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- Bernhardt, Peter, 1966, et al.
(författare)
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Model of metastatic growth valuable for radionuclide therapy
- 2003
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Ingår i: Medical physics. - 0094-2405. ; 30:12, s. 3227-32
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Tidskriftsartikel (refereegranskat)abstract
- The aim was to make a Monte Carlo simulation approach to estimate the distribution of tumor sizes and to study the curative potential of three candidate radionuclides for radionuclide therapy: the high-energy electron emitter 90Y, the medium-energy electron emitter 177Lu and the low-energy electron emitter 103mRh. A patient with hepatocellular carcinoma with recently published serial CT data on tumor growth in the liver was used. From these data the growth of the primary tumor, and the metastatis formation rate, were estimated. Assuming the same tumor growth of the primary and all metastases and the same metastatis formation rate from both primary and metastases the metastatic size distribution was simulated for various time points. Tumor cure of the metastatic size distribution was simulated for uniform activity distribution of three radionuclides; the high-energy electron emitter 90Y, the mean-energy electron emitter 177Lu and the low-energy electron emitter 103mRh. The simulation of a tumor cure was performed for various time points and tumor-to-normal tissue activity concentrations, TNC. It was demonstrated that it is important to start therapy as early as possible after diagnosis. It was of crucial importance to use an optimal radionuclide for therapy. These simulations demonstrated that 90Y was not suitable for systemic radionuclide therapy, due to the low absorbed fraction of the emitted electrons in small tumors (< 1 mg). If TNC was low 103mRh was slightly better than 177Lu. For high TNC values low-energy electron emitters, e.g., 103mRh was the best choice for tumor cure. However, the short half-life of 103mRh (56 min) might not be optimal for therapy. Therefore, other low-energy electron emitters, or alpha emitters, should be considered for systemic targeted therapy.
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- Bernhardt, Peter, 1966, et al.
(författare)
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Modelling of metastatic cure after radionuclide therapy: influence of tumor distribution, cross-irradiation, and variable activity concentration
- 2004
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Ingår i: Medical physics. - : Wiley. - 0094-2405. ; 31:9, s. 2628-35
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Tidskriftsartikel (refereegranskat)abstract
- The objective was to study the influence of tumor number and size, cross-irradiation from normal tissue, and of variable activity concentration on metastatic cure after radionuclide therapy. A model to calculate the metastatic cure probability (MCP) was developed, in which it was assumed that the tumor response was an exponential function of the absorbed dose. All calculations were performed for monoenergetic electron emitters with different energies (10-1000 keV). The influence of tumor size and number of tumors were investigated with different log uniform distributions; the basic tumor distribution consisted of tumors with 1, 10, ..., 10(11) cells. The influence of cross-irradiation was assessed by calculating MCP for various tumor-to-normal tissue activity concentration ratios (TNC). The influence of variable activity concentration between tumors was calculated by assuming that the activity concentration in tumors was an inverse power law function of tumor mass. The required activity concentration (C0.9) and absorbed dose (D0.9) to obtain MCP=0.9 was calculated in the different models. The C0.9 and D0.9 needed to obtain MCP were very high; more than 25 MBq/g and 80 Gy, respectively. The lowest C0.9 and D0.9 for equal activity concentration in the different tumor sizes were obtained for electron energies less than 80 keV. For higher energies the low absorbed energy fraction in small tumors will increase the required C0.9 and D0.9 markedly. Cross-irradiation from normal cells surrounding the tumor will cause sterilization of the smallest tumors and decrease the required C0.9 and D0.9 for higher electron energies. Assuming that the activity concentration decreased with increased tumor mass caused a marked increase in C0.9 and D0.9 in favor of higher electron energies. With the MCP model we demonstrated significant influence of the number of tumors, their size, TNC and variable activity concentration on MCP. The results are valuable when evaluating optimal choices for radionuclides for internal-emitter therapy.
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- Björk, Peter, et al.
