Dosimetric comparison of 3-dimensional conformal radiotherapy, volumetric modulated ARC therapy, and helical tomotherapy for postoperative gastric cancer patients

Poster Session, Sunday 29 January 2017 27.1%, respectively. Median pretreatment NLR and PLR were 3.6 (range 1.1–15.9) and 143.3 (range 42.3–846.4) respectively. Both NLR and PLR correlated significantly with tumor length, gross tumor volume, MTV and TLG value, while SUVmean was only correlated with PLR (p = 0.006). Both NLR and PLR were not correlated with primary tumor SUVmax . The 2-year overall survival (OS) and disease-free survival (DFS) rates were significantly higher in patients with NLR <3.6 compared to patients with NLR >3.6 (41.7% vs. 25.0%; p = 0.03 and 37.5% vs. 16.7%; p = 0.04, respectively). However 2-year OS (41.7% vs. 29.2%; p = 0.08) and DFS (37.5% vs. 20.8%; p = 0.17) for PLR subgroups did not differ significantly. A pretreatment NLR cut-point of 3.4 was determined for predicting disease recurrence (area under the curve [AUC] = 0.733, 95% CI 0.581–0.885; p = 0.02), with a sensitivity of 65.8% and a specificity 70.0%. For pretreatment PLR, the corresponding cut-point was 141.7 (AUC = 0.704, 95% CI 0.529–0.879, p = 0.04), with a sensitivity of 60.5% and a specificity of 60.0%. Conclusion: Pre-CRT NLR and PLR ratio correlated significantly with MTV and TLG value derivative of FDG-PET/CT, suggesting that larger tumors with higher glycolytic activities may also have higher inflammatory reactions leading to tumor progression and worse outcome. These hematologic parameters are a useful and relative cost effective in routine assessment of EC patients planned to be treated curatively. No conflict of interest. 616 POSTER Dosimetric comparison of 3-dimensional conformal radiotherapy, volumetric modulated ARC therapy, and helical tomotherapy for postoperative gastric cancer patients C. Onal1 , Y. Dolek1 , B. Akkus Yildirim1 . 1 Baskent University, Dept. of Radiation Oncology, Adana, Turkey Background: To compare dosimetric data for the planning target volume (PTV) and organs at risk (OARs) between 3-dimensional conformal radiotherapy (3DCRT), volumetric modulated arc therapy (VMAT), and helical tomotherapy (HT). Methods: We retrospectively analyzed dosimetric data for 15 gastric cancer patients whose postoperative treatment plans were generated using 3DCRT, VMAT, or HT. For all patients, the prescribed dose was 45 Gy delivered in 28 fractions. All plans were normalized to deliver 45 Gy to >95% of the PTV and 42.5 Gy to 99% of the PTV, but the PTV was not permitted to receive more than 115% of the prescribed dose (51.75 Gy). All plans were required to have the same PTV coverage. Cumulative dosimetric parameters, homogeneity index (HI), and conformal index (CI) were calculated and compared for the PTV and OARs. Results: For the PTV, the average maximum dose values were significantly higher in VMAT plans than in 3DCRT (p = 0.04) and HT (p = 0.02) plans, whereas minimum dose values were significantly lower in 3DCRT plans compared with VMAT (p < 0001) and HT (p = 0.02) plans. Mean HI was significantly higher in 3DCRT plans (0.11) compared with VMAT (0.07) and HT (0.06) plans. The HT plan achieved a superior CI (0.90) than did 3DCRT (0.76) and VMAT (0.76) plans. Liver Dmean, V20, and V30 values were significantly lower in HT plans than in 3DCRT and VMAT plans (all p < 005). Although liver V20 values were significantly higher in VMAT plans than in 3CRT plans (p = 0.03), the difference in Dmean and V30 between 3DCRT and VMAT plans did not differ significantly. The Dmean values of both kidneys were lower in HT plans than in 3DCRT and VMAT plans (all p < 005 except right kidney VMAT vs. HT [p = 0.05]). Although the left kidney Dmean was significantly lower in VMAT plans than in 3DCRT plans (p < 0001), there were no significant differences in the right kidney Dmean between these two techniques. V20 values for each kidney were better in VMAT and HT plans than in 3DCRT plans (all p  0.01); however, no difference in V20 was observed between VMAT and HT plans. Conclusions: The HT plans reduced the maximum dose applied to the target area and improved the conformality and homogeneity of radiation, while providing sufficient PTV coverage. Moreover, compared with 3DCRT and VMAT, HT significantly reduced liver and left kidney Dmean values. No conflict of interest. 617 POSTER Radiation-related lymphopenia association with worse prognosis in unresectable hepatocellular carcinoma patients Q. Zhao1,2 , X. Xu2 , J. Yue2 , H. Yan2 , R. Feng2 , Z. Qi1,2 , K. Zhu2 , S. Jiang2 , R. Wang2 . 1 University of Jinan-Shandong Academy of Medical Sciences, School of Medicine and Life Sciences, Jinan, China; 2 Shandong Cancer Hospital affiliated to Shandong University, Department of Radiation Oncology, Jinan, China Background: Effects of ionizing radiation on the immune system had showed both stimulation and suppression. The mechanisms of

