A new method to evaluate the residual activity in patients undergoing (131)I thyroid therapy.

The radioiodine administration is a standard therapeutic approach to both benign thyroid diseases, such as hyperthyroidism, and carcinomas. The high administered (131)I activities are of radiation protection concern, due to relevant patient residual contamination. The aim of this work was to develop a new procedure based on external radiometric surveys and on a mathematical model in order to estimate the (131)I activity in patients undergoing hyperthyroidism radioiodine therapy. In the first stage of this study, a suitable detector was chosen and its response vs. activity was characterized. The experimental verification was performed measuring the ambient dose equivalent rate from patients receiving radioiodine administration. The results confirm the reliability of the proposed method, as shown by the slight differences between the administered activities and the ones calculated from external measurements. Furthermore, the same procedure was applied to detect the percentage residual activity in patients at two preset time intervals: 4 hours and 4 days after the radioiodine administration. The obtained results clearly highlight that the method can ensure a level of reliability compatible with the radiation protection purposes.

The effects of focus-skin distance and shaping block tray on the calibration factor of in-vivo dosimetry diodes.

PURPOSE: In-vivo dose measurements during conformal treatment require correction factor evaluations for differences in block shapes, field size and source-skin distance (SSD). The aim of this paper is to evaluate a single correction factor, CFentranceSSD, depending only on source-skin distance, which takes into account both shape and size of blocked fields, in pelvic treatments. MATERIALS AND METHODS: A set of measurements was performed to investigate the effects of different block shapes and sizes, source-skin distances and collimator settings on the entrance dose values. For this reason EDP 20 Scanditronix diodes, with 20 mm water-equivalent build-up cap, were irradiated by 2 Varian linear accelerators (Clinac 1800 and Clinac 2100) 18 MV photon beams with 3 different collimator settings. Diodes were calibrated by comparison with a Farmer 2571 ionization chamber at reference conditions (10 cm x 10 cm open field, source-skin distance 100 cm, build-up depth 3.3 cm) in order to convert the semiconductor signal into water absorbed dose. Three sets of different measurements (regarding open beams, tray fields and shaped fields) were performed. Diode responses were compared with the ionization chamber ones, in the same irradiation conditions. RESULTS: The CFentranceSSD trends can be described by linear fits in dependence upon source-skin distance, and the effect with tray alone or with tray and blocks is stronger than in the open field. The observed effects can be interpreted by the influences of a) the different source distances of diode and reference point in the phantom and b) the secondary electron contamination of the photon beam upon the calibration factor of the diode. CONCLUSION: The effects of source-skin distance and of the shaping blocks and tray upon the diode calibration factor can be effectively accounted for by a single CFentranceSSD correction factor.

[Imaging quality of a digital Konica Regius 336 system for thoracic radiology]. / Qualità dell'immagine di un sistema digitale Konica Regius 336 per Radiologia Toracica.

INTRODUCTION: Digital radiographic systems permit to optimize execution, depiction and storage of radiological images. Since a Regius 336 digital system (Konica Corp., Tokyo, Japan) devoted to chest radiography was recently installed in the Radiology Department of S. Anna Hospital in Como, Italy, we investigated its performance relative to image quality. MATERIAL AND METHODS: Konica Regius 336 is a computed radiography system made of a phosphorescence detector plate which is scanned with an infrared semiconductor laser beam. The radiographic image obtained from the detector is subjected to image processing, which allows a stable output and the nonlinear curve typical of conventional radiographic systems. Image quality was assessed based on the following parameters: dose, contrast, noise, and spatial resolution. As reference, we assessed the same parameters on a Cronex 88 analogic chest-changer (DuPont Pharma, North Billerica, Mass, USA). RESULTS: The Regius 336 air kerma values were always higher than the analogic ones (about 10%), both with and without a chest phantom; noise was also greater than in analogic images, sometimes even doubled. The optical densities of a step wedge and the spatial resolution of the digital chest-changer are independent of the X-ray tube voltage consequent to broader optical latitude. Inversely, the analogic images of the wedges show great optical density variability as a function of the X-ray tube voltage (in a range of 2). The modulation transfer functions of the two systems have the same trend. DISCUSSION AND CONCLUSIONS: The performance of the Konica Regius 336 is nearly equivalent to that of an analogic system. The main advantages of the digital system are a standard output, lower consumption of radiographic films, higher productiveness and better image quality standard level.

Contrast improvement in a new radiotherapy imaging system.

