Page 206 - 2014 Printable Abstract Book
P. 206
variation as a function of the LET must be carefully considered when planning fractionated radiotherapy
treatment with protons and heavy ion beams.
(PS3-28) Modeling the radiobiological effect of the spread out Bragg peak shape in proton therapy using
the Microdosimetric Kinetic Model. Lorraine A. Courneyea, PhD; Nicholas B. Remmes, PhD; and Michael
G. Herman, PhD Mayo Clinic, Rochester, MN
Purpose: Evaluate the radiobiological impact of various spread out Bragg peak (SOBP) shapes on
intensity modulated proton therapy plans using the Microdosimetric Kinetic Model (MKM).
Methods: The MKM model was integrated into a TOPAS Monte Carlo simulation and the saturation-
corrected dose weighted specific energy (zd*) and percent depth dose (PDD) curves were simulated for
94 proton energies and a reference Co-60 beam. A dose weighted sum of these zd* values was then used
to calculate the RBE with respect to Co-60 for four cases of SOBP shapes. The SOBP shapes included a flat
SOBP (case 1), a SOBP linear decreasing with depth (case 2), a SOBP shaped like a one sided Gaussian
distribution (case 3), and a flat SOBP extending over only the proximal half of the target (case 4). For each
of these four shapes, two-field, parallel opposed proton beams were summed to provide a uniform
physical dose over a target extending 10 cm in length. Using this simulation, three clinical sites were
assessed: lung, breast and prostate cancer. These sites were taken to have tumor α/β ratios of 10.0, 4.6,
and 1.5 Gy and normal tissue α/β ratios of 3.0, 3.4 and 3.0 Gy respectively. Assuming a 2 Gy physical dose,
the isoeffective dose (DIsoE) was calculated in the tumor and normal tissue. These results were then
evaluated using two measures: the location of the maximum DIsoE (DIsoE_max) and the ratio of DIsoE in the
target center to the mean DIsoE in the target (DIsoE_ratio). Results: For each SOBP shape, the total physical
dose deposited in the target was within 2.0 ± 0.3 Gy, and the maximum dose was located inside the target.
DIsoE_max was located in normal tissue for lung cases 1 & 2, and breast case 1. For cases 1-3, DIsoE_ratio was
~1.0 for all sites. DIsoE_ratio was highest in case 4: 1.13 for lung, 1.18 for breast and 1.23 for prostate,
signifying hot spots in the target center. Such hot spots may be acceptable and even desirable in the
context of a lung treatment, but are clinically undesirable for breast and prostate plans. Conclusions:
Optimal SOBP shapes are site dependent, and the MKM predictions suggest that flat SOBP are rarely the
biologically optimal choice. In this analysis, acceptable SOBP shapes were found to be cases 3 & 4 for lung,
cases 2 & 3 for breast, and cases 1, 2 & 3 for prostate.
1
(PS3-29) Partial tumor radiation triggers aggressive tumor changes. Mary-Keara Boss, DVM ; Andrew
3
3
2
3
Fontanella, PhD ; Jason Somarelli, PhD ; Mariano Garcia-Blanco, MD, PhD ; Artak Tovmasyan, PhD ; Ines
3
4
3
Batinic-Haberle, PhD ; Sha Chang, PhD ; and Mark Dewhirst, DVM, PhD North Carolina State University
1
2
College of Vet Med, Raleigh, NC ; Memorial Sloan Kettering Cancer Center, New York, NY ; Duke
University, Durham, NC ; and University of North Carolina, Chapel Hill, NC
4
3
Purpose/Objectives: “Marginal miss”, or incomplete irradiation of a targeted tumor, is clinically
significant as irradiated cells can influence non-irradiated cells through bystander effects. We observed
bystander effects where irradiated tumor cells triggered aggressive changes in the non-irradiated tumor.
We hypothesize 1) Marginal miss will promote a more aggressive tumor phenotype in non-irradiated cells
204 | P a g e
treatment with protons and heavy ion beams.
(PS3-28) Modeling the radiobiological effect of the spread out Bragg peak shape in proton therapy using
the Microdosimetric Kinetic Model. Lorraine A. Courneyea, PhD; Nicholas B. Remmes, PhD; and Michael
G. Herman, PhD Mayo Clinic, Rochester, MN
Purpose: Evaluate the radiobiological impact of various spread out Bragg peak (SOBP) shapes on
intensity modulated proton therapy plans using the Microdosimetric Kinetic Model (MKM).
Methods: The MKM model was integrated into a TOPAS Monte Carlo simulation and the saturation-
corrected dose weighted specific energy (zd*) and percent depth dose (PDD) curves were simulated for
94 proton energies and a reference Co-60 beam. A dose weighted sum of these zd* values was then used
to calculate the RBE with respect to Co-60 for four cases of SOBP shapes. The SOBP shapes included a flat
SOBP (case 1), a SOBP linear decreasing with depth (case 2), a SOBP shaped like a one sided Gaussian
distribution (case 3), and a flat SOBP extending over only the proximal half of the target (case 4). For each
of these four shapes, two-field, parallel opposed proton beams were summed to provide a uniform
physical dose over a target extending 10 cm in length. Using this simulation, three clinical sites were
assessed: lung, breast and prostate cancer. These sites were taken to have tumor α/β ratios of 10.0, 4.6,
and 1.5 Gy and normal tissue α/β ratios of 3.0, 3.4 and 3.0 Gy respectively. Assuming a 2 Gy physical dose,
the isoeffective dose (DIsoE) was calculated in the tumor and normal tissue. These results were then
evaluated using two measures: the location of the maximum DIsoE (DIsoE_max) and the ratio of DIsoE in the
target center to the mean DIsoE in the target (DIsoE_ratio). Results: For each SOBP shape, the total physical
dose deposited in the target was within 2.0 ± 0.3 Gy, and the maximum dose was located inside the target.
DIsoE_max was located in normal tissue for lung cases 1 & 2, and breast case 1. For cases 1-3, DIsoE_ratio was
~1.0 for all sites. DIsoE_ratio was highest in case 4: 1.13 for lung, 1.18 for breast and 1.23 for prostate,
signifying hot spots in the target center. Such hot spots may be acceptable and even desirable in the
context of a lung treatment, but are clinically undesirable for breast and prostate plans. Conclusions:
Optimal SOBP shapes are site dependent, and the MKM predictions suggest that flat SOBP are rarely the
biologically optimal choice. In this analysis, acceptable SOBP shapes were found to be cases 3 & 4 for lung,
cases 2 & 3 for breast, and cases 1, 2 & 3 for prostate.
1
(PS3-29) Partial tumor radiation triggers aggressive tumor changes. Mary-Keara Boss, DVM ; Andrew
3
3
2
3
Fontanella, PhD ; Jason Somarelli, PhD ; Mariano Garcia-Blanco, MD, PhD ; Artak Tovmasyan, PhD ; Ines
3
4
3
Batinic-Haberle, PhD ; Sha Chang, PhD ; and Mark Dewhirst, DVM, PhD North Carolina State University
1
2
College of Vet Med, Raleigh, NC ; Memorial Sloan Kettering Cancer Center, New York, NY ; Duke
University, Durham, NC ; and University of North Carolina, Chapel Hill, NC
4
3
Purpose/Objectives: “Marginal miss”, or incomplete irradiation of a targeted tumor, is clinically
significant as irradiated cells can influence non-irradiated cells through bystander effects. We observed
bystander effects where irradiated tumor cells triggered aggressive changes in the non-irradiated tumor.
We hypothesize 1) Marginal miss will promote a more aggressive tumor phenotype in non-irradiated cells
204 | P a g e
