Hung-Sheng Tsao - Academia.edu (original) (raw)

Papers by Hung-Sheng Tsao

Cardiovascular Radiation Medicine, 2001

Intravascular brachytherapy is the leading modality being evaluated for treatment of instent rest... more Intravascular brachytherapy is the leading modality being evaluated for treatment of instent restenosis. Stent struts may have an effect on the dose distributions of various radiation sources. We evaluated dosimetry in a stented coronary artery model using a variety of beta and gamma sources and stent materials. Methods: We determined the dose distributions with and without stent in the in-stent restenosis model. Three beta-particle emitting radionuclides, 90 Y (2.3 MeV), 144 Pr (3.0 MeV), and 106 Rh (3.5 MeV), and two gamma-ray emitters, 192 Ir (380 keV) and 125 I (30 keV), were studied. Stent materials included stainless steel, nitinol, and tantalum. Monte Carlo dose calculations were performed in a stent model of multiple stent struts placed at 1.5 mm from the source. Isodose curves were generated and the ratios of dose rates with and without stent, the stent factors, were evaluated. A stent factor of greater or less than unity represents dose enhancement or reduction in the presence of a stent. Results: For the three beta radionuclides, dose reduction was found on the adventitial side of the stent strut and dose enhancement was noted on the luminal side. On the luminal side, the maximum dose enhancement ranges from 7% to 29%, and the dose reduction on the adventitial side ranges from 13% to 43%. Both the reduction and enhancement effects were most pronounced for the high atomic number material, tantalum. For a given stent material, the dose reduction and enhancement are similar for the three beta radionuclides. For the gamma sources, the stent had no effect for the high-energy 192 Ir, but for the low-energy 125 I, drastic dose reduction on the adventitial side was observed (up to 86% for tantalum stent), and about 10% dose enhancement on the luminal side was also noted. The dose reduction with 125 I was more pronounced than that seen with the beta sources. Conclusions: The presence of stent struts significantly affects dose distributions of 90 Y, 106 Rh, 144 Pr, and 125 I. The maximum dose reduction can be as much as 86%. 192 Ir was unaffected. These factors need to be considered in choosing radionuclides and dose prescriptions in treating in-stent restenosis.

Radiotherapy and Oncology, 2000

Physical Review Letters, 1978

Physical Review D, 1975

Renormalization constants for scalar, pseudoscalar, and tensor currents. Stephen L. Adler, EW Col... more Renormalization constants for scalar, pseudoscalar, and tensor currents. Stephen L. Adler, EW Colglazier, Jr., JB Healy, Inga Karliner, Judy Lieberman, Yee Jack Ng, and Hung -Sheng Tsao Institute for Advanced Study, Princeton, New Jersey 08540. Received 27 January 1975 ...

Physical Review D, 1975

%e apply current-algebra techniques to study the constraints imposed on neutral-currentinduced so... more %e apply current-algebra techniques to study the constraints imposed on neutral-currentinduced soft-pion production, using as input existing bounds on neutrino-proton elastic scattering and existing data on neutral-curreat-induced deep-inelastic scattering. In the case of a purely isoscalar weak neutral current, a simple soft-pion argument relates the cross section for threshold (in pion-nucleon invariant mass) weak pion production directly to the cross section for neutrino-proton elastic scattering. Hence, a bound on the latter cro88 8ection implies a bound on the former. To apply the method away from threshold and to nonisoscalar neutral currents, we extend a model which we had developed earlier for weak pion production in the (3,3) resonance region so as to include the low-energy-theorem constraints. Numerical work using the extended model shows that a threshold peak (now attributed to background) in preliminary Argonne data on i +n &+p+~mould have implied a threshold cross section much larger than can be obtained with any neutral current formed solely from members of the usual V, A. nonets. %e analyze recently reported Brookhaven National Laboratory results for neutral-current-induced soft-pion production under the simplifying assumption of a purely isoscalar V, A neutral current. Vfe find in this case that the magnitude of the Brookhaven observations exceeds the theoretical maximum by more than a factor of 2 unless the assumed isoscalar current either contains a vector part with an anomalously large gyromagnetio ratio (g[=~2M&Et/Et[ or involves the ninth (SU& singlet) axial-vector current. A vector part with a large~g~value leads to characteristic modifications in the pion-nucleon invariant-mass spectrum for M(~N) & 1. 4 GeV, an effect which should be testable in highstatistics experiments. Two other qualitative predictions of isoscalar V, A structures are {i) except for a narrow range of values of g, constructive V, A interference in v + N~+ N +~implies constructive interference in i + p i +P and vice versa, and (ii) if V, A interference is observed in neutral weak processes then (as is well-known) the neutral interaction may make a parity-violating contribution to the pp, ep, and pp interactions. These features may help to distinguish V, A neutral-current couplings from alternative coupling types, which will be discussed in detail in subsequent papers of this series.