PURPOSE: The aim of this paper is to compare the EC-L Kodak system for radiation therapy beam localization with a conventional one that could be daily employed in a radiotherapy department. BACKGROUND: The main purpose of portal images is to verify the treatment volume in actual clinical conditions. Low contrast is the main constraint affecting portal film image. METHODS: Kodak proposes a new imaging system (film and cassette) characterized by contrast enhancement as imaging standard for radiotherapy. The evaluation of system contrast was carried out by using a step-wedge consisting in 4 60 x 60 mm plexiglas steps and an anthropomorphic phantom. Portal films were exposed to a 6 MV photon beam by a linear accelerator (Varian Clinac 1800) with a 250 x 340 mm field size at the 1000 mm source film distance. The 2 imaging system performances were evaluated analyzing the image optical density. RESULTS: The use of the Kodak system results in a real contrast improvement, so it is satisfactory to describe the field placement as to the region of interest. CONCLUSIONS: The most critical characteristic attaining this method regards low contrast, i. e. the small optical density difference existing between different anatomical regions on the film. Since radiographic techniques can significantly influence quality of portal films, the adequate choice of film and screen combination, as well as the exposure technique is particularly useful in a radiotherapy quality assurance program.

[In vivo dosimetry. Assessment of exit dose correction factors]. / Dosimetria in vivo. Valutazione dei fattori di correlazione per la dose in uscita.

INTRODUCTION: In vivo dosimetry allows to verify dose delivering accuracy in radiotherapy treatments. Exit dose measurements add more information about delivered dose than entrance dose evaluations. MATERIALS AND METHODS: Commercial semiconductor diodes are used for exit dose measurements. The diodes are calibrated by comparison with an ionization chamber at a reference condition. Diode reading was compared with the dose measured by the ionization chamber at the exit point. The exit point is defined as the point on the central axis of the beam, at a distance equal to the maximum dose from the exit surface of a homogeneous water-like phantom. As clinical irradiation conditions are always different from reference conditions, exit dose correction factors have been investigated as a function of phantom thickness, field size at the isocenter, source-surface distance, wedge and tray. Measurements have been performed by irradiating a set of p-type semiconductor detectors with 6 MV photon beam (four diodes--mod. EDP10--Scanditronix) and 18 MV photon beam (three diodes--mod. EDP20--Scanditronix) from a Clinac 1800 linear accelerator (Varian, Palo Alto, CA, USA). RESULTS: The most relevant exit dose correction factors are related to field size and phantom thickness for 6 MV photons. The variation of these factors as a function of field size may be greater than 1% with a standard deviation of the same order. On the contrary, the correction factors for field, thickness and tray photons are negligible for 18 MV. CONCLUSIONS: Applying exit dose correction factors may require a great effort, particularly when many silicon diodes must be used. The actual effectiveness of each calibration factor is evaluated through the statistical analysis of experimental data. In this way, the usefulness of correction factor calculation, as depending from both experimental conditions and diode responses, can be derived from its effects on the exit dose value.

Radiological findings when very small lung volumes are irradiated in breast and chest wall treatment.

Acute pneumonitis following breast irradiation is a rare and transient phenomenon that can be easily managed by drugs. The aim of this study is to evaluate late sequelae on lung, after postoperative radiotherapy (RT) for breast cancer. We were concerned with investigating late radiological findings when very small lung volumes are involved in the irradiated volume. We studied 28 consecutive patients. They underwent clinical examination and all staging procedures before surgery, evaluation of pulmonary function with spirometry, postoperative chest x-ray and high resolution computed tomography (HRCT) of the lung before RT. Clinical examinations were usually performed every 3 months after RT. A second chest x-ray, HRCT and spirometry were carried out after nearly 7 months from the end of RT. We estimated the irradiated lung volume by measuring the area of the lung surface enclosed by the 50% isodose (LA50) in each profile. We found a significant correlation between LA50 and the score of radiological findings after RT. No correlations were found between other factors (i.e., adjuvant chemotherapy, age, weight, smoking) and lung fibrosis. No woman developed radiation pneumonitis syndrome or respiratory symptoms. Our results indicate that irradiation of the breast and/or chest wall is well tolerated if treatment planning is done accurately. The fibrosis likelihood is strongly correlated to the irradiated lung volume. The use of tangential fields limits radiological changes that can be detected only by HRCT examination and are not associated with clinical symptoms.

[Air bubble effect during alloy cooling in shielding blocks radiotherapy]. / Effetti della presenza di disomogeneità nelle fusioni impiegate nei campi radioterapici con forma irregolare.

