Kazuro Iwata

In vivo measurement of spatial dose distribution with thermoluminescent sheet around high dose-rate intracavitary source: application to rectal cancer.

For intracavitary high dose-rate radiation therapy, a thermoluminescent [TL] sheet for in vivo measurement of spatial dose distribution around source has been recently developed. The TL sheet was found to have a linear response with a very wide dynamic range from at least 0.002 cGy to 5000 cGy for 60Co gamma-rays. This TL sheet (40 cm x 50 cm x 200 microns), which is composed of Teflon mixed with BaSO4:Eu doped powder, is very flexible and can be cut to the desired size. In addition, this sheet is easy to handle because of its insensitivity to room light. The spatial dose distribution is displayed in a color mode by using a newly developed TL sheet readout system. For a clinical application, the TL sheet was wrapped on an applicator for intracavitary radiation therapy of a rectal cancer and was inserted into the rectum. The location of the TL sheet could be confirmed with diagnostic X ray film. After irradiation with high dose-rate 60Co source, the in vivo relative dose distribution on the surface of the rectum was determined. This TL sheet provided a convenient means of measuring the relative dose distributions around 60Co sources of various patterns in intracavitary radiation therapy.

Near-field dosimetry of 125I sources for interstitial brachytherapy implants measured using thermoluminescent sheets.

The dosimetric characteristics were measured for two types of 125I low-energy photon-emitting sources by using a wide and highly sensitive thermoluminescent (TL) sheet film, which was developed for two-dimensional dose distribution measurements. The TL film is made of Teflon homogeneously mixed with small powders of thermoluminescence (BaSO4:Eu doped). Various dosimetric parameters (i.e., radial dose function, 2D and 1D anisotropy functions) of model 6711 and 6702 125I sources were obtained at various distances from the source surfaces to 15 mm. These parameters obtained with TL sheet were compared with the data recommended in the updated AAPM TG-43 report. The radial dose functions measured with TL sheet are in agreement with those established data of model 6711 125I seed and model 6702 125I seed at most of the distances within 5% and 7%, respectively. All the measured anisotropy functions showed symmetry about the longitudinal source axis. The anisotropy of dose distributions was clearly present in the immediate vicinity of the source edges. The measured 2D anisotropy function values at 1 cm are in reasonably good agreement with the recommended values. The differences at two points in the 1D anisotropy functions measured with TL sheet and the established data at 1 cm from source center were 0.7% and 1.9% for model 6711 and 6702 125I sources, respectively; the differences at 0.5 cm were 1.5% and 1.7% for model 6711 and 6702 125I sources, respectively. The relative dosimetric characteristics in the vicinity of actual interstitial brachytherapy sources containing 125I have been experimentally determined by using the TL sheet as a 2D dosimeter.

Depression of Hyperthermic Potentiation in Cell Killing of Ultraviolet Light-irradiated Dictyostelium Discoideum by Pre-heat Treatment

Heat treatment of 30 degrees C for 15 min immediately after ultraviolet (UV) irradiation enhanced cell killing of Dictyostelium discoideum. However, when the cells were heated at 30 degrees C for 15 min and then cultured for more than 10 min at 23 degrees C prior to UV exposure, the hyperthermic potentiation in cell killing was depressed. When these preheated cells were cultured in the presence of cycloheximide, the depression of the hyperthermic potentiation disappeared. These results suggest that the depression in hyperthermic potentiation may be the result of the induction of some heat-shock-type proteins.

Hyperthermic Effects on DNA Repair of UV-irradiated Dictyostelium Discoideum

DNA repair of a lower eukaryote, Dictyostelium discoideum, has been investigated through the analysis of heat effects on cell mortality and DNA repair of UV-irradiated amoeboid cells. In a wild-type strain (NC4), an increase in temperature immediately after UV irradiation resulted in an increase in cell mortality, though similar heat treatment before UV irradiation had no such effect. Similar results were obtained in another wild-type strain, HPS83. In NC4, heat treatment after UV irradiation did not inhibit the nicking of DNA strands during excision repair processes, but did inhibit the rejoining of the DNA strand breaks. Removal of thymine-containing pyrimidine dimers from DNA molecules was also depressed by heat treatment after UV irradiation. In contrast, heat treatment before UV irradiation had no effect on any stage of the nicking process, the excision of the dimers or the rejoining. On the other hand, a radiation-sensitive mutant (TW8) defective in an incision step of the excision repair process did not show an increase in cell mortality in response to heat treatment administered either before or after UV irradiation. Though the optimum temperature for cell growth of the amoebae was 23 degrees C, the critical temperature for effective enhancement of cell killing was ca. 30 degrees C. Hence we assume that the excision repair of UV-damaged DNA is selectively sensitive to heat treatment.

