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Biomedical subjects

G M Cattaneo

Publications and source records attributed to G M Cattaneo.

At least 37 records · Page 2Linked to original sources
PubMed1997

Optimizing the movement of a single absorber for 1D non-uniform dose delivery by (fast) simulated annealing.

A new simplified technique for 1D non-uniform dose delivery using a single dynamic absorber, driven by a computer system, has been recently proposed together with a simple analytic algorithm. This technique uses an optimized 'stepped' absorber's speed profile and the generated fluence profile is an approximation of the desired radiation beam. In the case of non-uniform beam profiles with multiple maxima/minima, the original proposed 'stepping algorithm' has some limitations and produces a too rough approximation of the desired profiles. In order to increase the agreement between desired and generated profiles, more sophisticated optimization schemes are required. In this paper we have applied a variant of simulated annealing (SA) as a statistical optimization algorithm to further investigate the possibilities and the limits of the single-absorber technique in the field of 1D intensity modulation. In the current application the cost function used is the mean square root of the percentage differences between desired and generated profiles, the absorber's resting times have been chosen as optimization variables and at each iteration just one variable is randomly changed, adding an incremental 'grain'. A Cauchy generating function is used, different cooling schedules are evaluated; constraints related to our apparatus are introduced and starting annealing parameters are set after some initial optimization tests. The method is tested in reproducing theoretical non-uniform beams, by comparing desired modulated fluence profiles with calculated fluence profiles obtainable with the single absorber after the derivation of optimized speed profiles by the proposed SA approach. The results of these simulations show that the application of the SA method optimizes the single absorber's performance and that clinically important modulated beams useful for conformal radiotherapy can be accurately reproduced.

Algorithms↗
PubMed1997

Monitor unit calculation in 6 MV irregularly shaped beams--accuracy in clinical practice.

The results of an investigation of the accuracy of monitor unit (MU) calculation in clinical shaped beams are presented. Measured doses at the reference depth on the beam central axis (isocentre) or on a beam axis representative of the irradiated area (when the isocentre lies under a block or near the edges of the block's shadow) were compared with the expected doses when calculating MUs, by applying different methods normally used in clinical practice. Empirical (areas weighted, Wrede) and scatter summation (Clarkson) methods as well as a pencil-beam based algorithm were applied. 40 irregular fields (6 MV X-rays, CLinac, Varian 6/100), divided into six categories, were considered. Dose measurements were performed with a NE2571 ionization chamber in an acrylic 30 x 30 x 30 cm3 phantom. The depths in acrylic were converted into water-equivalent depths through a correction factor derived from TMR measurements. The method of dose measurements in acrylic was found to be sufficiently accurate for the purpose of this study by comparing expected and measured doses in open square and rectangular fields (mean deviation +0.2%, SD = 0.5%). Results show that all the considered methods are sufficiently reliable in calculating MUs in clinical situations. Mean deviations between measured and expected dose values are around 0 for all the methods; standard deviations range from 1% for the Wrede method to 0.75% for the pencil-beam method. The differences between expected and measured doses were within 1% for about 3/4 of the fields when calculating MUs with all the considered methods. Maximum deviations range from 1.6% (pencil-beam) to 3% (Wrede). Slight differences among the methods of MU calculation were revealed within the different categories of blocked fields analysed. The surprising agreement between measured and expected dose values obtained by using empirical methods (area weighted and Wrede) is probably due to the fact that the reference points were positioned in a "central" region of the unblocked areas.

Algorithms↗
PubMed1996

On-line exit dose profile measurements by a diode linear array.

The possibility of using a commercial diode linear array (BMS Schuster Inc.) in on-line portal dosimetry has been investigated. The system is composed of 88 equispaced diodes (distance between diodes, 0.5 cm; detection area, 2.5 x 2.5 mm2). The ability to measure exit dose profiles has been demonstrated by comparing relative exit dose profiles measured by an ionization chamber (NE 2571) with 'portal' profiles measured by the diode array on a number of homogeneous and inhomogeneous phantoms in 6 MV x-ray beams (from a Clinac Varian 6/100). The influence of the variation of the scattered radiation at the exit level with respect to the detector level has been discussed and investigated by varying the air gap (from 0 to 80 cm for a homogeneous phantom and from 0 to 25 cm for inhomogeneous phantoms) as well as the field width. A good agreement (maximum difference 3.8%; 2.5% when the array was positioned in contact with the phantoms) between 'portal' profiles and exit dose profiles in both homogeneous and inhomogeneous phantoms has been found if the array-phantom distance is kept below 7.5 cm. Results indicate that the system should be suitable for applications in transit dosimetry.

Air↗
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

Development of a computer-controlled moving bar (CCMB) conformal technique for neck irradiation.

The development of an original conformal technique for neck cancer is in progress in our Institute. This technique uses a computer-controlled moving bar (CCMB): a portion of a blocking bar rotates during the rotation of the gantry in a 2 pi arc field in order to shield the spinal cord over the whole irradiated volume. This technique should solve in a relatively simple way some problems for different clinical situations when cervical node irradiation is required together with the primary tumor. The technique has been tested in an acrylic cylindrical phantom and in the humanoid RANDO phantom for two different irradiation conditions (neck completely bent and partially aligned).

Head and Neck Neoplasms↗
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↗
PubMed1993

[Human errors in the calculation of the Monitor Unit in radiotherapy].

Human mistakes are a major source of error from the definition to the execution of a treatment planning. An unrevealed serious human error can cause therapy to fail therefore it is of fundamental importance to eliminate serious human errors during MU calculation. In this work the human error incidence in MU calculation is evaluated by an independent check. The investigation refers to 1,926 controls collected in about 18 months. Serious daily errors rate (errors causing a 5%, or higher, discrepancy on the daily reference dose) was 1.4% (27/1926). Serious global errors incidence (errors causing a 5%, or higher, discrepancy on the total reference dose) was 0.9% (15/1,731). The data show that the human error in MU calculation is not negligible; they also indicate the value of the independent control of MU, which is an important tool for quality assurance in radiotherapy (like in vivo dosimetry and portal imaging.

Bias↗
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↗