AAPM Banner
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 
Search Issue | RSS Feeds RSS
Previous Issue

Dec 1998

Volume 25, Issue 12, pp. 2265-2483

Page 1 of 4 Pages Next Page | Jump to Page

Proposition: Long‐term changes in irradiated tissues are due principally to vascular damage in the tissues

John Hopewell and H. Rodney Withers

Med. Phys. 25, 2265 (1998); http://dx.doi.org/10.1118/1.598455 (4 pages) | Cited 2 times

Full Text: | Download PDF

Abstract Unavailable
Show PACS
87.53.-j Effects of ionizing radiation on biological systems

Dosimetric prerequisites for routine clinical use of new low energy photon interstitial brachytherapy sources

Jeffrey Williamson, Chair, Bert M. Coursey, Larry A. DeWerd, William F. Hanson, and Ravinder Nath

Med. Phys. 25, 2269 (1998); http://dx.doi.org/10.1118/1.598456 (2 pages) | Cited 60 times

Full Text: | Download PDF

Abstract Unavailable
Show PACS
87.53.Jw Therapeutic applications, including brachytherapy
87.56.B- Radiation sources
87.55.N- Radiation monitoring, control, and safety

Anisotropy functions for 125I and 103Pd sources

Keith Weaver

Med. Phys. 25, 2271 (1998); http://dx.doi.org/10.1118/1.598458 (8 pages) | Cited 47 times

Full Text: | Download PDF

Show Abstract
The anisotropy function was defined by AAPM Task Group 43 in a recent report, and reference data were provided. However, some of the data appeared to have large experimental errors. In this work, anisotropy functions are presented for three low-energy photon-emitting sources commonly used for brachytherapy: 125I source models 6702 and 6711, and the model 200 103Pd source. The data were generated via a two-step process: the sources’ intrinsic radiation emission pattern was determined from in-air measurements, and these data were used as input to Monte Carlo calculations of the fluence distribution in water. The new anisotropy function values for iodine compare well with earlier data from diode measurements, and seem more physically realistic than some data provided by TG43. Previous palladium data measured with TLDs are more variable, but on the average are similar to the data presented here. The new data have estimated uncertainties of 3%–6%; this level of accuracy should be completely adequate for clinical calculations. © 1998 American Association of Physicists in Medicine.
Show PACS
87.53.Jw Therapeutic applications, including brachytherapy
29.25.Rm Sources of radioactive nuclei

Experimental determination of dosimetry functions of Ir-192 sources

Jean-Claude Anctil, Brenda G. Clark, and Clément J. Arsenault

Med. Phys. 25, 2279 (1998); http://dx.doi.org/10.1118/1.598457 (9 pages) | Cited 20 times

Full Text: | Download PDF

Show Abstract
Experimental data related to the dosimetric characteristics of Ir-192 brachytherapy sources are limited. The aim of this work was to obtain the dosimetry functions required by the American Association of Physicists in Medicine Task Group 43 for both a low and a high dose-rate iridium-192 brachytherapy source through dose measurements in a water-equivalent phantom. Dose measurements have been performed using lithium fluoride thermoluminescent detectors positioned in a polystyrene phantom at distances from the source that vary from 1 to 10 cm, with 1 cm intervals, and at angles that vary from 0° to 170° with 10° intervals. The anisotropy functions, radial dose functions, and dose rate constants were determined for both brachytherapy sources. The precision of results obtained on those relatively fine intervals of angles and distances provides clinics with the possibility to use and interpolate the complete data sets for treatment planning. © 1998 American Association of Physicists in Medicine.
Show PACS
87.53.Jw Therapeutic applications, including brachytherapy
29.25.Rm Sources of radioactive nuclei

Monte Carlo dose calculations for a new ovoid shield system for carcinoma of the uterine cervix

K. J. Weeks

Med. Phys. 25, 2288 (1998); http://dx.doi.org/10.1118/1.598459 (5 pages) | Cited 7 times

Full Text: | Download PDF

Show Abstract
The dose distribution for an ovoid with a new tungsten shielding design was determined using Monte Carlo simulation. Standard Cesium-137 tube sources, tungsten shielding, and aluminum ovoid applicator were each modeled as a collection of solid objects. Dose was calculated in planes above, below, in front of, and on the sides of the colpostat. The Monte Carlo results were compared with the results from a parametrized calculation algorithm and good agreement was obtained. The dose distribution matrix derived from the parametrized algorithm can be used for clinical treatment planning.© 1998 American Association of Physicists in Medicine.
Show PACS
87.53.Jw Therapeutic applications, including brachytherapy
87.55.N- Radiation monitoring, control, and safety
02.70.Rr General statistical methods

Correlation of medical dosimetry quality indicators to the local tumor control in patients with prostate cancer treated with iodine-125 interstitial implants

Ravinder Nath, Kenneth Roberts, Michelle Ng, Richard Peschel, and Zhe Chen

Med. Phys. 25, 2293 (1998); http://dx.doi.org/10.1118/1.598440 (15 pages) | Cited 19 times

