ESTRO 2020 Abstract Book

S573 ESTRO 2020

majority of departments (97%). The prescribed doses to the elective lymph node CTV ranged considerably from 30.6 Gy to 52.8 Gy, whereas the dose range for the involved lymph node CTV ranged from 30.6 to 59.4 Gy, but 87% of institutions prescribed doses from 50.4 – 55. 8 Gy. The dose to gross disease of cT1 or cT2 ASCC ranged from 50 to more than 60 Gy and for cT3 or cT4 tumors the target dose ranged from 54 to more than 60 Gy. Brachytherapy as alternative to a percutaneous boost is used in 15 (14.8%) departments. The majority of departments use 5- FU/Mitomycin C as chemotherapy, whereas 6 (6%) departments prescribed Capecitabine/Mitomycin C. HIV positive patients are treated with standard CRT without dose reduction in 87 (86.1%) institutions, whereas 5 (4.9%) institutions use a reduced dose of chemotherapy and another 5 (4.9%) did not prescribe concurrent chemotherapy. Regarding the timepoint for assessing whether the patient had a clinical remission (CR) or residual disease, 2 (2%) institutions use 4-6 weeks after end of treatment, 20 (19.8%) use 6-8 weeks after end of treatment and 79 (78%) wait up to 5 months after end of We observed several differences in radiotherapy doses, treatment technique and how HIV positive patients were treated among German-speaking radiation oncology institutions. These data further underline the need for an international consensus treatment guideline for ASCC. PO-1082 Identification of Cell-Free DNA profile in oligometastatic colorectal cancer M. Nakamura 1 , S. Kageyama 1 , A. Motegi 1 , H. Hojo 1 , T. Akimoto 1 1 National Cancer Center Hospital East, Radiation Oncology, Kashiwa-shi, Japan Purpose or Objective The optimal selection of patients who are suited for oligometastasis-directed ablative therapy remains a challenge. In recent years, liquid biopsy approaches analyzing cell-free DNA (cfDNA) from the blood samples of patients with cancer are increasingly utilized in clinical practice to predict metastatic potential of disease or prognosis. The purpose of this study was to determine the profile of cfDNA using next-generation sequencing of plasma cfDNA in patients with oligometastatic colorectal cancer (CRC) and investigate its association with progression-free survival (PFS) after ablative therapy. Material and Methods We analyzed oligometastatic CRC patients who underwent definitive irradiation using stereotactic body radiotherapy or proton beam therapy for metastatic lesion at National Cancer Center Hospital East in Japan between December 2011 and December 2017. In this study, cfDNA was purified from 4ml patient plasma and fragmented DNA was ligated with adapters to make libraries. Library construction and sequencing were performed using the Illumina Novaseq 6000 sequencing platform (Illumina, San Diego, CA) with SureSelect NCC oncopanel v.2 which can investigate 114 genes exon. We aligned FASTQs to the human genome (hg19), and identified point mutations using Sure call 4.1.1.5. Clinical data was extracted from medical records. PFS was statistically compared according to sequence data. Results A total of 20 patients with oligometastatic CRC (median age 72 [range, 54-85] years; 12 [60%] male) were included in this study. The median amount of cfDNA was 42.1 (range, 25.3-100.8) ng. The mutation of cfDNA were detected as follows; TP53 (9/20: 45%), APC (8/20: 40%), KRAS (3/20: 15%), PIK3CA (3/20: 15%), NF1 (1/20: 5%), BRCA1 (1/20: 5%), ERBB2 (1/20: 5%), FBXW7 (1/20: 5%), and KIT (2/20: 10%), respectively. Allele frequency was 0.6-7.8% (median 1.5%). Clonal mutations were confirmed in 11 cases and multiclonal mutations in 5 cases. The treatment. Conclusion

median follow-up period was 18 months for surviving patients (range, 3-71 months). The median PFS duration was 10 months (95%CI: 5- NA). The amount of cfDNA, number of mutations, and types of mutated genes were not associated with PFS. Multi clonality of the gene mutation showed tendency of poor PFS (14 vs 4 months, HR 3.1 [95%CI: 0.8-11.3], p=0.07). Conclusion This is the first study regarding genomic profiling of cfDNA from patients with oligometastatic colorectal cancer. Pre- irradiation cfDNA analysis would be predictive tool for early recurrence of oligometastatic CRC, although further accumulation of data are needed. PO-1083 Efficacy and tolerance of VMAT-SIB intensified neoadjuvant chemoradiation in rectal cancer patients A. Re 1 , V. Picardi 1 , F. Deodato 1 , A. Ianiro 2 , S. Cilla 2 , M. Boccardi 1 , M. Ferro 1 , A. Arcelli 3 , M. Buwenge 3 , S. Cammelli 3 , C. Romano 2 , G. Restaino 4 , M. Ferro 1 , M. Specchia 5 , A. Guido 1 , S. Mignogna 6 , V. Valentini 7 , A.G. Morganti 3 , G. Macchia 1 1 Fondazione "Giovanni Paolo II"- Università Cattolica del Sacro Cuore, UO di Radioterapia, Campobasso, Italy ; 2 Fondazione "Giovanni Paolo II"- Università Cattolica del Sacro Cuore, UO di Fisica Sanitaria, Campobasso, Italy ; 3 DIMES- Azienda Ospedaliera-Universitaria S.Orsola- Malpighi-, U.O. di Radioterapia – Dipartimento di Medicina Specialistica Diagnostica e Sperimentale- DIMES- Azienda Ospedaliera-Universitaria S.Orsola- Malpighi, Bologna, Italy ; 4 Fondazione "Giovanni Paolo II"- Università Cattolica del Sacro Cuore, UO di Radiologia, Campobasso, Italy ; 5 PO ‘Cardarelli’, UO di Oncologia Medica, Campobasso, Italy ; 6 Fondazione "Giovanni Paolo II"- Università Cattolica del Sacro Cuore, UO di Oncologia Medica, Campobasso, Italy ; 7 Fondazione Policlinico Universitario A. Gemelli- IRCCS, UOC di Radioterapia- Dipartimento di Scienze Radiologiche- Radioterapiche ed Ematologiche, Roma, Italy Purpose or Objective To assess the pathological complete response (pCR) and the toxicity profile of preoperative capecitabine-based intensified volumetric modulated arc therapy (VMAT) radiotherapy using simultaneous integrated boost (SIB) technique in locally advanced rectal cancer (LARC) patients (pts). Material and Methods Pts with cT2N+ or cT3T4N0-2 were enrolled into the protocol. Elective lymph nodes and the entire mesorectum received a total dose of 45 Gy at 1.8 Gy/fraction, while gross disease and the correspondent mesorectum were boosted with 57.5 Gy at 2.3 Gy/fraction. Capecitabine (1650 mg/mq/die) was prescribed throughout the whole radiotherapy treatment. Acute and late toxicities were recorded according to CTC-AE scale. Surgery was planned at least 7-8 weeks after the chemoradiotherapy (CRT) end. Results 21 LARC pts (median age: 67 years, range 42-81 years; Male/Female ratio:14/7) entered the analysis. The vast majority of pts had a cT3 tumor (N=16, 76%) with lymph nodal involvement in 90% of cases (cN1: 15 pts, cN2: 4 pts). All patients completed the prescribed treatment; overall, most of them (16 pts, 76%) suffered from mild gastrointestinal toxicity, while 2 pts (10%) from G3 adverse events. Genitourinary and hematological toxicities were less frequent, with 5 pts (24%) referring G1 dysuria and 1 pt (5%) G1 leucopenia. Twenty patients (95%) underwent surgery, after a median interval of 12 (range 7-19) weeks from the CRT’s end. Anterior or abdominoperineal resections were performed in 18 (86%) and in 2 (10%) cases, respectively. One pt (5%), having metastatic disease at re- evaluation, was judged unfit for surgery and started to systemic therapy. Six pts (29%) obtained a pCR, while TRG