ESTRO 36 Abstract Book

S68

ESTRO 36 2017

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were deformable registered to a reference patient,

focusing on the lungs with bone masked. Mean dose

distributions were created for patients alive or dead at a

set time-point, censored for follow-up. Dose differences

were tested for significance with permutation testing.

The most significant area defined an anatomical region of

interest and individual patient doses collected. A

multivariate analysis investigated the importance of this

region in patient survival, including tumour size. Cox-

regression survival curves were plotted with patients split

to those receiving less than or more than the same

biologically equivalent dose that optimally split survival in

the 20 fraction patients (α/β = 2).

Results

For 20 fraction patients, from 6 months, a significant

difference was seen in the dose difference between

patients alive and dead (p<<0.001). The most significant

area was in the base of the heart near the origin of the

coronary arteries, median dose of 16.3Gy (BED 10.3Gy).

Multivariate analysis showed that tumour size was highly

significant for patient survival (p<0.001) as was dose

received by the anatomical region (p=0.029), HR 1.21

(1.02–1.44), highlighting the importance of dose received

by this region. Cox-regression survival curves were plotted

with patients split by those receiving more than or less

than 8.5Gy, log-rank p<0.001, figure 1A, controlled for

tumour size (p<0.001) and age (p=0.11).

A cox-regression with the SABR patients split at 6.3Gy

(translated BED from the 20 fraction patients) was

plotted, figure 1B. A highly significant difference in

survival (log-rank p=0.016) was seen where patients

receiving more than 6.3Gy showed worse survival. Tumour

size was not significant in the SABR group.

Conclusion

Dose to a specific region in the base of the base heart

predicts for early death in lung cancer patients treated

with 55Gy in 20 fractions, as well as for SABR patients

treated to 60Gy in 5 fractions. The effect was seen for the

same BED (a/b = 2Gy). In the future, we will extend the

SABR group and initialise cardiac imaging studies to

identify a clinical cause for this effect.

OC-0142 Incidental dose to cardiac subvolumes does

not improve prediction of radiation pneumonitis in

NSCLC

R. Wijsman

, F. Dankers

, E. Troost

, A. Hoffmann

, J.

Bussink

Radboud University Medical Center, Radiation oncology,

Nijmegen, The Netherlands

Institute of radiooncology, Helmholtz-Zentrum Dresden-

Rossendorf, Dresden, Germany

Purpose or Objective

Conflicting results have been reported for the combined

effect of heart and lung irradiation on the development of

radiation pneumonitis (RP). The reported studies based on

3D-conformal radiotherapy considered the whole heart as

an organ-at-risk, thereby not distinguishing between dose

to the cardiac ventricles and atria. We assessed whether

inclusion of incidental dose to these cardiac subvolumes

improved the prediction of Grade ≥3 RP.

Material and Methods

We retrospectively assessed 188 consecutive patients with

stage III non-small cell lung cancer (NSCLC) having

undergone (chemo-)radiotherapy (≥60 Gy) using intensity-

modulated radiation therapy (until 2011) or volumetric-

modulated arc therapy (starting in 2011). Most patients

(n=182) received 66 Gy in 33 (once-daily) fractions to the

primary tumour and involved hilar/mediastinal lymph

nodes based on FDG-PET/CT. The lungs and heart

(ventricles and atria separately in 156 patients that

received a contrast enhanced planning CT) were re-

contoured to generate accurate dose-volume histogram

(DVH) data. RP was assessed using the Radiation Therapy

Oncology Group scoring criteria for pulmonary toxicity.

Since high multicollinearity was observed between the

DVH parameters, those with the highest Spearman

correlation coefficient (Rs) were selected for the

modelling procedure. Using a bootstrap approach, clinical

parameters [age, gender, performance, smoking status,

forced expiratory volume in 1 second, and cardiac

comorbidity (i.e., medical history of myocardial

infarction, heart failure, valvular heart disease, cardiac

arrhythmias and/or hypertension)] and DVH parameters of

lungs and heart (assessing atria and ventricles separately

and combined) were evaluated for RP prediction.

Results

Twenty-six patients (13.8%) developed RP (median follow-

up 18.4 months). Only the median mean lung dose (MLD)

differed between groups (15.3 Gy vs 13.7 Gy for the RP

and non-RP group, respectively; p=0.004). Most Rs of the

lung DVH parameters exceeded those of the heart DVH

parameters and only some lung DVH parameters were

significantly correlated with RP [See Figure 1; highest Rs

for MLD (0.21; p<0.01)]. Only cardiac comorbidity was

borderline associated with RP (p=0.066) on univariate

logistic regression analysis. After bootstrap modelling,

heart DVH parameters were seldom included in the model

predicting Grade ≥3 RP. The optimal model consisted of:

MLD (Odds ratio (OR) 1.28 per Gy increase; p=0.03) and

cardiac comorbidity (OR 2.45 in case of cardiac

comorbidity; p=0.04). The area under the receiver

operator characteristic curve was 0.71, with good

calibration of the model.