Two-dimensional dosimetry in the near field of the model 200 103Pd source for interstitial brachytherapy implants using a thermoluminescent sheet

A large area and highly sensitive thermoluminescent (TL) sheet film was used for two-dimensional dose distribution measurements at millimetre distances from a 103Pd interstitial brachytherapy source. The TL film is made of Teflon homogeneously mixed with small particles of thermoluminescent material (BaSO4: Eu doped). This TL sheet (5 cm x 5 cm) was used to determine the relative dosimetric characteristics (i.e., radial dose function, 2D and 1D anisotropy functions, as defined by the updated AAPM Task Group No 43 report) of the model 200 103Pd source that emits low energy photons (21 keV). The two-dimensional dosimetry data were obtained for distances from the source surface to 15 mm. The radial dose function measured with the TL sheet is in reasonable agreement within 11% with the values recommended in the updated AAPM TG-43 report. All the measured 2D dose distributions showed limited symmetry about the source axes. The differences between the 1D anisotropy function values measured with the TL sheet and the data recommended in the updated AAPM TG-43 report were 10% at 5 mm and 7.5% at 10 mm, respectively, for the model 200 103Pd seed. Our experiments have demonstrated that it is feasible to use the TL sheet as a dosimeter in the determination of the dosimetric characteristics in the immediate vicinity of interstitial brachytherapy sources emitting low energy photons.

In vivo measurement of spatial dose distribution around radioactive sources using a thermoluminescent BaSO4:Eu sheet

Abstract A thermoluminescent (TL) sheet for in vivo measurement of the spatial dose distribution around a radioactive source has been developed. The TL sheet is found to have a linear response with a very wide dynamic range from at least 0.002 to 5000 cGy absorbed dose. This TL sheet (40 cm × 50 cm × 200 μm), which is composed of Teflon mixed with BaSO 4 :Eu doped powder, is very flexible and can be cut to the desired size. In addition, it is easy to handle because of its insensitivity to room light. The spatial dose distribution is printed out with a newly developed TL sheet digital-readout system. Another high-resolution dosimetry system made by exposing X-ray film with TL photons emitted from the irradiated TL sheet at constant room temperature has been reported. For a clinical application, the TL sheet is wrapped on an applicator for intracavitary radiation therapy of rectal cancer and is inserted into the rectum. The location of the TL sheet can be confirmed with diagnostic X-ray film. After irradiation with a high dose-rate 60 Co source, the in vivo dose distribution on the surface of the rectal cancer is determined.

Usefulness of thermoluminescent sheet for measurement of dose distribution near radioactive sources

A thermoluminescent sheet (TL sheet) for in vivo measurement of spatial dose distribution near small radioactive sources (mm) and its digital readout system have been developed. The TL sheet, the size of which is 40 cm X 50 cm X 0.2 mm, is a teflon homogeneously mixed with BaSO4:Eu doped powder of about 5 micrometers . This thin TL sheet is very flexible and can be cut to the desired size and form. The sheet was insensitive to room-light, so it is easy to handle. The sheet was found to have a linear response with a very wide dynamic range from at least 0.002 cGy to 5000 cGy absorbed dose. The spatial resolution of the TL sheet was 62 micrometers corresponding to 8.1 line pairs/mm. These are suitable to measure the in vivo spatial dose distribution near sources because large dose gradients exist over a small area. For intracavitary radiation therapy of a rectal cancer, the in vivo dose distribution on the surface of the cancer was determined with the TL sheet. This TL sheet may provide a convenient means of measuring the dose distribution of various patterns in radiation therapies.