Dosimetric factors predicting radiation pneumonitis after CyberKnife stereotactic body radiotherapy for peripheral lung cancer.
OBJECTIVE
The aims of this study were to investigate the frequency of symptomatic radiation pneumonitis (RP) after CyberKnife lung stereotactic body radiotherapy (SBRT) and to evaluate predictive factors of symptomatic RP.


METHODS
56 patients with peripheral non-small-cell lung cancer were treated using the CyberKnife®VSI™System (Accuracy Inc., Sunnyvale, CA) between May 2013 and September 2015. Total radiation doses ranged from 48 to 56 Gy, as delivered in four equal fractions. Symptomatic RP was defined as a grade of ≥2. Predictive factors for symptomatic RP were evaluated using univariate and multivariate analyses.


RESULTS
With a median follow-up duration of 12.5 months (range, 3-27 months), symptomatic RP was observed in 6 (10.7%) of the 56 patients. In the univariate analysis, percent vital capacity (p < 0.05), maximum tumour diameter (p < 0.05), gross tumour volume (p < 0.05), planning target volume (p < 0.01), mean lung dose (p < 0.01) and a normal lung volume receiving 5-50 Gy of radiation (V5-50) (p < 0.01) were identified as significant predictive factors for symptomatic RP. In the multivariate analysis, only a V25>3.4% (p = 0.011) was identified as a significant predictive factor of symptomatic RP.


CONCLUSIONS
The incidence of symptomatic RP after CyberKnife SBRT was almost identical to the incidences reported in the linear accelerator-based SBRT. A significant association was observed between a V25>3.4% and the risk of developing symptomatic RP. Advances in knowledge: This is the first report that has investigated prognostic factors for symptomatic RP after CyberKnife SBRT for lung cancer. The newly developed scoring system may help to predict symptomatic RP.
1 Department of Radiation Oncology, Kobe Minimally Invasive Cancer Center, Kobe, Hyogo, Japan.
Masaki
http://orcid.org/0000-0002-4431-8892
M
Nakamura
1 Department of Radiation Oncology, Kobe Minimally Invasive Cancer Center, Kobe, Hyogo, Japan.
Hideki
H
Nishimura
1 Department of Radiation Oncology, Kobe Minimally Invasive Cancer Center, Kobe, Hyogo, Japan.
Masao
M
Nakayama
1 Department of Radiation Oncology, Kobe Minimally Invasive Cancer Center, Kobe, Hyogo, Japan.
Hiroshi
H
Mayahara
1 Department of Radiation Oncology, Kobe Minimally Invasive Cancer Center, Kobe, Hyogo, Japan.
Haruka
H
Uezono
1 Department of Radiation Oncology, Kobe Minimally Invasive Cancer Center, Kobe, Hyogo, Japan.
Aya
A
Harada
1 Department of Radiation Oncology, Kobe Minimally Invasive Cancer Center, Kobe, Hyogo, Japan.
Naoki
N
Hashimoto
2 Division of Radiation Oncology, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan.
Yasuo
Y
Ejima
2 Division of Radiation Oncology, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan.
Takeaki
T
Ishihara
2 Division of Radiation Oncology, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan.
Ryohei
R
Sasaki
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002289:Carcinoma, Non-Small-Cell Lung / Q000532:radiotherapy*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D017564:Radiation Pneumonitis / Q000453:epidemiology*; D016634:Radiosurgery / Q000009:adverse effects*; D011879:Radiotherapy Dosage; D012307:Risk Factors