title: Stereotactic ablative radiotherapy for adrenal gland metastases: Factors influencing outcomes, patterns of failure, and dosimetric thresholds for toxicity.
abstract: OBJECTIVE
  We report our single-institution experience with stereotactic ablative radiotherapy (SABR) for adrenal metastasis and identify factors influencing outcomes, patterns of failure, and dosimetric thresholds for toxicity.
  
  
  METHODS
  We identified patients with adrenal metastases treated with SABR from 2009 to 2015. Toxicity was evaluated with Common Terminology Criteria for Adverse Events v4.0. Local failures were categorized as in-field, marginal, or out-of-field. New or progressive disease outside the treated adrenal gland was considered distant failure. Survival and time to local and distant failure were estimated by the Kaplan-Meier method. Prognostic factors were evaluated with a Cox proportional hazards model. Fisher's exact tests were used to compare toxicity between dosimetric thresholds.
  
  
  RESULTS
  Forty-three patients with 49 adrenal metastases (84% from lung) were treated with SABR to a median prescribed dose of 60 Gy in 10 fractions. Median overall survival time was 19 months, and 1- and 2-year rates were 65% and 42%, respectively. Bilateral adrenal metastases were associated with worse overall survival (P = .01). Median progression-free survival (PFS) time was 6 months, with most progressions being distant failure (most often to brain or bone). PFS was better in patients with a solitary adrenal metastasis (P = .03). Median time to local failure was not reached; the 1-year freedom from local failure rate was 74%. Nine failures were in field and 1 was marginal; no local failures occurred in lesions treated with biologically equivalent doses of >100 Gy. No patient experienced grade 3-5 toxicity. Low-grade gastrointestinal toxicity was common, but grade 2 toxicity was avoided in patients with a maximum stomach-bowel point dose of ≤50 Gy (P = .03). Low-grade adrenal insufficiency was common with bilateral treatment.
  
  
  CONCLUSIONS
  SABR was well tolerated and resulted in good 1-year local control; PFS was promising for patients with solitary metastases. Low-grade toxicity was common, but can be minimized with strict dosimetric constraints.
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: William W
authors.initials: WW
authors.lastname: Chance
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Quynh-Nhu
authors.initials: QN
authors.lastname: Nguyen
authors.affiliation: Department of Thoracic and Cardiovascular Surgery, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Reza
authors.initials: R
authors.lastname: Mehran
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: James W
authors.initials: JW
authors.lastname: Welsh
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Gomez
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Peter
authors.initials: P
authors.lastname: Balter
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Ritsuko
authors.initials: R
authors.lastname: Komaki
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Zhongxing
authors.initials: Z
authors.lastname: Liao
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas. Electronic address: jychang@mdanderson.org.
authors.forename: Joe Y
authors.initials: JY
authors.lastname: Chang
mesh_terms: D000310:Adrenal Gland Neoplasms / Q000401:mortality / Q000532:radiotherapy* / Q000556:secondary*; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology; D008297:Male; D008875:Middle Aged; D016016:Proportional Hazards Models; D011832:Radiation Injuries / Q000209:etiology; D016634:Radiosurgery / Q000009:adverse effects* / Q000379:methods*; D011879:Radiotherapy Dosage; D017211:Treatment Failure; D016896:Treatment Outcome