Biomedical subjects

Ravinder Nath

Publications and source records attributed to Ravinder Nath.

42 records · Page 3Linked to original sources

PubMed2002

Experimental determination of dosimetric characterization of a newly designed encapsulated interstitial brachytherapy source of 103Pd-model Pd-1.

A newly designed encapsulated 103Pd source has been introduced (BrachySeed-Pd-103, also named Model Pd-1, manufactured by DRAXIMAGE Inc. and distributed by Cytogen Corp.) for interstitial brachytherapy to provide more isotropic dose distributions. In this work, the dosimetric characteristics of the 103Pd source were measured with micro LiF TLD chips and dosimetry parameters were characterized based upon the American Association of Physicists in Medicine (AAPM) Task Group No. 43 formalism. The dose rate constant of the sources was determined to be 0.66 +/-0.05 cGy h(-1) U(-1). The radial dose function was measured and was found to be similar to that of the Theragenics Model 200 103Pd source. The anisotropy constant for the Model Pd-1 source was determined to be 1.03.

Anisotropy↗

PubMedDate not supplied

Effects of off-centering on dose uniformity along and around blood vessels undergoing catheter-based intravascular brachytherapy.

PURPOSE: In intravascular brachytherapy, either photon or beta emitters are often used in a linear arrangement so that blood vessels of lengths in the range of several centimeters can be treated. With a line source, the dose uniformity and the range of doses that various components of the blood vessels receive depend not only on the type of radionuclides used in the treatment but also on the geometric position of radioactive source relative to the blood vessel walls. The aim of this study is to investigate the dose uniformity around the blood vessel and the effects on the uniformity due to the changes of the off-centering of different photon and beta emitters within the lumen. MATERIALS AND METHODS: Dose distributions were calculated on a cylindrical blood vessel of various radii. The radioactive sources of (192)Ir, (125)I, (103)Pd, (188)Re, (32)P, and (90)Y/Sr were studied. All the sources were assumed to be in the form of a line and had a length of 2 cm. The dose rate at a point in space produced by a radioactive source was computed by integrating the point dose rate kernel of the corresponding radionuclide over the 2-cm-long radioactive line. The point dose rate kernel was computed with Monte Carlo simulation of radiation transport. Dosimetric calculations were performed for both concentric and nonconcentric radioactive line source locations. Off-centering effects on the dosimetry were characterized with two newly defined quantities LDU and ADU: LDU describes the longitudinal dose uniformity along blood vessels and ADU describes the azimuthal dose uniformity, i.e., the dose deviation from the expected delivery dose around blood vessels. RESULTS: The longitudinal dose uniformity did not change significantly with the off-center distance. The azimuthal dose uniformity around the blood vessel deteriorated as the off-center distance increased. The ADU was worse for nonconcentric beta emitters than the photon emitters. For example, if the off-center distance was 1 mm and the radial distance was 1.5 mm, the range of dose around the blood vessel on the central transverse plane (normalized to the corresponding dose under the concentric condition) was from 0.55 to 3.3, 0.56 to 3.3, 0.53 to 3.4, 0.43 to 6.0, 0.38 to 4.3, and 0.31 to 4.7 for (192)Ir, (125)I, (103)Pd, (90)Y/Sr, (188)Re, and (32)P sources, respectively. However, it appeared that there existed a lower limit of underdosing (about 40% of desired delivery dose) caused by the off-centering for the photon emitters. It was also found that both ADU and LDU became almost independent of source length when the length was longer than or equal to 20 mm. CONCLUSIONS: A generalized formalism for expressing the dose uniformity along and around blood vessels generated with a linear source was developed and used to study the longitudinal and azimuthal dose uniformity for different types of radionuclides. Although concentric beta emitters provide uniform dose coverage along blood vessels, nonconcentric beta emitters produced larger dose deviations and worse dose uniformity around the blood vessels than photon emitters. The off-centering introduced significantly higher dose on proximal vessel walls for both beta and photon emitters; however, the underdosing at distal points due to off-centering was somewhat limited for the high-energy photon emitters. The magnitude of off-centering effects for the low-energy photon emitters ((103)Pd) was less than that for beta emitters but more than that for higher energy photon emitters ((125)I and (192)Ir).

