ESTRO 2021 Abstract Book

S817

ESTRO 2021

PO-0983 early prediction of parotid gland function based on ADC during radiotherapy for NPC: a phase Ⅱ study M. Feng 1,2 , H. Wang 1 , J. Yin 1 , J. Ren 1 , J. Lang 1 1 Sichuan Cancer Hospital & Institute, Sichuan Cancer Center, School of Medicine, University of Electronic Science and Technology of China, Department of Radiation Oncology, Sichuan Cancer Hospital & Institute, Sichuan Cancer Center, Radiation Oncology Key Laboratory of Sichuan Province, Chengdu, China; 2 The Third People's Hospital of Sichuan Province, Department of Oncology, The Third People's Hospital of Sichuan Province, Chengdu, China Purpose or Objective Xerostomia remains a common side effects for radiotherapy(RT) of nasopharyngeal carcinoma(NPC) patients and severely affects their quality of life.To investigate the feasibility of predicting parotid glands(PG) secretary function based on the apparent diffusion coefficient(ADC) from diffusion weighted MRI(DWI) of bilateral PG during RT for NPC and to analyze the correlations between the delivered radiation dose,volume of PG and the salivary gland secretary function. Materials and Methods 80 NPC treated with IGRT were enrolled in the study.DWI data were acquired on 3.0T MRI system at pre-RT, 5th, 15th fractions and immediately post-RT.The ADC of the ipsilateral (IP) and contralateral PG (CP) were automatic extracted by MIM software respectively.Chewing stimulating test and salivary gland scintigraphy were used to evaluate the PG secretion function.Pearson analysis was used to assess the correlation between ADC and delivered dose,volume, PG secretary function.Binary logistic regression analysis was used to investigate the relationship between ADC changes and PG secretary function.The cut-off value of ADC changes for predicting the salivary gland secretary function was calculated by Receiver operating characteristic curve (ROC). Results Mean ADC increase and volume reduction in both PG were observed during RT.These changes generally occurred in two stages.The mean ADC were 1118.4mm 2 /s(pre- RT),1307.5mm 2 /s(5th),1455.6mm 2 /s(15th),1644.8mm 2 /s(post-RT) for IP and 1144.5 mm 2 /s(pre- RT),1323.8mm 2 /s(5th),1435.6mm 2 /s(15th),1608.3mm 2 /s (post-RT) for CP.At the 5th fraction,with the mean delivered doses of 4.8Gy(IP) and 4.7Gy(CP),the average saliva secretions reduced from 2.4g(pre-RT) to 2.3g(5th fraction).The mean ADC value increased significantly by 17.7 %(IP),16.3%(CP),while the volume of PG had minimal changes(IP:24.2cm 3 vs23.8cm 3 ,CP:23.5cm 3 vs23.1cm 3 ).The increased mean ADC value had a positive correlation with the delivered dose(r1=0.57, r2=0.54).In the second stage (from the 5th fraction to post-RT),with total mean doses of 31.9Gy(IP) and 31.2Gy(CP),the average saliva secretion decreased to 1.7g(15th fraction) and 1.3g(post-RT).The mean ADC value was increased by 26.2%(IP), 22.4%(CP), while the volumes of PGs decreased by 39.4%(IP),37.1%(CP).The increased ADC value was positively correlated with the volume reduction rates(r1=0.53, r2=0.55).Binary logistic regression analysis showed the changes of mean 3D- ADC value from pre-RT to the 5 th RT(ΔADC5) was an independent predictor of PG secretary function during RT. ROC found that the cut-off value of the ΔADC5 was 194.1mm 2 /s and 179.6mm 2 /s for IP and CP(IP:AUC=0.772;CP:AUC=0.766). Conclusion The increased mean 3D-ADC values of PG were positively correlated with the delivered dose and the volume reduction,and negatively correlated with PG secretary function during RT.The mean 3D-ADC changes from pre- RT to the 5th RT might be an early independent predictor for PG secretary during RT, and the cut-off value of it was 194.1mm 2 /s and 179.6mm 2 /s for IP and CP. PO-0984 Impact of anterior commissure involvement in early glottic cancer treated with radical IMRT P. Ahlawat 1 , M. Gairola 2 , S. Purohit 1 , S. Tandon 2 , N. Sachdeva 1 , M.I. Sharief 2 , T. Singh 1 , K. Dobriyal 2 , A. Krishnan 1 1 Rajiv Gandhi Cancer Institute and Research Centre, New Delhi, Radiation Oncology, New Delhi, India; 2 Rajiv Gandhi Cancer Institute and Research Centre, New Delhi, Radiation Oncology, Delhi, India Purpose or Objective Early glottic cancers (EGC) with anterior commissure (AC) involvement deserve special attention, as it is considered a weak point for tumour spread because in this area there is no cartilage perichondrium to resist tumour spread. AC involvement has been found to be a poor prognostic factor in patients treated with conventional radiotherapy (RT) technique in few studies. Relapses in such scenario are possibly due to an underdosage in this region. Bolus is one strategy which is often used in cases with AC involvement as it increases dose in this region. However, now in the era where intensity modulated radiotherapy (IMRT) is increasingly used in most tumours it is important to know if EGC with AC involvement can be treated without compromising outcome. The aim of this study was to compare treatment outcomes between patients with EGC with or without AC involvement treated with radical IMRT. Materials and Methods It was a retrospective study in which newly diagnosed 200 patients with EGC were included. There were 71 patients with AC involved and remaining 128 patients had no AC involvement. All patients were treated with IMRT with 66 to 70 Gy with 2 Gy per fraction. Bolus was not used during the treatment. The end points for this study were loco-regional control (LRC) and overall survival (OS). LRC and OS were computed with Kaplan-Meier curve with log-rank test for comparison between the two groups. Univariate analysis and Multivariate Cox proportional hazards regression analysis was performed to estimate the impact of known relevant prognostic factors on LRC and OS. Results The median follow up of AC involvement group was 51.90 months (range; 3.7 – 110.7) and 57.68 months (range; 6.9 – 124.3) in AC uninvolved group. Patients and disease related characteristics were comparable