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Biomedical subjects

G M Cattaneo

Publications and source records attributed to G M Cattaneo.

At least 19 recordsLinked to original sources
PubMed1995

Dynamic beam modulation by using a single computer-controlled absorber.

The authors have developed an apparatus able to generate ID intensity-modulated beams, using only one moving absorber within the irradiation field. A procedure for deriving optimized absorber-speed profiles in order to produce the desired fluence/dose profiles has been suggested. Experimental tests show that the system should be sufficiently reliable in reproducing modulated beam profiles of different shape: expected relative doses against measured relative doses have been found to be in agreement in a number of situations within 3% using a nonfocused device. A better agreement should be expected using a focused apparatus (which is currently being developed). Beam modulation by single absorber cannot modulate the beam fluence in any was one wishes, due to physical constraints, which depend on the absorber and field widths and on the shape of the desired fluence profile. However, the authors show that this simple and low-cost tool could offer, with a sufficient degree of accuracy, the possibility of modulating the beam fluence with a high degree of versatility. In particular, a procedure or performing tissue-missing compensation by single-absorber dynamic beam modulation is suggested. Moreover, 'strongly' modulated beam profiles can be created, showing that this simple technique could also have some interesting applications in the field of conformal radiotherapy by non-uniform dose delivery.

Algorithms↗
PubMed1994

Skin-sparing reduction effects of thermoplastics used for patient immobilization in head and neck radiotherapy.

Skin-sparing benefits derived from the use of megavoltage photon beams can be strongly reduced when filters are inserted between the source and the patient. The use of plastic masks for immobilizing the patient is the most important cause of this reduction in head and neck treatments. The influence of thermoplastics, commercially available for patient immobilization systems (Orfit Raycast (Luxilon Ind. Co.), Posicast (Sinmed bv) and Optimold (WFR Aquaplast Corp.)), on the patient skin dose value has been investigated by using an NE2534 'Markus' chamber. Indicative measurements with moulded masks (carried out with 2-mm Orfit and 3.2-mm Optimold layers) show significant differences between masks moulded with the two thermoplastics.

Acrylic Resins↗
PubMed1994

Cable-induced effects on plane-parallel ionization chamber measurements in large clinical electron beams.

The interaction between photon or electron fields and cables of ionization chambers induces the flow of leakage currents affecting the measured signal; this "cable effect" is particularly important when large electron and photon fields are used, i.e., when large portions of cable are irradiated. Therefore it is more interesting to investigate cable-induced effects when ionization chambers are used for clinical situations where large fields are used, for example, total body and total skin electron irradiations (TSEI). In TSEI fields these effects are particularly important. Cable and connector effects using an NE2534 Markus chamber in total skin irradiation conditions with different electron energies (from 1.6 to 4.5 MeV) have been investigated. These effects are significant and show that for TSI dosimetry it is vital to take them into account.

Electrons↗
PubMed1993

Exit dose measurements by portal film dosimetry.

Portal in vivo dosimetry is a very attractive tool for patient dose measurements because of the large amount of information that portal film systems can easily collect, once positioned at the exit surface of the patient. The first step in the verification of the reliability of portal films as in vivo dosimeters is the evaluation of the agreement between exit patient dose profiles and optical density profiles measured on the portal film. We checked the possibilities for exit dose measurements of a commercial portal film system (Film Kodak X-Omat V and Localization Kodak Cassette) verifying the agreement between relative exit doses (measured by ionization chamber and film dosimetry, calculated by our treatment planning system (Cadplan Dosetek)) and relative optical densities on portal films in cubic homogeneous and inhomogeneous, cylindrical and humanoid phantoms. In particular, a good agreement (mean difference in absolute value: 2%) between optical densities and calculated exit doses for the Rando phantom were found, once the optical densities values are corrected for an inverse square correction factor, taking into account the variation of the profile of the phantom.

Absorptiometry, Photon↗
PubMed1993

Human errors in the calculation of monitor units in clinical radiotherapy practice.

Human mistakes are an important source of error in all steps of radiotherapy planning and their incidence should be investigated. As has been recognized by different authors and by the ICRU [4], the human error rate in the calculation of monitor units (MU) is relatively high. At our institute, we measured the human error rate in the calculation of MU by an independent check of the calculation. From September 1991 to June 1992 we identified and corrected 17 serious errors (deviation from the prescribed dose > or = 5%) over 890 controls (1.9%) (daily dose errors). We also found a serious global dose error rate (i.e. the errors induced on the total reference dose for the complete course of the treatment) of 1.3% (9/685) during the period November 1991-June 1992. These values suggest the importance of human errors in the calculation of MU and also confirm the validity of the independent check of MU calculation as one of the simplest ways of avoiding erroneous dose delivery by incorrect calculation of MU.

Humans↗
PubMed1992

[Dosimetric problems and their solution in the preparation of a 6-dual-field total-skin technique].

The six-field total skin electron irradiation (TSEI) technique needs an accurate preliminary dosimetric study. The American Association Physics in Medicine (AAPM) defined a dosimetric protocol that recommends the careful dosimetry of the horizontal, the dual and the six-dual fields by using both a cubic and a cylindrical phantoms. In our Institute, in a TSEI development program, we carried out the preliminary dosimetry according to AAPM criteria. We also investigated some dosimetric problems--e.g., the so-called "cable effect", which takes place when the detector cable in a TSEI field is not well shielded, polarity effects and photon contamination. As to the "cable effect", it is especially marked with the Markus NE2534 chamber; moreover, this effect, if not considered, can lead to overestimation of X-rays contamination.