Medical Physics, 1986

Monte Carlo calculations of radiation dosimetry using MORSE code are performed for 125I and 60Co ... more Monte Carlo calculations of radiation dosimetry using MORSE code are performed for 125I and 60Co point sources in a cylindrical head phantom that simulates the geometry of eye plaque therapy for choroidal melanoma. We obtain the dose variation in the eye at submillimeter intervals over distances as close as 1 mm and up to 2.5 cm from the source. The calculations for 125I are performed for the phantom media of water, protein, and a homogenized protein-water mixture simulating the composition of the eye. Relative dose functions for 125I for these phantom media are fitted to second-degree polynomials. Agreement is found with published results. The relative dose function for 60Co at eye position in the water head phantom is fitted to a third-degree polynomial and compared with that for 60Co at the center of a large water sphere. A boundary effect due to the head phantom-air interface on the dose distribution for 60Co is demonstrated. The dose falloff with distance is faster for the eye geometry compared with the bulk geometry. We also show that the relative dose distributions within the tumor are comparable for 125I and 60Co by comparing their relative dose functions. This result is consistent with the success of clinical trials of large melanoma treatments with 125I plaques.

International Journal of Radiation Oncology*Biology*Physics, 2002

AIP Conference Proceedings, 1981

It is shown that the dynamically broken symmetry M/sub z/costheta = M/sub w/ is a result of the m... more It is shown that the dynamically broken symmetry M/sub z/costheta = M/sub w/ is a result of the maximum parity violating nature of the techni-fermion representation. (AIP)

Physics Letters B, 1974

Abstract The interactions between the quantized Einstein and quantized Yang-Mills fields are one-... more Abstract The interactions between the quantized Einstein and quantized Yang-Mills fields are one-loop nonrenormalizable.

Physical Review D, 1974

We argue that for spin- 1/2 and spin-1 particles bootstraps may be trivial. In many instances suc... more We argue that for spin- 1/2 and spin-1 particles bootstraps may be trivial. In many instances such particles can be embedded in a renormalizable Lagrangian formalism in which they may Reggeize. In such instances a correctly carried out calculation will produce bootstraps for any values of mass and coupling constant.

Monte Carlo calculations of radiation dosimetry using m-smcapso-smcapsr-smcapss-smcapse-smcaps co... more Monte Carlo calculations of radiation dosimetry using m-smcapso-smcapsr-smcapss-smcapse-smcaps code are performed for /sup 125/I and /sup 60/Co point sources in a cylindrical head phantom that simulates the geometry of eye plaque therapy for choroidal melanoma. We obtain the dose variation in the eye at submillimeter intervals over distances as close as 1 mm and up to 2.5 cm from the source. The calculations for /sup 125/I are performed for the phantom media of water, protein, and a homogenized protein--water mixture simulating the composition of the eye. Relative dose functions for /sup 125/I for these phantom media are fitted to second-degree polynomials. Agreement is found with published results. The relative dose function for /sup 60/Co at eye position in the water head phantom is fitted to a third-degree polynomial and compared with that for /sup 60/Co at the center of a large water sphere. A boundary effect due to the head phantom--air interface on the dose distribution for /s...

ABSTRACT Point splitting regularization is discussed in a supersymmetric Yang-Mills field theory.... more ABSTRACT Point splitting regularization is discussed in a supersymmetric Yang-Mills field theory. A supersymmetry and gauge invariant point-split supercurrent operator, along with the point-split lagrangian density, is constructed. A superconformal anomaly is computed. Work supported by the Department of Energy Contract No. EY76-C-02-2232B.004.

