RESUMEN
An important factor in dose calculations for targeted radionuclide therapy is the cell-cluster model used. We developed a cell-cluster model based on optimization through mechanical hard-sphere collisions. The geometrical properties and the dosimetric effects of the new model were compared with those of two previous models, i.e. the traditional lattice model and our CellPacker model in which the cells are individually and systematically piled as a cluster. The choice of the cell-cluster model has an effect on the calculated mean absorbed doses in the cells. While CellPacker produces clusters with distinct tumour-healthy tissue interface, our new model is able to make the interface diffuse. Outside the interface the new model is capable to pack cells tighter than CellPacker enabling the description of tissues of higher cellular density. Our two cluster models make it possible to construct the cluster model according to the tissue in question.
Asunto(s)
Modelos Teóricos , Neoplasias/radioterapia , Dosificación Radioterapéutica , Agregación Celular , Humanos , Radioisótopos de Indio/uso terapéutico , Terapia por Captura de Neutrón , RadioinmunoterapiaRESUMEN
The radiation spectra of 111In, 113In, and 114mIn are calculated with the Monte Carlo computer program IMRDEC. The relaxation probabilities are taken from the EADL file of the Lawrence Livermore National Laboratory. Because this file does not include data for some N and O transitions, these were additionally determined by applying the Kassis rule. Two schemes are applied to calculate the transition energies: 1) a simple (Z + 1)/Z scheme, and 2) accurate calculation solving the relativistic Dirac equations. It is shown that using the extended set of relaxation probabilities leads to generation of many additional low-energy Auger and CK electrons if the (Z + 1)/Z rule is applied. On the other hand, the emissions of almost all these electrons are rejected if their energies are calculated solving the Dirac equations taking into consideration realistic electron vacancies.
Asunto(s)
Electrones , Radioisótopos de Indio/química , Fenómenos Biofísicos , Biofisica , Simulación por Computador , Humanos , Radioisótopos de Indio/farmacocinética , Radioisótopos de Indio/uso terapéutico , Método de MontecarloRESUMEN
PURPOSE: To analyse factors behind the variation of patient doses from barium enema (BE) examinations. MATERIAL AND METHODS: The patients' (n=89) organ and effective doses (E) due to BE examinations were computed with the ODS-60 program. An average risk factor for BE examinations was derived using the BEIR V schema. The correlation of E with several independent variables was analysed. RESULTS: Median Es at five hospitals were 4.4, 6.1, 7.1, 13 and 16 mSv. The E of the female patients (median 9.2 mSv) was higher than that of the males (median 5.4 mSv) (p<0.001) due to the higher female doses to the gonads, bladder and uterus, resulting from different body structure. An average fatal risk factor of 0.02%. per one BE examination was derived. Factors controlled by the radiologist (screening time, number of exposures) explained 40% and patient-related factors explained 16% of the total variation of E. The equipment-related factors are included in the residual 44%. CONCLUSION: Due to the large contribution of the radiologists' examination technique in the value of E, an optimal examination technique is essential in reducing doses and the stochastic risk to patients.
Asunto(s)
Sulfato de Bario , Medios de Contraste , Enfermedades Intestinales/diagnóstico por imagen , Monitoreo de Radiación , Adulto , Anciano , Anciano de 80 o más Años , Enema , Femenino , Humanos , Masculino , Persona de Mediana Edad , Dosis de Radiación , Radiografía , Factores de Riesgo , Tecnología RadiológicaRESUMEN
A program for calculating absorbed dose was developed for radioimmunotherapy (RIT) purposes. It was used to determine the difference in the therapeutic effect of (111)In electrons when using a close-packed cubic geometry and a cell cluster model developed in this project. Our cluster model piles the cells individually. The cells were modelled as spheres of diameters of 12 (tumour) and 30 (healthy) microm. Both models were used to generate clusters with spherical tumours inside healthy tissue. The program uses Monte Carlo-based dose kernels. The radiation spectra were calculated from the Auger and x-ray transition strengths and fluorescence yields of (111)In. The results show the importance of the cluster model in cellular level dose calculations. Near the tumour/healthy tissue interface in particular, the doses differ because of geometrical differences. In the case of a small cluster with tumour and total diameters of 30 and 150 microm, the ratio of the therapeutic effects is 20.
Asunto(s)
Células/efectos de la radiación , Electrones , Radioinmunoterapia , Radiometría , Absorción , Análisis por Conglomerados , Humanos , Radioisótopos de Indio/uso terapéutico , Método de Montecarlo , Células Tumorales CultivadasRESUMEN
A method for determining absorbed doses to organs in systemic radiation therapy (SRT) is evaluated. The method, based on thermoluminescent (TL) dosimeters placed on the patient's skin, was validated and justified through a phantom study showing that the difference between measured (TL dosimeters in the phantom) and derived (TL method) values is within 10%. Six radioimmunotherapy (RIT) patients with widespread intraperitoneal pseudomyxoma were also studied. In dose evaluations, special emphasis was on kidneys. In addition to the TL method, the absorbed doses to kidneys were calculated using MIRD formalism and a point dose kernel technique. We conclude that in SRT the described TL method can be used to estimate the absorbed doses to those critical organs near the body surface within 50% (1 SD).
