[Brachytherapy in prostate cancer: the use of QuickLink® system within the real-time technique. A new technique is presented].

UNLABELLED: INTRODUCTION. Brachytherapy with real-time technique allows the ultrasound transperineal implant of needles and the release of I125 seeds in the prostate, with intraoperative dosimetry carried out by a special software. After performing this seed-releasing technique on 160 patients, we present 15 cases treated with strand seeds using the QuickLink®system. MATERIALS AND METHODS. INCLUSION CRITERIA: CaP clinical stage T1-T2, PSA ≤10 ng/ml, prostate volume ≤ 50g, Gleason score ≤3+3=6, Q maximum >13-15 ml/sec., and I-PSS score <10. METHODICAL. In ultrasound-guided transrectal technique the needles are inserted near the prostatic capsule. A 5mm section plan is performed; the computer allows identifying the contours of prostate, rectum, urethra, and the position of needles to be inserted. The total activity is defined, as well as the number and location of the sources to be included; isodoses are calculated, the correct position of seeds and spacers is printed. The strand seeds are prepared on the basis of this scheme, using the QuickLink® system, and placed into the prostate tissue. RESULTS. The QuickLink® system allows reducing the operative time (110 min, range 95-125). The pelvic CT assessing the post-planning has shown a more regular distribution of seeds. The cut-off of D90≥140 Gy was reached in all patients, with doses at urethra and rectum within the prescribed limits. CONCLUSIONS. The brachytherapy real-time with strand seeds QuickLink® combines the flexibility of planning intraoperative real-time with a faster process, and less tendency for the relocation of the seeds.

[The application of the multileaf collimator in radiotherapy: the dosimetric problems and the technical implications for its clinical use]. / Applicazione del collimatore multilamellare nella radioterapia: problematiche dosimetriche e implicazioni tecniche per l'uso clinico.

INTRODUCTION: The multileaf collimator (MLC) now commercially available as an integral or optional retrofit component of linear accelerator heads, permitting to shield automatically irregular fields by computerized movements of multiple tungsten leaves. In the present paper we discuss the main characteristics of different MLC versions, MLC dosimetric drawbacks and the clinical fields where the MLC could he widely used. MATERIALS AND METHODS: Since February, 1995, we have studied the dosimetric characteristics and clinical implications of a multileaf collimator of a Clinac 2100 C/D linear accelerator used to replace conventional low melting alloy blocks. The scalloping effect of isodoses and the effective penumbra produced by the multileaf collimator in an irregular field were analyzed accurately. Secondly, radiation leakage through tungsten leaves was measured and compared with the values of low melting alloy blocks. Finally, the MLC was extensively used in clinical practice for the radiotherapy of different tumors. RESULTS: Different dosimetric steps were followed to obtain the monitor units/dose ratio. Our single MLC-shielded irregular fields measurements also showed several physical and dosimetric disadvantages related to wider effective penumbra than with conventional shielding when the angle between field margin and the normal to the direction of leaf travel is 45 degrees. In clinical practice, the MLC can be widely used for the conformal radiotherapy of pelvic and thoracic tumors. Conventional low melting alloy blocks should be replaced with MLC for radiotherapy of selected brain and head and neck cancers. DISCUSSION: The current use of a multileaf collimator improves both the accuracy and the effectiveness of radiation therapy and reduces the time for every treatment dose, which potentially increases the number of patients treated every day. The multileaf collimator is presently an important technical tool either to replace conventional shielding for static conformational radiotherapy or to administer 3D-planned dynamic radiotherapy.

[Accuracy of distribution of the doses obtained with electron beams of irregular shape and in the presence of inhomogeneous structures]. / Accuratezza delle distribuzioni di dose ottenute con fasci di elettroni di forme irregolari e in presenza di strutture disomegenee.

The authors have addressed the problem of dose distribution calculation accuracy when irregularly shaped electron beams are used and structural dishomogeneities are present. The mathematical model used for the electrons from the "scattering foil" and from the colimator walls is the "gaussian pencil beam", and the total dose is obtained by adding to the above mentioned components the dose from the electrons diffused by the field defining frame and from bremsstrahlung photons. Depth dose curves, with and without frames, are compared with a satisfactory correspondence between the calculated and the measured curves. The calculation method is considered accurate within 2% of dose and 2 mm in position. When dishomogeneous structures are present and treated as semi-infinite layers, corrections are referred in 2-D to a single anatomical section and can be extended to 3-D if a sufficient number of sections is available for the whole volume definition. However current algorithms need to be improved when there is the possibility to use a much more powerful hardware.

[A proposal for the treatment technique for the breast and regional lymph nodes in patients with conservatively operated neoplasms]. / Una proposta tecnica per il trattamento della mammella e dei linfonodi regionali in pazienti affette da neoplasia operate conservativamente.

Adequate irradiation of regional lymph-nodes in selected patients seems to improve disease-free and over-all survival rates. Technically, regional lymph-nodes are generally treated separately (supra-infra clavicular, apex of axilla and internal mammary chain-IMC). About the treatment of the IMC nodes, there are two main problems: the identification of the individual target volume, and its correct irradiation. For the latter problem, the most employed solutions are: the inclusion of IMC in the tangential fields, the use of the direct or oblique electron beam for IMC alone. None of them is optimal regarding to the tolerance of adjacent critical organs and from a geometric and dosimetric point of view. In this paper we propose and discuss a modified method. The IMC nodes together with the breast are irradiated by a three field technique (two tangential photon beams and one oblique electron beam). Their arrangement allows to treat every part of the target by two fields, reducing the risk of hot and cold spots. This is obtained by extending the internal tangential photon beams to cover the electron beam. Wedges and different weights must be used to achieve an uniform dose distribution.