Biomedical subjects

Cheng-Shie Wuu

Publications and source records attributed to Cheng-Shie Wuu.

8 recordsLinked to original sources

PubMed2006

Calculated microdosimetric characteristics of 125I and 103Pd brachytherapy seeds at different depths in water.

Both (125)I and (103)Pd sources have been widely used in the permanent prostate implant. An important consideration for the choice of brachytherapy sources is the relative biological effectiveness (RBE) for the source/seed used in the implantation. As RBE is closely related to the microdosimetric parameter, it is desirable to calculate the dose mean lineal energies for both (125)I and (103)Pd at various radial distances to the seed surface. Monte Carlo simulation was performed for photons emitted from (125)I and (103)Pd. Energy depositions from photons and all their secondary electrons were tracked. Dose distributions of lineal energy, d(y), were calculated for spheres of 1 microm in diameter and at various radial distances to the seed surface. From the dose distribution of lineal energy, the dose mean lineal energy, y(D), was derived. The results showed that the radiation qualities are constant in the distance range from 0.5 to 5 cm. In this distance range, the quality factor, relative to gamma rays from (60)Co, is 2.2 for (125)I and 2.5 for (103)Pd.

Brachytherapy↗

PubMed2006

Three-dimensional dose verification for intensity modulated radiation therapy using optical CT based polymer gel dosimetry.

Dose distributions generated from intensity-modulated-radiation-therapy (IMRT) treatment planning present high dose gradient regions in the boundaries between the target and the surrounding critical organs. Dose accuracy in these areas can be critical, and may affect the treatment. With the increasing use of IMRT in radiotherapy, there is an increased need for a dosimeter that allows for accurate determination of three-dimensional (3D) dose distributions with high spatial resolution. In this study, polymer gel dosimetry and an optical CT scanner have been employed to implement 3D dose verification for IMRT. A plastic cylinder of 17 cm diameter and 12 cm height, filled with BANG3 polymer gels (MGS Research, Inc., Madison, CT) and modified to optimal dose-response characteristics, was used for IMRT dose verification. The cylindrical gel phantom was immersed in a 24 x 24 x 20 cm water tank for an IMRT irradiation. The irradiated gel sample was then scanned with an optical CT scanner (MGS Research Inc., Madison, CT) utilizing a single He-Ne laser beam and a single photodiode detector. Similar to the x-ray CT process, filtered back-projection was used to reconstruct the 3D dose distribution. The dose distributions measured from the gel were compared with those from the IMRT treatment planning system. For comparative dosimetry, a solid water phantom of 24 x 24 x 20 cm, having the same geometry as the water tank for the gel phantom, was used for EDR2 film and ion chamber measurements. Root mean square (rms) deviations for both dose difference and distance-to-agreement (DTA) were used in three-dimensional analysis of the dose distribution comparison between treatment planning calculations and the gel measurement. Comparison of planar dose distributions among gel dosimeter, film, and the treatment planning system showed that the isodose lines were in good agreement on selected planes in axial, coronal, and sagittal orientations. Absolute point-dose verification was performed with ion chamber measurements at four different points, varying from 48% to 110% of the prescribed dose. The measured and calculated doses were found to agree to within 4.2% at all measurement points. For the comparison between the gel measurement and treatment planning calculations, rms deviations were 2%-6% for dose difference and 1-3 mm for DTA, at 60%-110% doses levels. The results from this study show that optical CT based polymer gel dosimetry has the potential to provide a high resolution, accurate, three-dimensional tool for IMRT dose distribution verification.

Algorithms↗

PubMed2004

Performance of a commercial optical CT scanner and polymer gel dosimeters for 3-D dose verification.

Performance analysis of a commercial three-dimensional (3-D) dose mapping system based on optical CT scanning of polymer gels is presented. The system consists of BANG 3 polymer gels (MGS Research, Inc., Madison, CT), OCTOPUS laser CT scanner (MGS Research, Inc., Madison, CT), and an in-house developed software for optical CT image reconstruction and 3-D dose distribution comparison between the gel, film measurements and the radiation therapy treatment plans. Various sources of image noise (digitization, electronic, optical, and mechanical) generated by the scanner as well as optical uniformity of the polymer gel are analyzed. The performance of the scanner is further evaluated in terms of the reproducibility of the data acquisition process, the uncertainties at different levels of reconstructed optical density per unit length and the effects of scanning parameters. It is demonstrated that for BANG 3 gel phantoms held in cylindrical plastic containers, the relative dose distribution can be reproduced by the scanner with an overall uncertainty of about 3% within approximately 75% of the radius of the container. In regions located closer to the container wall, however, the scanner generates erroneous optical density values that arise from the reflection and refraction of the laser rays at the interface between the gel and the container. The analysis of the accuracy of the polymer gel dosimeter is exemplified by the comparison of the gel/OCT-derived dose distributions with those from film measurements and a commercial treatment planning system (Cadplan, Varian Corporation, Palo Alto, CA) for a 6 cm x 6 cm single field of 6 MV x rays and a 3-D conformal radiotherapy (3DCRT) plan. The gel measurements agree with the treatment plans and the film measurements within the "3%-or-2 mm" criterion throughout the usable, artifact-free central region of the gel volume. Discrepancies among the three data sets are analyzed.

