth (initialized with the MRI patient) with observed growth six months later. The average and the odd ratio of image difference between observed and simulated images are computed. Displacements of reference points are compared to those simulated by the model. The results of our simulation have shown a good correlation with tumor growth, as observed on an MRI patient. Different tumor aggressiveness can also be simulated by tuning additional parameters. This work has demonstrated that modeling the complex behavior of brain tumors is feasible and will account for further validation of this new conceptual approach.

This paper presents an optimization framework for improving case-based computer-aided decision (CB-CAD) systems. The underlying hypothesis of the study is that each example in the knowledge database of a medical decision support system has different importance in the decision making process. A new decision algorithm incorporating an importance weight for each example is proposed to account for these differences. The search for the best set of importance weights is defined as an optimization problem and a genetic algorithm is employed to solve it. The optimization process is tailored to maximize the system's performance according to clinically relevant evaluation criteria. The study was performed using a CAD system developed for the classification of regions of interests (ROIs) in mammograms as depicting masses or normal tissue. The system was constructed and evaluated using a dataset of ROIs extracted from the Digital Database for Screening Mammography (DDSM). Experimental results show that, according to receiver operator characteristic (ROC) analysis, the proposed method significantly improves the overall performance of the CAD system as well as its average specificity for high breast mass detection rates.

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Several institutes are currently working on the development of a radiotherapy treatment system with online MR imaging (MRI) modality. The main difference between their designs is the magnetic field strength of the MRI system. While we have chosen a 1.5 Tesla (T) magnetic field strength, the Cross Cancer Institute in Edmonton will be using a 0.2 T MRI scanner and the company Viewray aims to use 0.3 T. The magnetic field strength will affect the severity of magnetic field dose effects, such as the electron return effect (ERE): considerable dose increase at tissue air boundaries due to returning electrons. This paper has investigated how the ERE dose increase depends on the magnetic field strength. Therefore, four situations where the ERE occurs have been simulated: ERE at the distal side of the beam, the lateral ERE, ERE in cylindrical air cavities and ERE in the lungs. The magnetic field comparison values were 0.2, 0.75, 1.5 and 3 T. Results show that, in general, magnetic field dose effects are reduced at lower magnetic field strengths. At the distal side, the ERE dose increase is largest for B = 0.75 T and depends on the irradiation field size for B = 0.2 T. The lateral ERE is strongest for B = 3 T but shows no effect for B = 0.2 T. Around cylindrical air cavities, dose inhomogeneities disappear if the radius of the cavity becomes small relative to the in-air radius of the secondary electron trajectories. At larger cavities (r > 1 cm), dose inhomogeneities exist for all magnetic field strengths. In water–lung–water phantoms, the ERE dose increase takes place at the water–lung transition and the dose decreases at the lung–water transition, but these effects are minimal for B = 0.2 T. These results will contribute to evaluating the trade-off between magnetic field dose effects and image quality of MR-guided radiotherapy systems.

Magnetic resonance elastography (MRE) has been demonstrated to have potential as a clinical tool for assessing the stiffness of tissue in vivo. An essential step in MRE is the generation of acoustic mechanical waves within a tissue via a coupled mechanical driver. Motivated by an increasing volume of human imaging trials using MRE, the objectives of this study were to audit the vibration amplitude of exposure for our IRB-approved human MRE studies, to compare these values to a conservative regulatory standard for vibrational exposure and to evaluate the applicability and implications of this standard for MRE. MRE displacement data were examined from 29 MRE exams, including the liver, brain, kidney, breast and skeletal muscle. Vibrational acceleration limits from a European Union directive limiting occupational exposure to whole-body and extremity vibrations (EU 2002/44/EC) were adjusted for time and frequency of exposure, converted to maximum displacement values and compared to the measured in vivo displacements. The results indicate that the vibrational amplitudes used in MRE studies are below the EU whole-body vibration limit, and the EU guidelines represent a useful standard that could be readily accepted by Institutional Review Boards to define standards for vibrational exposures for MRE studies in humans.