Full Text: | Download PDF

Show Abstract
The treatment of prostate cancer by 125I interstitial implants has been extensively studied with mixed results by one institution or another. A recent study from Hahnemann [Int. J. Radiat. Oncol., Biol., Phys. 21 955–960 (1991)] reported results that were extremely poor compared to those reported in an earlier study at Yale [Int. J. Radiat. Oncol., Biol., Phys. 14, 1153–1157 (1988)] or those in an Eastern Virginia Study [Cancer 63, 2415–2420 (1989)]; differences in 5-yr survival rates being more than a factor of 2. Such large discrepancies from institution to institution led us to a reexamination of the dosimetry. This study analyzed quantitatively three-dimensional dosimetric parameters of 110 prostate cancer patients treated with 125I interstitial implants. The study searched for “cutoff” values in each parameter that divided the patients into two groups with statistically significant differences in the local recurrence-free survival rates. A comparison of the three-dimensional isodose surfaces of patients with favorable values in all of the parameters to those patients with all unfavorable parameters show how these characteristics translated into poor dose coverage and much inhomogeneity within the implant even for cases that met the traditional criteria for adequacy (160 Gy to the tumor volume). Patients in the favorable group had 10-yr survival rates higher by a factor of up to 2 compared to those in the unfavorable group. The strong correlation of three-dimensional volume-dose parameters to the local control rate observed in this study further emphasizes how important it is to assess the three-dimensional dosimetric adequacy of interstitial implants before deciding on their clinical efficacy. If implants are performed with appropriate attention to dosimetry parameters, excellent clinical results are obtained. On the other hand, if dosimetry parameters are not correct, the implant results can be poor. © 1998 American Association of Physicists in Medicine.
Show PACS
87.53.Jw Therapeutic applications, including brachytherapy

A new genetic algorithm technique in optimization of permanent 125I prostate implants

Guozhen Yang, L. E. Reinstein, S. Pai, Zhigang Xu, and D. L. Carroll

Med. Phys. 25, 2308 (1998); http://dx.doi.org/10.1118/1.598460 (8 pages) | Cited 29 times

Full Text: | Download PDF

Show Abstract
Real time optimized treatment planning at the time of the implant is desirable for ultrasound-guided transperineal 125I permanent prostate implants. Currently available optimization algorithms are too slow to be used in the operating room. The goal of this work is to develop a robust optimization algorithm, which is suitable for such application. Three different genetic algorithms (sGA, sureGA and securGA) were developed and compared in terms of the number of function evaluations and the corresponding fitness. The optimized dose distribution was achieved by searching the best seed distribution through the minimization of a cost function. The cost function included constraints on the periphery dose of the planned target volume, the dose uniformity within the target volume, and the dose to the critical structure. Adjustment between the peripheral dose, the dose uniformity and critical structure dose can be achieved by varying the weighting factors in the cost function. All plans were evaluated in terms of the dose nonuniformity ratio, the conformation number and the dose volume histograms. Among these three GA algorithms, the securGA provided the best performance. Within 2500 function evaluations, the near optimum results were obtained. For a large target volume (5 cm×4 cm×4.5 cm) including urethra with 20 needles, the computer time needed for the optimization was less than 5 min on a HP735 workstation. The results showed that once the best set of parameters was found, they were applicable for all sizes of prostate volume. For a fixed needle geometry, the optimized plan showed much better dose distribution than that of nonoptimized plan. If the critical structure was considered in the optimization, the dose to the critical structure could be minimized. In the cases of irregular and skewed needle geometry, the optimized treatment plans were almost as good as ideal needle geometry. It is concluded that this new genetic algorithm (securGA) allows for an efficient and rapid optimization of dose distribution, which is suitable for real time treatment planning optimization for ultrasound-guided prostate implant. © 1998 American Association of Physicists in Medicine.
Show PACS
87.53.Jw Therapeutic applications, including brachytherapy
87.56.Fc Quality assurance equipment
87.63.D- Ultrasonography
02.60.-x Numerical approximation and analysis

Magnetic resonance imaging of microbubbles in a superheated emulsion chamber for brachytherapy dosimetry

Michael Lamba, Scott K. Holland, Howard Elson, Francesco d’Errico, and Ravinder Nath

Med. Phys. 25, 2316 (1998); http://dx.doi.org/10.1118/1.598441 (10 pages) | Cited 5 times

Full Text: | Download PDF

Show Abstract
This paper describes development of magnetic resonance imaging (MRI) techniques for three-dimensional (3D) imaging of a position-sensitive detector for brachytherapy dosimetry. The detector is a 0.5 l chamber containing an emulsion of halocarbon-115 droplets in a tissue-equivalent glycerin-based gel. The halocarbon droplets are highly superheated and expand into vapor microbubbles upon irradiation. Brachytherapy sources can be inserted into the superheated emulsion chamber to create distributions of bubbles. Three-dimensional MRI of the chamber is then performed. A 3D gradient-echo technique was optimized for spatial resolution and contrast between bubbles and gel. Susceptibility gradients at the interfaces between bubbles and gel are exploited to enhance contrast so microscopic bubbles can be imaged using relatively large voxel sizes. Three-dimensional gradient-echo images are obtained with an isotropic resolution of 300 μm over a 77 mm×77 mm×9.6 mm field-of-view in an imaging time of 14 min. A post-processing technique was developed to semi-automatically segment the bubbles from the images and to assess dose distributions based on the measured bubble densities. Relative dose distributions are computed from MR images for a 125I brachytherapy source and the results compare favorably to relative radial dose distributions calculated as recommended by Task Group 43 of the American Association of Physicists in Medicine. © 1998 American Association of Physicists in Medicine.
Show PACS
87.61.-c Magnetic resonance imaging
87.53.Jw Therapeutic applications, including brachytherapy

The radiation induced magnetic resonance image intensity change provides a more efficient three-dimensional dose measurement in MRI–Fricke–agarose gel dosimetry

W. C. Chu, W. Y. Guo, M. C. Wu, W. Y. Chung, and David H. C. Pan

Med. Phys. 25, 2326 (1998); http://dx.doi.org/10.1118/1.598442 (7 pages) | Cited 9 times

Full Text: | Download PDF

Show Abstract
A detailed methodology has been developed to map the spatial dose distribution in a Fricke–agarose gel based on the radiation induced image intensity change in the gel’s magnetic resonance (MR) images. Besides the linear correlation between the change in the gel’s spin-lattice relaxation rate and the absorbed dose, it is shown here that the radiation induced image intensity change for T1-weighted spin-echo images with TE≪TR correlates exponentially to the absorbed dose. Furthermore, at the lower dose region (<15 Gy), the correlation is fairly linear and its sensitivity is high. The minimum detectable dose is shown to be equivalent to the one obtained using the conventional R1-based approach. Since only one T1-weighted image is required for the dose evaluation, compared to the R1-based method, the total MR imaging time can be reduced from hours to a few minutes. This extensive time reduction avoids ferric ion diffusion effects and provides a practical way to simply and effectively measure the three-dimensional dose distribution using the Fricke–agarose dosimeter gel. © 1998 American Association of Physicists in Medicine.
Show PACS
87.61.-c Magnetic resonance imaging

Rapid portal imaging with a high-efficiency, large field-of-view detector

M. A. Mosleh-Shirazi, P. M. Evans, W. Swindell, J. R. N. Symonds-Tayler, S. Webb, and M. Partridge

Med. Phys. 25, 2333 (1998); http://dx.doi.org/10.1118/1.598443 (14 pages) | Cited 31 times

Full Text: | Download PDF

Show Abstract
The design, construction, and performance evaluation of an electronic portal imaging device (EPID) are described. The EPID has the same imaging geometry as the current mirror-based systems except for the x-ray detection stage, where a two-dimensional (2D) array of 1 cm thick CsI(Tl) detector elements are utilized. The ∼18% x-ray quantum efficiency of the scintillation detector and its 30×40 cm2 field-of-view at the isocenter are greater than other area-imaging EPIDs. The imaging issues addressed are theoretical and measured signal-to-noise ratio, linearity of the imaging chain, influence of frame-summing on image quality and image calibration. Portal images of test objects and a humanoid phantom are used to measure the performance of the system. An image quality similar to the current devices is achieved but with a lower dose. With ∼1 cGy dose delivered by a 6 MV beam, a 2 mm diam structure of 1.3% contrast and an 18 mm diam object of 0.125% contrast can be resolved without using image-enhancement methods. A spatial resolution of about 2 mm at the isocenter is demonstrated. The capability of the system to perform fast sequential imaging, synchronized with the radiation pulses, makes it suitable for patient motion studies and verification of intensity-modulated beams as well as its application in cone-beam megavoltage computed tomography. © 1998 American Association of Physicists in Medicine.
Show PACS
87.56.Fc Quality assurance equipment
87.53.-j Effects of ionizing radiation on biological systems
Page 1 of 4 Pages Next Page | Jump to Page
Close

Medical Physics is an official science journal of the AAPM and of the COMP/CCPM/IOMP
William R. Hendee, Editor
Departments of Radiology, Radiation Oncology, Biophysics, Community and Public Health, Medical College of Wisconsin
One Physics Ellipse
College Park, Maryland 20740
301-209-3352

© 2013, American Association of Physicists in Medicine. Individual readers of this journal, and nonprofit libraries acting for them, are freely permited to make fair use of the material in it, such as to copy an article for use in teaching or research. (For other kinds of copying see "Copying Fees.") Permission is granted to quote from this journal in scientific works with the customary acknowledgment of the source. To reprint a figure, table, or other excerpt requires, in addition, AAPM may require that permission also be obtained from one of the authors. Address inquiries and notices to Penny Slattery, Journal Manager, Medical Physics Journal, AAPM, One Physics Ellipse, College Park, MD 20740-3846; email: journal@aapm.org.

close