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Differences in biological effectiveness of brachytherapy sources
318
Radiation Oncology, Biology, Physics
Volume 30, Supplement 1
Results: The modified and control PVU II genes were successfully cloned into the pKK plasmid as confirmed by restriction enzyme analysis of the constructs. Both the modified and control PVU II genes were functional. The control PVU II gene demonstrated 5 logs restriction of phage lambda compared to MA2 cells transformed with pKK alone. The modified PVU II gene product demonstrated 2 logs of phage restriction. There was no restriction of phage methylated by the PVU II methylase. Work is now underway to transfer the modified gene into the vector system for mammalian cell expression to determine whether RE activity is under the tight control df estrogen. Conclusion: The PVU II gene has been successfully modified for mammalian cell expression and is functional, as evidenced by phage restriction in E. coli transformed with this gene. Once transfected into mammalian cells, we predict this system will afford tight control of intracellular RE activity by estrogen, providing a means to study DNA dsb in the absence of other changes generated in irradiated cells. Current results will be presented.
1136 DIFFERENCES IN BIOLOGICAL EFFECTlVENESSOF BRACHYTHERAPY SOURCES D. L. Zellmer ??and J. D. Shadley Medical College of Wisconsin, Milwaukee, WI 53226
&Qgthesls. . .
The underling hypotheses of this Investigation are that: Differences in RBE of common brachytherapy sources that can be assessed through microdosimetric and I) biological measurements and That radiation effects are produced by two double stranded DNA breaks. 2) Introduction: Microdosimetric measurements of brachytherapy sources have shown differences in the single event lineal energy (microscopic analog of LET) spectra for brachytherapy sources compared to 6oco. The theory of dual radiation (TDRA) predicts that for low dose rates used in brachytherapy, these differences translate into observable changes in the biological effect (asumlng cellular repair/recovery). Methods and Material&. Mlcrodosimetric measurements were made with Ross1proportional counters that show a significant difference in the dose average lineal energy ,Td, between 92lr, 169Yb,1251and 103~ with respect to 6oco. The emulated tissue volume varied from 0.5 to 20 micrometers in diameter, which is smaller than the cell nucleus. One of the most accepted hypothesis is that the lesion causing cell death or chromosomal aberrations consists of two double strand breaks (DSB) of DNA. Three CHO ceil lines were selected for the experimentation: I) EM-9 (single strand repair deficient); 2) xrs-5 (double strand break repair deficient); and 3) K-I (single and double stand break repair proficient). All CHO cells (K-l, xrs-5 and EM-g) held In plateau phase were irradiated wlth SoCoand lelr sources at dose rates from 4 cGy/hr to 450 cGy/min. These cell lines were scored for ceil survival and chromosomal aberrations. Results: The initial slopes of the K-I and the NM-9 survlval and aberration curves were found to be slgnlflcantly dlfferent for the two sources while the xrs-5 line showed no effect of dose rate or source type. The KI llne showed a monoexponentlal response with no dose rate effect from 0.30 Gy/hr to 0.08 Gy/hr for ‘9%. The response !o %o was linear quadratic for all dose rates and rate independent from I.I;IGy/hr to 0.30 Gylhr. The low dose RBE’s of I.6 and I.8 for 1% with respect to WCo and were predicted by TDRA. The RBE at 20 Gy fell to 0.9. The xrs-5 line showed no change in response either to source or dose rate. Which is consistent with the double DSB hypothesis. Conclusions: The initial conclusions were as follows: I) The RBE’s for both cell survival and chromosomal aberrations for 19% were 9 I .5. 2) The primary DNA @Ion were dual double strand breaks. 3) The slte size was between 0.5 and I .Omicrons. 4) The RBE Is qualitatively and quantitatively predlcted by TDRA. Thisworkwassupported In partby ACS grants#EDT-77 & #FIG-170 andBestIndustries.
Radiation Oncology, Biology, Physics
Volume 30, Supplement 1
Results: The modified and control PVU II genes were successfully cloned into the pKK plasmid as confirmed by restriction enzyme analysis of the constructs. Both the modified and control PVU II genes were functional. The control PVU II gene demonstrated 5 logs restriction of phage lambda compared to MA2 cells transformed with pKK alone. The modified PVU II gene product demonstrated 2 logs of phage restriction. There was no restriction of phage methylated by the PVU II methylase. Work is now underway to transfer the modified gene into the vector system for mammalian cell expression to determine whether RE activity is under the tight control df estrogen. Conclusion: The PVU II gene has been successfully modified for mammalian cell expression and is functional, as evidenced by phage restriction in E. coli transformed with this gene. Once transfected into mammalian cells, we predict this system will afford tight control of intracellular RE activity by estrogen, providing a means to study DNA dsb in the absence of other changes generated in irradiated cells. Current results will be presented.
1136 DIFFERENCES IN BIOLOGICAL EFFECTlVENESSOF BRACHYTHERAPY SOURCES D. L. Zellmer ??and J. D. Shadley Medical College of Wisconsin, Milwaukee, WI 53226
&Qgthesls. . .
The underling hypotheses of this Investigation are that: Differences in RBE of common brachytherapy sources that can be assessed through microdosimetric and I) biological measurements and That radiation effects are produced by two double stranded DNA breaks. 2) Introduction: Microdosimetric measurements of brachytherapy sources have shown differences in the single event lineal energy (microscopic analog of LET) spectra for brachytherapy sources compared to 6oco. The theory of dual radiation (TDRA) predicts that for low dose rates used in brachytherapy, these differences translate into observable changes in the biological effect (asumlng cellular repair/recovery). Methods and Material&. Mlcrodosimetric measurements were made with Ross1proportional counters that show a significant difference in the dose average lineal energy ,Td, between 92lr, 169Yb,1251and 103~ with respect to 6oco. The emulated tissue volume varied from 0.5 to 20 micrometers in diameter, which is smaller than the cell nucleus. One of the most accepted hypothesis is that the lesion causing cell death or chromosomal aberrations consists of two double strand breaks (DSB) of DNA. Three CHO ceil lines were selected for the experimentation: I) EM-9 (single strand repair deficient); 2) xrs-5 (double strand break repair deficient); and 3) K-I (single and double stand break repair proficient). All CHO cells (K-l, xrs-5 and EM-g) held In plateau phase were irradiated wlth SoCoand lelr sources at dose rates from 4 cGy/hr to 450 cGy/min. These cell lines were scored for ceil survival and chromosomal aberrations. Results: The initial slopes of the K-I and the NM-9 survlval and aberration curves were found to be slgnlflcantly dlfferent for the two sources while the xrs-5 line showed no effect of dose rate or source type. The KI llne showed a monoexponentlal response with no dose rate effect from 0.30 Gy/hr to 0.08 Gy/hr for ‘9%. The response !o %o was linear quadratic for all dose rates and rate independent from I.I;IGy/hr to 0.30 Gylhr. The low dose RBE’s of I.6 and I.8 for 1% with respect to WCo and were predicted by TDRA. The RBE at 20 Gy fell to 0.9. The xrs-5 line showed no change in response either to source or dose rate. Which is consistent with the double DSB hypothesis. Conclusions: The initial conclusions were as follows: I) The RBE’s for both cell survival and chromosomal aberrations for 19% were 9 I .5. 2) The primary DNA @Ion were dual double strand breaks. 3) The slte size was between 0.5 and I .Omicrons. 4) The RBE Is qualitatively and quantitatively predlcted by TDRA. Thisworkwassupported In partby ACS grants#EDT-77 & #FIG-170 andBestIndustries.