In this study, we evaluate the feasibility of designing a beveled fiber-optic probe coupled with a ball lens for improving depth-resolved fluorescence measurements of epithelial tissue using Monte Carlo (MC) simulations. The results show that by using the probe configuration with a beveled tip collection fiber and a flat tip excitation fiber associated with a ball lens, discrimination of fluorescence signals generated in different tissue depths is achievable. In comparison with a flat-tip collection fiber, the use of a large bevel angled collection fiber enables a better differentiation between the shallow and deep tissue layers by changing the excitation–collection fiber separations. This work suggests that the beveled fiber-optic probe coupled with a ball lens has the potential to facilitate depth-resolved fluorescence measurements of epithelial tissues.

Single photon emission computed tomography (SPECT) can be performed with various collimator types, which have an inherent tradeoff between the properties of sensitivity, resolution, field of view and complete sampling. Slit–slat collimation, which has seen recent interest in the literature, combines a slit parallel to the axis of rotation of a gamma camera with a set of septa perpendicular to the slit. This collimator geometry exhibits properties that may enhance some SPECT imaging applications, specifically imaging of the breast, limbs and medium-sized animals. However, a complete description of its system response is critical for a comparison to other collimator types and for accurate reconstruction of projection data. Herein, experimental and Monte Carlo methods are used to determine the sensitivity and transaxial and axial resolutions as a function of the incidence angle θ, which is the angle formed by the line from the photon source to the center of the slit and the plane of the slit, to compare to theoretical expectations. Four configurations are investigated by varying the slit width, septal spacing and septal height. Monte Carlo sensitivity data not modeling penetration and scatter exhibit a sin³θ dependence. Experimental and Monte Carlo-derived sensitivity data modeling scatter and penetration are consistent with each other and have a sin^xθ dependence, where x is greater than 3. Transaxial resolution data show a small dependence on θ, and axial resolution data are consistent with no angular dependence.

The paper presents a computationally efficient 3D–2D image registration algorithm for automatic pre-treatment validation in radiotherapy. The novel aspects of the algorithm include (a) a hybrid cost function based on partial digitally reconstructed radiographs (DRRs) generated along projected anatomical contours and a level set term for similarity measurement; and (b) a fast search method based on parabola fitting and sensitivity-based search order. Using CT and orthogonal x-ray images from a skull and a pelvis phantom, the proposed algorithm is compared with the conventional ray-casting full DRR based registration method. Not only is the algorithm shown to be computationally more efficient with registration time being reduced by a factor of 8, but also the algorithm is shown to offer 50% higher capture range allowing the initial patient displacement up to 15 mm (measured by mean target registration error). For the simulated data, high registration accuracy with average errors of 0.53 mm ± 0.12 mm for translation and 0.61° ± 0.29° for rotation within the capture range has been achieved. For the tested phantom data, the algorithm has also shown to be robust without being affected by artificial markers in the image.

Inherently, IMRT treatment planning involves compromising between different planning goals. Multi-criteria IMRT planning directly addresses this compromising and thus makes it more systematic. Usually, several plans are computed from which the planner selects the most promising following a certain procedure. Applying Pareto navigation for this selection step simultaneously increases the variety of planning options and eases the identification of the most promising plan. Pareto navigation is an interactive multi-criteria optimization method that consists of the two navigation mechanisms 'selection' and 'restriction'. The former allows the formulation of wishes whereas the latter allows the exclusion of unwanted plans. They are realized as optimization problems on the so-called plan bundle—a set constructed from pre-computed plans. They can be approximately reformulated so that their solution time is a small fraction of a second. Thus, the user can be provided with immediate feedback regarding his or her decisions. Pareto navigation was implemented in the MIRA navigator software and allows real-time manipulation of the current plan and the set of considered plans. The changes are triggered by simple mouse operations on the so-called navigation star and lead to real-time updates of the navigation star and the dose visualizations. Since any Pareto-optimal plan in the plan bundle can be found with just a few navigation operations the MIRA navigator allows a fast and directed plan determination. Besides, the concept allows for a refinement of the plan bundle, thus offering a middle course between single plan computation and multi-criteria optimization. Pareto navigation offers so far unmatched real-time interactions, ease of use and plan variety, setting it apart from the multi-criteria IMRT planning methods proposed so far.

