Computed chest radiography for total body irradiation: image quality and clinical feasibility.

In myeloablative total body irradiation (TBI), lung shielding blocks are used to reduce the dose to the lungs and hence decrease the risk of radiation pneumonitis. Some centers are still using mega-Volt (MV) imaging with dedicated silver halide-based films during simulation and treatment for lung delineation and position verification. However, the availability of these films has recently become an issue.

Survey on fan-beam computed tomography for radiotherapy: Current implementation and future perspectives of motion management and surface guidance devices.

Background And Purpose: This work reports on the results of a survey performed on the use of computed tomography (CT) imaging for motion management, surface guidance devices, and their quality assurance (QA). Additionally, it details the collected user insights regarding professional needs in CT for radiotherapy. The purpose of the survey is to understand current practice, professional needs and future directions in the field of fan-beam CT in radiation therapy (RT).

Survey on fan-beam computed tomography for radiotherapy: Imaging for dose calculation and delineation.

Background And Purpose: To obtain an understanding of current practice, professional needs and future directions in the field of fan-beam CT in RT, a survey was conducted. This work presents the collected information regarding the use of CT imaging for dose calculation and structure delineation.

Materials And Methods: An online institutional survey was distributed to medical physics experts employed at Belgian and Dutch radiotherapy institutions to assess the status, challenges, and future directions of QA practices for fan-beam CT.

Measurement-based validation of a commercial Monte Carlo dose calculation algorithm for electron beams.

Purpose: This work presents the clinical validation of RayStation's electron Monte Carlo code by the use of diodes and plane parallel radiation detectors in homogenous and heterogeneous tissues. Results are evaluated against internationally accepted criteria.

Methods: The Monte Carlo-based electron beam dose calculation code was validated using diodes, air- and liquid-filled parallel radiation detectors on an Elekta linac with beam energies of 4, 6, 8, 10, and 12 MeV.

The influence of small field sizes, penumbra, spot size and measurement depth on perturbation factors for microionization chambers.

The purpose of this study was the investigation of perturbation factors for microionization chambers in small field dosimetry and the influence of penumbra for different spot sizes. To this purpose, correlated sampling was implemented in the EGSnrc Monte Carlo (MC) user code cavity: CScavity. CScavity was first benchmarked against results in the literature for an NE2571 chamber.

Measurement techniques, modeling strategies and pitfalls to avoid when implementing a mini MLC in a non dedicated planning system.

Background And Purpose: Ghent University Hospital investigated the feasibility of the Pinnacle system for planning intracranial stereotactic treatments. The aim was to perform precise dose computation using the collapsed cone engine for treatment delivery with the Moduleaf mini-MLC mounted on an Elekta accelerator.

Material And Methods: The Moduleaf was commissioned using dose rate corrected data recorded by a diamond detector and using data measured by cylindrical chambers each limited to restricted field sizes.

Monte Carlo modeling of the ModuLeaf miniature MLC for small field dosimetry and quality assurance of the clinical treatment planning system.

The purpose of this investigation was the verification of both the measured data and quality of the implementation of the add-on ModuLeaf miniature multileaf collimator (ML mMLC) into the clinical treatment planning system for conformal stereotactic radiosurgery treatment. To this end the treatment head with ML mMLC was modeled in the BEAMnrc Monte Carlo (MC) code. The 6 MV photon beams used in the setup were first benchmarked with a set of measurements.

The influence of cooling rate on the accuracy of normoxic polymer gel dosimeters.

Polymer gel dosimeters offer a wide range of applications in the three-dimensional verification of complex radiation dose distributions such as in intensity-modulated radiotherapy (IMRT). With the release of polymer gel dosimeters that can be fabricated in normal atmospheric ('normoxic') conditions, the gel manufacturing process has been significantly simplified. Gel dosimeters are calibrated by use of a series of calibration vials irradiated with known doses or by use of a calibration phantom with a known dose distribution.

Decoupling initial electron beam parameters for Monte Carlo photon beam modelling by removing beam-modifying filters from the beam path.

A new method is presented to decouple the parameters of the incident e(-) beam hitting the target of the linear accelerator, which consists essentially in optimizing the agreement between measurements and calculations when the difference filter, which is an additional filter inserted in the linac head to obtain uniform lateral dose-profile curves for the high energy photon beam, and flattening filter are removed from the beam path. This leads to lateral dose-profile curves, which depend only on the mean energy of the incident electron beam, since the effect of the radial intensity distribution of the incident e- beam is negligible when both filters are absent. The location of the primary collimator and the thickness and density of the target are not considered as adjustable parameters, since a satisfactory working Monte Carlo model is obtained for the low energy photon beam (6 MV) of the linac using the same target and primary collimator.

Ultrasonic velocities of concentric laminated uric acid stones.

In concentric laminated uric acid samples two different sound velocities are observed with very different values, the one in the organic matrix varies from 670 to 1170 m s(-1), the other in the crystalline layers between 3200 and 5300 m s(-1). This large difference illustrates the importance of the internal stone structure on the fracture behaviour of urinary stones and reveals the weakness of the actual disintegration models, attributing the destructive effect of shock waves on the differences in acoustical impedance at the water/stone interface and not on the differences in acoustical impedance at the matrix/crystalline interfaces inside the urinary calculus.

