[The radon exposure in mine: risk evaluation, risk assessment and health effects]. / L'esposizione a radon in miniera: valutazione del rischio, misure di prevenzione ed effetti sulla salute.

In mining sector, the natural presence of radon determines an exposition which deserves substantive consideration. The results of radon measure from '90 years in a talc mining show levels of radon below to the threshold limit of 400 Bq/m3, values influenced from air forced systems. The epidemiologic studies updated in a cohort of talc workers between 1946 and 1995 showed no excess for lung cancer mortality. No excess was found for lung cancer mortality in miners exposed to low dose of radon.

The behavior of several microionization chambers in small intensity modulated radiotherapy fields.

The aim of this work is to compare different ion chambers available for dose measurements in small fields used in intensity modulated radiotherapy. Some dosimetric aspects, related to these small radiation fields, i.e., lack of electronic lateral equilibrium and steep dose region, must be evaluated, in order to obtain an accurate technique implementation. Furthermore, the size of the sensitive volume of the chambers compared with the mapping of the beams or segments needs consideration. If the size of the chamber is too large for the flatness of the field, the measurement can deviate from the expected absorbed dose at a point. We propose a comparison of various dosimetric values between different microionization chambers with respect to a smaller dosimeter, such as the diamond detector.

Two-dimensional and quasi-three-dimensional dosimetry of hadron and photon beams with the Magic Cube and the Pixel Ionization Chamber.

Two detectors for fast two-dimensional (2D) and quasi-three-dimensional (quasi-3D) verification of the dose delivered by radiotherapy beams have been developed at University and Istituto Nazionale di Fisica Nucleare (INFN) of Torino. The Magic Cube is a stack of strip-segmented ionization chambers interleaved with water-equivalent slabs. The parallel plate ionization chambers have a sensitive area of 24 x 24 cm2, and consist of 0.375 cm wide and 24 cm long strips. There are a total of 64 strips per chamber. The Magic Cube has been tested with the clinical proton beam at Loma Linda University Medical Centre (LLUMC), and was shown to be capable of fast and precise quasi-3D dose verification. The Pixel Ionization Chamber (PXC) is a detector with pixel anode segmentation. It is a 32 x 32 matrix of 1024 cylindrical ionization cells arranged in a square 24 x 24 cm2 area. Each cell has 0.4 cm diameter and 0.55 cm height, at a pitch of 0.75 cm separates the centre of adjacent cells. The sensitive volume of each single ionization cell is 0.07 cm3. The detectors are read out using custom designed front-end microelectronics and a personal computer-based data acquisition system. The PXC has been used to verify dynamic intensity-modulated radiotherapy for head-and-neck and breast cancers.

Monte Carlo simulation of the photoneutron field in linac radiotherapy treatments with different collimation systems.

Bremsstrahlung photon beams produced by linac accelerators are currently the most commonly used method of radiotherapy for tumour treatments. When the photon energy exceeds 10 MeV the patient receives an undesired dose due to photoneutron production in the accelerator head. In the last few decades, new sophisticated techniques such as multileaf collimators have been used for a better definition of the target volume. In this case it is crucial to evaluate the photoneutron dose produced after giant dipole resonance (GDR) excitation of the high Z materials (mainly tungsten and lead) constituting the collimator leaves in view of the optimization of the radiotherapy treatment. A Monte Carlo approach has been used to calculate the photoneutron dose arising from the GDR reaction during radiotherapy with energetic photon beams. The simulation has been performed using the code MCNP4B-GN which is based on MCNP4B, but includes a new routine GAMMAN to model photoneutron production. Results for the facility at IRCC (Istituto per la Ricerca e la Cura del Cancro) Candiolo (Turin), which is based on 18 MV x-rays from a Varian Clinac 2300 C/D, are presented for a variety of different collimator configurations.

Implementation of an integrated "record and verify" system for data and images in radiotherapy.

