Stereotactic body radiation vs. intensity-modulated radiation for unresectable pancreatic cancer.

Abstract

353 Background: Stereotactic body radiation therapy (SBRT) is an emerging treatment option for unresectable pancreatic cancer, and may be more effective and less toxic than intensity modulated radiation therapy (IMRT). Methods: We retrospectively reviewed unresectable stage I-III pancreatic adenocarcinoma treated with SBRT (5 fractions, 30-33Gy) or IMRT (25-28 fractions, 45-56Gy with concurrent chemotherapy) between 2008-2016 at our institution. The groups were compared with respect to overall survival (OS), local failure (LF), distant failure (DF), any failure (AF), proportion of patients becoming resectable, and incidence of acute toxicity. Competing risks methods were used for univariate (UVA) and multivariate analysis (MVA) for LF, DF and AF. All endpoints were calculated from end of RT. Results: Median follow-up for surviving patients was 12.9 months. 44 patients received SBRT and 226 patients received IMRT. Patients who received SBRT were older (45% vs 29% > 70 years old, p = 0.05). Otherwise there was no significant difference in baseline characteristics, including stage and duration of induction chemotherapy. On MVA, there was no significant difference in OS, LF, DF, or AF between IMRT and SBRT (p = 0.73, 0.81, 0.44, and 0.39 respectively). Median OS was 15.7 months, and the 1-year rate of LF was 34.4% for SBRT and 30.2% for IMRT. Response to induction chemotherapy was associated with longer OS (p = 0.03). There was no significant difference in the proportion of patients who were subsequently resected between IMRT (17%) and SBRT (7%; p = 0.11). Significantly more IMRT patients experienced acute G2+ GI toxicity (24% vs. 7%, p = 0.008), G2+ fatigue (42% vs. 7%, p < 0.0001), and G3+ hematologic toxicity (26% vs. 5%, p = 0.001) compared to SBRT. Conclusions: SBRT achieves similar disease control outcomes as IMRT, and is associated with less acute toxicity. This data suggests SBRT is an attractive technique for pancreatic radiotherapy because of improved convenience and tolerability with equivalent efficacy. However, the lack of observed advantages in disease control with this moderate-dose SBRT regimen suggests a role for increasing SBRT dose, if this can be accomplished without significant increase in toxicity.