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Biomedical subjects

L Begnozzi

Publications and source records attributed to L Begnozzi.

12 recordsLinked to original sources
PubMed2003

Dosimetric, mechanical, and geometric verification of conformal dynamic arc treatment.

A conformal dynamic arc (CD-arc) technique has been implemented at the S. Giovanni Calibita-Fatebenefratelli Hospital Radiotherapy Center. This technique is performed by rotational beams and a dynamic multileaf collimator (DMLC): during the treatment delivery the gantry rotates and the field shape, formed by the DMLC changes continuously. The aim of this study was to perform dosimetric, mechanical, and geometric verification to ensure that the dose calculated by a commercial treatment planning system and administered to the patient was correct, before and during the clinical use of this technique. Absolute dose values, at the isocenter and at other points placed in dose heterogeneity zone, have been verified with an ionization chamber in a solid homogeneous phantom. In uniform dose regions measured dose values resulted in agreements with the calculated doses within 2%. Isodose distributions have also been determined by radiographic films and compared with those predicted by the planning system. Distance to agreement between calculated and measured isodoses in dose gradient zone was within 2 mm. In conclusion, our results demonstrated the feasibility and the accuracy of the CD-arc technique for achieving highly conformal dose distributions. Up till now 20 patients have been treated with CD-arc therapy.

Humans↗
PubMed1994

Study on the reference dose level in radiotherapy treatment planning.

PURPOSE: The reference dose level of the dose distribution in the tumor volume is studied. METHODS AND MATERIALS: The study is performed using a formula based on the Linear Quadratic (LQ) model. The calculated reference dose level to which the prescribed dose must be referred, for the eradication of a homogeneous tumor, is investigated by varying the dose distribution, that is, the dose volume histogram shape, its range, the prescribed total dose, the fraction size and the linear quadratic model parameters, alpha and beta. RESULTS: For all the simulated dose volume histograms the calculated reference dose level is lower than the mean dose level, depending on the range of dose variation and the considered tumor sensitivity. When the dose nonuniformity is not too great the reference dose level is very near to the mean dose level; when the inhomogeneity of dose distribution is high the reference level is clearly lower than the mean level but not necessarily equal to the minimum level in the tumor. For the dose volume histograms derived from the actual dose distributions obtained from a two tangential beams technique, a four beams technique and a moving beam technique, the reference levels are calculated and compared with the ICRU 29 reference point dose level. In two cases the reference levels are lower than the level at the ICRU 29 reference point. In the case of the four beams technique, the two levels are equal. CONCLUSION: These theoretical results show the possibility of administering the prescribed dose to a dose level higher than the minimum in the tumor, with the same value of Tumor Control Probability (TCP) as the one corresponding to a uniform tumor irradiation. The application of the proposed study can offer a general support to the choice of the reference dose level, based on the actual dose distribution in the tumor volume.

Humans↗
PubMed1994

Magnetic resonance guided radiosurgery in children: tridimensional extrapolation from isodose neuroimaging superimposition.

In stereotactic radiosurgery, thin external beams of ionizing radiation concentrated in a single dose onto a sharply defined target are employed to treat lesions within the brain, avoiding doses which may produce unwanted damage to the surrounding healthy tissue. The dynamic irradiation technique used with the linear accelerator employs variable arcs of irradiation rotating around the isocenter of the target. The technique of stereotactic magnetic resonance (MR) guided radiosurgery is supported by a dedicated computerized system for treatment planning simulation. The system, based on a personal computer, allows the acquisition, reconstruction, and visualization of the target volume from MR images, and permits calculation and visualization of a three-dimensional dose distribution directly superimposed upon MR images of the lesion. The desired goal of destroying neoplastic tissue without damaging cerebral parenchyma is of particular importance in children. Consequently, adapting the three-dimensional isodose profiles to the morphology of the lesion to be treated is crucial. From this, the importance of the computer simulation is evident, as it permits one to go deeply into the study of isodose distribution, changing beam collimation, and the number and amplitude of arcs of irradiation.

Brain Neoplasms↗
PubMed1994

A simple method to calculate the influence of dose inhomogeneity and fractionation in normal tissue complication probability evaluation.

PURPOSE: Since volumetric dose distributions are available with 3-dimensional radiotherapy treatment planning they can be used in statistical evaluation of response to radiation. This report presents a method to calculate the influence of dose inhomogeneity and fractionation in normal tissue complication probability evaluation. METHODS: The mathematical expression for the calculation of normal tissue complication probability has been derived combining the Lyman model with the histogram reduction method of Kutcher et al. [14] and using the normalized total dose (NTD) instead of the total dose. RESULTS: The fitting of published tolerance data, in case of homogeneous or partial brain irradiation, has been considered. For the same total or partial volume homogeneous irradiation of the brain, curves of normal tissue complication probability have been calculated with fraction size of 1.5 Gy and of 3 Gy instead of 2 Gy, to show the influence of fraction size. The influence of dose distribution inhomogeneity and alpha/beta value has also been simulated: considering alpha/beta = 1.6 Gy or alpha/beta = 4.1 Gy for kidney clinical nephritis, the calculated curves of normal tissue complication probability are shown. CONCLUSION: Combining NTD calculations and histogram reduction techniques, normal tissue complication probability can be estimated taking into account the most relevant contributing factors, including the volume effect.

