Page 292 - 2014 Printable Abstract Book
P. 292
(PS5-09) The need for standardization of dosimetry in experimental radiobiology. Kurt Pedersen; Keith
Kunugi; Larry A. DeWerd, PhD; and Wesley S. Culberson, PhD; University of Wisconsin-Madison, Madison,
WI
In the past decade there has been significant interest in the standardization of dosimetry of
radiobiological irradiators. Many of these are self-contained x-ray irradiators. Due to this containment,
the test object being irradiated may be subject to scatter absent in other irradiation methods, which can
result in dosimetric inaccuracies. Also, the reporting of dosimetry in numerous radiobiology publications
is inadequate. We found that the validity of the published work may be brought into question due to
inaccurate ionizing radiation dosimetry. A recent symposium on dosimetry in radiobiological research
“The importance of standardization of dosimetry in radiobiology” developed a set of 12 criteria necessary
for adequate irradiation methodology. Our review of the dosimetry methodology in 28 publications
showed that none fully satisfied all 12 criteria. Additionally, only three of the criteria were followed by all
the investigators. Without accurately detailed dosimetry for the research, the reproducibility of the work
and the validity of the results come into question. The UWMRRC performed an irradiator output
verification study in 12 laboratories using acrylic mouse phantoms and thermoluminescent detectors
(TLDs). The laboratories were asked to deliver two doses, 1 Gy and 4 Gy Absorbed Dose to Water (ADW),
the standard dose unit in radiation therapy, to individual mouse phantoms in triplicate. Simultaneously,
mouse phantoms at the UWMRRC were irradiated to NIST-traceable reference doses using beam energies
representative of the subject laboratories’ beam energies. The irradiated mouse phantoms were returned
to the UWMRRC and the TLDs were processed, comparing their measured output to the reference TLDs.
Of the five x-ray irradiators tested, only one showed output comparison results within 5%. The discrepancy
in the other four ranged from 16.4% to 54.1%. These reviews demonstrate the need for standardization
and more oversight of the performance of dosimetry in radiobiology studies. Without accurately and
precisely knowing the dose delivered to subjects in these studies, the significance of the results cannot be
fully understood and the efficacy of different compounds cannot be appropriately compared.
(PS5-11) Estimation of DNA damage with path length convolution with damage probabilities. Piotr
Pater; Jan Seuntjens; and Issam El Naqa, McGill University, Montreal, Canada
The purpose of this study is to obtain the probability distributions of various DNA damage types
as a function of the incident electron kinetic energy. We used Geant4-DNA electron ionisation cross-
sections and we calculated path length distributions for electrons of energies between 10 eV and 1 MeV.
The path length is defined as the length between two subsequent interactions. These path lengths were
then convolved with the probability distributions for the creation of same-strand damage, opposite-
strand damage, clustered damage, isolated damage, and same DNA strand target damage. These
probability distributions of DNA damage were obtained by a Monte Carlo routine calculating probabilities
of interaction in DNA targets inside a nucleosome geometrical model. Our results represent the
probability of a secondary electron, initially created inside a DNA strand target, of undergoing its next
interaction: (1) in the opposite strand (DSB), (2) in the same strand (SSB+), (3) in either the opposite or
same-strand (clustered), (4) in the same DNA target (multiple-hit) or (5) more than 10 base pairs away
(isolated). Our results show that electrons with kinetic energy between 50 and 250 eV have a maximal
290 | P a g e
Kunugi; Larry A. DeWerd, PhD; and Wesley S. Culberson, PhD; University of Wisconsin-Madison, Madison,
WI
In the past decade there has been significant interest in the standardization of dosimetry of
radiobiological irradiators. Many of these are self-contained x-ray irradiators. Due to this containment,
the test object being irradiated may be subject to scatter absent in other irradiation methods, which can
result in dosimetric inaccuracies. Also, the reporting of dosimetry in numerous radiobiology publications
is inadequate. We found that the validity of the published work may be brought into question due to
inaccurate ionizing radiation dosimetry. A recent symposium on dosimetry in radiobiological research
“The importance of standardization of dosimetry in radiobiology” developed a set of 12 criteria necessary
for adequate irradiation methodology. Our review of the dosimetry methodology in 28 publications
showed that none fully satisfied all 12 criteria. Additionally, only three of the criteria were followed by all
the investigators. Without accurately detailed dosimetry for the research, the reproducibility of the work
and the validity of the results come into question. The UWMRRC performed an irradiator output
verification study in 12 laboratories using acrylic mouse phantoms and thermoluminescent detectors
(TLDs). The laboratories were asked to deliver two doses, 1 Gy and 4 Gy Absorbed Dose to Water (ADW),
the standard dose unit in radiation therapy, to individual mouse phantoms in triplicate. Simultaneously,
mouse phantoms at the UWMRRC were irradiated to NIST-traceable reference doses using beam energies
representative of the subject laboratories’ beam energies. The irradiated mouse phantoms were returned
to the UWMRRC and the TLDs were processed, comparing their measured output to the reference TLDs.
Of the five x-ray irradiators tested, only one showed output comparison results within 5%. The discrepancy
in the other four ranged from 16.4% to 54.1%. These reviews demonstrate the need for standardization
and more oversight of the performance of dosimetry in radiobiology studies. Without accurately and
precisely knowing the dose delivered to subjects in these studies, the significance of the results cannot be
fully understood and the efficacy of different compounds cannot be appropriately compared.
(PS5-11) Estimation of DNA damage with path length convolution with damage probabilities. Piotr
Pater; Jan Seuntjens; and Issam El Naqa, McGill University, Montreal, Canada
The purpose of this study is to obtain the probability distributions of various DNA damage types
as a function of the incident electron kinetic energy. We used Geant4-DNA electron ionisation cross-
sections and we calculated path length distributions for electrons of energies between 10 eV and 1 MeV.
The path length is defined as the length between two subsequent interactions. These path lengths were
then convolved with the probability distributions for the creation of same-strand damage, opposite-
strand damage, clustered damage, isolated damage, and same DNA strand target damage. These
probability distributions of DNA damage were obtained by a Monte Carlo routine calculating probabilities
of interaction in DNA targets inside a nucleosome geometrical model. Our results represent the
probability of a secondary electron, initially created inside a DNA strand target, of undergoing its next
interaction: (1) in the opposite strand (DSB), (2) in the same strand (SSB+), (3) in either the opposite or
same-strand (clustered), (4) in the same DNA target (multiple-hit) or (5) more than 10 base pairs away
(isolated). Our results show that electrons with kinetic energy between 50 and 250 eV have a maximal
290 | P a g e
