摘要:

Relative dose distributions in the vicinities of two new prototypes of ytterbium‐169 brachytherapy sources have been measured using lithium fluoride thermoluminescent dosimeters (TLD) placed in a solid water phantom. The type 6 seed consists of four Yb2O3spheres contained in a 0.075‐mm thick titanium tube, with overall dimensions of 4.5 mm in length and 0.8 mm in diameter. The type 8 seed contains a cylindrical segment of Yb wire, 2.5 mm long, sealed in a 0.075‐mm thick titanium tube 4 mm in length and 0.5 mm in diameter. The relative dose distributions, measured with TLD, were compared with those predicted by Monte Carlo simulations (MCNP code). Experimental and theoretical dose distributions were generally in agreement within 5% of the local dose value. Source strength was determined from activity measurements using a high purity germanium (HPGe) spectrometer. With source strengths established, thermoluminescence was then used to measure the dose rate constant, Λ0, for the type 8 seed. The measured Λ0of 1.34±0.10 cGy U−1for the type 8 seed agrees, within statistical uncertainty, with the value of 1.25±0.05 cGy U−1predicted through Monte Carlo simulation. Comparisons are made with experimental data reported by other investigators.

ISSN:0269-3127    

DOI:10.1118/1.597597

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Although conceptually straightforward, dosimetry of permanent125I seed prostate implants is not necessarily easy to implement in clinical practice, especially for institutions that are unwilling or unable to modify their commercial RTP systems. Spreadsheet techniques that aid in both preimplant treatment planning and post‐implant dosimetric evaluation have been developed. The first spreadsheet converts the seed distribution expressed in terms of template grid coordinates to the format suitable for input into the RTP system, and determines the positions and loading patterns of individual needles. The second spreadsheet macroprogram is designed, as a modification of the Royetal. [Int. J. Radiat. Oncol. Biol. Phys.26, 163–169 (1993)] technique, to interactively determine physical seed locations from the post‐implant CT images. Although less automated than described elsewhere, this approach was found acceptable for clinical practice at our institution.

ISSN:0269-3127    

DOI:10.1118/1.597526

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Magnetic induction heating of thermoseed implants can be used to produce highly localized hyperthermia in deep‐seated tumors. Automatic temperature control throughout the tumor can be achieved by the self‐regulating character of ferromagnetic seeds, which corrects for local variations in heat loss due to blood perfusion. An increased sharpness of the ferromagnetic transition at the Curie temperature,Tc, improves the performance of self‐regulating control. This was realized for palladium–nickel alloys by a “cold working” procedure preceded and followed by annealing. Palladium–nickel seeds with a predeterminedTcwere produced, showing a sharp decrease atTcof the magnetic susceptibility and the heat production.

ISSN:0269-3127    

DOI:10.1118/1.597527

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Interstitial laser heating of tissues is influenced by blood flow in the treatment region. Temperature gradients around large blood vessels may result in local underheating of tissues. A three‐dimensional, time‐dependent finite difference model of interstitial laser heating around large vessels is presented. A thermal conduction model was developed using a transport theory approximation for the energy distribution from an optical line source. Calculated transient temperature profiles and temperature reductions around 0.144 and 0.400 cm diam vessels show qualitative agreement with those measured in a series of tissue phantom studies. Experiments and calculations for a large vessel located ∼1.0 cm from the optical source indicate that temperature reductions are less than 1 °C at distances greater than ∼1.0 cm from the vessel surface. The model also indicates that significant reductions in the extent of a thermal coagulation boundary can occur if a large vessel is situated inside the normal coagulation zone.

ISSN:0269-3127    

DOI:10.1118/1.597598

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

ISSN:0269-3127    

DOI:10.1002/j.2473-4209.1995.tb00965.x

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY