ESTRO 36 Abstract Book

S321 ESTRO 36 _______________________________________________________________________________________________

lesion glycolysis (TLG) and 5) SUVpeak. Univariate and multivariate Cox regression were employed throughout. Results In the univariate analysis, SUVpeak in the primary GTV was associated with local control (HR=1.084; p=0.03). The regional nodal SUVpeak was associated with distant control (HR=1.11; p=0.003). The other tumor volume and SUV parameters were also associated with clinical endpoints (p<0.05). In the multivariate analysis on OS, the model included tumor stage (HR =1.41; p=0.02), ECOG status (HR=2.92; p<0.001), Charlson comorbidity index (HR=1.37; p=0.005), pack years of smoking (HR=1.015; p<0.001) and primary GTV volume (HR=1.0074; p=0.02). The model on DFS included ECOG status (HR=2.13; p<0.001) and the union of all GTV volume (HR=1.0080; p<0.001). These models were not improved by including SUV parameters. However, analyzing the subgroup of HPV negative OPC and non-OPC (n=77), the model on OS could be improved by including MTV (HR=1.018; p<0.001) or TLG (HR=1.0015; p=0.007). The model on DFS could be improved by including one of the following parameters: MTV (HR=1.040; p<0.001), TLG (HR=1.0036; p<0.001) or SUVpeak of regional nodes (HR=1.15; p=0.001). Conclusion Accounting for clinical risk factors in the multivariate modeling of survival after radiochemotherapy of head and neck cancer, the SUV parameters appear less important than found in previous studies. The association between the SUV parameters and survival seems to be stronger for HPV negative patients. PO-0615 Can diffusion-weighted MRI predict for xerostomia and QoL in head and neck patients receiving RT? K. Nguyen 1 , M. Min 1,2,3 , L. Holloway 1,2,3,4 , M. Jameson 1,2 , C. Rumley 1,2 , A. Fowler 1 , M. Lee 1,3 , D. Forstner 1,2,3 , R. Rai 1 , G. Liney 1,2,3,5 1 Liverpool Hospital, Radiation Oncology, Liverpool, Australia 2 Ingham Institute of Applied Medical Research, Radiation Oncology, Liverpool, Australia 3 University of New South Wales, Department of Medicine, Sydney, Australia 4 University of Western Sydney, Medicine, Sydney, Australia 5 University of Wollongong, Medicine, Wollongong, Australia Purpose or Objective Diffusion-weighted MRI (DWI) has the ability to identify specific cellular characteristics of tissues. Although DWI has not been traditionally used in RT planning, there is increasing interest regarding its potential worth in predicting RT-related toxicities. Our study aims to investigate 1) serial changes in apparent diffusion coefficient (ADC) maps of salivary glands quantified from DWI and 2) whether DWI can predict for xerostomia and quality-of-life (QoL) in patients with mucosal primary head and neck cancer (MPHNC) receiving primary RT. Material and Methods 19 patients with newly diagnosed MPHNC receiving RT were included. DWIs were acquired before, during (week 2,3,5,6) and after RT (post-RT week 4,12). Parotid and submandibular glands were contoured on DWI and corresponding estimated ADCs extracted (Figure1). 'Dry mouth” according to Common Terminology Criteria for Adverse Events (CTCAE) v4.0 and 'saliva” QoL according to University of Washington QoL (UW-QoL) questionnaire v4.0 were recorded for a follow-up period of 11-23months post- RT. A Spearman Correlation test was used to evaluate associations (p≤0.05=significant) between ADC mean of ipsilateral/contralateral/bilateral parotid and submandibular glands and CTCAE, as well as UW-QoL scores.

Results Serial ADC mean

for parotid and submandibular glands, both ipsilateral and contralateral to primary cancer, showed an increasing trend from pre-RT to post-RT (Figure2).

On analysis of parotid glands, a statistically significant positive correlation existed between xerostomia and bilateral parotid ADC mean on week5 DWI 0.624(p=0.023), while a statistically significant negative correlation existed between "saliva” QoL and bilateral parotid ADC mean on week5 DWI -0.629(p=0.038). Similarly, on analysis of submandibular glands, a positive correlation existed between xerostomia and bilateral submandibular ADC mean on week5 DWI 0.751(p=0.008), while "saliva” QoL and change in bilateral submandibular ADC mean between pre- RT and week5 DWI recorded a significant negative correlation -0.791(p=0.034). Conclusion Our study shows an increasing trend in ADC mean on DWI in salivary glands pre- to post-RT. As ADC is an inverse measure of cellular density, this suggests there is a decrease in the cellularity of salivary glands pre- to post-RT detectable on DWI. Correlations between ADC mean and xerostomia were identified at week5 which suggests ADC mean measurements at this time-point (approximately mid-RT) may be most sensitive to predict for late xerostomia, rather than at any other time-point studied. The significant negative Spearman correlation between QoL following RT and change in ADC mean suggests a link between worsening QoL and increased ADC mean (or decreased cellularity) of salivary glands. In conclusion, DWI may be a valuable predictive tool for late toxicities in MPHNC patients receiving RT. DWI has potential to aid adaptive radiotherapy which spares salivary glands depending on areas of high cellularity and should be further explored.