Cardiovascular Radiation Medicine, 2001

To explore the feasibility of 169 Yb (g, 93 keV) as a new radionuclide for intravascular brachyth... more To explore the feasibility of 169 Yb (g, 93 keV) as a new radionuclide for intravascular brachytherapy (IVBT) in terms of dose distribution, penetration power, and radiation safety features as compared with 125 I and 192 Ir. Methods: The dose distributions for catheter-based sources, 169 Yb, 125 I, and 192 Ir, in homogeneous water and in the presence of calcium and a steel stent have been determined and compared using the Monte Carlo method (MCNP4B2 code). The dose rates of the sources were evaluated from 0.02 to 100 cm. Results: In the short distance range (0.02 < r < 1.0 cm), the dose distributions in homogeneous water are very similar for the three radionuclides when the dose rates are normalized at 2 mm. Between 1 and 20 cm, the relative dose rates fall off similarly for 169 Yb and 192 Ir, whereas for 125 I, it decreases much more rapidly. At a distance further away (r $ 100 cm), the dose rate of 169 Yb is about 10 times lower than that of 192 Ir, indicating the cathlab radiation shielding requirement for 169 Yb is substantially reduced as compared with 192 Ir. Calcified plaques and stents cause a drastic dose reduction in the arterial wall for 125 I, but have no effect for 192 Ir grays. Only slight dose reductions were detected for 169 Yb beyond a layer of 1.0-mm calcium (2-3%), and behind a steel stent strut (5%). Conclusion: 169 Yb is a promising new radionuclide for IVBT. It has a much better penetrating power through calcified plaques and stents compared with the low-energy source 125 I. It also provides easier radiation protection measures for cardiac cathlab personnel than the high-energy source 192 Ir, while preserving a favorable dose distribution in tissues surrounding an arterial vessel.

Cardiovascular Radiation Medicine, 2001

Intravascular brachytherapy (IVBT) is an emerging modality for the treatment of atherosclerotic l... more Intravascular brachytherapy (IVBT) is an emerging modality for the treatment of atherosclerotic lesions in the artery. As part of the refinement in this rapidly evolving modality of treatment, the current simplistic dosimetry approach based on a fixed-point prescription must be challenged by future rigorous dosimetry method employing image-based three-dimensional (3D) treatment planning. The goals of 3D IVBT treatment planning calculations include (1) achieving high accuracy in a slim cylindrical region of interest, (2) accounting for the edge effect around the source ends, and (3) supporting multiple dwell positions. The formalism recommended by Task Group 60 (TG-60) of the American Association of Physicists in Medicine (AAPM) is applicable for gamma sources, as well as short b sources with lengths less than twice the b particle range. However, for the elongated b sources and/or seed trains with lengths greater than twice the b range, a new formalism is required to handle their distinctly different dose characteristics. Specifically, these characteristics consist of (a) flat isodose curves in the central region, (b) steep dose gradient at the source ends, and (c) exponential dose fall-off in the radial direction. In this paper, we present a novel formalism that evolved from TG-60 in maintaining the dose rate as a product of four key quantities. We propose to employ cylindrical coordinates (R, Z, f), which are more natural and suitable to the slim cylindrical shape of the volume of interest, as opposed to the spherical coordinate system (r, q, f) used in the TG-60 formalism. The four quantities used in this formalism include (1) the distribution factor, H(R, Z), (2) the modulation function, M(R, Z), (3) the transverse dose function, h(R), and (4) the reference dose rate at 2 mm along the perpendicular bisector, D(R 0 = 2 mm, Z 0 = 0). The first three are counterparts of the geometry factor, the anisotropy function and the radial dose function in the TG-60 formalism, respectively. The reference dose rate is identical to that recommended by TG-60. The distribution factor is intended to resemble the dose profile due to the spatial distribution of activity in the elongated b source, and it is a modified Fermi-Dirac function in mathematical form. The utility of this formalism also includes the slow-varying nature of the modulation function, allowing for more accurate treatment planning calculations based on interpolation. The transverse dose function describes the exponential fall-off of the dose in the radial direction, and an exponential or a polynomial can fit it. Simultaneously, the decoupling nature of these dose-related quantities facilitates image-based 3D treatment planning calculations for long b sources used in IVBT. The new formalism also supports the dosimetry involving multiple dwell positions required for lesions longer than the source length. An example of the utilization of this formalism is illustrated for a 90 Y coil source in a carbon dioxide-filled balloon. The pertinent dosimetric parameters were generated and tabulated for future use.

Physical Review D, 1975

ABSTRACT

Cardiovascular Radiation Medicine, 2001

Radiotherapy and Oncology, 2000

Physical Review Letters, 1978

Physical Review D, 1975

Medical Physics, 1986

International Journal of Radiation Oncology*Biology*Physics, 2002

AIP Conference Proceedings, 1981

Physics Letters B, 1974

Physical Review D, 1974

Cardiovascular Radiation Medicine, 2001

Physical Review D, 1975

ABSTRACT