RESUMEN
Dosimetric characteristics of shielded vaginal applicators containing encapsulated 241Am sources are investigated in this work. Encapsulated 241Am sources emit primarily 60-keV photons which are more effectively shielded by thin layers of high atomic number materials than the 662-keV photons from 137Cs sources. With 241Am, it is possible to achieve almost unidirectional irradiation of localized vaginal tumors. The drastic decrease in irradiation volume on the contralateral side (uninvolved with tumor) is observed to decrease dose by up to 20%, even in the forward direction (unshielded side toward the tumor) of the applicator. A possible explanation for the observed effects of shields in both the forward and backward directions is the reduction of scattered photon fluence due to absorption of photons in the lead shield via photoelectric effect. Current theoretical models do not include this perturbation effect caused by shields on brachytherapy applicators.
Asunto(s)
Americio/uso terapéutico , Braquiterapia/instrumentación , Neoplasias Vaginales/radioterapia , Braquiterapia/métodos , Femenino , Humanos , Protección Radiológica/instrumentación , Dosificación Radioterapéutica , Dosimetría TermoluminiscenteRESUMEN
There is a new radiochromic film, a highly uniform, thin (100-microns) detector whose sensitive layer (6 microns thick) changes from colorless to blue by dye polymerization without processing, upon exposure to ionizing radiation. Because the dose gradients around brachytherapy sources are steep, the high spatial resolution offered by film dosimetry is an advantage over other detectors such as thermoluminescent dosimeters (TLDs). This compares the photon energy dependence of the sensitivities of GafChromic film, silver halide verification film (Kodak X-Omat V Film), and lithium fluoride TLDs (Harshaw), over the photon energy range 28 keV to 1.7 MeV, which is of interest in brachytherapy. Sensitivity of the radiochromic film is observed to decrease by about 30% as effective photon energy decreases from 1710 keV (4-MV x rays) to 28 keV (60-kV x rays, 2-mm A1 filter). In contrast, the sensitivity of verification film increases by 980% and that of LiF TLDs increases by 41%. The variation of the sensitivity of radiochromic film with photon energy is considerably less than that for silver halide film and similar to that for LiF TLDs, but in the opposite direction. Radiochromic film, like LIF TLDs, does not exhibit the drastic sensitivity changes below 127 keV that silver halide film exhibits. Dose distribution in the immediate vicinity of a high activity (370 GBq) brachytherapy 192Ir source has been mapped using radiochromic film and is presented to illustrate the applicability of this new technology to brachytherapy dosimetry.
Asunto(s)
Braquiterapia/métodos , Dosificación Radioterapéutica , Radioisótopos de Cromo , Humanos , Modelos Teóricos , Radiación , Plata , Rayos XRESUMEN
Endoscopic restoration of a totally obstructed ureteroileal anastomosis was accomplished in 3 patients. The combined use of rigid endoscopy of the ileal conduit and flexible nephroureteroscopy provided full visualization of the blind-ending segments and allowed location of the shortest segment between the lumina. A guide wire was passed through intervening tissue with fluoroscopic monitoring to re-establish internal drainage. This technique offers an alternative to laparotomy and reimplantation in selected cases of ureteroileal stricture.