Asunto(s)
Riñón/efectos de la radiación , Neoplasias Peritoneales/radioterapia , Seudomixoma Peritoneal/radioterapia , Dosimetría Termoluminiscente/normas , Adulto , Anciano , Anciano de 80 o más Años , Relación Dosis-Respuesta en la Radiación , Femenino , Humanos , Masculino , Persona de Mediana Edad , Fantasmas de Imagen , Dosificación Radioterapéutica/normas , Dosimetría Termoluminiscente/instrumentaciónRESUMEN
The exposure and geometrical data for 89 barium enema examination patients were recorded manually in five hospitals in Finland. From the recorded data, organ and primary exit doses as well as effective individual doses were calculated for each patient using the ODS-60 program, which is capable of adjusting the calculation phantom according to a patient's size and sex. The mean (and standard deviation, SD) and median effective individual doses for the patients were 9.3 (5.7) and 6.8 mSv, respectively. Conversion functions from dose-area product to relevant organ doses and to effective individual dose were presented as a function of patient sex and weight. Mean primary exit dose values were calculated for each exposure. These were used to compare a theoretically justified exposure control (EC) function with the function of the automatic exposure (rate) control, AEC (AERC), at different hospitals. According to the analysis of primary exit doses, the implementation of the EC was far from optimum. With EC function proposed in this study the SD of effective individual doses to patients could be lowered considerably.
Asunto(s)
Sulfato de Bario , Medios de Contraste , Enema , Dosis de Radiación , Programas Informáticos , Peso Corporal , Femenino , Finlandia , Humanos , Masculino , Factores SexualesRESUMEN
A new computer program was developed to calculate the absorbed dose. The program is based on the use of the convolution method and abdominal SPECT/MR fusion images. The applicability of the method was demonstrated by using data from (111)In-labeled thrombocyte and 99mTc-labeled colloid studies of three healthy volunteers. Dose distributions in the volunteers and the average absorbed doses in liver and spleen were calculated. The average doses for 99mTc-labeled colloid study were 0.07 +/- 0.02 (liver) and 0.046 +/- 0.005 mGy/MBq (spleen). The results are in good agreement with a Monte Carlo (MC) based method (0.074 for liver and 0.077 mGy/MBq for spleen) used by the International Commission on Radiological Protection (ICRP). For (111)In-labeled thrombocyte study the doses were 0.33 +/- 0.05 (liver) and 8.9 +/- 1.2 mGy/MBq (spleen) versus 0.730 and 7.50, respectively. The differences in dose estimates in the (111)In-labeled thrombocyte study are mainly due to the approximation used in activity quantitation. Convolution of the activity distribution with a point dose kernel is an effective method for calculating absorbed dose distribution in a homogeneous media. Activity distribution must be aligned to anatomical data in order to utilize the calculated dose distribution. The program developed is applicable to and practical for clinical use provided that the input data needed are available.
Asunto(s)
Imagen por Resonancia Magnética/estadística & datos numéricos , Planificación de la Radioterapia Asistida por Computador/métodos , Programas Informáticos , Tomografía Computarizada de Emisión de Fotón Único/estadística & datos numéricos , Humanos , Radioisótopos de Indio/uso terapéutico , Hígado/anatomía & histología , Hígado/diagnóstico por imagen , Fantasmas de Imagen , Bazo/anatomía & histología , Bazo/diagnóstico por imagen , Tecnecio/uso terapéuticoRESUMEN
Both the use of traditional fluoroscopy and the increasing use of modern digital techniques in radiology and interventional radiology demand the development of versatile computer programs for patient dose determinations. Long computing times restrict the use of Monte Carlo (MC) methods in dose monitoring applications where the radiological views change frequently. In the Organ Doses Calculation Software application (ODS-60), the phantom model is similar in principle to the Alderson-Rando (A-R) phantom, but its sex, size and shape is modified according to a particular patient. Organ and effective doses are computed online (in a few seconds) using a method similar to the traditional dose planning systems used in radiotherapy. In this paper, the new ODS-60 software is presented in detail and its capabilities are demonstrated. Software performance was determined by comparing the results with those from independent methods. In the case of a reference man-sized male, the effective dose was about 7% larger than the effective dose given in another publication. In the case of a reference woman-sized female, the disagreement with the other method was greater (33%). Anatomical differences between the phantom models (ODS-60 and MC) were found to be the main reasons for these findings. This paper shows the advantage of using a patient size- and sex-adaptable phantom for patient dose determinations; the conversion coefficient from entrance surface dose-to-effective dose ratio between male (170 cm, 85 kg) and a female (160 cm, 43 kg) varies in the range 1.5-2.