Abstracts

S81

immunosuppressive effect are complex, in which apoptosis of circulating lymphocytes induced by radiation may plays an important role. Thus we examined the relationship between the minimum of absolute lymphocyte counts (Min ALCs) during radiotherapy (RT) and clinical outcomes in the patients with hepatocellular carcinoma (HCC). Material and Methods: A total of 69 HCC patients who had received RT were retrospectively analyzed. Peripheral blood lymphocyte was measured before, weekly during and after RT. Regression and mixed effects models were used to assess the relationship and potential predictors for overall survival(OS). Receiver operating characteristic curve analysis was used to define optimal cutoff points of continuous variables for outcomes. Results: The average value of circulating lymphocyte counts was declined during RT (1493.19 vs. 503.48 cells/uL, P < 0001). Lower Min ALCs level was associated with worse OS (P = 0.001), with the cutoff value of 450 cells/uL (sensitivity and specificity, 50% and 70.6%, respectively). The MST, 1-year OS rate and 2-year OS rate were 15 months vs 47 months, 27% vs 78% and 4% vs 71%, respectively (P < 0001) in relatively lower Min ALCs level (450 cells/uL) group and higher Min ALCs level (>450 cells/uL) group. Controlling for age, sex and performance status, Barcelona Clinic Liver Cancer (BCLC) score, higher serum AFP level (>400 ng/ml) before RT and a lower serum Min ALCs level (450 cells/uL) during RT were independent negative prognostic factors for OS (all P < 005). Conclusions: Radiation-related lymphopenia may act as a worse prognostic factor for HCC after RT. No conflict of interest. 617A POSTER Acute toxicity of the bowel after stereotactic radiotherapy for abdominopelvic oligometastases M. Frelinghuysen1 , W. Schillemans2 , L. Hol3 , C. Verhoef4 , M. Hoogeman2 , J. Nuyttens1 . 1 Erasmuc MC, Radiation Oncology, Rotterdam, Netherlands; 2 Erasmus MC, Radiation Oncology, Rotterdam, Netherlands; 3 Erasmus MC, Gastroenterology, Rotterdam, Netherlands; 4 Erasmuc MC, Surgical Oncology, Rotterdam, Netherlands Purpose: To correlate dose-volume histogram (DVH) parameters with appearance of grade 2 acute gastrointestinal toxicity of stereotactic body radiotherapy (SBRT) in patients with solitary or abdominopelvic oligometastatic disease. Methods and Materials: Acute and late bowel toxicity of 84 abdominopelvic oligo metastatic patients was registered. A logistic regression was performed between DVH parameters and presence of grade 2 acute toxicity. The odds of acute toxicity per cm3 were estimated. A Normal Tissue Complication Probability (NTCP) model was built with the most significant parameter to determine complication probabilities (CP). Results: Thirteen of 84 patients experienced grade 2 acute toxicity, while 8 reported late toxicity complications. A significant relationship was found for EQD2 (V30 Gy, V40 Gy, V50 Gy and V65 Gy) and grade 2 acute toxicity. Dmax and D2 were not significant. According to the NTCP model, an irradiated volume of 10 cm3 resulted in grade 2 acute toxicity of less than 10%. Local control was 87% at 2 years and 82% at 5 years. Overall survival was 61% at 2 years and 32% at 5 years. Conclusion: In SBRT for abdominopelvic oligometastases, a significant relationship was found for EQD2 (V30 Gy, V40 Gy, V50 Gy and V65 Gy) grade 2 acute toxicity with good local control. No conflict of interest. 618 POSTER Radiation pneumonitis in patients with esophageal cancer after intensity modulated radiotherapy − incidence and correlation with DVH parameters J. Tonison1 , S.G. Fischer1 , B. Klumpp2 , M. Viehrig1 , D. Zips1 , C. Gani1 . University Hospital Tubingen, ¨ Radiation Oncology, Tubingen, ¨ Germany; 2 University Hospital Tubingen, ¨ Radiology, Tubingen, ¨ Germany 1

Background: Radiation pneumonitis (RP) is a serious complication that can occur after thoracic radiotherapy. Most data on RP is derived from 3D conventional radiotherapy of lung cancer and data on RP after IMRT of esophageal cancer is sparse. Therefore this study investigates the prevalence of RP in patients with esophageal cancer after IMRT and correlates this with dose volume histogram (DVH) parameters. Material and Methods: In this retrospective study, we included patients with esophageal cancer who were treated at the University Hospital of Tuebingen between 2006 and 2013. Patients received either definitive or neoadjuvant radiochemotherapy. Patient charts were screened for clinical signs of radiation pneumonitis during follow-up and DVH parameters of the lungs (V5-V65, MLD) were extracted from treatment plans. Furthermore