Brain↗
PubMed1993

Estimate of normal tissue damage in treatment planning for stereotactic radiotherapy.

A personal computer (PC) system was developed to perform treatment planning for radiosurgery and stereotactic radiotherapy. These techniques of irradiation of the brain may be accomplished with a linear accelerator by performing several non-coplanar arcs of a highly collimated beam focused at a fixed point. The PC system allows the acquisition, reconstruction and the visualization of the target volume from CT or MR images, and then it permits to calculate a three-dimensional (3-D) dose distribution due to small photon beams and to visualize it. The software calculates not only total dose distribution, administered fractionated or in single fraction, but also the NTD2 (normalized total dose) predicted to have a biological effect equivalent to the single irradiation. The choice of the best technique is supported by the dose volume histograms (DVH) calculation and by an estimate of complication probability to the brain normal tissue (NTCP). The algorithm for NTCP calculation is based on two models: the linear quadratic and the logistic. A comparison of three different dose calculations for a typical cerebral target volume is presented to demonstrate the system performances.

Algorithms↗
PubMed1992

Ideal dose level in treatment planning optimization.

The biological response of the tumor is expressed in terms of tumor control probability (TCP) and its dependence on the inhomogeneous dose distribution throughout the tumor volume is studied. The ideal dose level to which the prescribed dose must be referred is derived, by employing a formula based on the linear quadratic model. To administer the prescribed dose to the ideal dose level renders the tumor control probability equal to that one corresponding to a uniform irradiation of the tumor. For the normal tissue irradiated a normal tissue complication probability index (NTCPI) is also defined and calculated. The comparison between NTCPIs of competing plans supports the optimization. In general the resulting ideal dose level is lower than the mean dose level, but not necessarily equal to the minimum in the tumor. This result shows the possibility of administering the prescribed dose to a dose level higher than the minimum, maintaining the tumor control probability at a good level and consequently lowering the complications to the normal tissue. The method offers a general support for the choice of the reference dose level and of the better technique. An example of application of the method is shown.

Humans↗
PubMed1991

One versus four heat treatments in combination with radiotherapy in metastatic mammary carcinoma.

To optimize the total and the weekly number of heat treatments to be combined with a conventional radiotherapy course, a study was designed on a 75-year-old woman with 40 cutaneous nodules of metastatic mammary carcinoma. All nodules were individually irradiated by means of orthovoltage radiation to doses of 36 to 44 Gy, given in 20 equal fractions in 4 weeks. The nodules were randomly assigned to receive radiotherapy alone or radiotherapy combined with one or four heat treatments. Eight lesions were left untreated as a control arm of the systemic therapy (endocrine manipulation). Hyperthermia at a minimum temperature of 43 degrees C was applied for 45 min once per week for four times or only once, during a course of radiotherapy. Percent mean diameter of the treated lesions continuously decreased, reaching a minimum of 25-30% of the initial value after 4 months from the beginning of treatment with no difference between the three arms. After this period, tumors treated with radiotherapy alone or radiotherapy plus one heat treatment started to regrow, whereas those treated with radiotherapy plus four heat treatments continued to decrease slowly. The actuarial analysis of freedom from local progression showed a trend of improvement of response duration with four hyperthermic treatments with respect to radiotherapy alone or combined with one hyperthermic treatment.

Aged↗
PubMed1990

Practical experience in electromagnetic hyperthermia quality control procedures within the context of international guidelines.

Recent international guidelines on hyperthermia (HT) quality assurance have pointed out the necessity of defining standard operative procedures and technical checks to guarantee an accurate performance of HT treatments. In the present paper, experience is described of quality control procedures that are performed in agreement with the more general guidelines concerning thermometry, sensor positioning, phantoms, applicator characterisation, and electromagnetic (EM) radiation leakage. This practical experience comes from the use of equipment for superficial and loco-regional HT working in the range 13.56-915 MHz.

Evaluation Studies as Topic↗
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↗
PubMedDate not supplied

A treatment planning system for stereotactic radiotherapy.

Stereotactic radiotherapy to treat neoplastic lesions or artero-venus malformations in the brain may be accomplished with a linear accelerator by performing several non-coplanar arcs of irradiation with a highly collimated beam focused on a fixed point. This paper introduces a system to perform treatment planning. It is based on a Personal Computer and allows the acquisition, reconstruction and visualization of the target volume, within the brain, from CT (Computerized Tomography) or MR (Magnetic Resonance) images, and then it permits calculation and visualization of a 3-D (three-dimensional) dose distribution due to small photon beams. The performances of the system and its use in a practical case are described.

Brain Neoplasms↗