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• SABR provides high rates of local control to lung oligometastases. • Local control of colorectal lung metastases seems lower compared to other tumors. • We identified predictive factors of SABR response and polymetastases development. • Predictive factors of local control are BED ≥125 Gy and lesion diameter ≤20 mm. • Having lesion >20 mm and 4–5 metastases predicted for a polymetastatic evolution. Stereotactic ablative radiotherapy (SABR) has been shown to increase survival in oligometastatic disease, but local control of colorectal metastases remains poor. We aimed to identify potential predictive factors of SBRT response through a multicenter large retrospective database and to investigate the progression to the polymetastatic disease (PMD). The study involved 23 centers, and was approved by the Ethical Committee (Prot. Negrar 2019-ZT). 1033 lung metastases were reported. Clinical and biological parameters were evaluated as predictive for freedom from local progression-free survival (FLP). Secondary end-point was the time to the polymetastatic conversion (tPMC). Two-year FLP was 75.4%. Two-year FLP for lesions treated with a BED < 00 Gy, 100–124 Gy, and ≥125 Gy was 76.1%, 70.6%, and 94% (p = 0.000). Two-year FLP for lesion measuring ≤10 mm, 10–20 mm, and >20 mm was 79.7%, 77.1%, and 66.6% (p = 0.027). At the multivariate analysis a BED ≥125 Gy significantly reduced the risk of local progression (HR 0.24, 95%CI 0.11–0.51; p = 0.000). Median tPMC was 26.8 months. Lesions treated with BED ≥125 Gy reported a significantly longer tPMC as compared to lower BED. The median tPMC for patients treated to 1, 2–3 or 4–5 simultaneous oligometastases was 28.5, 25.4, and 9.8 months (p = 0.035). The present is the largest series of lung colorectal metastases treated with SABR. The results support the use of SBRT in lung oligometastatic colorectal cancer patients as it might delay the transition to PMD or offer relatively long disease-free period in selected cases. Predictive factors were identified for treatment personalization. [ABSTRACT FROM AUTHOR]

Poster: Clinical track: Upper GI (oesophagus, stomach, pancreas, liver) PO-1062: Stereotactic body radiotherapy can delay polymetastatic conversion in liver oligometastatic patients L. Nicosia, F. Cuccia, V. Figlia, N. Giaj-Levra, R. Mazzola, F. Ricchetti, M. Rigo, M. Bonù, F. Alongi. [Extracted from the article]

B TYPE: b Abstract Publication B TOPIC: b Lung Cancer B PURPOSE: b Stereotactic body radiotherapy (SBRT) is a standard treatment for inoperable early-stage NSCLC, with local control rates comparable to surgical series. B CONCLUSIONS: b The results of our study indicated a high local control, survival and tolerability after a long-term follow-up with the use of SBRT 30 Gy single dose. B CLINICAL IMPLICATIONS: b Single dose SBRT is a promising and useful technique in the treatment of early stage NSCLC with high efficacy and limited side effects B DISCLOSURE: b No significant relationships. [Extracted from the article]

Objectives To evaluate the local control (LC) and long term adverse effects in a series of patients with lung metastases who received 30 Gy in single dose with stereotactic technique. Materials and Methods Between December 2008 and April 2016, a total of 166 lung metastases in 129 patients affected by oligometastatic disease were treated at our Institution with stereotactic body radiotherapy (SBRT). Mainly, the primary tumors were non small-cell lung cancer and colorectal cancer (45.2% and 28.8%, respectively). Prognostic factors were also assessed. Results The median follow-up was 38 months. Local progression occurred in 24 (14.4%) lesions in 21 patients. Intra-thoracic progression (new lung lesions or thoracic lymph node metastases) occurred in 59 (45.7%) patients. Forty-five (34.8%) patients had distant progression after a median time of 14 months. The 3- and 5-years local relapse-free survival (LPFS) were 80.1% and 79.2% (median not reached), respectively. One-hundred forty-eight patients were evaluated for late toxicity (follow-up >6 months): 51 (34.4%) patients had grade ≤2 fibrosis, 11 (7.4%) patients experienced grade 3 fibrosis. Two (1.3%) cases of rib fracture occurred. One case of toxic death (grade 5) has been reported. Median OS was 39 months. At the univariate analysis, lesion diameter ≤18 mm correlated significantly with a longer LPFS (p = 0.001). At the multivariate analysis, lesion diameter <18 mm was predictive for longer LPFS (p = 0.006). Also, oligometastases from primary colorectal cancer was a significant predictive factor for worse LPFS (p = 0.041) and progression-free survival (p = 0.04). Conclusions To our knowledge, the current study represents the largest series on the use of SBRT 30 Gy single dose for lung metastases. Our results confirm the effectiveness and safety of this schedule administered in selected oligometastatic patients. Further prospective series could better validate these results. [ABSTRACT FROM AUTHOR]

