[Imaging quality of a digital Konica Regius 336 system for thoracic radiology]. / Qualità dell'immagine di un sistema digitale Konica Regius 336 per Radiologia Toracica.

INTRODUCTION: Digital radiographic systems permit to optimize execution, depiction and storage of radiological images. Since a Regius 336 digital system (Konica Corp., Tokyo, Japan) devoted to chest radiography was recently installed in the Radiology Department of S. Anna Hospital in Como, Italy, we investigated its performance relative to image quality. MATERIAL AND METHODS: Konica Regius 336 is a computed radiography system made of a phosphorescence detector plate which is scanned with an infrared semiconductor laser beam. The radiographic image obtained from the detector is subjected to image processing, which allows a stable output and the nonlinear curve typical of conventional radiographic systems. Image quality was assessed based on the following parameters: dose, contrast, noise, and spatial resolution. As reference, we assessed the same parameters on a Cronex 88 analogic chest-changer (DuPont Pharma, North Billerica, Mass, USA). RESULTS: The Regius 336 air kerma values were always higher than the analogic ones (about 10%), both with and without a chest phantom; noise was also greater than in analogic images, sometimes even doubled. The optical densities of a step wedge and the spatial resolution of the digital chest-changer are independent of the X-ray tube voltage consequent to broader optical latitude. Inversely, the analogic images of the wedges show great optical density variability as a function of the X-ray tube voltage (in a range of 2). The modulation transfer functions of the two systems have the same trend. DISCUSSION AND CONCLUSIONS: The performance of the Konica Regius 336 is nearly equivalent to that of an analogic system. The main advantages of the digital system are a standard output, lower consumption of radiographic films, higher productiveness and better image quality standard level.

Contrast improvement in a new radiotherapy imaging system.

PURPOSE: The aim of this paper is to compare the EC-L Kodak system for radiation therapy beam localization with a conventional one that could be daily employed in a radiotherapy department. BACKGROUND: The main purpose of portal images is to verify the treatment volume in actual clinical conditions. Low contrast is the main constraint affecting portal film image. METHODS: Kodak proposes a new imaging system (film and cassette) characterized by contrast enhancement as imaging standard for radiotherapy. The evaluation of system contrast was carried out by using a step-wedge consisting in 4 60 x 60 mm plexiglas steps and an anthropomorphic phantom. Portal films were exposed to a 6 MV photon beam by a linear accelerator (Varian Clinac 1800) with a 250 x 340 mm field size at the 1000 mm source film distance. The 2 imaging system performances were evaluated analyzing the image optical density. RESULTS: The use of the Kodak system results in a real contrast improvement, so it is satisfactory to describe the field placement as to the region of interest. CONCLUSIONS: The most critical characteristic attaining this method regards low contrast, i. e. the small optical density difference existing between different anatomical regions on the film. Since radiographic techniques can significantly influence quality of portal films, the adequate choice of film and screen combination, as well as the exposure technique is particularly useful in a radiotherapy quality assurance program.

[In vivo dosimetry. Assessment of exit dose correction factors]. / Dosimetria in vivo. Valutazione dei fattori di correlazione per la dose in uscita.

INTRODUCTION: In vivo dosimetry allows to verify dose delivering accuracy in radiotherapy treatments. Exit dose measurements add more information about delivered dose than entrance dose evaluations. MATERIALS AND METHODS: Commercial semiconductor diodes are used for exit dose measurements. The diodes are calibrated by comparison with an ionization chamber at a reference condition. Diode reading was compared with the dose measured by the ionization chamber at the exit point. The exit point is defined as the point on the central axis of the beam, at a distance equal to the maximum dose from the exit surface of a homogeneous water-like phantom. As clinical irradiation conditions are always different from reference conditions, exit dose correction factors have been investigated as a function of phantom thickness, field size at the isocenter, source-surface distance, wedge and tray. Measurements have been performed by irradiating a set of p-type semiconductor detectors with 6 MV photon beam (four diodes--mod. EDP10--Scanditronix) and 18 MV photon beam (three diodes--mod. EDP20--Scanditronix) from a Clinac 1800 linear accelerator (Varian, Palo Alto, CA, USA). RESULTS: The most relevant exit dose correction factors are related to field size and phantom thickness for 6 MV photons. The variation of these factors as a function of field size may be greater than 1% with a standard deviation of the same order. On the contrary, the correction factors for field, thickness and tray photons are negligible for 18 MV. CONCLUSIONS: Applying exit dose correction factors may require a great effort, particularly when many silicon diodes must be used. The actual effectiveness of each calibration factor is evaluated through the statistical analysis of experimental data. In this way, the usefulness of correction factor calculation, as depending from both experimental conditions and diode responses, can be derived from its effects on the exit dose value.