Beta Particles↗

PubMedDate not supplied

Effects of vessel curvature on dose distributions in catheter-based intravascular brachytherapy for various radionuclides.

PURPOSE: When radioactive sources are used to treat restenosis, the blood vessels are usually curved. In catheter-based intravascular brachytherapy systems, this curvature introduces dose deviations from the idealized situation used for treatment planning, in which both blood vessels and sources are assumed to be straight. Because of the different depth characteristics of different radionuclides, it is foreseeable that the curvature effects on dosimetry might vary with the different types of radionuclides. In this study, curvature effects on dose distributions along and around a blood vessel were investigated for different gamma and beta emitters. MATERIALS/METHODS: A blood vessel was modeled as a cylinder that could be curved as a circular arc of different degrees. Dose calculations were performed on the cylindrical surfaces of the model vessel for the radioactive sources of (192)Ir, (125)I, (103)Pd, (188)Re, (32)P, and (90)Y/Sr. The radius of the vessel was assumed to be 1.0, 1.5, 2.0, and 2.5 mm, respectively. A catheter-based radiation delivery system was simulated to consist of a line source with a length of 2 cm. The dose rate at a point in space produced by the radioactive source was computed by integrating the point dose rate kernel of the corresponding radionuclide over the entire radioactive line, which was assumed to curve with the blood vessel along its central axis. Dosimetric calculations were performed for different curvature angles. The curvature effects on the dosimetry were characterized with two quantities, LDU and ADU, where LDU described the longitudinal dose uniformity (LDU) along blood vessels and ADU described the azimuthal dose uniformity (ADU) from the expected delivery dose around blood vessels. RESULTS: Vessel and source curvatures barely changed the LDU for the gamma emitters (within 2%). The curvature effects on the LDU were relatively larger for the beta emitters (less than 5%). The dose deviations caused by curvature around a blood vessel were more significant. Depending on the radius of the vessel and degree of curvature, the deviation could be as much as 25% for the gamma emitters and 30% for the beta emitters. The curvature effects became larger with the increase of vessel radius and, obviously, with the increase of curvature. There seemed to be no significant differences in the curvature effects among different types of gamma emitters and among different types of beta emitters. CONCLUSIONS: Curvature-induced effects on dose distribution are similar for both the gamma and the beta emitters. The LDU along the vessels does not change significantly with curvature. The dose changes around the vessels are more pronounced and can be as high as 30%.

Blood Vessels↗

PubMedDate not supplied

Measured TG-60 dosimetric parameters of the Novoste Beta-Cath 90Sr/Y source trains for intravascular brachytherapy.

Measurements were performed on the 30, 40 and 60-mm 90Sr/Y beta-emitter source trains used in the Novoste Beta-Cath system to determine the dosimetric characteristics of the sources at millimeter distances and provide the necessary TG-60 dosimetry parameters for mapping the dose distributions. These measurements were carried out in a Solid Water phantom where MD-55-2 Gafchromic films were placed in direct contact with a 5 French (F) catheter used for the 30 and 60-mm source trains and a 3.5 F catheter used for a thinner 40-mm source train. The dosimetric analysis was performed according to the AAPM TG-60 formalism. For the 30-mm source train, data were collected with the source axis at distances of 0.41 and 1.19 mm from the film surface, respectively, in order to investigate possible dosimetric effects due to the intrinsic off centering of the source train lumen within the 5 F catheter. Absolute dose rates at 2 mm were determined by calibrating the radiochromic film in a high energy electron beam from a radiotherapy accelerator. The dose rates at a radial distance of 2 mm were found to be within 10% of the values provided by Novoste. Radial dose functions from this study were in good agreement (< or = 10%) with a 30-mm, 90Sr/Y source train dose data generated from C. G. Soares et al. 90Sr/Y single seed data. However, larger differences were observed at distances shorter than 1 mm when compared to radial dose functions from the Novoste Monte Carlo data.

Beta Particles↗

PubMedDate not supplied

Brachytherapy for in-stent restenosis in general interventional practice: a single institution's experience using four radiation devices.

