Abstract Book

S807

ESTRO 37

cancer patients undergoing concurrent chemo- radiotherapy (RT-CT). Material and Methods A total of 161 patients with clinical stage T1-T4/N0- N3/M0 were treated according to the Nigro’s regimen. Response to treatment was assessed at 2 time-points: at 6 weeks and 3 months after RT-CT. Two different radiation approaches were used: a) a simultaneous integrated boost (SIB) strategy with dose prescription following the RTOG 0529 indications; b) a first sequence of RT, delivering 45 Gy/25 fractions (1.8 Gy/fr) to the macroscopic primary and nodal tumor and prophylactic volumes. In the second sequence, an adjunctive dose of 9-14.4 Gy in 5-8 fractions was delivered sequentially to the macroscopic disease up to 54-59.4 Gy. Results Mean baseline Hb was 13.1 g/dl. Complete (CR) and partial response (PR) rates were 76.4% and 17.4%. Median follow-up was 27 months. Three- and 5-year Progression- Free Survival (PFS) were 71.9%; 3- and 5-year Overall Survival (OS) were 83.1% and 76.1%. On univariate analysis, baseline Hb levels (continuous variable) had a significant correlation to both PFS (HR:0.57;p=0.049) and OS (HR:0.53;p=0.047). On multivariate analysis, baseline Hb was significantly correlated to OS (HR:0.50;p=0.0051), but not to PFS (HR:0.80;p=0.40). Comparison of mean pre-treatment Hb values for patients with a CR (mean:13.2g/dl) and those without (mean:12.9 g/dl and 11.7 g/dl for stable disease/progressive disease) showed a significant difference (t-test,p=0.013). Employing a cut- off point at Hb=12g/dl, patients with pre-treatment Hb>12 g/dl had a 5-year PFS of 82.2% vs 29.3% for those with Hb<12 g/dl. Five-year OS was 82.2% for patients with Hb>12 g/dl and 32.8% for those below the cut-off point (Fig.1). Weighted linear regression between CR rate and mean Hb values (Fig.2), showed a positive trend, with the likelihood of response increasing at higher Hb values (p=0.11). Analyzing the slope of the linear regression curve and the intercept, the lowest Hb level category had a 55% chance to achieve a CR after CT-RT. This likelihood increased by 5.6% for every single-unit (g/dl) increase in Hb level .

Conclusion Pre-treatment Hb levels were significantly correlated to overall survival. A 50% decrease in the risk of death at each time-point for a single unit increase in Hb was found. The effect was also observed for Hb levels above 11 g/dl. Hb level is associated to the likelihood of achieving a CR, an independent prognostic factor for survival. The chance to achieve a CR increases by 5.6% for every single-unit increase in Hb level. Conversely, low Hb levels do predict for worse outcome. EP-1488 A matched pair analysis of hypofractionated IMRT-SIB versus concomitant boost in rectal cancer L. Nicosia 1 , C. Reverberi 1 , L. Marinelli 1 , V. De Sanctis 1 , G. Minniti 1 , M. Valeriani 1 , M.F. Osti 1 1 University of Rome "Sapienza", Radiation Oncology, Roma, Italy Purpose or Objective T o compare treatment outcome and toxicity between a hypofractionated neoadjuvant radiochemotherapy (hN- RCT) with IMRT-SIB and conventionally fractionated neoadjuvant radiochemotherapy (cN-RCT) with concomitant boost, through a retrospective matched-pair analysis. Concomitant fluoropyrimidine was administered in both regimens. Material and Methods Between April 2014 and February 2017, 62 patients with locally advanced rectal cancer who were treated with a hN-RCT regimen (55 Gy in 2.2 Gy/fr) were individually matched with 62 patients with locally advanced rectal cancer treated with cN-RCT with concomitant boost (45 Gy in 1.8 Gy/fr plus 1 Gy biweekly boost up to 10 Gy), according to clinical stage (as determined by pelvic MRI and CT scan), distance from anal verge and age. All these patients performed surgery 8-10 weeks after the completion of chemoradiotherapy. Pathological complete response rate, downstaging, treatment and surgery- related toxicity, local control, MFS, DFS and OS were evaluated. Results Median follow-up was 20 and 28 months for hN-RCT and cN-RCT, respectively. Pathologic complete response and T-downstaging rates were 29% versus 16,1% (P=0.08) and 75% versus 48,3% (P=0,003) in the hN-RCT and cN-RCT cohorts, respectively. Actuarial 2 years local control is 98,4% and 96,85 (P=0,34). No significant differences is OS, DFS and MFS are reported. No differences in acute and late G3-4 toxicity were observed (11,2% and 9,6% for hN-RCT and cN-RCT, respectively). No differences in surgical morbidity and time to the recanalization were observed.