Calibration↗
PubMed1992

[Conformal technics by the movement of bars in pendular fields. 1. Prototype realization and the possible applications].

The growing interest for conformal radiotherapy originates from the need of giving the prescribed dose to the target volume, by sparing, at the same time, surrounding healthy tissues and organs. More dose to the target volume with respect to the healthy tissues always increases the curative possibilities of the treatment. However, the development of conformal techniques implies an increased complexity of the treatment and the solution of many technical and dosimetric problems. In our Institute we are developing new conformal techniques, based on the use of moving bars driven by a computer-controlled system in arc therapy. This paper refers to the conclusion of the preliminary part of our work: a movement (translating or rotating) of bars in arc therapy seems to have good chances to tailor dose distribution in a relatively simple way. We realized two mechanical systems driven by computer for translating and rotating movements of a bar. The two techniques have been tested by TLD and film dosimetry on acrylic phantoms. We present the results of these tests, and describe technical problems and the clinical possibilities of this method.

Equipment Design↗
PubMed1992

[Conformal technics by the movement of bars in pendular fields. 2. The dosimetric aspects].

The development of conformal techniques by movement of bars in pendular fields requires a careful examination of many physical and dosimetric problems: bar-critical organ synchronization problems, dose calculation problems, and problems relative to the "shadow effect". The use of a bar in an arc field, causes to a slow gradient of dose between shielded zone and target volume with a loss of homogeneity in dose distribution. This effect is well known ("shadow effect") and depends on the fact that different points spend different times beyond the bar's shadow. In this work the problem is investigated in the case of moving bar technique, mainly for dose calculation possibilities; then the possibility is analyzed of optimizing dose distribution by means of filters whose profile can be calculated for simple geometric conditions (fixed bar on the isocenter without considering the profile of the patient). These filters will be made in our Institute and they will be tested in various conditions, for both fixed bars and moving bars in arc fields.

Equipment Design↗
PubMed1990

[Description and results of a simplified procedure for intraoperative electron radiotherapy].

In San Raffaele Institute a simplified procedure for intraoperative radiotherapy (IORT) was developed. An applicator system of "guide-containers" was used to facilitate the use of IORT (with electron beam) with different treatment fields. Application of this technique was studied; no IORT related complications was observed in phase I and clinical good results are reported.

Combined Modality Therapy↗
PubMed1985

Increased glomerular thromboxane synthesis as a possible cause of proteinuria in experimental nephrosis.

Altered glomerular metabolism of arachidonic acid (AA) has already been demonstrated in experimental nephrotoxic nephritis. The enhanced synthesis of thromboxane A2 (TxA2) in isolated glomeruli that has been found may mediate changes in renal hemodynamics. The objectives of this investigation were: to check whether glomerular AA metabolism is also altered in a model of glomerulopathy in which no leukocyte infiltration or platelet deposition could be demonstrated; to establish a correlation between the altered AA metabolism and proteinuria; and to explore whether the alteration of the prostaglandin (PG) pathway found in isolated glomeruli is an in vitro artifact or reflects a modification in vivo. We used a model of glomerular damage characterized by heavy and persistent proteinuria, which was induced in the rat by a single intravenous injection of adriamycin. At light microscopy, minimal glomerular abnormalities were found in this model. Electron microscopy showed profound alterations of glomerular epithelial cells with extensive fusion of foot processes and signs of epithelial cell activation. Electron microscopy of numerous glomeruli showed no platelet deposition or macrophage and leukocyte infiltration in this model. Isolated glomeruli from nephrotic rats studied 14 or 30 d after a single intravenous injection of adriamycin (7.5 mg/kg) when animals were heavily proteinuric generated significantly more TxB2, the stable breakdown product of TxA2, than normal glomeruli. No significant changes were found in the other major AA metabolites formed through cyclooxygenase. Urinary excretion of immunoreactive TxB2 was also significantly higher in nephrotic than in normal animals. Administration of a selective Tx synthetase inhibitor, UK-38,485, from day 14 to day 18 after adriamycin resulted in a significant reduction of proteinuria compared with pretreatment values. Glomerular synthesis and urinary excretion of TxB2 were normal during the UK-38,485 treatment. Additional experiments showed that elevated glomerular synthesis and urinary excretion of TxB2 were not a consequence of increased substrate availability. Maximal stimulation of the renin-angiotensin axis with furosemide increased glomerular TxB2 synthesis in normal rats, which was significantly lower than in nephrotic animals. Finally, experiments using a unilateral model of adriamycin nephrosis indicated that the enhancement of glomerular TxB2 synthesis is not simply a consequence of the nephrotic syndrome. We conclude that: there is an abnormality of glomerular AA metabolism in nephritic syndrome, which leads to increased TxA2 production; the increased Tx generation correlates with protein excretion and might be responsible for altering the glomerular basement membrane permeability to protein; and the alteration found in isolated glomeruli probably reflects a modification in vivo, in that urinary excretion of immunoreactive TxB2 is also consistently increased in adriamycin nephrosis.

Animals↗