A study on maximum skin dose in cerebral embolization procedures.

BACKGROUND AND PURPOSE: It is essential to measure the skin dose of radiation received by patients during interventional neuroradiologic procedures performed under fluoroscopic guidance, such as embolization of cerebral aneurysms, which is regarded as a high-dose interventional radiology procedure. In this study, we report a method for evaluating maximum skin dose (MSD), an ideal marker of radiation-induced effects, based on an innovative use of radiochromic films. MATERIALS AND METHODS: Forty-eight procedures were studied in 42 patients undergoing embolization of cerebral aneurysms. Fluoroscopic and digital dose-area product (DAP), fluoroscopy time, and total number of acquired images were recorded for all procedures. The MSD was measured using Gafchromic XR type R films. RESULTS: The MSD was measured in one group of 21 procedures. The coefficient (kappa) of the interpolation line between the skin dose and the DAP (kappa = 0.0029 cm(-2)) was determined. An approximate value of MSD from the DAP for the remaining 27 procedures was estimated by means of an interpolation line. The mean MSD was found to be 1.16 Gy (range, 0.23-3.20 Gy). CONCLUSION: The use of radiochromic XR type R films was shown to be an effective method for measuring MSD. These films have the advantage of supplying information on both the maximum dose and the distribution of the dose: this satisfies the most stringent interpretation of Food and Drug Administration, American College of Radiology, and international recommendations for recording skin dose.

Treatment planning for radiotherapy in northern Italy: a survey by the National AIFB-AIRO Committee on 3D-Treatment Planning. Italian Association for Biomedical Physics. Italian Association for Radiation Oncology.

BACKGROUND AND PURPOSE: A survey was performed in 1996 to investigate the structures and the process of radiation therapy treatment planning in clinical practice within northern Italy, with particular emphasis on the current and future implementation of 3D equipment and techniques. MATERIALS AND METHODS: Of 57 existing radiation therapy (RT) centres covering a population of 25 million people (45% of the total population of Italy) and treating over 58,000 cancer patients (70% of the cancer cases in Italy) each year, 46 centres were deemed eligible for the survey; a questionnaire was sent to a medical physicist working in each eligible RT centre, 40 of whom responded, making the basis for this report. RESULTS: A dedicated CT scanner was available in 25% of the responding centres and a total of 49 radiation therapy planning systems (RTPS) were reported; none of the RTPS were able to perform 3D calculations, but 50% of the centres had an advanced 2D or 2.5D system. Connection between CT scan and RTPS was by tape or disk in 62% of centres. Immobilization devices were used frequently for head and neck patients (88% of centres), but not for lung (16%) or prostate cancer (24%) patients; the number of contoured slices was largely variable, exceeding 10 in only about 30% of the responding centres. The average working time per patient seemed to closely reflect the number of slices used and the number of critical organs contoured. Finally, the majority of the responding physicists did not favour the use of more than 20 CT slices for 3D treatment planning, nor did they forecast a general spread of this technique in the next 2-3 years. CONCLUSIONS: This survey has shown (1) a heterogeneous picture, with 20% of centres ready to implement 3D techniques and 20% of centres lacking the possibility of planning treatments and (2) a general difficulty in coping with the workload represented by 3D treatment planning.

Simulation of soft-tissue tumor excisions: a multimodal interactive approach.

Total 3-D reconstruction of the tumor size, shape, and relations with surrounding structures using CT, MRI, sonography, and angiography images can make simulated radical resection of soft-tissue sarcomas possible, thus sparing normal tissues. With our approach, starting from three MR images for a given patient, a new single image representation of all three parameters is generated by using two different techniques on a workstation in a standard UNIX and X-11 environment. The first one is a transformation linking together the MR parameters and the RGB (red, green, blue) color components. The second one is an unsupervised segmentation method based on a number of neural and fuzzy models. We can dinamically render and update a stereo display using field sequential presentation of left and right eye views on the monitor, with Cristal Eyes LCD shutter eyewear (StereoGraphics Inc., San Rafael, CA) to view it. As 3D locating tool, a 3D locating control system based on low-frequency magnetic fields (Polhemus Fastrak) has been chosen. Simulations of soft-tissues excisions may be performed in this interactive environment with augmented-reality modalities. All this, in our experience, has greatly facilitated the simulation of soft-tissue sarcoma excisions.

