Subregional analysis of the parotid glands: predicting late xerostomia in head and neck cancer
Berger, T. Noble, D. J. Shelley, L. E. McMullan, T. Romanchikova, M. Carruthers, L. J. Cebamanos, L. Beckett, G. Duffton, A. Paterson, C.
Berger, T.
Noble, D. J.
Shelley, L. E.
McMullan, T.
Romanchikova, M.
Carruthers, L. J.
Cebamanos, L.
Beckett, G.
Duffton, A.
Paterson, C.
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Abstract
Several studies have investigated the relationship between
the clinical symptoms of xerostomia and the radiotherapy
dose received by subregions of the parotid glands (e.g.
superficial lobe/stem cell region). The purpose of this
study was to compare the predictive power of image
biomarkers (IMB) calculated on the superficial lobe (SL),
deep lobe (DL) and whole parotid (WP) gland for
identifying late xerostomia in head and neck (H&N) cancer
patients.
Material and Methods
All patients (N=60) received 30 fractions (fx) on a
TomoTherapy HiArt System (Accuray, Sunnyvale, CA, USA)
with daily mega-voltage CT (MVCT) images with CTCAE
toxicity recorded at 12 months. As illustrated in Figure 1,
the MVCT images (0.76 x 0.76 x 6 mm) were used to
calculate by textural analysis, seventy-three IMBs
consisting of first and higher order features on the SL, DL
and WP gland. For each feature, their values for the period
1-20fx were used to perform linear regressions and their
slopes considered as potential predictors. LASSO analysis
was used (100 times) with 4-fold cross validation to select
the best predictors (<9) for each region. To evaluate the
robustness of each of the 100 combinations, the patients
were split into four folds. The training set made up of 3
folds and the testing set, the remaining fold, were used to
test the predictive power of each of the LASSO
combinations using a logistic regression model. This was
evaluated by the Area Under the Curve (AUC), resulting in
4 AUCtest and 4 AUCtrain values which were averaged
(mAUCtest and mAUCtrain). For robustness, this process was
repeated 100 times for each combination of predictors and
the median mAUCtest and mAUCtrain calculated. The 50
combinations of predictors with the highest median mAUC
were selected for the SL, DL and WP and their median
mAUCtest distributions compared using a t-test.
Results
Of the 60 patients, 27% reported xerostomia (grade>1) at
12 months. The highest median mAUCtrain / mAUCtest were
0.93/0.83, 0.90/0.79 and 0.93/0.80 for the SL, DL and WP,
respectively. As shown in Figure 2, the 50 combinations of
predictors that were selected for the WP gland yielded a
significantly higher median mAUCtest compared to the DL
(p<0.01). The selected combinations of the SL yielded
higher median mAUCtest compared to the WP (p<0.01).
Conclusion
The slopes of the IMBs extracted from the DL (from
fraction 1-20) have a lower predictive power compared to
those extracted from the WP gland. Despite the smaller
number of voxels considered when analyzing the SL, the
IMBs extracted from the SL have a higher predictive power
compared to those from the WP. However, this requires
further validation on a larger cohort and different selected
periods. To obtain a greater understanding of the
differences in predictive power of each of these subregions
requires further information on the underlying biological
processes.
Description
Date
2020
Publisher
Collections
Keywords
Type
Meetings and Proceedings
Citation
Berger T, Noble DJ, Shelley LE, McMullan T, Romanchikova M, Carruthers LJ, et al. PO-1585: Subregional analysis of the parotid glands: predicting late xerostomia in head and neck cancer. Radiotherapy and Oncology . 2020 Nov;152:S860–1.