PubMed Health⌕ Search

Biomedical subjects

M Benassi

Publications and source records attributed to M Benassi.

At least 37 records · Page 2Linked to original sources
PubMed1990

[Dosimetry problems of radiotherapy with electron fields of small dimension or partially shielded].

In radiotherapy in many clinical cases it is necessary to employ electron beams of small dimensions and/or shielded in order to have shaped fields. It is well known that percentage depth dose and output depend on the energy, on the field dimensions and on the collimation system. In order to evaluate separately the influence of these factors measurements were performed with electron beams of nominal energy from 6 to 14 MeV, of a linear accelerator Philips SL/75. Measurements were performed in standard dimension phantoms and in a small perspex phantom, 3 cm diameter. The values obtained in this small phantom were compared with the ones obtained for the same diameter collimator in order to have information on effect of missing lateral scatter equilibrium. Other measurements for an applicator, open and partially shielded, were performed. The results of these measurements are shown in graphics. Data show that the percentage depth dose ionization curves at fixed energy depend on the collimator linear dimension in particular, when these dimensions are smaller than the range of secondary electrons. However it is evident the difficulty to find a correlation between linear field dimensions and the percentage depth ionization curves. In the clinical practice it is important to take into account this difficulty when employing small or irregular electron fields.

Electrons↗
PubMed1990

[Intraoperative radiotherapy with electrons (IORT). Dosimetry problems, first experience].

In this paper, preliminary results on the IORT dosimetry performed on the two radiotherapy centers, "Regina Elena National Cancer Institute" and "S. Cuore Catholic University", are presented. The absolute dosimetry has been performed with ion chambers (ENEA chamber and Markus flat chamber) using a water phantom. The relative measurements have been performed with solid state diodes and radiographic films, calibrated on absolute dosimetry system.

Combined Modality Therapy↗
PubMed1989

The responsiveness of bone metastases to radiotherapy: the effect of site, histology and radiation dose on pain relief.

281 patients with a total of 463 symptomatic osseous metastases treated for palliation between 1975 and 1985 have been retrospectively analysed. The most frequent primary sites were breast (50.1%) prostate (16.6%) and lung (11%), accounting for more than three fourths of all metastatic areas. Other primaries were represented by bladder, kidney, colorectal, uterus (corpus and cervix) melanoma and thyroid tumors, and by cancer from unknown origin. Palliation was evaluated only on a subjective pain score. Complete response meant complete pain relief, and partial response meant more than 50% and less than complete pain relief in all treated sites. Complete response rates were similar independently from the primary site, except for the adenocarcinomas of the kidney and for non-small cell carcinomas of the lung in which the response tended to be lower. A correlation was also found between the incidence of pain relief and the site of bone metastases, in that a lower response was shown in limb localizations. Also, the number of metastatic sites did not influence the complete response rate. As expected, the response rate in all cases seemed to be dependent on total absorbed dose while, surprisingly, it could not be shown to be affected by the fraction size. A similar trend was shown for the pain recurrence.

Adult↗
PubMed1989

A stochastic model of the acquisition of drug resistance during antineoplastic chemotherapy.

A stochastic model is proposed to simulate the phenomenon of acquisition of genetic resistance by a tumor cell population treated with antineoplastic cytotoxic agents. In the model, stochastic differential equations are numerically integrated to simulate the expected response after treatment with two different agents. The model takes into account the initial number of cells, the sequence of the agents, the time intervals between administrations, the birth and death rates of the untreated cells, the probabilities of mutations to resistance, and the induced cell-killing kinetics. Satisfactory demonstration runs of the model indicate that it could represent a useful tool in verifying the results of experimental and clinical chemotherapy courses and planning treatment strategies.

Antineoplastic Agents↗
PubMed1989

Mathematical models of cell survival after ionizing radiation: application to radiotherapy planning.

The work described here represents an attempt to use mathematical models of single-cell survival for radiotherapy planning. The aim of the study is to develop a procedure in which the distribution of the effects achieved by optimizing physical radiation dose is implemented by taking into account radiobiological terms. An algorithmic model has been developed to evaluate the probability of tumor control and of excessive damage to normal tissue on the basis of the linear-quadratic model of cell survival. In its present preliminary form, the procedure can be used to predict differential isoeffect distributions obtained by varying the total dose and the fraction size of multifraction radiotherapy courses. This approach can also be used to extract from historical clinical results, by maximum-likelihood methods, parameters related to the cellular response to radiation (for instance, alpha and beta of the linear-quadratic model).