In November 1999, new radiotherapy and medical physics departments began to operate in our institution. In the departments' project, considerable emphasis had been placed on the integration of the equipment through networking. In particular, a "record and verify" (R&V) system for data and images (Varian "Varis" and "Vision") has been employed in the daily routine since the beginning of treatments. After one year, more than 600 patients have been treated, and a first evaluation of the system can be carried out. In clinical practice, the software required no significant changes in the already-established radiotherapy workflow and has been successfully configured in an acceptable time. On the other hand, the way information is exchanged and shared has dramatically changed towards a nearly paperless and filmless way of working. A good application reliability has been experienced, and the client-server structure has been proven useful by avoiding loss of data in critical situations. The staff time spent for the application to run is now well balanced by the increased safety in daily practice, and digital archiving of all the radiotherapy activity has increased the effectiveness of routine tasks and statistical researches. The critical aspects we have experienced in the application are the proper user rights definition and a minor rounding error in the daily dose accumulation. Future developments in implementation of the system will be aimed to a better integration with the Hospital Information System and to a further exploitation of the RT-PACS features of the "Vision" application.

Effective penumbra and scalloping effect: a dosimetric study in multifield radiotherapy with multileaf collimator for prostate cancer treatment.

AIMS AND BACKGROUND: The aim of the study was to test whether the multileaf collimator can be used to replace divergent alloy blocks for field shaping and to evaluate the dosimetric impact of the scalloping effect and the effective penumbra in multifield isocentric configurations routinely used at our department to treat early stage prostate tumor in supine patients. Deviations between measurements and treatment planning system calculations are also discussed in order to estimate the accuracy of effective penumbra calculations carried out by the software in the presence of blocks or a multileaf collimator. METHODS: The multileaf collimator installed on a dual energy (6 and 18 MV) linear accelerator Varian CLINAC 2100 C/D is an add-on component positioned below the standard jaws, with 40 computer-controlled opposed pairs of tungsten leaves. Transmission, effective penumbra and scalloping measurements were performed with films placed at different depths in a (30 x 30 x 20 cm3) acrylic phantom. A laser scanning photodensitometer was used to obtain the optical density and the relative dose profile. Effective penumbra and scalloping effect measured data were tested on a software phantom; the phantom, automatically performed with the treatment planning system, was a regular parallelepiped measuring 30 x 30 x 20 cm3 and the acrylic electronic density value. RESULTS: For one multileaf collimator-shaped field, the width of effective penumbra was about 2 mm wider than penumbra for cerrobend blocks, at a 45 degrees angle between leaf motion direction and the field edge. Collimator rotation, automatically performed by the treatment planning system, by minimizing the sum of over- and underblocked areas, reduces the differences between the multileaf collimator and blocks. The differences between measured and treatment planning system calculated data were within the treatment planning system dose calculation accuracy limits, as recommended in ICRU Report No. 42. CONCLUSIONS: Penumbra and, for the multileaf collimator, scalloping effect values seem to depend on the gantry angle, i.e., on the fields path of entry. The values for even fields are higher than the those for odd fields, because the dose gradient at the target edges is steeper for a single field than for two opposite fields, and the interplay of doses from the individual beams increases the distance between the isodose levels. Therefore, in order to reduce scalloping and effective penumbra values, it would be better to rotate the collimators, above all in even-number field techniques. In particular, the six-field technique, used mostly in prostate treatment, shows the same effective penumbra values with the multileaf collimator, with proper collimator rotation, and in blocked fields.

[Dosimetric characterization of a multileaf collimator]. / Caratterizzazione dosimetrica di un collimatore multilamellare.