Cone beam digital tomosynthesis (CBDT) is a new imaging technique proposed recently as a rapid approach for creating tomographic images of a patient in the radiotherapy treatment room. The purpose of this work is to investigate the feasibility of performing megavoltage (MV) CBDT clinically. A clinical investigational MV-CBDT system was installed on an existing LINAC. After the installation, the treatment machine can be operated in two distinct modes: (1) normal clinical treatment mode; (2) CBDT mode, in which tomographic images of the patient can be obtained using MV-CBDT. Various calibration and phantom measurements were performed on the system, followed by a patient study. Our phantom measurements have shown that: (1) for the same imaging dose, MV-CBDT has the same signal-difference-to-noise ratio as megavoltage cone beam computed tomography (MV-CBCT); (2) MV-CBDT has a better spatial resolution than MV-CBCT in the planes of reconstruction but a worse spatial resolution in the direction perpendicular to the planes of reconstruction. MV-CBDT patient images were also obtained and compared to that of MV-CBCT. We have demonstrated that it is clinically feasible to perform MV-CBDT in the treatment room for image-guided radiotherapy.

Recently, x-ray differential phase contrast computed tomography (DPC-CT) has been experimentally implemented using a conventional tube combined with gratings. Images were reconstructed using a parallel-beam reconstruction formula. However, parallel-beam reconstruction formulae are not applicable when the parallel-beam approximation fails. In this paper, we present a new image reconstruction formula for fan-beam DPC-CT. There are several novel features of the new image reconstruction formula: (i) when the scanning angular range of data acquisition is larger than π + γ_m (γ_m is the full fan angle), the entire field of view can be exactly reconstructed; (ii) when the scanning angular range is smaller than π + γ_m, a local region of interest (ROI) can be exactly reconstructed; (iii) it enables an exact reconstruction for a local ROI when the projection data are truncated at some view angles; (iv) it enlarges the imaging field of view when the detector is asymmetrically placed. In this last case, the data are truncated from every view angle. Numerical simulations have been conducted to validate the new reconstruction formula.

The effects of calculational uncertainties on 3D and distal edge tracking (DET) intensity modulated proton therapy (IMPT) treatment plans have been investigated. Dose calculation uncertainties have been assessed by comparing analytical and Monte Carlo dose calculations, and potential range uncertainties by recalculating plans with all CT values modified by ±3%. Analysis of the volume of PTV agreeing to within ±3% between the two calculations shows that the 3D approach provides significantly improved agreement (87.1 versus 80.3% of points for the 3D and DET approaches, respectively). For the DET approach, doses in the CTV have also been found to globally change by 5% as a result of 3% changes in CT value. When varying the intra-field gradients of the plans a similar trend is seen, but with the more complex plans also being found to be more sensitive to both uncertainties. In conclusion, the DET approach has been found to be relatively sensitive to the calculational errors investigated here. In contrast, the 3D approach appears to be quite robust, unless strong internal gradients are present. Nevertheless, the routine use of uncertainty analysis is advised when assessing all forms of IMPT plans.