Equipment Design↗

PubMed2003

Radiation-induced second cancers: the impact of 3D-CRT and IMRT.

Information concerning radiation-induced malignancies comes from the A-bomb survivors and from medically exposed individuals, including second cancers in radiation therapy patients. The A-bomb survivors show an excess incidence of carcinomas in tissues such as the gastrointestinal tract, breast, thyroid, and bladder, which is linear with dose up to about 2.5 Sv. There is great uncertainty concerning the dose-response relationship for radiation-induced carcinogenesis at higher doses. Some animal and human data suggest a decrease at higher doses, usually attributed to cell killing; other data suggest a plateau in dose. Radiotherapy patients also show an excess incidence of carcinomas, often in sites remote from the treatment fields; in addition there is an excess incidence of sarcomas in the heavily irradiated in-field tissues. The transition from conventional radiotherapy to three-dimensional conformal radiation therapy (3D-CRT) involves a reduction in the volume of normal tissues receiving a high dose, with an increase in dose to the target volume that includes the tumor and a limited amount of normal tissue. One might expect a decrease in the number of sarcomas induced and also (less certain) a small decrease in the number of carcinomas. All around, a good thing. By contrast, the move from 3D-CRT to intensity-modulated radiation therapy (IMRT) involves more fields, and the dose-volume histograms show that, as a consequence, a larger volume of normal tissue is exposed to lower doses. In addition, the number of monitor units is increased by a factor of 2 to 3, increasing the total body exposure, due to leakage radiation. Both factors will tend to increase the risk of second cancers. Altogether, IMRT is likely to almost double the incidence of second malignancies compared with conventional radiotherapy from about 1% to 1.75% for patients surviving 10 years. The numbers may be larger for longer survival (or for younger patients), but the ratio should remain the same.

Adenocarcinoma↗

PubMed2003

Dosimetry study of Re-188 liquid balloon for intravascular brachytherapy using polymer gel dosimeters and laser-beam optical CT scanner.

Angioplasty balloons inflated with a solution of the beta-emitter Re-188 have been used for intravascular brachytherapy to prevent restenosis. Coronary stents are in extensive clinical use for the treatment of de novo atherosclerotic stenoses. In this study, the effect of an interposed stent on the dose distribution has been measured for Re-188 balloon sources using the proprietary BANG polymer gel dosimeters and He-Ne laser-beam optical CT scanner. In polymer gels, after ionizing radiation is absorbed, free-radical chain-polymerization of soluble acrylic monomers occurs to form an insoluble polymer. The BANG polymer gel dosimeters used in these measurements allow high resolution, precise, and accurate three-dimensional determination of dosimetry from a given source. Re-188 liquid balloons, with or without an interposed metallic stent, were positioned inside thin walled tubes placed in such a polymer dosimeter to deliver a prescribed dose (e.g., 15 Gy at 0.5 mm). After removing the balloon source, each irradiated sample was mounted in the optical scanner for scanning, utilizing a single compressed He-Ne laser beam and a single photodiode. In the absence of a stent, doses at points along the balloon axis, at radial distance 0.5 mm from the balloon surface and at least 2.5 mm from the balloon ends, are within 90% of the maximum dose. This uniformity of axial dose is independent of the balloon diameter and length. Dose rate and dose uniformity for intravascular brachytherapy with Re-188 balloon are altered by the presence of stent. The dose reduction by the stent is rather constant (13%-15%) at different radial distances. However, dose inhomogeneity caused by the stent decreases rapidly with radial distance.

Brachytherapy↗

PubMed2003

Determining optimal gel sensitivity in optical CT scanning of gel dosimeters.