INTRODUCTION: We studied the dosimetric characteristics of a multileaf collimator (MLC) installed on a dual energy accelerator with 6 and 18 MV photon beams in the Radiotherapy Department of Mauriziano Umberto I Hospital in Turin initiating its use in clinical practice. In particular, measurements included transmission through and between the leaves and at the junction under closed-leaves, central axis percentage depth dose, output factors and effective penumbra. MATERIAL AND METHODS: The MLC installed on the dual energy (6 and 18 MV) linear accelerator Varian Clinac 2100 C/D used in our radiotherapy department is an add-on component positioned below the standard jaws; it consists of 40 computer-controlled opposed pairs of 5 cm thick tungsten leaves, each projecting a 1 cm width at the isocenter, and it provides a maximum treatment field of 40 x 40 cm2 at 100 cm SAD. Transmission, penumbra and scalloping values were measured with the standard radiographic film routinary used in our department. A laser scanning photodensitometer (WP102, Wellhofer) with a 450 microns spot was used to obtain the optical density and the relative dose profile. Radiographic films had been calibrated with an ionization chamber, by irradiating samples to known doses; this calibration was used to correct the film scanner readings to dose. Percentage depth doses were also measured in an automatic water phantom (WP600, Wellhofer) for irregular fields defined by either MLC or alloy blocks, in order to test the differences in the build-up region due to the presence of the acrylic accessory tray. Measured and calculated output factors were compared for some irregular fields defined by the MLC. This comparison tested the algorithm accuracy of our Treatment Planning System 3D CadPlan 3.1.1 Varian-Dosetek. RESULTS AND DISCUSSION: For both energies, approximately 2% of the incident radiation on the MLC is transmitted and an additional 0.5% leakage occurs between adjacent leaves. The leakage under closed-leaves junction is remarkable: about 25-33%. Relative depth dose curves are similar for two fields shaped by either MLC or conventional jaws. Skin dose with MLC-shaped field is less (3.5%) than the one with cerrobend block-shaped fields. The monitor unit calculation procedure used in our treatment planning system can be applied to the MLC (the difference is less than 1%). Effective penumbra in MLC-shaped irregular fields is on the average 11 mm, which is slightly wider (2-3 mm) than the conventional cerrobend blocks penumbra. Effective penumbra increases with depth, field width and leaves positioning. CONCLUSIONS: The MLC, if properly used (collimator rotation, jaws and leaves position, high number of fields), can be applied to conformal radiotherapy with good results. The MLC is better than conventional cerrobend blocks both to improve the treatment reproducibility and accuracy, and relative to dosimetric characteristics like dose transmission and skin dose. The use of MLC to modulate beam fluence (IMRT) will permit to modify beam intensity for improved shaping of the treated volume and to overcome the static therapy dosimetric limitations.

[The Monte Carlo method and parallel estimation in the drawing up of radiosurgery treatment plans]. / Metodo Monte Carlo e calcolo parallelo nella stesura dei piani di trattamento radiochirurgici.

PURPOSE: We investigated the practical application of a calculation algorithm based on the Monte Carlo method to stereotactic radiosurgery treatment planning. In radiosurgery, high dose gradients and the lack of electronic disequilibrium make high resolution matrices and high computing power and speed necessary to obtain accurate dose distribution. To date, the main obstacle to the wider-spread use of the Monte Carlo method has been the huge computing time necessary to obtain a dose distribution on current hardware. MATERIAL AND METHODS: In this project, developed within the ESPRIT program, funded by the European Union, a Parsytec CC (Cognitive Computing) computer was used with 9 processors (Power PC 604, 133 Mhz, RAM 64 Mb) with IBM AIX/EPX OS and availability for Fortran parallel codes compilation, connected to a PC for data input, results rendering, and dose distribution calculation with a conventional algorithm for comparison with the Monte Carlo code (an EGS4 user code). The module named Rapt Region Extractor performs data compression with an octree method without decreasing resolution, for RAM and computing time requirements to remain acceptable. A model of the 6 MV photon beam from Clinac 2100C Varian linear accelerator was devised, based on incident photon energy spectrum and, for each collimator dimension, on bidimensional dose distribution orthogonal to beam direction measured at SSd = SAD = 100 cm. RESULTS: Parallelization was carried out on event numbers, allowing a simulation speed to number of processor ratio close to unity. A new random number generator was used, capable of correctly running on the parallel architecture. The simulation procedure includes: 1) CT acquisition in DICOM 3.0 format, Analyze or with scanner; 2) Target delineation, treatment arc definition. 3) Dose calculation, with both conventional and Monte Carlo methods. 4) Dose distribution rendering on every transverse, sagittal or coronal planes overlapped in color wash on anatomical representation. Comparison between conventional and Monte Carlo algorithms were carried out on an anthropomorphic phantom and 10 real patients, with 2.5 mm anatomical resolution and standard deviation never exceeding 2%. A simulation with 10,000,000 events and 1% maximum variance can be run in 43'. When PTV is an homogeneous areas the differences between the two methods are around 5%, while when PTV is localized in dishomogeneous areas discrepancies reach 20% in the bone. CONCLUSIONS: In conclusion, the feasibility of direct simulation with the Monte Carlo method in radiosurgery has been demonstrated within time and hardware costs compatible with clinical practice.

[Radiometabolic therapy: dose equivalents from external exposure and internal contamination]. / Terapia radiometabolica: equivalenti della dose da esposizione esterna e contaminazione interna.