An "augmented-reality" aid for plastic and reconstructive surgeons.

Starting from MR and CT images for a given patient, a new single image representation of all parameters has been generated by using false-color techniques in a standard UNIX and X-11 environment. A transformation linking together the MR, CT parameters and the RGB (red, green, blue) color components has been used. Moreover an unsupervised segmentation method based on a number of neural and fuzzy models may directly produce segmented image volumes. Each image of the various sequences has been interactively displayed by using a specifically designed application. The resulting images have been displayed on a stereo monitor allowing the three-dimensional rendering of visual data through LCD shuttered glasses. Moreover, a 3-D control system based on low frequency magnetic fields has been used, while a bandheld Polhemus stylus could be used as an electronic knife for dissecting the 3-D data set and for defining flaps and grafts. Bone or soft-tissue contour can be analyzed, and sections can be removed from the model to allow a view of the underlying structures. Flaps and grafts obtained utilizing the above-reported techniques can be fitted exactly, without repeated removal and recarving. Nuances of depth, tapering, and arc are carved directly into the bone, while chances of asymmetry are markedly diminished. In this way, moreover, anesthetic times are reduced by more efficient utilization of operative time, which usually offsets the increased cost of imaging.

Segmentation of multivariate medical images via unsupervised clustering with "adaptive resolution".

The need for quantitative information is becoming increasingly important in the clinical field. In this paper we present an interactive X11 based system, devoted to segmentation of multivariate medical images, including an unsupervised neural network approach to clustering. The following steps are considered in the analysis sequence: feature extraction, reduction of dimensionality, unsupervised data clustering, voxel classification, interactive post-processing refinement. The environment turns out to be extremely interactive, thus making the user able to display and modify data during processing, to set parameters, to choose different methods and different tools for each step, and to define online the whole analysis sequence.

[An expert system for the planning of whole-body irradiation treatments]. / Un sistema esperto per la pianificazione dei trattamenti di irradiazione corporea totale.

Total body irradiation (TBI) combined with intensive chemotherapy and bone marrow transplantation is used with increasing success for the treatment of hematologic malignancies with severe prognosis. An expert system, developed on the basis of the experience acquired during the last years in our department, has been designed to optimize the different treatment steps. The choice of an expert system is based on its capabilities in reconstructing a rule-based reasoning through the combination of theoretical and empirical knowledge. Particularly, a subsystem dealing with the steps to be taken to optimize treatment in TBI has been designed using medical and physical data. Our system can determine radiation treatment variables together with a sequence of quality control procedures. Moreover, indications are given about short, medium and long term damage probabilities and toxicity estimates, both derived from literature data and our personal series of cases. Treatment quality can be assessed and the different techniques compared using these data. This project is aimed at providing physicians and physicists with useful clinical suggestions for TBI setting for bone marrow transplantation.

[The proton radiotherapy of melanoma of the uvea. The technic, methodology and first clinical observations]. / La radioterapia del melanoma dell'uvea con protoni. Tecnica, metodologia e prime osservazioni cliniche.

Since June 1991, a Cyclotron unit with a proton beam of 65 MeV has been working at the Institute Antoine Lacassagne in Nice, France. An international cooperative group has been founded to guarantee the thorough exploitation of the facility through complete cooperation. From June 17 to December 20, 1991, 47 patients with uveal melanoma were treated; 4 of them entered the study by means of the Italian team and were treated in cooperation with the Cyclotron staff. Treatment modalities and preliminary observations are described.

[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.