Abstract Book

ESTRO 37

S394

1 Istituto Clinico Humanitas, Radiotherapy and Radiosurgery, Rozzano Milan, Italy

recurrence within the primary regions. However, these patients may not be amenable for surgery or chemotherapy due to its poor response rates and toxicities. Furthermore, conventional radiotherapy may not be appropriate in the setting of re-irradiation of pancreatic cancer owing to its inclination to exceed dose constraints of organs at risk resulting in severe adverse effects, while SBRT has been taken as the option for re- irradiation of pancreatic cancer. Therefore, the aim of the study was to develop a novel score predicting potential survival benefits for decision making of re- irradiation with stereotactic body radiation therapy (SBRT) for pancreatic cancer. Material and Methods From 2012 to 2015, 25 patients received two courses of SBRT due to recurrence at the same irradiated region (the primary lesion) were included and formed re- irradiation group of the training cohort. Besides, 50 patients treated with one course of SBRT with overall survival more than 12 months were selected as the control group of the training cohort for further comparison. Cox proportional hazards regression was used to identify factors predictive of survival. Results were then verified in the validation cohort (260 patients from 2015 to 2016). Results The median overall survival (OS) of the re-irradiation and control group was 22.5 months and 29.5 months, respectively. Regarding re-irradiation group, the median prescription dose and BED 10 at the first SBRT were 36Gy (range: 30-45Gy) and 59.5Gy (range: 48-85.5Gy), in 5-6 fractions respectively. The median prescription dose and BED 10 at the second SBRT were 32Gy (range: 25-40Gy) and 50.22Gy (range: 37.5-72Gy) in 5-6 fractions, respectively. In the control group, the median prescription dose and BED 10 were 36.5Gy (range: 30-46.8Gy) and 63.15Gy (range: 48-88.32Gy) in 5-6 fractions, respectively. After Cox regression analysis, ECOG (before the first SBRT), history of previous treatment, CA19-9 response and tumor response correlated with survival and used to create the CAPER-score (named after acronyms of included factors). In the training cohort, patients with a CAPER-score of 0-7.0 points had a 2-year OS rate of 89.5% (95% CI: 74.3%-95.9%), while those with a CAPER-score of >7.0 points had a 2-year OS rate of 29.7% (95% CI: 16.4%-44.3%; P <0.001). In the validation cohort, the median OS of patients with a CAPER-score of 0-7 points was 11.2 months (95%: 10.5-11.9 months), which was longer than that of patients with >7 points (6.6 months, 95% CI: 6.2-7.0 months; P <0.001). Additionally, in both cohorts with varied tumor stages, prescription doses and nutritional status, longer survival was found in patients with a CAPER-score of 0-7 points. Conclusion Patients with a CAPER-score of 0-7 points prior to the second SBRT may benefit from further SBRT. PO-0764 Treatment sequences and strategies for locally advanced unresectable pancreatic cancer X. Zhu 1 , L. Fuqi 1 , S. Dongchen 1 , J. Xiaoping 1 , C. Yangsen 1 , S. Yuxin 1 , C. Fei 1 , Q. Shuiwang 1 , F. Fang 1 , J. Zhen 1 , Z. Huojun 1 1 Changhai Hospital, Radiation Oncology, Shanghai, China Purpose or Objective Despite potential survival benefits over radiotherapy or chemotherapy alone produced by concurrent chemoradiotherapy, contrary conclusions were also clarified. As a result, there is no consensus on the optimal management of locally advanced pancreatic cancer (LAPC). Although chemotherapy and radiotherapy have played a pivotal role in the treatment for patients with LAPC, several controversial issues remain unresolved. Particularly, the best up-front combined

Purpose or Objective Colorectal cancer (CRC) is the third most common malignancy worldwide. Thirty to 70 % of patients affected by CRC will develop liver metastases, often isolated sites of disease. In patients not suitable for resection of metastases both thermal ablation and Stereotactic body radiation therapy (SBRT) demonstrated high rates of control of disease. The outcome after treatment with SBRT seems not to be affected by the size of lesions. Considering that Microwave ablation (MWA) seems to be more efficient in the treatment of larger lesions compared to Radiofrequency ablation (RFA). The study aim was to compare the disease control in two groups of patients affected by liver metastases from CRC treated with SBRT or MWA. Material and Methods We conducted a retrospective comparative analysis of all patients with CRC liver metastases who underwent either MWA or SBRT between January 2009 to October 2016 from a prospectively maintained registry database . Inclusion criteria were: 1) maximum diameter of the liver lesions less than 4 cm; 2) no more than 3 liver lesions; 3) no evidence of progressive or untreated gross disease outside the liver; 4) no concurrent chemotherapy; 5) minimum age of 18. Tumour response was classified according to European Organization for Research and Treatment of Cancer Response Evaluation Criteria In Solid Tumours (EORTC-RECIST) criteria version 1.16. Toxicity was classified according to Common Terminology Criteria for Adverse Events (CTCAE) version 3. Results A total of 135 patients with 214 liver lesions were included in the analysis. Patients were more likely treated with SBRT if they were male and older than 70 years old. MWA was more likely the treatment of choice in case of smaller lesion and in the presence of one single metastasis. Median follow-up time was 24.5 months (range 2.4 – 95.8). A total of 41 lesions relapsed after the treatment (21 for MWA group and 20 for SBRT group). The 1-year FFLP was 88% (95%CI 80 – 92). In the SBRT group, FFLP was statistically longer than MWA group (p = 0.0214), the 1-year FFLP was 91% (95%CI 81 - 95) in SBRT group and 84% (95%CI 0.72 - 0.91 in MWA group. Patients treated with SBRT showed a reduce risk of local relapse compared to MWA (adjusted HR 0.31; 95%CI 0.13 - 0.70, p= 0.005). As expected analogous result, was obtained in the inverse probability weighting analysis (HR 0.38; 95%CI 0.18 - 0.80; p = 0.011). Stratified analysis by lesion dimension confirmed the better prognosis in SBRT than in MWA group in patients with at least one lesion bigger than 30 mm and not in patients with all lesions equal or smaller than 30 mm. Conclusion In conclusion, there seems to be an advantage of SBRT compared to MWA in treating CRC liver metastases, particularly for lesions bigger than 30 mm. For this reason SBRT may be considered the option to choose in case of inoperable big lesions. PO-0763 The assessment of re-irradiation with stereotactic body radiation therapy for pancreatic cancer X. Zhu 1 , S. Dongchen 1 , J. Xiaoping 1 , C. Yangsen 1 , S. Yuxin 1 , C. Fei 1 , Q. Shuiwang 1 , F. Fang 1 , J. Zhen 1 , Z. Huojun 1 1 Changhai Hospital, Radiation Oncology, Shanghai, China Purpose or Objective Despite advances of management of pancreatic cancer, disease recurrence is still the predominant cause of death. A significant number of patients may develop local