Biomedical subjects

R Fragomeni

Publications and source records attributed to R Fragomeni.

5 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↗

PubMed1996

Dosimetric protocols in radiotherapy: a computer program.

A computer program to evaluate the dose to water in a specified point for low, medium and high energy photon and electron radiotherapeutic beams using different ionization chambers, phantom materials and new dosimetric standard protocols has been developed. The absorbed dose to air cavity calibration factors of the ionization chambers at the radiation quality, the updated physical quantities and dosimetric parameters are part of the data base, which is extendable to individual users' needs. Moreover, the management software permits comparison of different dosimetric protocols and reduction of errors on the dose delivered to patients.

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↗

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↗

PubMed1985

Proximal arteriovenous fistulas for vascular access in periodic hemodialysis.

Six proximal arteriovenous fistulas were created in 6 uremic patients on periodic hemodialysis, in whom previous distal shunts or the interposition of heterologous materials had failed. The operations were performed with the vascularization of the upper limbs and a cutaneous incision at the bend of the arm. All patients were women. All the arteriovenous fistulas showed good functioning at the end of the procedure and follow-up from 0 to 45 months.

Adult↗