BACKGROUND: The effectiveness of brachytherapy for the treatment of in-stent restenosis (ISR) has been established in a number of large randomized controlled trials. Efficacy of this therapy in general population is less well established. METHODS AND MATERIALS: We report our experience of 207 patients, 236 coronary lesions, treated with brachytherapy between November 2000 and November 2002. All commercially available brachytherapy devices, as well as one investigational device, were utilized. This cohort was followed over 9 months and clinical outcomes were obtained with subsequent analysis of patient and lesion-specific characteristics. RESULTS: Average treatment age was 62.5 years; 73% were male and the most frequent presentation was unstable angina (74%). All patients had successful delivery of radiation, with no in-hospital deaths. Novoste BetaCath device was used for 163 (65%) lesions, Cordis Checkmate for 56 (24%) lesions, Interventional Therapies device in 13 (8%) lesions, and Guidant Galileo in 4 lesions (3%). At a mean follow-up of 9.1 months, 78.7% were free of major adverse cardiac event (MACE). Twenty-one patients required repeat PTCA (10.1%), 19 had CABG (9.2%), 3 had MI (1.4%), and there was 1 death (0.5%). Unadjusted MACE rates for each device were 21% for Novoste, 28% for Checkmate, 8% for Interventional Therapies, and 50% for Galileo. Lesion length, minimal lumen diameter, renal failure, diabetes, and smoking did not predict treatment failure; only age was inversely correlated with MACE (P=.002). CONCLUSION: When applied across a spectrum of patients, lesions, and devices, brachytherapy retains its effectiveness with outcomes similar to those reported in randomized clinical trials.

Adult↗

PubMedDate not supplied

Iodine 125 versus palladium 103 implants for prostate cancer: clinical outcomes and complications.

PURPOSE: The purpose of this study was to evaluate the clinical outcomes and compare complication rates for patients with prostate cancer treated with iodine 125 ((125)I) and palladium 103 ((103)Pd) prostate brachytherapy at a single institution. PATIENTS AND METHODS: Between 1992 and 2002, 272 patients with prostate cancer were treated with ultrasound-guided transperineal implantation incorporating (125)I (107 patients) or (103)Pd (165 patients). Three months of hormonal therapy was incorporated into the treatment program in 33% of the patients in both groups. Nineteen percent of those treated with (125)I were treated with a combination of implantation plus external-beam radiation therapy. Only 6% of the group receiving (103)Pd implants were treated with such a combination. For those treated with (125)I implantation alone, the minimum tumor dose was 145 Gy. The minimum tumor dose for those treated with (103)Pd alone was 125 Gy. Those treated with a combination of external-beam radiation therapy and (125)I received 45 Gy via 1.8-Gy fractions followed by implantation with a minimum tumor dose of 110 Gy. For those treated with external-beam radiation therapy and (103)Pd, the doses were 45 Gy via 1.8-Gy fractions followed by implantation with minimum tumor dose of 98 Gy. Outcomes were evaluated based on radionuclide used, T stage, Gleason score, prostate-specific antigen, and prognostic group. Complications were also evaluated for each radionuclide. The mean follow-up for the (125)I group was 55 months, and the range was 12-108 months. The mean follow-up for the (103)Pd group was 44 months, and the range was 12-72 months. RESULTS: The 5-year biochemical disease-free survival rates for those in the favorable group (clinical stage T1c or T2, prostate-specific antigen level <10, Gleason score <7) were 92% for the (125)I group and 92% for the patients treated with (103)Pd. The 5-year disease-free survival rates for those in the intermediate and poor prognostic groups, which were combined, was 72% and 74%, respectively, for (125)I and (103)Pd. There was no statistically significant difference for either modality for any treatment group tested. In those treated with implantation alone, patients treated with (125)I had higher complication rates than those treated with (103)Pd (15% vs 4%). (125)I-treated patients had a grade 2 complication rate of 8% and a grade 3-4 complication rate of 7%, compared with 3% and 1%, respectively, for the (103)Pd-treated patients. CONCLUSION: Despite the different management recommendations that evolved during the study period, the clinical outcome for patients treated with either radionuclide were similar with respect to biochemical disease-free survival. Although specific dosimetric comparisons are not valid given differences in imaging over the study course, the complication rate appears to be somewhat higher for (125)I, which is consistent with a radiobiologic model.

Academic Medical Centers↗