[Air bubble effect during alloy cooling in shielding blocks radiotherapy]. / Effetti della presenza di disomogeneità nelle fusioni impiegate nei campi radioterapici con forma irregolare.

INTRODUCTION: Shaped fields are widely used in radiotherapy to protect critical organs and to avoid unnecessary normal tissue irradiation. The most common system for photon beam shaping consists in a low melting point alloy. We studied the air bubbles which can occur during alloy cooling with both new and remelted alloys and when different cooling techniques are chosen. MATERIAL AND METHODS: Forty cone samples (18 of remelted alloy and 22 of new alloy) were prepared to evaluate the frequence of air bubble recurrence, with reproducible geometric sizes (height = 70 mm, major base surface diameter = 60 mm, minor base surface diameter = 40 mm). Air bubble sizes and dose inhomogeneity were evaluated by reproducing 60Co radiograph of each sample (two orthogonal projections: 6 x 7 cm). The samples were cooled at a constant temperature, following three different modalities: high (25 degrees C), medium (5 degrees C), low (-20 degrees C) temperature. Owing to the small geometrical magnification, air bubble sizes were determined by measuring their surface on samples lateral projections, taking into account the sight detectable bubble edges. RESULTS: Up to 300 mm2 lateral surface bubbles are always present in all castings. Casting inhomogeneities can produce a film-density inhomogeneity ranging from 9% to 40%. The spatial distribution of bubbles seems to be random. CONCLUSIONS: Bubble recurrence is independent of both the metal alloy (repeatedly used castings) and the different block cooling modalities. The effect of air bubbles on the shielded areas dose inhomogeneity is generally of no relevant importance. However, these inhomogeneities can produce hot spots which must be taken into accurate consideration only in the particular treatments where critical small size organ dose sparing represents a basic issue (i.e. the shielding of eye lens).

[The estimation of the variation in the effective dose in the most frequent nuclear medicine studies]. / Valutazione della variazione della dose efficace nelle più frequenti indagini mediconucleari.

INTRODUCTION: The evaluation of effective doses in nuclear medicine investigations is generally referred to the average man, with no relevant associated diseases, during standard examinations. The effective dose in nuclear medicine examinations can be measured directly with ICRP 68. In clinical practice, the many variables related to patients characteristics and examination type may cause major differences between practical and theoretical doses. Thus, we investigated the factors which may affect internal irradiation in some of the most common nuclear medicine investigations. MATERIALS AND METHODS: We analyzed the most frequent examinations carried out on 177 patients in the Nuclear Medicine Department of S. Anna Hospital, namely thyroid scintigraphy, total body bone scan, dynamic and static renal scintigraphy. The administered activity data were analyzed as a function of the withdrawn activity and that remaining in the syringe after i.v. administration and of time delays, and then they were submitted to statistical analysis (mean, standard deviation, 95% confidence range). RESULTS: Equivalent and effective dose changes had no correlation with patient anatomy and associated diseases on the basis of history alone, while radiopharmaceutical preparation and administration methods exhibited a real influence on effective dose: the difference between nominal and administered activity ranged 11-14.5%. CONCLUSIONS: The patients submitted to nuclear medicine investigations receive an effective dose ranging from < .5 mSv to > 4 mSv in total body scan. Our results, related to the different examination techniques, represent a confident evaluations of patient doses, as required by the relevant normative law.

An ICRU 50 radiotherapy treatment chart.

We illustrate a radiotherapy treatment chart elaborated to fulfil the necessity for clarity in reporting information about radiotherapeutic treatment. The schematic configuration of the chart results from the experience and the cooperation of physicists, physicians and technicians, and an effort has been made to satisfy Levels 2/3 of the ICRU 50 recommendations. The chart has been divided into four sections corresponding to different kinds of information: a cover sheet, a section containing data about the treatment planning geometry and the console parameters adopted, a section showing dosimetric data, and a section showing treatment data. The chart seems to give a good level of accuracy in reporting treatment plan information.

An equivalent square method for irregular photon fields.

A quick formula is proposed for calculating equivalent squares of irregularly shaped photon fields. No complex calculations are required. Three different energies (60Co; 6 MV and 18 MV x-rays) were investigated. Comparison with results utilizing the Clarkson technique (60Co) and with experimental measurements (6 MV and 18 MV x-rays) indicates that the method is accettable in a wide variety of clinical situations. The applied procedure introduces an indetermination lower than 4%, with maximum absolute percentage errors of 3%, 2.7%, and 3.6% for 6 MV, 18 MV, and 60Co photon fields respectively.