PURPOSE: We describe our method for evaluating the dose received by external irradiation and internal contamination during radiometabolic therapy considering the daily activity at Ente Ospedaliero Ospedali Galliera, Genova, Italy. MATERIAL AND METHODS: We used environmental and personal thermoluminescence dosimeters (LiF-100) and a whole-body counter system (WBC 6000 Harshaw) for direct activity measurements within the body after radionuclides administration. RESULTS: Measurements were carried out both on workers allowed to access the restricted area and on people volunteering to assist non-self-sufficient patients. In the latter, we estimated the doses from activity measurements and using ICRP's radiometabolic models: more definite access to the treatment room and higher doses were the main reasons for a more accurate evaluation of volunteers than of workers. The combined study of 1-meter exposure immediately before the patient's discharge and both environmental and personal dosimetry on volunteers showed about the same value (50 microSv/hr) as mean exposure rate at 1 meter. Internal intake in workers showed similar contamination dose values. DISCUSSION AND CONCLUSIONS: These results, combined with the average working time of individual workers, permitted an a priori evaluation for different professional categories; the highest estimated value (< 75 microSv/month) for both irradiation and internal intake, is in agreement with the results of direct controls on workers. Therefore, we concluded that WBC controls should be carried out to verify the estimated doses. Routine monitoring is not useful because, I-131 half-life being very short, frequent periodic evaluations would turn out too expensive. Finally, these measurements would be affected by major errors because atypical ways of contamination do not permit to apply the strict protocols used in radiometabolic models.

Halo ring supporting the Brown-Roberts-Wells stereotactic frame for fractionated radiotherapy.

The authors describe a new instrumentation for repositioning of the Brown-Roberts-Wells (BRW) stereotaxic system, useful for precise fractionated radiotherapy. A lucite ring is fixed to the patient's skull with four screws. Another ring, partially open, is then firmly connected co-axially to the lower part of the first one with four spacer-bars. The fixture permits an exact repositioning of the B.R.W. stereotaxic system, placing the target point in the linear accelerator isocenter. The preliminary technical results obtained in five children are reported and the fixture performance, advantages, and perspectives are discussed.

[Physics, dosimetry, and quality control in mammography]. / Fisica, dosimetria e controlli della qualità nella mammografia.

The diagnostic value of mammography, especially in the early diagnosis of breast cancer, is closely related to examination optimization in terms of high-quality images with the lowest possible dose to the organ. Currently, "optimal" beams are produced by X-ray tubes with a Molybdenum anode, their voltage reaching 35 kV, using the K fluorescence line at 17.48 keV and absorption of photons with > 20 keV energy, through Mo filtration. The dose delivered with a mammographic examination is expressed differently in the literature reports on the subject: air exposure, skin exposure, dose at the midplane and mean dose; currently, it is recommended to specify the dose as "average glandular tissue dose", considering beam quality and the ratio between transmissions in perspex and tissues respectively. Threshold values for the average dose to the glandular tissue range 1.8 to 3 mGy with a grid and 0.9 to 1.5 mGy without the grid. The high quality standard of mammography requires quality assurance programs including the mammographic unit and the image acquisition and treatment systems. In Italy the "Dose and Quality in Mammography" program is in progress. According to the acceptance quality criteria established in the program and on the basis of the investigation of 272 centers, an acceptable dose-quality ratio was seen in 37.5% of the centers, low quality was found in 24.5%, high dose in 23.7% and high dose plus low quality in 14.1% of the whole of centers.

[Comparison of acceptance tests of 5 linear electron accelerators for radiotherapy]. / Confronto tra i test di accettazione di cinque acceleratori lineari di elettroni per radioterapia.

The acceptance tests of five electron linear accelerators have been analyzed to compare their completeness, the standards specified by the manufacturers and the measured deviations. Involved tests were relative to geometrical and mechanical parameters, photon and electron beam characteristics, dose monitoring systems, treatment table and safety systems. The comparison of acceptance tests has shown a significant nonuniformity, also due to the absence of a specific legislation; anyway, the measured deviations generally appeared to be within internationally recommended values.

[131I]metaiodobenzylguanidine therapy in advanced neuroblastoma.

