Density variation of parotid glands during IMRT for head-neck cancer: correlation with treatment and anatomical parameters.
OBJECTIVE
Measuring parotid density changes in patients treated with IMRT for head-neck cancer (HNC) and assessing correlation with treatment-related parameters.


METHODS
Data of 84 patients treated with IMRT for different HNC were pooled from three institutions. Parotid deformation and average Hounsfield number changes (ΔHU) were evaluated through MVCT (with Helical Tomotherapy) or diagnostic kVCT images taken at the treatment start/end. Parotids were delineated in the first image and propagated to the last using a previously validated algorithm based on elastic registration. The correlation between ΔHU and several treatment-related parameters was tested; then, logistic uni- and multi-variate analyses taking "large" ΔHU as end-point were carried out. Due to the better image quality, analyses were repeated considering only kVCT data.


RESULTS
ΔHU was negative in 116/168 parotids (69%; for kVCT patients: 72/92, 78%). The average ΔHU was significantly different from zero (-7.3, 0.20-0.25 HU/fraction, p<0.001). Individual ΔHU was highly correlated with parotid deformation both in terms of volume change and mean value of the Jacobian of the deformation field (Jac_mean), and with neck thickness variation; these correlations were much stronger for kVCT data. Logistic analyses considering ΔHU<-11 (quartile value) as the end-point showed a two-variable model including large deformation (Jac_mean<0.68) and initial neck thickness to be the most predictive variables (p<0.0005, AUC=0.683; AUC=0.776 for kVCT); the odd ratio of large vs moderate/small parotid deformation was 3.8 and 8.0 for the whole and the kVCT population respectively.


CONCLUSIONS
Parotid density reduced in most patients during IMRT and this phenomenon was highly correlated with parotid deformation. The individual assessment of density changes was highly reliable just with diagnostic KvCT. Density changes should be considered as an additional objective measurement of early parotid radiation-induced modifications; further research is warranted.
San Raffaele Scientific Institute, Milano, Italy. fiorino.claudio@hsr.it
Claudio
C
Fiorino
Giovanna
G
Rizzo
Elisa
E
Scalco
Sara
S
Broggi
Maria Luisa
ML
Belli
Italo
I
Dell'Oca
Nicola
N
Dinapoli
Francesco
F
Ricchetti
Aldo Mejia
AM
Rodriguez
Nadia
N
Di Muzio
Riccardo
R
Calandrino
Giuseppe
G
Sanguineti
Vincenzo
V
Valentini
Giovanni Mauro
GM
Cattaneo
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D002294:Carcinoma, Squamous Cell / Q000473:pathology / Q000532:radiotherapy*; D015331:Cohort Studies; D005260:Female; D006258:Head and Neck Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D010306:Parotid Gland / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000473:pathology* / Q000528:radiation effects*; D011829:Radiation Dosage; D011874:Radiometry; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012189:Retrospective Studies; D018570:Risk Assessment; D036542:Tomography, Spiral Computed; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome