Image segmentation of trabecular spongiosa by visual inspection of the gradient magnitude.

Recent advances in physical models of skeletal dosimetry utilize high-resolution 3-dimensional microscopic computed tomography images of trabecular spongiosa. These images are coupled to radiation transport codes to assess energy deposition within active bone marrow and trabecular endosteum. These transport codes rely primarily on the segmentation of the spongiosa images into bone and marrow voxels. Image thresholding has been the segmentation of choice for bone sample images because of its extreme simplicity. However, the ability of the segmentation to reproduce the physical boundary between bone and marrow depends on the selection of the threshold value. Statistical models, as well as visual inspection of the image, have been employed extensively to determine the correct threshold. Both techniques are affected by partial volume effect and can provide unexpected results if performed without care. In this study, we propose a new technique to threshold trabecular spongiosa images based on visual inspection of the image gradient magnitude. We first show that the gradient magnitude of the image reaches a maximum along a surface that remains almost independent of partial volume effect and that is a good representation of the physical boundary between bone and marrow. A computer program was then developed to allow a user to compare the position of the iso-surface produced by a threshold with the gradient magnitude. The threshold that produces the iso-surface that best coincides with the maximum gradient is chosen. The technique was finally tested with a set of images of a true bone sample with different resolutions, as well as with three images of a cube of Duocell aluminium foam of known mass and density. Both tests demonstrate the ability of the gradient magnitude technique to retrieve sample volumes or media volume fractions with 1% accuracy at 30 microm voxel size.

A hyperboliod representation of the bone-marrow interface within 3D NMR images of trabecular bone: applications to skeletal dosimetry.

Recent advances in physical models of skeletal dosimetry utilize high-resolution NMR microscopy images of trabecular bone. These images are coupled to radiation transport codes to assess energy deposition within active bone marrow irradiated by bone- or marrow-incorporated radionuclides. Recent studies have demonstrated that the rectangular shape of image voxels is responsible for cross-region (bone-to-marrow) absorbed fraction errors of up to 50% for very low-energy electrons (<50 keV). In this study, a new hyperboloid adaptation of the marching cube (MC) image-visualization algorithm is implemented within 3D digital images of trabecular bone to better define the bone-marrow interface, and thus reduce voxel effects in the assessment of cross-region absorbed fractions. To test the method, a mathematical sample of trabecular bone was constructed, composed of a random distribution of spherical marrow cavities, and subsequently coupled to the EGSnrc radiation code to generate reference values for the energy deposition in marrow or bone. Next, digital images of the bone model were constructed over a range of simulated image resolutions, and coupled to EGSnrc using the hyperboloid MC (HMC) algorithm. For the radionuclides 33P, 117mSn, 131I and 153Sm, values of S(marrow<--bone) estimated using voxel models of trabecular bone were shown to have relative errors of 10%, 9%, <1% and <1% at a voxel size of 150 microm. At a voxel size of 60 microm, these errors were 6%, 5%, <1% and <1%, respectively. When the HMC model was applied during particle transport, the relative errors on S(marrow<--bone) for these same radionuclides were reduced to 7%, 6%, <1% and <1% at a voxel size of 150 microm, and to 2%, 2%, <1% and <1% at a voxel size of 60 microm. The technique was also applied to a real NMR image of human trabecular bone with a similar demonstration of reductions in dosimetry errors.

Final report on the second British Institute of Radiology fractionation study: short versus long overall treatment times for radiotherapy of carcinoma of the laryngo-pharynx.

The second British Institute of Radiology trial of dose fractionation in radiotherapy compared two groups of prospectively randomized patients with squamous carcinoma of the laryngo-pharynx; one group was treated in a short (less than or equal to 4 weeks) and the other in a long (greater than 4 weeks) overall time. Treatment in any one centre could be given, with no planned gap in the course of treatment, either as a conventional, daily (5 fractions per week regime) or as 3 fractions per week. A total of 611 patients were allocated to treatment, of whom nine have had to be excluded from the analysis for a lack of information. Patients were admitted to the trial from January 1976 to December 1985 and were followed up for a maximum of 10 years and a minimum of 3 years. A reduction in total dose was made for use in the short compared with the long treatment regime. This reduction in total dose varied between 18% and 22% depending on whether 5 fractions or 3 fractions per week regimes were used. Overall, no statistically significant differences have been found between the two arms of the trial. The patients treated with 5 fractions per week in a short overall treatment time showed fewer late normal tissue effects. An analysis based on stratification by age, stage and anatomical site gave a relative risk (short/long overall treatment time) for deaths of 1.23 with a 95% confidence interval from 0.96 to 1.59. Analyses stratified for stage and site gave relative risks with 95% confidence intervals of 1 x 10 (0.84-1.44) for local recurrences/tumour persistence, and 1.01 (0.70-1.45) for laryngectomies.

Final report of the general clinical results of the British Institute of Radiology fractionation study of 3F/wk versus 5F/wk in radiotherapy of carcinoma of the laryngo-pharynx.

The 10 year follow-up of a clinical trial involving the comparison of 3F/wk versus 5F/wk in radiotherapy of squamous cell carcinoma of the larynx and hypopharynx has now been completed. The trial involved an intake of 734 patients between 1966 and 1975. The classification of all patients has been revised to conform with the latest TNM publication. A reduction in total dose was made for 3F/wk compared with 5F/wk. This varied between 13% and 11% in centres treating over 3 weeks and 6 weeks, respectively. No statistically significant differences have been found between the two arms (3F/wk versus 5F/wk) of the trial in any of the main group analyses. A number of sub-group analyses relating to survival, tumour-free and laryngectomy-free rates and to the comparison of acute or late normal-tissue radiation damage have also been performed. No differences have been found that could be considered to be statistically significant in relation to the particular sub-group. Previous interim reports suggested minor differences in sub-group analyses between the 3F/wk and 5F/wk regimes in this trial; these have diminished now that the full follow-up data are available. This trial has provided evidence on which clinicians may base their choice between either a 3F/wk fractionation regime or a conventional 5F/wk treatment protocol in the treatment of carcinoma of the laryngo-pharynx.

First interim progress report on the second British Institute of Radiology Fractionation Study: short versus long overall treatment times for radiotherapy of carcinoma of the laryngopharynx.

Preliminary data from a second British Institute of Radiology Fractionation Trial comparing short (less than or equal to 4 weeks) and long (greater than 4 weeks) overall treatment times are reported. The intake of patients ran from January, 1975 to December, 1985 when 611 patients with carcinoma of the laryngo-pharynx were registered in this prospective, randomized, multicentre clinical trial. No significant differences have, so far, been demonstrated between the two arms of the trial with respect to observed survival rates, tumour-free or laryngectomy-free rates. Further long-term follow-up is continuing.