Cell Survival↗
PubMed1989

In vivo ESR dosimetry in total body irradiation.

Total body irradiation (TBI) using high doses (about 10 Gy) with photons in the range between 1 and 10 MV combined with intensive chemotherapy has been used successfully in treatment of acute and chronic leukemia before bone marrow transplantation. One of the principal international guidelines in TBI is to use in vivo dosimetry in order to compare the prescribed dose with that absorbed. The use of in vivo dosimetry is also useful as a retrospective evaluation of any deviation from the prescribed dose greater than +/- 5% for relevant parts of the body, especially in the lung and in other organs at risk. In this paper, Electron Spin Resonance (ESR), using alanine dosimeters, is demonstrated to be a powerful tool for absorbed dose evaluation in TBI by detection of free radicals produced in alanine by ionizing radiation. In this study, we present the results obtained using ESR dosimetry in eleven patients undergoing TBI. The major advantages appear to be: 1. the ESR signal in alanine dosimetry is stable for years without fading: 2. the detection of the ESR signal does not destroy the information and so enables a retrospective judgment of the TBI plan adopted.

Alanine↗
PubMed1988

Establishment, characterization and chemosensitivity of two human glioma derived cell lines.

Two continuous human glioma derived cell lines, LI and DF, were established in our laboratory. Both cell lines showed cytological features and in vitro behavior similar to those of the respective original neoplasms. These two lines were characterized for their main biological properties including in vitro and in vivo growth rate, clonogenic ability and tumorigenicity in nude mice. The plating efficiencies were generally high both during exponential and stationary growth phases and a high tumorigenicity was observed. All injected nude mice developed tumors. The two lines were tested for chemosensitivity to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and cis-Diamminedichloroplatinum II (DDP). Heterogeneity in biological features and in drug sensitivity was observed. Exposure of the two lines to BCNU and DDP showed that the glioblastoma (LI) was less sensitive than the anaplastic astrocytoma (DF). For both lines BCNU was more effective on cells in plateau than in exponential phase, while the killing effect of DDP was not phase-dependent.

Animals↗
PubMed1987

Radiotherapy and hyperthermia. Analysis of clinical results and identification of prognostic variables.

Site- and tumor-specific data obtained from two groups of patients with head and neck and melanoma lesions, respectively, showed that both immediate response and response duration were enhanced by the addition of heat. Two important variables, however, such as tumor volume and "isoeffect thermal dose" appeared to influence local tumor control. The volume effect was less pronounced in the lesions treated with radiotherapy plus heat than in those treated with radiotherapy alone, suggesting that the addition of heat was more damaging to the large than to the small lesions. Furthermore, a striking isoeffect thermal dose-response relationship was shown in head and neck lesions. Those data were collected and used to design a mathematical model relating the probability of local control to clinical and treatment variables. The analysis shows that, by using the same radiation parameters, the probability of local tumor control is a function of both "isoeffect thermal dose" and tumor volume.

Carcinoma, Squamous Cell↗
PubMed1976

The measure-unit of evolution.

A theoretical study on evolution has been carried out, with the aim of disproving some value judgements essentially represented by the idea that the degree of evolution can increase. Our conclusions are based upon the preliminary statement that efficiency of survival is directly related to regulative ability. On this ground our reasoning led us to conclude that: (i) actual fitness measure units derive from an anthropocentric bias, and they mainly evaluate similarity to man rather than some objective parameter; (ii) a complete and meaningful unit is, at present, impossible to achieve in practice; (iii) since the study of evolution is only descriptive, and since the evolutionary process is time dependent, every ecological dominant living today must be considered as the most fitted to its environment; (iv) the view we can have of evolution is simply a transection, so that many generalized phyletic trees are trivial and it is impossible to claim the persistence today of those "ancestor organisms" upon which such trees are constructed. Moreover, a functional definition of the term "organism" is given, following criteria drawn from bioenergetics and from biological hierarchization. The concluding step is the assemblage of a slightly heterodox model for evolution.

Base Sequence↗
PubMedDate not supplied

Metabolic evaluation of sexual dimorphism. V. Action of testosterone on the phosphofructokinase of mice submaxillary gland cells in vitro.

1) The kinetics of phosphofructokinase and growth rate of submaxillary gland cells of C3H mice of both sexes in presence and in absence of testosterone have been studied. 2) Both enzymes show sigmoidal kinetics, with Hill's coefficient higher for the females. 3) The maximal activity is remarkably more elevated for the males. 4) The testosterone modifies the growth rate and the kinetic properties of the phosphofructokinase and these modifications depend on the sex.

Animals↗