Neoadjuvant hormonal therapy before radical prostatectomy decreases the number of positive surgical margins in stage T2 prostate cancer: interim results of a prospective randomized trial. The Belgian Uro-Oncological Study Group.

Purpose: We investigated the effect of neoadjuvant treatment before radical prostatectomy for clinically localized prostate cancer.

Materials And Methods: A total of 130 patients with stages T2b and T3 prostate cancer was randomized in a multicenter study: 62 underwent immediate radical prostatectomy and 65 received 560 mg. estramustine phosphate daily for 6 weeks preoperatively.

Importance of the implosion of ESWL-induced cavitation bubbles.

The damage induced by an extracorporeal shock wave lithotripter is observed with a fiber optic stress sensing technique. When a stone is placed in the focus, besides the expected stress induced by the incoming shock wave emitted by the ESWL apparatus, a second delayed stress is observed some hundreds of microseconds later. The second stress is induced by a shock wave generated at the collapse of a cavitation bubble.

Macroscopic ESWL-induced cavitation: in vitro studies.

The rarefaction shock wave results in a liquid failure at the target/fluid interface. In the wake of the reflected ESWL-induced shock wave, a macroscopic cavity is generated in filtered water. The cavity implosion induces a large shock wave, divulging the bubble existence and lifetime.

The influence of internal stone structure upon the fracture behaviour of urinary calculi.

In vitro extracoporeal shock wave lithotripsy (ESWL) on different types of urinary calculi, in combination with microfocus x-ray and microphotography, illustrates the importance of the internal stone structure. Calculi with a rough surface layered structure (calcium oxalate monohydrate) and untextured calculi (cystine) are characterized by a low stone fragility, whereas coarse-grain calculi (calcium oxalate dihydrate, struvite), and calculi with a smooth surface layered structure (uric acid), are very fragile. Shell-like fragmentation in layered calculi, with smooth surface of the crystalline laminations, suggests that the stone matrix influenced the propagation of the shock wave energy inside the stone.

In vitro analysis of urinary calculi: type differentiation using computed tomography and bone densitometry.

Thirty-six urinary stones were studied by computed tomography and bone densitometry in order to find a correlation between the chemical composition of the stones and the densitometric data. In vitro, the more common cases of lithiasis can be divided into 3 main groups: uric acid, cystine and the calcium salts, e.g.

Stone geometry and structure dependence on extracorporeal shock wave lithotripsy.

The in vitro fragmentation effects of electromagnetic-induced shock wave lithotripsy (Siemens Lithostar) were studied on parallel laminated schists in relation to the incoming shock wave energy and the incoming angle of the incident shock wave. Well above the threshold energy, the total amount of acoustic energy required for fragmentation remained unchanged regardless of the power setting of the high-tension supply. The amount of energy transmitted to the stone was limited by a total reflection angle, restricting the available transmission surface.

High pressure versus low pressure electromagnetic extracorporeal lithotripsy.

A low pressure and an upgraded high pressure electromagnetic lithotriptor were compared for the treatment of calculi within the ureter. The upgrading allows for increased energy density onto the stone surface. We targeted 139 ureteral calculi (average diameter 8.

Effect of alkalinization on calcium oxalate monohydrate calculi during extracorporeal shock wave lithotripsy: in vivo experiments.

Previous in vitro experiments demonstrated the reduced microhardness of calcium oxalate monohydrate (COM) calculi, relative to dry values, when saturated with an alkaline solution (pH = 9.5). Nineteen patients with a COM calculus in the distal ureter which had been resistant to prior extracorporeal shock wave lithotripsy in situ, were treated when the stone was surrounded by alkaline urine.

High energy pulsed dye laser lithotripsy: management of ureteral calcium oxalate monohydrate calculi.

High energy pulsed dye laser lithotripsy (Candela MDL-2000), with energy output upgraded to a maximum of 140 mJ. at the laser fiber tip using the 320 mu core fiber, was compared to the initially commercialized device, with the energy output fixed at 60 mJ. using the 200 mu core fiber (Candela MDL-1).

Combined extracorporeal shock wave lithotripsy and percutaneous alkalinization in uric acid calculi.

The combination of percutaneous alkaline irrigation and lithotripsy was performed in 5 cases of uric acid calculi obstructing the ureter. Shock wave lithotripsy accelerates the dissolution of uric acid stones.

Anesthetic requirements during electromagnetic extracorporeal shock wave lithotripsy.

An important aspect of modern extracorporeal shock wave lithotripsy is the ability to perform the procedure without anesthesia. Between June 1987 and April 1990, a total of 7,500 treatments were performed in our Lithotripsy Unit, using the Lithostar (Siemens AG, Erlangen, FRG): moreover 80% of the treatments were carried out as an anesthesia-free outpatient service. All treatments were reviewed for anesthetic requirements.