Poster: Clinical track: Palliation PO-1256: Feasibility and initial results of Linac-based Stereotactic Body Radiotherapy in spinal metastases N. Giaj Levra, M. Niyazi, V. Figlia, G. Napoli, R. Mazzola, L. Nicosia, S. Corradini, R. Ruggieri, G. Minniti, F. Alongi. [Extracted from the article]

Purpose/objective(s): MR-guided radiotherapy is a potential game changer in the field of radiation oncology, given the optimal visualization of the pelvic anatomy and the possibility to daily recalculate the plan based on real-time anatomy conditions. We report preliminary dosimetric data concerning the use of 1.5-T MR-guided daily-adaptive radiotherapy for abdomino-pelvic lymph-nodal oligometastases. We aimed to assess the impact of this technology on mitigating daily variations for both target coverage and organs-at-risk (OARs) sparing.Materials/methods: A total of 150 sessions for 30 oligometastases in 23 patients were analyzed. All patients were treated with MR-guided stereotactic body radiotherapy (SBRT) for a total dose of 35 Gy in 5 fractions. For each fraction, a quantitative analysis was performed for PTV volume, V35 Gy and Dmean. Similarly, for OARs we assessed daily variations of volume, Dmean, Dmax. Any potential statistically significant change between baseline planning and daily-adaptive sessions was assessed using the Mann-Whitney test, assuming a P-value < 0.05 as significant.Results: Median baseline PTV, bowel, bladder and single intestinal loop (in the case of targets very close to intestine) volumes were respectively 6.2cc (range, 0.7-41.2cc), 993cc (119-3654cc), 75cc (39.7-202.9cc), 15.7cc (9.1-37.7cc). No significant volume variations were detected for PTV (P = 0.17) bowel (P = 0.12), bladder (P = 0.14) and single intestinal loops (P = 0.21). Median baseline V35 Gy and Dmean for PTV were respectively 83.75% (72-98.8%) and 35.6 Gy (34.6-36.1 Gy). We recorded a positive trend in favor of daily-adaptive strategy vs baseline planning for improved target coverage (P = 0.06 and P = 0.07 for PTV-V35 Gy and PTV-Dmean). Concerning OARs, a significant difference was observed in favor of daily-adapted treatments in terms of single intestinal loop Dmax [26.9 Gy (13.2-26.9 Gy) at baseline vs 24 Gy (12.1-24 Gy); P = 0.014] and Dmean [16 Gy (6.518 Gy) at baseline vs 13.7 Gy (6.7-17.6 Gy); P = 0.0016]. For both bladder and bowel no significant differences were observed for Dmax and Dmean: for bladder, median Dmax was 15.3 Gy (0.4-34.3 Gy) at baseline vs 14.6 Gy (0.7-34.3 Gy), P = 0.24; median Dmean was 2.2 Gy (0.2-16.6 Gy) at baseline vs 2.2 Gy (0.2-16.4 Gy), P = 0.30. Similarly for bowel, no differences in terms of Dmax [28.7 Gy (7.7-34 Gy) vs 27.9 Gy (7.8-33.1 Gy); P = 0.06] and Dmean [4.3 Gy (1.3-10.9 Gy) vs 3.9 Gy (1.4-10.5 Gy); P = 0.25] were observed.Conclusion: Daily-adaptive MR-guided SBRT reported a significantly improved single intestinal loop sparing for lymph-nodal oligometastases. A minor advantage was also reported in terms of PTV coverage, although not statistically significant. The potentially improved safety profile of MR-guided SBRT may lead the way to propose ultra-hypofractionated schedules or single fraction treatments.Author Disclosure: F. Cuccia: None. M. Rigo: None. D. Gurrera: None. L. Nicosia: None. V. Figlia: None. N. Giaj-Levra: None. R. Mazzola: None. F. Ricchetti: None. G. Attinà: None. A. De Simone: None. S. Naccarato: None. G. Sicignano: None. R. Ruggieri: Honoraria; Elekta, Stockholm, Sweden. Consultant; Elekta, Stockholm, Sweden. F. Alongi: Honoraria; Elekta, Stockholm, Sweden. Consultant; Elekta, Stockholm, Sweden. [ABSTRACT FROM AUTHOR]

Poster: Clinical track: Prostate PO-1163: 68Ga-PSMA PET-Guided metastases directed stereotactic body radiotherapy in prostatic cancer patients M. Rigo, R. Mazzola, V. Figlia, L. Nicosia, N. Giaj-Levra, F. Ricchetti, C. Francesco, F. Alongi. [Extracted from the article]