Biomedical subjects
A Filimonov
Publications and source records attributed to A Filimonov.
Radiation-induced effects in multiprogrammable pacemakers and implantable defibrillators.
Twenty-three multiprogrammable pacemakers and four implantable cardioverter defibrillators (ICDs) containing either complementary metal-oxide semiconductor (CMOS) or CMOS/Bipolar integrated circuit (IC) technology were exposed to 6-MV photon and 18-MeV electron radiation at various dose levels. Of the 17 pacemakers exposed to photon radiation eight failed before 50 Gy, whereas four of the six pacemakers exposed to electron radiation failed before 70 Gy. Photon scatter doses were well tolerated. For the ICDs detection and charging time increased with accumulated radiation dose, the charging time increased catastrophically at less than 50 total pulses delivered when compared with the charging time of six implanted ICDs. Sensitivity and output energy delivered by the ICD pulse were constant during the test. It was found that devices using the shorter channel length IC technology (i.e., 3 microns CMOS) were per se harder to ionizing radiation than the devices using larger channel length IC technologies (i.e., either 8 microns CMOS or combined 5 microM CMOS/20 V Bipolar). In fact, none of the devices based on 3 microns CMOS IC technology failed before 76 Gy, which is above the highest dose level (70 Gy) normally used in radiation oncology treatments.
Response of a brachytherapy model using 125I in a murine tumor system.
The effects of low-dose-rate irradiation (brachytherapy) were investigated in vivo using a murine mammary adenocarcinoma (MTG-B) growing in the flank of C3H mice. For local tumor irradiations, a noninvasive cap was devised to cover the tumor and house three 125I seeds (average apparent activity 5.2 mCi each) located at 120 degree intervals around the circumference of the hemispherical cap (13 mm i.d.). Mice were secured during treatment in a tube allowing limited mobility while restricting access to the seeds. Tumors were exposed to a series of dose rates ranging from 14-40 cGy/h, and the total dose over the treatment interval (48 or 72 h) ranged from 830 to 2378 cGy. A total of nine experiments were conducted using the caps over a 10-week interval. In each experiment three groups (irradiated tumors, sham controls, and untreated controls) were analyzed, each containing 8-15 mice (N = 34, untreated control; N = 46, sham control; N = 91, brachytherapy irradiation). The brachytherapy results are compared to the effects of external beam irradiation in the same tumor system. A linear relationship was observed between the total radiation dose and doubling volume growth delay (GDDV) or treatment volume growth delay (GDTV) for the brachytherapy and external beam irradiation. The slopes of the dose-response curves are steeper for the acute dose (517 cGy/min) external beam irradiation (0.0072 day/cGy, GDDV; 0.00695 day/cGy, GDTV) than for the brachytherapy (0.0050 day/cGy, GDDV; 0.0057 day/cGy, GDTV) using both GDTV and GDDV end points. Comparison of the tumor volume regrowth slopes indicates that the tumor bed effect is larger for external beam irradiation than for brachytherapy, suggesting that the tumor bed effect may be dose-rate dependent.
Acoustical holography: physical parameters and potential clinical applications.
Acoustical holography achieves real-time imaging of bodily structures through ultrasound. The fundamentals of acoustical holography and a description of a prototype unit undergoing trials at the authors' institution are presented. Physical parameters and means of calibrating the acoustic beam are discussed, and results of preliminary experimental and clinical studies reviewed. Acoustical holography has the potential for providing complementary diagnostic information which, after further technical developments, may furnish clinically useful information.
Treatment of the intact breast using tangent split beam fields and half 15 degree wedges as tissue compensators.
A 15 degree wedge inserted half way into the radiation field can be used effectively as a tissue compensator, in some cases reducing dose inhomogeneity by as much as 25%. The 15 degrees half wedge dosimetry and its application to a specific therapy technique is discussed in this article.