Simple tools for studying the effects of inter-fraction and inter-field motions on intensity modulated proton therapy (IMPT) plans have been developed, and have been applied to both 3D and distal edge tracking (DET) IMPT plans. For the inter-fraction motion, we have investigated the effects of misaligned density heterogeneities, whereas for the inter-field motion analysis, the effects of field misalignment on the plans have been assessed. Inter-fraction motion problems have been analysed using density differentiated error (DDE) distributions, which specifically show the additional problems resulting from misaligned density heterogeneities for proton plans. Likewise, for inter-field motion, we present methods for calculating motion differentiated error (MDE) distributions. DDE and MDE analysis of all plans demonstrate that the 3D approach is generally more robust to both inter-fraction and inter-field motions than the DET approach, but that strong in-field dose gradients can also adversely affect a plan's robustness. An important additional conclusion is that, for certain IMPT plans, even inter-fraction errors cannot necessarily be compensated for by the use of a simple PTV margins, implying that more sophisticated tools need to be developed for uncertainty management and assessment for IMPT treatments at the treatment planning level.

We describe the application of a Bayesian variable-number sample-path (VNSP) optimization algorithm to yield a robust design for a floating sleeve antenna for hepatic microwave ablation. Finite element models are used to generate the electromagnetic (EM) field and thermal distribution in liver given a particular design. Dielectric properties of the tissue are assumed to vary within ± 10% of average properties to simulate the variation among individuals. The Bayesian VNSP algorithm yields an optimal design that is a 14.3% improvement over the original design and is more robust in terms of lesion size, shape and efficiency. Moreover, the Bayesian VNSP algorithm finds an optimal solution saving 68.2% simulation of the evaluations compared to the standard sample-path optimization method.

An add-on multileaf collimator for electrons (eMLC) has been developed that provides computer-controlled beam collimation and isocentric dose delivery. The design parameters result from the design study by Gauer et al (2006 Phys. Med. Biol.51 5987–6003) and were configured such that a compact and light-weight eMLC with motorized leaves can be industrially manufactured and stably mounted on a conventional linear accelerator. In the present study, the efficiency of an initial computer-controlled prototype was examined according to the design goals and the performance of energy- and intensity-modulated treatment techniques. This study concentrates on the attachment and gantry stability as well as the dosimetric characteristics of central-axis and off-axis dose, field size dependence, collimator scatter, field abutment, radiation leakage and the setting of the accelerator jaws. To provide isocentric irradiation, the eMLC can be placed either 16 or 28 cm above the isocentre through interchangeable holders. The mechanical implementation of this feature results in a maximum field displacement of less than 0.6 mm at 90° and 270° gantry angles. Compared to a 10 × 10 cm applicator at 6–14 MeV, the beam penumbra of the eMLC at a 16 cm collimator-to-isocentre distance is 0.8–0.4 cm greater and the depth–dose curves show a larger build-up effect. Due to the loss in energy dependence of the therapeutic range and the much lower dose output at small beam sizes, a minimum beam size of 3 × 3 cm is necessary to avoid suboptimal dose delivery. Dose output and beam symmetry are not affected by collimator scatter when the central axis is blocked. As a consequence of the broader beam penumbra, uniform dose distributions were measured in the junction region of adjacent beams at perpendicular and oblique beam incidence. However, adjacent beams with a high difference in a beam energy of 6 to 14 MeV generate cold and hot spots of approximately 15% in the abutting region. In order to improve uniformity, the energy of adjacent beams must be limited to 6 to 10 MeV and 10 to 14 MeV respectively. At the maximum available beam energy of 14 MeV, radiation leakage results mainly from the intraleaf leakage of approximately 2.5% relative dose which could be effectively eliminated at off-axis distances remote from the field edge by adjusting the jaw field size to the respective opening of the eMLC. Additionally, the interleaf and leaf-end leakage could be reduced by using a tongue-and-groove leaf shape and adjoining the leaf-ends off-axis respectively.

A method is presented for extraction of intra and inter fraction motion of seeds/markers within the patient from cone beam CT (CBCT) projection images. The position of the marker is determined on each projection image and fitted to a function describing the projection of a fixed point onto the imaging panel at different gantry angles. The fitted parameters provide the mean marker position with respect to the isocentre. Differences between the theoretical function and the actual projected marker positions are used to estimate the range of intra fraction motion and the principal motion axis in the transverse plane. The method was validated using CBCT projection images of a static marker at known locations and of a marker moving with known amplitude. The mean difference between actual and measured motion range was less than 1 mm in all directions, although errors of up to 5 mm were observed when large amplitude motion was present in an orthogonal direction. In these cases it was possible to calculate the range of motion magnitudes consistent with the observed marker trajectory. The method was shown to be feasible using clinical CBCT projections of a pancreas cancer patient.