A method for determining the gel sensitivity that is necessary for obtaining optimal image contrast in optical CT scanning of gel dosimeters is presented. The effective dynamic range of the OCTOPUS-ONE research scanner (MGS Research, Inc., Madison, CT) is analyzed. Optical density increments for selected straight-line paths across a gel cylinder to be scanned are calculated based on the optical properties of the polymer gel and the dose distribution from a commercial treatment planning system (Cadplan, Varian Corporation, Palo Alto, CA). Maximum optical density increment across the entire gel is obtained by searching the gel cylinder over a set of transverse planes at different rotational angles. The application of this quantity as a criterion for optimizing the quality of the optical CT scanning is demonstrated through dose verification of two representative treatment plans. When the MU dependence of the dose distribution for a treatment plan is linear, as is the case for static field irradiation, it is possible to scale the treatment plan such that the intensity variation of the signals received by the photodetector spans its entire dynamic range. For treatment plans that are possibly nonlinear, IMRT plans, for example, modification of the sensitivity of the gel material is necessary for the high-dose signals to be collected at a certain signal-to-noise ratio. Results obtained using the optimized CT scanning approach are compared with those from the treatment planning system and the film measurement.

Algorithms↗

PubMed2002

Ultrasonic spectrum-analysis and neural-network classification as a basis for ultrasonic imaging to target brachytherapy of prostate cancer.

Conventional B-mode ultrasound is the standard means of imaging the prostate for guiding prostate biopsies and planning brachytherapy of prostate cancer. Yet B-mode images do not allow adequate visualization of cancerous lesions of the prostate. Ultrasonic tissue-typing imaging based on spectrum analysis of radiofrequency echo signals has shown promise for overcoming the limitations of B-mode imaging for visualizing prostate tumors. Tissue typing based on radiofrequency spectrum analysis uses nonlinear methods, such as neural networks, to classify tissue by using spectral-parameter and clinical-variable values. Two- and three-dimensional images based on these methods show potential for improving the guidance of prostate biopsies and the targeting of radiotherapy of prostate cancer. Two-dimensional images have been imported into instrumentation for real-time biopsy guidance and into commercial dose-planning software for brachytherapy planning. Three-dimensional renderings seem to be capable of depicting locations and volumes of cancer foci.

Brachytherapy↗

PubMedDate not supplied

Improved biochemical control and clinical disease-free survival with intraoperative versus preoperative preplanning for transperineal interstitial permanent prostate brachytherapy.

PURPOSE: We hypothesized that intraoperative preplanning for transperineal interstitial permanent prostate brachytherapy may yield better prostate cancer control than preoperative preplanning. We tested this hypothesis by comparing treatment outcomes of patients who underwent implantation using these two preplanning methods. PATIENTS AND METHODS: We analyzed the data of 135 consecutive patients with localized prostate cancer treated from 1996 to 2001 with transperineal interstitial permanent prostate brachytherapy+/-preimplantation hormonal therapy: 42 received preoperative preplanning (group 1), and 93 underwent intraoperative preplanning (group 2). Biochemical status was assessed using two failure definitions: American Society for Therapeutic Radiology and Oncology (ASTRO) (three consecutive rises in prostate-specific antigen level) and Houston (prostate-specific antigen level>or=current nadir+2 ng/mL). Clinical disease-free survival and postimplantation dosimetry were also examined. RESULTS: All disease control outcomes were superior for group 2. The 4-year ASTRO biochemical no evidence of disease rate was 80% for group 1 versus 94% for group 2. The 4-year Houston biochemical no evidence of disease rate was 82% for group 1 versus 96% for group 2. The 4-year clinical disease-free survival rate was 87% for group 1 versus 99% for group 2. Preplanning method (preoperative versus intraoperative) remained predictive of disease control outcomes in multivariate analyses with the covariates of pretreatment prostate-specific antigen level, Gleason score, clinical stage, and case sequence number (proxy for brachytherapist experience and "stage migration"). Dosimetric prostate coverage was superior for group 2. The mean percentage of the prescription dose delivered to 90% of the prostate volume (%D90) was 75% for group 1 versus 90% for group 2. A %D90>or=70% predicted for improved disease control; fewer group 1 than 2 patients met this dosimetric criterion (55% versus 87%). DISCUSSION: Intraoperative preplanning yielded superior disease control outcomes in this analysis, likely due at least in part to improved dosimetric prostate coverage with this method. Although not mandatory for obtaining high prostate brachytherapy efficacy, intraoperative preplanning nevertheless may offer an excellent means of improving dosimetric prostate coverage and therefore disease control outcomes.

Adenocarcinoma↗