Dose-volume factors predicting esophageal after SBRT for ultra-central lung tumors
PO-1545
Abstract
Dose-volume factors predicting esophageal after SBRT for ultra-central lung tumors
Authors: Jackson|, Andrew(1)*;Wang|, Chunyu(2);Yorke|, Ellen(1);Gelblum|, Daphna(2);Apte|, Aditya(1);Yang|, Jie(1);Rimner|, Andreas(2);Wu|, Abraham(2)[wua@mskcc.org];
(1)Memorial Sloan Kettering Cancer Center, Medical Physics, New York- NY, USA;(2)Memorial Sloan Kettering Cancer Center, Radiation Oncology, New York- NY, USA;
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Purpose or Objective
The safety of SBRT for ultra-central tumors remains unclear. We studied dose-volume correlates of esophageal toxicity after ultra-central SBRT.
Material and Methods
88 patients with lung tumors abutting proximal bronchial tree (PBT) or PTV overlapping esophagus (n=76 and 23; 11 met both criteria) were included. All had 5, 8 or 15 fractions of image-guided RT with BED ≥84Gy (α/β=10 Gy). Primary endpoint was grade ≥2 esophageal toxicity (E2+, defined by CTCAE v4 criteria). Dose-volume histograms (DVHs) using linear-quadratic equivalent doses in 2 Gy fractions (LQED) were calculated for esophagus (esoph) with α/β= 3 Gy. Variables tested for correlation with E2+ using Cox proportional hazards (CPH) models were: equivalent (equiv) dose D to absolute volume V of esoph (DV) for volumes from 0-70 cc; absolute vol V of esoph receiving at least equiv dose D (VD) for doses from 5-80 Gy; mean, max, and min equiv doses to the esoph; age, sex, KPS, smoking history, anti-angiogenic agents, stage, GTV size, and whether GTV abutted esoph. Multivariate CPH models were tested, including the most significant DVand VDvariables, using a step-up procedure. For significant variables, the log rank test was used to assess thresholds for clinical use.
Results
Median followup was 14.3 months (mos). There were 14 cases of E2+ (16%), mostly acute esophagitis. There were 2 cases of grade 3 (one severe esophagitis, one esophageal bleed) and 2 cases of grade 4 toxicity (both fistulae). One fistula occurred in a patient with antiangiogenic exposure. Median time to E2+ was 0.78 mos after SBRT (range: 0- 13.8 months). E2+ was significantly correlated with: DVfor volumes from 0-10 Gy, with most significant volume at 3cc (p= 1.4 X 10-6), Fig 1; VDfor doses from 25-80 Gy with most significant equivalent dose at 60 Gy (p=6.6 X 10-8); mean and max equivalent dose to the esoph (p=1.8x10-5and 0.016, respectively); GTV abutting esoph (p=0.0024). There were no significant multivariate models. Incidence of E2+ was significantly different with D3cc< or > the median of 25.7 Gy (p=0.011), Fig 2, with actuarial rates of 4.5% vs. 20.5% at 6 mos and 4.5% vs. 33% at 18 mos. Incidence of E2+ was significantly different in patients with V60Gy> 0cc (p = 0.041), with actuarial rates of 8.5% vs. 17.1% at 6 mos and 8.5% vs. 30.2% at 18 mos.
Conclusion
We observed a 16% rate of grade ≥2 esoph toxicity after ultra-central SBRT. Incidence of E2+ was significantly correlated with LQED to 3cc of esoph, and absolute vol receiving LQED 60 Gy. This suggests that limiting D3cc to <25.7Gy results in 18-mo actuarial incidence and a raw rate of G2+ <5%; and that limiting max LQED to 60Gy results in an 18-mo actuarial incidence and a raw rate of G2+ <8.5%. With α/β=3Gy, an LQED of 25.7Gy corresponds to 18.9, 22.2, and 26.8Gy in 5, 8 and 15 fractions while an LQED of 60 Gy corresponds to 32.0, 38.4, and 48.3Gy in 5, 8 and 15 fractions. These represent practical dose-volume limits that could be implemented to limit the incidence of esophageal complications.
