Abstract Book

S94

ESTRO 37

3 UMC Utrecht, Surgical Oncology, Utrecht, The Netherlands

Figure 2:

Purpose or Objective The role of neoadjuvant chemoradiotherapy (CRT) in the management of resectable esophageal cancer is growing. The advantage of nCRT followed by a 6-8-week period before surgery is that this approach can induce significant tumor regression and downstaging, which leads to an increased rate of microscopically radical resections, decrease in local recurrences, a pathologic complete response in 28-34% of the patients and an overall survival benefit. Accurate identification of non-responders early during nCRT would allow individualized decision making in continuation or discontinuation of nCRT. Furthermore, a tool is desirable to accurately assess the treatment response after nCRT to identify patients with a complete response. DW-MRI imaging during the first 2-3 weeks of nCRT has shown promising results in the prediction of pathological response. However, the optimal timing of scanning for pathological response prediction is unclear. The purpose of this study was to assess and evaluate the optimal time of DW-MRI scanning during nCRT to predict pathological response to nCRT with pathology of the resected specimen as reference standard. Material and Methods Patients with esophageal cancer who underwent nCRT according to the CROSS regimen (weekly administration of carboplatin/paclitaxel combined with 41.4Gy in 23 fractions), followed by an esophagectomy were eligible for inclusion. Patients underwent 6 sequential MRI scans. One MRI scan was performed in the week prior to nCRT in addition to the conventional diagnostic work-up. Subsequently, weekly MRI scans were performed during nCRT (Figure 1). The median tumor apparent diffusion coefficient (ADC) was determined at these six time points. Response to nCRT was reported using the Mandard system based on histopathologic evaluation of the resection specimen. Results To date, a total of 48 MRI scans of 8 patients with esophageal cancer were analyzed in this study. Most patients (5, 62.5%) had an adenocarcinoma, the remaining 3 patients (37.5%) had a squamous cell carcinoma. Mandard 1 was found at histopathological evaluation of the resection specimen in 3 patients (37.5%), Mandard 2 in 1 patient (12.5%), Mandard 3 and 4 both in 2 patients (25%). The percentage of change in tumor ADC values during nCRT with respect to the first MRI scan prior to treatment with nCRT is depicted in Figure 2. As highlighted in this figure, the difference in the change in tumor ADC values between good responders (Mandard 1 and 2) and to poor responders (Mandard 3 and 4) was most prominent in week 3 of nCRT (after 12-14 fractions). However, due to the limited number of patients enrolled, no statistical analyses could be performed to confirm these descriptive results. Figure 1: Study design

Conclusion The treatment-induced change in ADC during the first 3 weeks of nCRT for esophageal cancer seems most promising for prediction of histopathologic response. Our series is currently further extended to verify these results. OC-0179 Weekly, early assessment trends of FDG PET metrics and their relation to overall survival M. La Fontaine 1 , N. Bruin 1 , S.R. Van Kranen 1 , W. Vogel 2 , J. Knegjens 1 , J. Belderbos 1 , J. Van de Kamer 1 , J.J. Sonke 1 1 Netherlands Cancer Institute, Radiotherapy, Amsterdam, The Netherlands 2 Netherlands Cancer Institute, Nuclear Medicine, Amsterdam, The Netherlands Purpose or Objective Early response assessment of FDG PET may impact treatment options for patients with NSCLC. However, uncertainty exists in early response assessment in relation to the choice of imaging time point during treatment. In addition, the response of PET metrics from the beginning through the end of treatment is still unclear. This study aimed to investigate the response of PET metrics throughout treatment using weekly FDG PET scans. PET metrics were investigated for time points and trends associated with overall survival. Material and Methods The study included 22 patients with stage II-III NSCLC, who underwent concurrent chemoradiotherapy in 24 fractions of 2.75 Gy. During treatment, patients received five weekly FDG PET/CT scans from day 0 of treatment through day 28. Various PET metrics were measured at each time point, including SUVmax, total lesion glycolysis (TLG), SUVpeak, tumor volume, and SUVmean. Metrics were tested against one another for independence (r < 0.7). Linear regression was performed to determine the slope of each metric during treatment. For Kaplan-Meier survival analysis, the metrics were separated based on either the median slope or median metric value. Imaging time points were tested for PET metric association with overall survival with the Cox hazard ratio (HR) reported for significant differences. Results SUVmax and TLG were independent metrics for analysis. SUVmean (r=0.85) and SUVpeak (r=0.98) were highly correlated to SUVmax, while tumor volume was highly correlated to TLG (r = 0.83). Linear regression over the time points resulted in high correlation coefficients for both SUVmax (median: -0.90 [IQR:-0.95- -0.72]), and TLG (median: -0.95 [-0.97- -0.93]) (Figure 1). No associations to overall survival were found with SUVmax for any time point, slope, nor relative response. Overall survival was associated with a decrease as TLG increased. The absolute TLG slope was significantly associated with overall survival (p=0.001, HR =0.01), although absolute TLG values were not significant throughout treatment. In contrast, the relative TLG slope was marginally associated (p=0.09, HR=0.28) with overall survival, with relative values (Figure 2) being significant for the final