ESTRO 36 Abstract Book

S486 ESTRO 36 _______________________________________________________________________________________________

1 San Raffaele Scientific Institute, Medical Physics, Milan, Italy 2 San Raffaele Scientific Institute, Radiotherapy, Milan, Italy 3 San Raffaele Scientific Institute, Nuclear Medecine, Milan, Italy Purpose or Objective To investigate the predictive role of early changes of 18 F- fluorodeoxyglucose (FDG) positron emission tomography (FDG-PET) based biomarkers in locally advanced pancreatic carcinoma (LAPC) patients (pts) treated with induction and concomitant chemo-radiotherapy (CRT) on overall survival (OS), local relapse free survival (LRFS), distant relapse free survival (DRFS) and progression free survival (PFS). Material and Methods Data of 39 pts included in an Institutional trial were considered. Most pts (92%) received neoadjuvant chemotherapy, followed by CRT. Pts received 44.25Gy in 15 fractions to the tumor: a simultaneous integrated boost (SIB) to the sub-volume infiltrating the great abdominal vessels up to 48-58Gy was delivered in 17/39 pts. FDG- PET-CT was performed in all pts before (PET_pre) and after CRT (PET_post), at a median time of 3-months after the end of CRT. The predictive value of the % difference of FDG-PET parameters between PET_post and PET_pre was investigated, including maximum standard uptake value (∆SUVmax), metabolic tumor volume (∆MTV) and total lesion glycolysis (∆TLG), these last twos estimated considering different uptake thresholds (40-50-60%) of SUVmax. The % difference between gastrointestinal cancer-associated antigen (GICA) levels measured at roughly the same timing of PET scan (pre and post) was also considered. For each parameter, median ∆ values were used to categorize the pts in high vs low risk groups: logrank tests and univariable Cox regression analyses were performed to assess the prognostic value of the considered parameters on OS, LRFS, DRFS and PFS. Results The median follow-up was 11 months (range: 3.7-106); the median age was 63 years (35-84). Median OS, LRFS, DRFS and PFS after the start of CRT were 22, 10, 4.3, 5.3 months, respectively. No uptake was present at PET_pre in 9 pts: a longer median time to progression for PET negative pts (9.0 vs 3.7 months, p =0.06) was found compared to pts with positive PET_pre. Focusing on the 30/39 pts with positive PET-pre, ∆MTV-60 was the most significant predictor of LRFS ( p =0.007; RR=0.16) and PFS ( p =0.04; RR=0.41). Median LRFS were 4.3 and 23 months for pts with ∆MTV-60< 35% and pts with ∆MTV-60> 35%, respectively ( p =0.002; RR=3.8, Figure1); the corresponding median PFS were 3.2 vs 6.7 months ( p = 0.03; RR=2.2, Figure2). ∆TLG-50 and ∆TLG-60 showed borderline significance in predicting OS ( p = 0.05; RR=0.33). No correlation was found between the % variation of PET parameters and DRFS while the % change of GICA levels was a significant predictor ( p =0.03; RR=0.28). Conclusion The early assessment of FDG-PET biomarkers response predicts clinical outcome in LAPC pts, except DRFS. The early variation of GICA values predicts DRFS suggesting that the integration of the information concerning early changes of PET biomarkers and GICA may be useful in identifying patients at higher risk of early local and/or distant relapse and to discriminate the pattern of relapse.

Conclusion Tumor voxel metabolic ratio determined us ing multiple FDG PET images can be used to assess tumor voxel dose response, SF2, which shows an excellent predictive value for tumor local radioresistance and failure. Our results demonstrate that a heterogeneous dose distribution in tumor should be prescribed to optimize cancer radiotherapy. Tumor voxel TMR determined at the early treatment will be good bio-parametric matrix to determine a new tumor dose prescription function at the voxel level for the treatment of adaptive dose-painting- by-number. PO-0886 Early changes of FDG-PET markers predict the outcome after chemo-radiotherapy for pancreatic cancer S. Broggi 1 , P. Passoni 2 , E.G. Vanoli 3 , C. Fiorino 1 , G.M. Cattaneo 1 , C. Gumina 2 , P. Mapelli 3 , E. Incerti 3 , L. Gianolli 3 , N. Slim 2 , M. Picchio 3 , R. Calandrino 1 , N.G. Di Muzio 2