抄録
Ultrasonic hyperthermia has been employed as a modality for cancer therapy because of the feasibility of penetration and focusing.The absorbed-dose of ultrasound depends on frequency, intensity and sonication time and estimating dose-distribution is crucial for the clinical application of ultrasound. This study was performed to improve a chemical dosimeter using the Weissler reaction (determination of iodine liberated from potassium iodide due to ultrasonic cavitation). A KI-starch solution containing chloral hydrate (CH) or trichloroacetic acid (TCA) saturated with air in a polystyrene dish was irradiated with 1.0 MHz ultrasound.For measurement of liberated iodine, absorbance at 555 nm was measured with a spectrophotometer. A "lattice" vessel consisting of 100 small containers was used for the estimation of dose-distribution. The absorbed-dose was calculated as a"Gy-equivalent" from the relation between radiation dose (Gy) and the change in absorbance by X-rays. When KI-starch solutions containing TCA instead of CH were sonicated, the absorbance increased at a higher rate by a factor of approximately 2. However, almost no difference in threshold-intensity was observed. When KI-starch solutions containing CH were sonicated after adjustment of the pH to 2.0, almost equal enhancement of the absorbance increase was recognized. These results indicate that pH during sonication is an important factor in KI-chemical dosimetry. When a "lattice" vessel containing KI-starch solution with TCA was sonicated to determine the dose-distribution using a large transducer for therapeutic use,. the two-dimensional distribution of the absorbed-dose was easily visualized and estimated. These methods appear to be useful for the estimation of ultrasonic absorbed-dose.