Forty-two children with advanced neuroblastoma who either failed with first-line therapy or relapsed after achieving a complete remission, were considered for treatment with [131I]metaiodobenzylguanidine (131I-MIBG). We subdivided 42 cases into 5 groups, in accordance with the stage of disease at diagnosis, response to first-line therapy and relapse. A total of 99 courses of 131I-MIBG were administered with doses ranging from 2.8 to 6.0 GBq. One child received six courses, 3 four courses, 18 three courses, 6 two courses and 15 one course of 131I-MIBG. The total delivered dose in single measurable lesions ranged from 286 to 1691 cGy with an uptake factor ranging from 3% to 10%. We obtained a major response in primary tumors, and a long-term response was observed in 5 cases, lasting more than 2 years without further chemotherapy.

[Preliminary evaluation of the clinical use of a system for intraoperative radiotherapy with electrons (IORT)]. / Valutazioni preliminari all'impiego clinico di un sistema dedicato per radioterapia intraoperatoria con elettroni (IORT).

The preliminary evaluation of the dosimetric characteristics of a dedicated intraoperative electron beam therapy system is described (Bionix Corporation). The linear accelerator is the Varian 2100 C with electron beam energies of 6, 9, 12, 16 e 20 MeV. The isodose distribution for each of 15 available applicators (5 plane and 10 beveled) has been studied with a water phantom. The problems of the homogeneity of dose distribution, scattered and leakage radiation outside the applicators and X-ray contamination of the electron beams have been addressed, at the nominal 20 MeV energy for exemplification. The accurate knowledge of such physical and dosimetric properties are necessary for the implementation of the IORT techniques in terms of choice of the applicator size and electron beam energy for tumor coverage and dose sparing of critical organs.

[Physico-technical aspects of total skin irradiation with high-intensity-dose electrons]. / Aspetti fisico-tecnici nell'irradiazione cutanea totale con elettroni in alta intensità di dose.

The authors have addressed the physical and technical problems involved in the total skin irradiation with a linear accelerator Varian Clinac 2100 C expressly preset for this modality with electrons of 6 MeV nominal energy and dose rate of about 2500 UM/min at the isocenter. The six dual field technique has been implemented and the effect of interposed degrading filters has been evaluated with film dosimetry on an anthropomorphic phantom. It was verified that the total skin electron irradiation expressly offered by the manufacturer as an established treatment option on the Clinac 2100 C with high performance ionizing chambers and high dose rate makes the all procedure safer and simpler.

[Radiotherapy with electron beams in Italy]. / La radioterapia con fasci di elettroni in Italia.

The use in Italy of high energy electrons in radiotherapy is analyzed following the answers of 29 Centres to a questionnaire. The CISDR (AIFB) dosimetric protocol, some noticeable clinical, technical and dosimetric experiences are underlined. At the moment computerized dosimetry, intraoperative radiotherapy and total skin electron irradiation are the topical subjects in high energy electron radiotherapy.

[Verification of 3 computerized systems for drafting a plan for treatment with electrons]. / Verifica di tre sistemi computerizzati per la stesura dei piani di trattamento con elettroni.

The electron beam treatment planning systems, with the availability of more and more developed hardware for complex calculation algorithms, need quality controls of accuracy and comparability of treatment plans from different systems. In this paper three systems have been evaluated; their similar computation algorithms (pencil beam) have been used but in some conditions (beam reconstruction, oblique incidence and dishomogeneity) different results have been drawn. The basic data (PDD, dose profile, etc.) were the same for every system, therefore it has been observed that different results are mainly due to differences in: a) input of parameter values, b) calculation algorithm approximations, c) image acquisitions and elaboration.

[High-dose gynecologic endocavitary brachytherapy. Technical and dosimetric aspects]. / Brachiterapia endocavitaria ginecologica ad alta intensità di dose. Aspetti tecnici e dosimetrici.

The technical and dosimetric aspects are presented of high-dose intracavitary brachytherapy in gynecology. Fifty-five patients (203 insertions) were examined over two years with a remote loading Selectron HDR 60Co unit installed in a dedicated bunker. The dose to the rectal and bladder markers on AP and LL films was calculated before every irradiation, in order to allow the necessary corrections to be made. Uniform irradiation conditions were obtained at each treatment set-up for both tumoral target and bladder and rectal doses. High-dose intracavitary brachytherapy proved to be a safe, reliable and versatile method from the technical and dosimetric point of view both in the treatment of unoperated gynecological malignancies and in postoperative therapy.