title: Dose--volume metrics associated with radiation pneumonitis after stereotactic body radiation therapy for lung cancer.
abstract: OBJECTIVE
  To identify dose-volume factors associated with radiation pneumonitis (RP) after stereotactic body radiation therapy (SBRT) for lung cancer.
  
  
  METHODS
  This study analyzed 74 patients who underwent SBRT for primary lung cancer. The prescribed dose for SBRT was uniformly 48 Gy in four fractions at the isocenter. RP was graded according to the Common Terminology Criteria for Adverse Events (CTCAE) v.3. Symptomatic RP was defined as grade 2 or worse. Optimal cut-offs dividing the patient population into two subgroups based on the incidence of symptomatic RP were sought using the following dose-volume metrics: PTV volume (ml), mean lung dose (Gy), and V5, V10, V15, V20, V25, V30, V35, and V40 (%) of both lungs excluding the PTV.
  
  
  RESULTS
  With a median follow-up duration of 31.4 months, symptomatic RP was observed in 15 patients (20.3%), including 1 patient with grade 3. Optimal cut-offs for pulmonary dose-volume metrics were V25 and V20. These two factors were highly correlated with each other, and V25 was more significant. Symptomatic RP was observed in 14.8% of the patients with V25 <4.2%, and the rate was 46.2% in the remainder (p = 0.019). PTV volume was another significant factor. The symptomatic RP rate was significantly lower in the group with PTV <37.7 ml compared with the larger PTV group (11.1% vs. 34.5%, p = 0.020). The patients were divided into three subgroups (patients with PTV <37.7 ml; patients with, PTV ≥37.7 ml and V25 <4.2%; and patients with PTV ≥37.7 ml and V25 ≥4.2%); the incidence of RP grade 2 or worse was 11.1%, 23.5%, and 50.0%, respectively (p = 0.013).
  
  
  CONCLUSIONS
  Lung V25 and PTV volume were significant factors associated with RP after SBRT.
authors.affiliation: Department of Radiation Oncology and Image-applied Therapy, Kyoto University, Kyoto, Japan. ymatsuo@kuhp.kyoto-u.ac.jp
authors.forename: Yukinori
authors.initials: Y
authors.lastname: Matsuo
authors.forename: Keiko
authors.initials: K
authors.lastname: Shibuya
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Nakamura
authors.forename: Masaru
authors.initials: M
authors.lastname: Narabayashi
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Sakanaka
authors.forename: Nami
authors.initials: N
authors.lastname: Ueki
authors.forename: Ken
authors.initials: K
authors.lastname: Miyagi
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Norihisa
authors.forename: Takashi
authors.initials: T
authors.lastname: Mizowaki
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Nagata
authors.forename: Masahiro
authors.initials: M
authors.lastname: Hiraoka
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002289:Carcinoma, Non-Small-Cell Lung / Q000473:pathology / Q000601:surgery*; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D017564:Radiation Pneumonitis / Q000209:etiology*; D016634:Radiosurgery / Q000009:adverse effects* / Q000379:methods; D011879:Radiotherapy Dosage; D047368:Tumor Burden