(författare)
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Comparative dosimetry of diode and diamond detectors in electron beams for intraoperative radiation therapy
- 2000
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Ingår i: Medical Physics. - : Wiley. - 0094-2405. ; 27:11, s. 2580-2588
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the present study is to examine the validity of using silicon semiconductor detectors in degraded electron beams with a broad energy spectrum and a wide angular distribution. A comparison is made with diamond detector measurements, which is the dosimeter considered to give the best results provided that dose rate effects are corrected for. Two-dimensional relative absorbed dose distributions in electron beams (6-20 MeV) for intraoperative radiation therapy (IORT) are measured in a water phantom. To quantify deviations between the detectors, a dose comparison tool that simultaneously examines the dose difference and distance to agreement (DTA) is used to evaluate the results in low- and high-dose gradient regions, respectively. Uncertainties of the experimental measurement setup (+/- 1% and +/- 0.5 mm) are taken into account by calculating a composite distribution that fails this dose-difference and DTA acceptance limit. Thus, the resulting area of disagreement should be related to differences in detector performance. The dose distributions obtained with the diode are generally in very good agreement with diamond detector measurements. The buildup region and the dose falloff region show good agreement with increasing electron energy, while the region outside the radiation field close to the water surface shows an increased difference with energy. The small discrepancies in the composite distributions are due to several factors: (a) variation of the silicon-to-water collision stopping-power ratio with electron energy, (b) a more pronounced directional dependence for diodes than for diamonds, and (c) variation of the electron fluence perturbation correction factor with depth. For all investigated treatment cones and energies, the deviation is within dose-difference and DTA acceptance criteria of +/- 3% and +/- 1 mm, respectively. Therefore, p-type silicon diodes are well suited, in the sense that they give results in close agreement with diamond detectors, for practical measurements of relative absorbed dose distributions in degraded electron beams used for IORT.
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- Båth, Magnus, 1974, et al.
(författare)
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Determination of the two-dimensional detective quantum efficiency of a computed radiography system.
- 2003
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Ingår i: Medical physics. - : Wiley. - 0094-2405. ; 30:12, s. 3172-82
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Tidskriftsartikel (refereegranskat)abstract
- Based on a recently described method for determining the two-dimensional presampling modulation transfer function (MTF), the aperture mask method, a method for determining the two-dimensional detective quantum efficiency (DQE) of a digital radiographic system was developed. The method was applied to a new computed radiography (CR) system and comparisons with one-dimensional determinations of the presampling MTF and the DQE were performed. The aperture mask method was shown to agree with the conventional tilted slit method for determining the presampling MTF along the axes. For the particular CR system studied, the mean of one-dimensional determinations of the DQE in orthogonal directions led to a representative measure of the average DQE behavior of the system up to the Nyquist frequency along the axes, but a deviation was observed above this frequency. In conclusion, the method developed for determining the two-dimensional DQE can be used to determine the imaging properties of a digital radiographic detector system over almost the entire frequency domain, the exception being the lowest frequencies (< or = 0.1 mm(-1)) at which the validity and the reliability of the method are low.
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- Båth, Magnus, 1974, et al.
(författare)
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Evaluation of the imaging properties of two generations of a CCD-based system for digital chest radiography.
- 2002
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Ingår i: Medical physics. - : Wiley. - 0094-2405. ; 29:10, s. 2286-97
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Tidskriftsartikel (refereegranskat)abstract
- Two generations of a CCD-based detector system with lens-based optical coupling for digital chest radiography were evaluated in terms of presampling MTF, NPS, NEQ, DQE, linearity in response, and SNR over the detector area. Measurements were performed over a wide exposure range and at several different beam qualities. Neither the presampling MTF nor the DQE showed any general strong beam quality dependence, whereas the NPS and NEQ did when compared at specific entrance air kerma values. The exposure dependency for the DQE was found to be considerable, with the detectors showing low DQE at low exposures, and higher DQE at higher exposures. It was found that the second generation has been substantially improved compared to its predecessor regarding all the relevant parameters. The DQE(0) at an entrance air kerma of 5 microGy increased from 9% to 15%, mainly due to a better system gain (including optical coupling efficiency and matching of the energy of the emitted light photons to the sensitivity of the CCD camera). The first generation of detectors was found to have problems with bad peripheral resolution [MTF(muN/2) <0.1]. This problem was nonexistent for the second generation for which uniform resolution has been obtained [MTF(muN/2)=0.3]. A theoretical calculation of the DQE of two model systems similar to the ones evaluated was also performed, and the results were comparable to the experimentally determined data at high exposures. The model shows that both systems suffer from low optical coupling efficiency due to the large demagnification used. The main conclusion is that although the second generation has been improved, there is still a problem with low system gain leading to relatively modest DQE values, especially at low exposures.
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- Carlsson, F, et al.
(författare)
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On the use of curvature information in IMRT optimization
- 2004
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Ingår i: Medical physics (Lancaster). - RaySearch Labs AB, Stockholm, Sweden. Royal Inst Technol, Stockholm, Sweden. : AMER ASSOC PHYSICISTS MEDICINE AMER INST PHYSICS. - 0094-2405. ; 31:6, s. 1906-1906
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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