Abstract
Purpose
Conformality index of the 50% prescription isodose volume (CI50) is an important variable in lung stereotactic body radiotherapy (SBRT) planning but has not been previously correlated to radiation pneumonitis (RP). We hypothesized that adherence to recommended CI50 for patients undergoing lung SBRT would result in decreased incidence and/or severity of RP compared to that for patients with minimal deviations and unacceptable deviations.
Methods and materials
We retrospectively identified patients treated between 2006 and 2016, with > 3 months follow up from lung SBRT treatment. CTCAE v4.0 toxicity grades were used to classify RP. Clinically significant RP was defined as grade ≥ 2 toxicity. Using Radiation Therapy Oncology Group CI50 planning guidelines, patients were separated into three groups: acceptable, minor deviation, and unacceptable deviation. CI25 and CI75 values in patients with and without clinically significant RP were also reported in this study.
Results
One hundred seventy-four patients with a median follow-up time of 26.8 months were included in this analysis. Overall incidence of grade ≥ 2 RP was 12.7%. Thirty-eight (21.8%) patients had acceptable CI50, 100 (57.5%) had minor deviations, and 36 (20.7%) had unacceptable deviations. Incidence of RP did not significantly differ between patients with acceptable, minor deviation, and unacceptable CI50. Additionally, CI25 and CI75 did not significantly differ between patients with and without clinically significant RP.
Conclusions
Adhering to recommended CI50 values does not significantly decrease the incidence of clinically significant RP in patients with NSCLC treated with SBRT. To the authors’ knowledge, this observation has not been published previously.
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Funding
This work was supported by the Department of Radiation Oncology, Loyola University Chicago in Chicago, IL.
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All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
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Hutten, R., Surucu, M., Joyce, C. et al. Association of conformality index and post-treatment radiation pneumonitis in early-stage non-small cell lung cancer treated with stereotactic body radiotherapy. J Radiat Oncol 7, 63–67 (2018). https://doi.org/10.1007/s13566-018-0342-y
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DOI: https://doi.org/10.1007/s13566-018-0342-y