Current requirements of molecular imaging lead to the complete integration of complementary modalities in a single hybrid imaging system to correlate function and structure. Among the various existing detector technologies, which can be implemented to integrate nuclear modalities (PET and/or single-photon emission computed tomography with x-rays (CT) and most probably with MR, pixellated wide bandgap room temperature semiconductor detectors, such as CdZnTe and/or CdTe, are promising candidates. This paper deals with the development of a simplified simulation model for pixellated semiconductor radiation detectors, as a first step towards the performance characterization of a multimodality imaging system based on CdZnTe. In particular, this work presents a simple computational model, based on a 1D approximate solution of the Schockley–Ramo theorem, and its integration into the Geant4 application for tomographic emission (GATE) platform in order to perform accurately and, therefore, improve the simulations of pixellated detectors in different configurations with a simultaneous cathode and anode pixel readout. The model presented here is successfully validated against an existing detailed finite element simulator, the multi-geometry simulation code, with respect to the charge induced at the anode, taking into consideration interpixel charge sharing and crosstalk, and to the detector charge induction efficiency. As a final point, the model provides estimated energy spectra and time resolution for ⁵⁷Co and ¹⁸F sources obtained with the GATE code after the incorporation of the proposed model.

The ability of the Monte Carlo (MC) particle transport codes GEANT4.8.1 and GEANT4.8.2, FLUKA2006 and MCNPX2.4.0 to model proton transport at grazing incidence onto tungsten blocks has been tested and compared to experimental measurements. The test geometry consisted of a narrow proton beam of two energies, 98 MeV and 180 MeV, impinging on a thick tungsten alloy block at grazing incidence. The distribution of forward out-scatter from the tungsten alloy block was measured with a fluorescent screen viewed with a CCD camera via a mirror. In the MC simulations, the experimental setup was modelled and the dose deposited to the fluorescent screen material was scored. Simulations and measurements were made for four different incidence angles (3.5, 5.0, 7.5 and 10°). Several different sets of calculations were performed, studying the impact of different user-defined settings in the different MC packages. The study of different parameters settings in the GEANT4.8.1 simulation showed a strong dependence of the calculated out-scatter probability on the maximum allowed step length. For the largest incidence angle an increase of 60% in the out-scatter probability was found when restricting the maximum allowed step length to 0.05 cm. We also observed that the stepping algorithm of GEANT4.8.1 and 4.8.2 introduces a small non-physical directional and positional asymmetry at the exit boundary of the tungsten alloy block. The shape of the energy spectrum of protons being out-scattered agreed between the codes. The dose-weighted forward out-scatter probability, i.e. the ratio between the total signal from the unscattered beam and the out-scattered beam, showed a qualitative agreement of simulations compared to measurements. Quantitatively, the deviation of the simulations reached as high as 37%, while the experimental uncertainty was 14%. The mean emission angle of the simulations was within 16% of the measurement for all incidence angles with a measurement uncertainty of 8%.

Interstitial photodynamic therapy (PDT) has seen a rebirth, partially prompted by the development of photosensitizers with longer absorption wavelengths that enable the treatment of larger tissue volumes. Here, we study whether using diffusers with customizable longitudinal emission profiles, rather than conventional ones with flat emission profiles, improves our ability to conform the light dose to the prostate. We present a modified Cimmino linear feasibility algorithm to solve the treatment planning problem, which improves upon previous algorithms by (1) correctly minimizing the cost function that penalizes deviations from the prescribed light dose, and (2) regularizing the inverse problem. Based on this algorithm, treatment plans were obtained under a variety of light delivery scenarios using 5–15 standard or tailored diffusers. The sensitivity of the resulting light dose distributions to uncertainties in the optical properties, and the placement of diffusers was also studied. We find that tailored diffusers only marginally outperform conventional ones in terms of prostate coverage and rectal sparing. Furthermore, it is shown that small perturbations in optical properties can lead to large changes in the light dose distribution, but that those changes can be largely corrected with a simple light dose re-normalization. Finally, we find that prostate coverage is only minimally affected by small changes in diffuser placement. Our results suggest that prostate PDT is not likely to benefit from the use of tailored diffusers. Other locations with more complex geometries might see a better improvement.

