SFTPD and Interstitial pneumonitis: Although these markers await prospective validation, Yamashita et al. was able to show a reduction in pneumonitis risk (18.8% to 3.5% grade 4–5 RP) when patients with elevated levels of KL-6 and SP-D and obvious interstitial pneumonitis (IP) shadows on CT were excluded from receiving SBRT [66].