Biomedical subjects

J N Roy

Publications and source records attributed to J N Roy.

5 recordsLinked to original sources

PubMed1998

Three-dimensional lookup tables for Henschke applicator cervix treatment by HDR 192IR remote afterloading.

PURPOSE: We have generated three-dimensional (3D) lookup tables for dosimetric analysis and optimization of high-dose rate (HDR) gynecological treatments using the Henschke applicator. The new dosimetry data have been compared with two-dimensional (2D) data currently in use. The 3D dosimetry tables have been implemented in an existing cervix treatment-planning system and have been evaluated through analysis of clinical cases. METHODS AND MATERIALS: A general Monte Carlo N-Particles (MCNP) transport code was used to compute absorbed dose distributions around the intrauterine tandem and tungsten-shielded ovoid separately. The dosimetry data are represented in the x-y coordinate system for the intrauterine tandem table. The 3D table for the ovoid contains a radial dose function and an anisotropy function, as formulated in the spherical coordinate system. Absorbed dose at a spatial point is calculated by applying bilinear interpolation for the anisotropy function and linear interpolation for the radial dose function. The geometry factor for a finite line source is used. 3D dose calculations and optimization were performed for 20 treatments of 10 patients. The absorbed dose to critical structures, bladder and rectum, was compared by applying both the 2D table currently in use and the new tables. RESULTS: The new 2D table for the intrauterine tandem yields doses different by less than 10% from those with the current table. The 3D table for the shielded ovoids shows as large as a factor of 4 reduction of dose behind the shield compared with the present 2D table. This shielding effect leads to 21.6 +/- 9.3% and 20.0 +/- 6.6% dose reduction at rectum and bladder, respectively, for actual treatments. CONCLUSION: Our analysis indicates a need for patient-specific 3D dosimetry to permit more accurate dosimetric evaluation of HDR cervix treatments using shielded applicators. We have also shown that a Monte Carlo simulation code enabled us to derive the lookup tables necessary for 3D planning.

Brachytherapy↗

PubMed1993

A CT-based evaluation method for permanent implants: application to prostate.

A computerized tomography-based 3-dimensional evaluation scheme, using semi-automatic seed localization from transverse computerized tomography-images, has been developed for permanent implants. The treatment isodose contour is generated at each scan plane and overlaid on the corresponding target contour for coverage visualization. Volume and surface dose histograms are generated for the target and neighboring normal structures. Dose inhomogeneity within the target is also estimated from the full-width at half maximum of the differential volume dose histogram. The matched peripheral dose is calculated from the ellipsoidal volume approximation for the target. The present evaluation method has been applied here to 10 actual permanent I-125 prostatic implantations. Coverages by 150 Gy and 100 Gy levels are found to range from 78-96% and 91-99% of the target volume, respectively. The average matched peripheral dose is found to be about two times the average peripheral dose (the dose encompassing 99% target) and about three times the average minimum peripheral dose (the dose encompassing 100% target). The dose inhomogeneities within the target volume, in these 10 cases, range from 220-420 Gy.

Brachytherapy↗

PubMed1993

Tumor control probability for permanent implants in prostate.

The tumor control probabilities (TCPs) for 11 transperineal permanent implants of the prostate with 125I seeds have been computed, based on target-specific volume-dose histogram data. Prostate dose-response of this modality is converted from that of external beam therapy based on biologically effective dose derived from the alpha beta model. The calculated TCPs for these transperineal prostate cases are compared with the results of 679 previous retropubic implants, providing interesting insight about these two techniques. Further refinement and validation of this model await long-term followup results of sufficient number of patients.

Brachytherapy↗

PubMed1991

CT-based optimized planning for transperineal prostate implant with customized template.

A computerized planning procedure has been developed for CT-guided transperineal prostate implants. The segment for custom planning of perineal needle orientations allows placement of I-125 seeds in the entire prostate gland while avoiding the pubic bones. Least-squares optimization (LSO) is used to obtain the seed-loading pattern along the needles. The optimized seed distribution produces a better fit between treatment and target volumes than that obtained from our previous manual technique. Also, the present semi-automatic technique reduces planning time by about a factor of 10 compared to that of the manual approach.

Brachytherapy↗

PubMedDate not supplied

Overlap detection and contour-tracking algorithms for critical organs--application to kidney.

An auto-contouring technique has been developed for critical structures on transverse Computer Tomographic (CT) images with one or two overlap regions where object and background have similar CT values. In this technique, those regions are identified and skipped during contour tracking. The contours thus obtained are discontinuous which are corrected afterwards by suitable interpolations. The overlap detection criterion is never satisfied in a nonoverlapping environment and the contour, in this case, is essentially tracked on the basis of CT value threshold alone. The entire process can be initiated by minimal operator intervention. The method has been successfully tested for kidneys and several examples are furnished. The success and concomitant limitations of this technique are also discussed.

Algorithms↗