INTRODUCTION: Shaped fields are widely used in radiotherapy to protect critical organs and to avoid unnecessary normal tissue irradiation. The most common system for photon beam shaping consists in a low melting point alloy. We studied the air bubbles which can occur during alloy cooling with both new and remelted alloys and when different cooling techniques are chosen. MATERIAL AND METHODS: Forty cone samples (18 of remelted alloy and 22 of new alloy) were prepared to evaluate the frequence of air bubble recurrence, with reproducible geometric sizes (height = 70 mm, major base surface diameter = 60 mm, minor base surface diameter = 40 mm). Air bubble sizes and dose inhomogeneity were evaluated by reproducing 60Co radiograph of each sample (two orthogonal projections: 6 x 7 cm). The samples were cooled at a constant temperature, following three different modalities: high (25 degrees C), medium (5 degrees C), low (-20 degrees C) temperature. Owing to the small geometrical magnification, air bubble sizes were determined by measuring their surface on samples lateral projections, taking into account the sight detectable bubble edges. RESULTS: Up to 300 mm2 lateral surface bubbles are always present in all castings. Casting inhomogeneities can produce a film-density inhomogeneity ranging from 9% to 40%. The spatial distribution of bubbles seems to be random. CONCLUSIONS: Bubble recurrence is independent of both the metal alloy (repeatedly used castings) and the different block cooling modalities. The effect of air bubbles on the shielded areas dose inhomogeneity is generally of no relevant importance. However, these inhomogeneities can produce hot spots which must be taken into accurate consideration only in the particular treatments where critical small size organ dose sparing represents a basic issue (i.e. the shielding of eye lens).

[Exclusive irradiation of clinically localized prostatic carcinoma: comparison with various techniques]. / L'irradiazione esclusiva del carcinoma prostatico clinicamente localizzato: confronto fra diverse tecniche.

The frequency of prostate cancer is on the increase and many intracapsular tumors are diagnosed in asymptomatic and relatively young patients. Radiotherapy is an effective alternative to surgery when the technique which reduces the rate of acute reactions and late side-effects is chosen. On the other hand, dose distribution on the target volume and dose delivered to surrounding tissues (rectum and femoral heads) depend on several variables, namely irradiation technique, treatment planning simulation procedures and study and patient positioning. 5 by 5 mm CT studies of the prostate and/or seminal vesicles and the execution of retrograde urethrography to define the prostatic apex plan are essential steps of the simulation procedure. To compare the adequacy of various techniques, we analyzed several isodose distribution maps of nonconformational treatments, calculated by our radiotherapy planning system on the central slice. Arc and multiportal (3 or 4 fields) techniques were considered. The statistical analysis of our results demonstrated that the 4-field perpendicular technique permits better dose distribution to the target volume than the 3-field perpendicular technique; it also reduces the dose to the femoral heads. However, a combination of anterior irradiation with two oblique posterior fields is preferred in hip prosthesis patients. The comparison between arc and static multiportal techniques shows that the former gives a markedly lower dose (up to 50%) to posterior rectal wall. The bilateral arc appears to be the best technique, especially when the patient restraining device is good, because it permits homogeneous irradiation of the target volume, even at high doses, and marked reduction of the dose to the posterior rectal wall and femoral heads; consequently, treatment morbidity is lower.

[The estimation of the variation in the effective dose in the most frequent nuclear medicine studies]. / Valutazione della variazione della dose efficace nelle più frequenti indagini mediconucleari.

INTRODUCTION: The evaluation of effective doses in nuclear medicine investigations is generally referred to the average man, with no relevant associated diseases, during standard examinations. The effective dose in nuclear medicine examinations can be measured directly with ICRP 68. In clinical practice, the many variables related to patients characteristics and examination type may cause major differences between practical and theoretical doses. Thus, we investigated the factors which may affect internal irradiation in some of the most common nuclear medicine investigations. MATERIALS AND METHODS: We analyzed the most frequent examinations carried out on 177 patients in the Nuclear Medicine Department of S. Anna Hospital, namely thyroid scintigraphy, total body bone scan, dynamic and static renal scintigraphy. The administered activity data were analyzed as a function of the withdrawn activity and that remaining in the syringe after i.v. administration and of time delays, and then they were submitted to statistical analysis (mean, standard deviation, 95% confidence range). RESULTS: Equivalent and effective dose changes had no correlation with patient anatomy and associated diseases on the basis of history alone, while radiopharmaceutical preparation and administration methods exhibited a real influence on effective dose: the difference between nominal and administered activity ranged 11-14.5%. CONCLUSIONS: The patients submitted to nuclear medicine investigations receive an effective dose ranging from < .5 mSv to > 4 mSv in total body scan. Our results, related to the different examination techniques, represent a confident evaluations of patient doses, as required by the relevant normative law.