A great deal of current research is directed to finding a way to minimize thermal injury in the esophagus during radiofrequency catheter ablation of the atrium. A recent clinical study employing a cooling intraesophageal balloon reported a reduction of the temperature in the esophageal lumen. However, it could not be determined whether the deeper muscular layer of the esophagus was cooled enough to prevent injury. We built a model based on an agar phantom in order to experimentally study the thermal behavior of this balloon by measuring the temperature not only on the balloon, but also at a hypothetical point between the esophageal lumen and myocardium (2 mm distant). Controlled temperature (55 °C) ablations were conducted for 120 s. The results showed that (1) the cooling balloon provides a reduction in the final temperature reached, both on the balloon surface and at a distance of 2 mm; (2) coolant temperature has a significant effect on the temperature measured at 2 mm from the esophageal lumen (it has a less effect on the temperature measured on the balloon surface) and (3) the pre-cooling period has a significant effect on the temperature measured on the balloon surface (the effect on the temperature measured 2 mm away is small). The results were in good agreement with those obtained in a previous clinical study. The study suggests that the cooling balloon gives thermal protection to the esophagus when a minimum pre-cooling period of 2 min is programmed at a coolant temperature of 5 °C or less.

The purpose was to develop a fast needle insertion system to shorten the implantation time and to restrain prostate swelling during the implantation, thus reducing the seed setup error. The basic idea is to insert all the needles simultaneously using ultrasound guidance. The developed system consists of two similar templates that are connected. All the needles are set and locked to a moveable rear template according to the dose plan. The needle pack is then pushed into position, the lock released and seeds implanted needle by needle. A test and training phantom was also built.

A classical trajectory model has been used to predict total cross sections of single and double ionizing processes (including capture processes) for several ion-biological molecule collisional systems in the intermediate and high energy range. In this work, the systems studied are water, adenine or cytosine targets ionized by protons and α-particles with kinetic energies ranging from 25 keV amu⁻¹ to 3000 keV amu⁻¹. In our approach, we have combined several features of two classical methods namely the classical trajectory Monte Carlo (CTMC) and the classical over-barrier (COB) models. For the water target, our results are compared, for high kinetic energies of incident particles, to the available experimental and theoretical results, and reasonable agreement are generally observed especially for the single ionization (liberated electron moves freely after the collision) and the single capture (liberated electron captured by the projectile), both processes representing ionizing processes. Considering the double ionizing processes which have been largely less studied, the unique comparison concerns the double capture process for α+H₂O collision for which we reproduce the experiment reasonably well. Finally, we present total cross sections of single and double ionizing processes for biological targets such as adenine and cytosine where no experimental results exist till now.

Polymeric gel dosimeters are being used to verify three-dimensional (3D) dose distributions of different types of radiotherapy treatments, especially the most complexes ones. An important factor that can limit the wider use of this kind of dosimeter is temperature, as gel melting can destroy 3D information. This work shows that adding formaldehyde to the gel preparation increases the melting point, allowing its use in warmer environments, including up to body temperature. An addition of 3% in mass of the formaldehyde solution to a MAGIC type gel dosimeter increased its melting point from 25 to 69 °C. Also important were a 12.5% increase in gel sensitivity and an expressive decrease in relaxation rate R2 uncertainty.

The alignment of data in table 2 is corrected in the pdf provided