Improved critical structure sparing with biologically based IMRT ...
Improved critical structure sparing with biologically based IMRT ...
Improved critical structure sparing with biologically based IMRT ...
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<strong>Improved</strong> <strong>critical</strong> <strong>structure</strong><br />
<strong>sparing</strong> <strong>with</strong> <strong>biologically</strong> <strong>based</strong><br />
<strong>IMRT</strong> optimization<br />
X.Sharon Qi, Vladimir A. Semenenko and X. Allen Li<br />
Department of Radiation Oncology, Medical College of<br />
Wisconsin
Introduction<br />
DVH <strong>based</strong> algorithm ignore the nonlinear dose<br />
response of both tumor and normal <strong>structure</strong><br />
Dose-<strong>based</strong> optimization is insufficient to predict<br />
any biological end point of radiotherapy<br />
Biologically <strong>based</strong> radiation treatment planning<br />
can substantially improve the quality of the plan<br />
generated
Purpose<br />
to study the impact of using biological models on<br />
plan quality by evaluating commercially available<br />
treatment planning systems
Methods and materials
A. TPS<br />
TPS: CMS (Monaco, XiO)<br />
Philips Pinnacle<br />
Tomotherapy
Biological objective functions in TPS
Physical objective functions
B. Study design<br />
Five clinical cases: brain, H&N, lung, pancreas<br />
and prostate<br />
The original treatment plans were generated by<br />
using XiO or Tomotherapy<br />
Two physically <strong>based</strong> <strong>IMRT</strong>(p<strong>IMRT</strong>) and two<br />
<strong>biologically</strong> <strong>based</strong> (b<strong>IMRT</strong>) plans were generated<br />
for each cases utilizing different TPSs<br />
Same planning CT and <strong>structure</strong> set<br />
Same beam numbers and orientations
Fix angles:<br />
p<strong>IMRT</strong>: XiO (XiO)<br />
p<strong>IMRT</strong>: Pinnacle (Pinn_phy)<br />
b<strong>IMRT</strong>: Monaco (Monaco)<br />
b<strong>IMRT</strong>: Pinnacle (Pinn_bio)<br />
Rotation:<br />
Tomotherapy (Tomo)
C. Plan comparison (p<strong>IMRT</strong> vs. b<strong>IMRT</strong>)<br />
DVH<br />
Heterogeneity index (HI): the ratio of the<br />
minimum dose delivered to the hottest 5% of the<br />
PTV to the minimum dose delivered to the<br />
hottest 95% of the PTV<br />
Conformity index (CI): the ratio of volume inside<br />
the isodose surface corresponding to the<br />
prescription dose compared to the volume of the<br />
target<br />
Overall plan ranking index (fEUD)
EUD<br />
The uniform dose that gives the same biological effect as a<br />
given nonuniform dose distribution<br />
a: the tumor or normal tissue specific parameter<br />
a=1/n for the relationship of Lyman model<br />
Malignant tumor targets general have large negative values<br />
serial-type organ has a large positive value (penalize hot<br />
spots)<br />
parallel <strong>structure</strong> organ use a small positive value
fEUD: EUD-<strong>based</strong> figure-of-merit<br />
Weighting factors, correspond to the<br />
complication probability (for ith<br />
OAR) and/or control probability for<br />
jth target<br />
The relative importance factor<br />
between the weighted sums of EUDs<br />
for all targets and OARs
Results<br />
A. Dose distributions and DVHs
Head and Neck case in target: Similar
Head and Neck case: DVH of OARs
Prostate case
Prostate case
Comparison of the dose ranges from the minimum to maximum doses<br />
and the mean doses for the five cases(1)
Comparison of the dose ranges from the minimum to maximum doses and the mean<br />
doses for the five cases(2)
<strong>IMRT</strong> plans offer improved OAR <strong>sparing</strong><br />
The target coverage for both p<strong>IMRT</strong> and b<strong>IMRT</strong><br />
plans are comparable; Tomo plans are slightly<br />
more uniform<br />
Monaco plans show slightly more heterogeneous<br />
dose distributions in targets compared <strong>with</strong> other<br />
plans
B. Dose conformity and hetergenetiy<br />
Monaco plans and Pinn_bio plans: more conformal<br />
Monaco: similar or higher HI<br />
Pinn_phy and Pinn_bio: similar HI<br />
Tomo: similar or lower values of CI and HI
C: The equivalent uniform dose
All five plans give similar EUDs<br />
Monaco plan results in slightly greater EUDs<br />
values in 11 out of 12 targets in all five cases<br />
Compared to Pinn_phy plans, Pinn_bio plans<br />
lead to 7 out of 12 targets receiving higher EUDs,<br />
while 32 out of 37 OARs receive lower EUDs<br />
The Monaco and Pinn_bio plans yield similar<br />
OAR <strong>sparing</strong>
D. Overall plan figure-of-merit(fEUD)
E. DVH dependence of parameter a<br />
cord Right parotid
Conclusion<br />
The use of biological models in treatment<br />
planning optimization can generate <strong>IMRT</strong> plans<br />
<strong>with</strong> significantly improved normal tissue<br />
<strong>sparing</strong> <strong>with</strong> similar or slightly increased dose<br />
heterogeneity in target<br />
Caution should be exercised in choosing<br />
appropriate models and/or model parameters<br />
and in evaluating the plan obtained when using<br />
the <strong>biologically</strong> <strong>based</strong> treatment planning system
Thank you!
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