An ICRU 50 radiotherapy treatment chart.

We illustrate a radiotherapy treatment chart elaborated to fulfil the necessity for clarity in reporting information about radiotherapeutic treatment. The schematic configuration of the chart results from the experience and the cooperation of physicists, physicians and technicians, and an effort has been made to satisfy Levels 2/3 of the ICRU 50 recommendations. The chart has been divided into four sections corresponding to different kinds of information: a cover sheet, a section containing data about the treatment planning geometry and the console parameters adopted, a section showing dosimetric data, and a section showing treatment data. The chart seems to give a good level of accuracy in reporting treatment plan information.

An equivalent square method for irregular photon fields.

A quick formula is proposed for calculating equivalent squares of irregularly shaped photon fields. No complex calculations are required. Three different energies (60Co; 6 MV and 18 MV x-rays) were investigated. Comparison with results utilizing the Clarkson technique (60Co) and with experimental measurements (6 MV and 18 MV x-rays) indicates that the method is accettable in a wide variety of clinical situations. The applied procedure introduces an indetermination lower than 4%, with maximum absolute percentage errors of 3%, 2.7%, and 3.6% for 6 MV, 18 MV, and 60Co photon fields respectively.

Internal irradiation from nuclear medicine investigations: a comparison between effective dose equivalent and effective dose.

ICRP Publication 60 (1990) proposes a partially revised method to calculate effective dose, a quantity previously defined in ICRP Publication 26 (1977) as effective dose equivalent. The authors applied these two different approaches to calculate the effective dose equivalent and the effective dose, in the case of internal irradiations from the most common nuclear medicine investigations. The results show clear differences between the two examined quantities, even if the differences are not statistically significant.

Evaluation of most frequent errors in daily compilation and use of a radiation treatment chart.

Between 1 March and 30 April (1994) we recorded the errors detected by the physician, the radiographer or the physicist during prescription, preparation and execution phases of 227 treatment plans. The radiation treatment modalities used were the following: (i) single or opposed fields, moulded or not; and (ii) multiple fields or kinetic techniques. The total number of sessions performed is 1613 with the cobalt unit and 2131 with the linear accelerator (total, 3744). The total number of wrong data is 155, consisting of 24/227 (10.5%) in compilation, 22/3744 (0.58%) in execution and 109/3744 (2.9%) in registration phases. The number of missing data is 140, consisting of 10/227 (4.4%) in compilation, 9/3744 (0.2%) in execution and 121/3744 (3.2%) in registration phases. Wrong data of compilation, even if in high rate (10.5%), were all found during the same compilation phase or at the first treatment, so that they did not alter the exactness of the treatment plan. Wrong and missing data, found in the registration phase (2.9% and 3.2%, respectively), depend on the repetition of daily treatment and on the registration of data on the chart after having digitized them on the display.

["Indirect" radioisotope cystography after the furosemide test: its diagnostic efficacy compared to "direct" study]. / La cistografia radioisotopica "indiretta" dopo test alla furosemide: efficacia diagnostica comparata all'indagine "diretta".

The diagnostic efficacy was investigated of "indirect" radionuclide cystography after a furosemide test in the detection of vesicoureteral reflux. A single i.v. injection of 99mTc-diethylenetriaminepentacetic acid (DTPA) was administered during sequential renal scintigraphy. "Direct" radionuclide cystography with 99mTc-DTPA was assumed as the "golden standard". Thirty-three patients, 24 of whom in pediatric age, were examined with "indirect" radionuclide cystography after a furosemide test: the method had 32% sensitivity according to restrictive positivity criteria versus 59% according to less restrictive ones. In conclusion, "indirect" radionuclide cystography, in spite of the advantages coming from the use of the diuretic, cannot be considered as an efficient technique to recognize vesicoureteral reflux, especially when the latter is present at a low degree.

[Evaluation of the dose equivalent absorbed by the population of Como and surrounding area following the nuclear reactor accident at Chernobyl]. / Valutazione della dose equivalente ricevuta dalla popolazione di Como e del suo circondario a seguito dell'incidente al reattore nucleare della centrale di Chernobyl.

The effects produced as a consequence of the Chernobyl nuclear reactor accident in the population of Como are assessed on the basis of the measurements taken in the environment and on the food. Exposure measurements produced by external radiation and the activities of the different radionuclides introduced into the body, by ingestion and inhalation, made it possible to obtain an estimate of the dose equivalent and its somatic and genetic effects on the population. The results show that such effects may produce 0.5-2 cases of malignant tumour in the next 25 years and 0.2-1 case of genetic damage in the next 60 years and are therefore statistically insignificant.