Impact of residual setup errors after image guidance on heart dose in NSCLC patients
Johnson-Hart, Corinne Price, G. McWilliam, Alan Abravan, Azadeh Van Herk, Marcel
Johnson-Hart, Corinne
Price, G.
McWilliam, Alan
Abravan, Azadeh
Van Herk, Marcel
Citations
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Abstract
Purpose or Objective
A recent study of NSCLC patients showed small residual
setup errors (shifts) in the direction of the heart following
image-guidance were significantly related to overall
survival. This study of the dosimetric effects of these
residual shifts investigates the hypothesis that observed
survival differences were related to a change in heart
dose.
Material and Methods
Accumulated doses including shifts for each fraction were
determined for 546 NSCLC patients treated with 55Gy in
20 fractions, assuming shift invariance (validated in a
subset). Planning CTs and corresponding dose distributions
were deformed to a reference case. Image-based datamining
and permutation testing techniques were then
applied to the difference between the planned and
accumulated dose (Δdose) to determine where Δdose
relates to 1-year survival. The significance of Δdose in the
identified region was assessed using multivariable Cox
analysis, correcting for age, sex, GTV, N stage and ECOGPS.
The cohort was then split into octiles, based upon
planned dose to the region, and multivariable Cox analysis
performed for each sub-cohort to explore the dose
response relationship. The identified dose threshold for
damage was then tested in an independent validation
cohort of 1482 NSCLC patients (treated with 55Gy in 20
fractions) from the same institution, based upon the
planned dose to the region (as shifts were unavailable for
this cohort).
Results
Permutation testing identified a small region in the heart
base, near the right coronary artery, where Δdose
correlated with 1-year survival (Figure 1). Δdose in this
region showed no correlation with tested common clinical
variables – meaning it is likely not confounded and thus is
a sensitive test metric. Δdose was significant in
multivariable Cox regression (p<0.001, HR 1.221/Gy), with
increasing change in dose from plan resulting in greater
risk of death. Octile analysis revealed Δdose to be
significant only in the 7th octile, planning dose range 16.2–
23.4Gy, suggesting a steep dose-effect relation for heart
damage in this range. Taking 16.2Gy as a conservative
threshold dose, this result was successfully validated. Conclusion
This study suggests the relation between residual setup
errors and survival could be explained by changes in
cardiac dose. It identifies an area at the heart base where
dose is correlated with survival. Our results suggest the
dose threshold for cardiac damage is between 16.2–23.4Gy
in the base of the heart, which was validated in an
independent cohort. This study provides further evidence
supporting the use of stricter heart dose constraints, and
explores what these constraints should be. The dose effect
in other regions of the heart should also be investigated.
Description
Date
2020
Publisher
Collections
Keywords
Type
Meetings and Proceedings
Citation
Johnson-Hart C, Price G, McWilliam A, Abravan A, Faivre-Finn C, Van Herk M. PO-0991: Impact of residual setup errors after image guidance on heart dose in NSCLC patients. Radiotherapy and Oncology . 2020 Nov;152:S528.