Parenchymal and Functional Lung Changes after Stereotactic Body Radiotherapy for Early-Stage Non-Small Cell Lung Cancer—Experiences from a Single Institution

Abstract

IntroductionThis study aimed to evaluate parenchymal and functional lung changes following stereotactic body radiotherapy (SBRT) for early-stage non-small cell lung cancer (NSCLC) patients and to correlate radiological and functional findings with patient and treatment characteristics as well as survival.Materials and methodsSeventy patients with early-stage NSCLC treated with SBRT from 2004 to 2015 with more than 1 year of CT follow-up scans were analyzed. Incidence, morphology, severity of acute and late lung abnormalities as well as pulmonary function changes were evaluated and correlated with outcome.ResultsMedian follow-up time was 32.2 months with 2-year overall survival (OS) of 83% and local progression-free survival of 88%, respectively. Regarding parenchymal changes, most patients only developed mild to moderate CT abnormalities. Mean ipsilateral lung dose (MLD) in biological effective dose and planning target volume size were significantly associated with maximum severity score of parenchymal changes (p = 0.014, p < 0.001). Furthermore, both maximum severity score and MLD were significantly connected with OS in univariate analysis (p = 0.043, p = 0.025). For functional lung changes, we detected significantly reduced total lung capacity, forced expiratory volume in 1 s, and forced vital capacity (FVC) parameters after SBRT (p ≤ 0.001). Multivariate analyses revealed SBRT with an MLD ≥ 9.72 Gy and FVC reduction ≥0.54 L as independent prognostic factors for inferior OS (p = 0.029, p = 0.004).ConclusionSBRT was generally tolerated well with only mild toxicity. For evaluating the possible prognostic impact of MLD and FVC reduction on survival detected in this analysis, larger prospective studies are truly needed.

Progression of Pulmonary Function and Correlation with Survival Following Stereotactic Body Radiotherapy of Central and Ultracentral Lung Tumors

“…However, we did not analyze singular post-treatment PFT values, but the dynamic changes in PFT compared to baseline pulmonary function. Similarly, a previous analysis from our department including mainly peripheral tumors showed that the actual decline in the VC was an independent predictor of worse OS [ 14 ]. The progression of predicted FEV 1s between 6 and 12 months had the highest impact on OS, yielding a hazard ratio of 0.90 per 1% absolute increase or 1.11 per 1% absolute decrease.…”

“…Due to the application of an internal target volume (ITV) concept for motion management, the mean PTV size of 105 cm³ was somewhat elevated compared to prior reports of lung SBRT [ 14 , 17 ], which might have contributed to a more pronounced decline in pulmonary function. Nevertheless, declines in pulmonary function remained modest.…”

“…These numbers suggest a smaller decline than the one we observed. Hörner-Rieber et al showed a significant decline in FEV 1s by absolute 5.2% at a median of 9 months after SBRT, including a small number of central tumors ( n = 12/70) [ 14 ]. Guckenberger et al investigated PFT values following SBRT in a patient cohort potentially including central tumors, finding a significant relative −8.1% change in FEV 1s between 7 and 24 months [ 20 ].…”

“…Potentially, SBRT dose was chosen more aggressively to improve tumor control in patients with better pulmonary function. Prior studies showed a weak [ 15 ] or no correlation of PFT decrease with higher lung doses [ 14 , 20 ]. Accordingly, interaction terms between mean BED 3 in both lungs and time after SBRT showed a statistically significant but clinically moderate correlation with VC.…”

“…However, data on pulmonary function testing following central and especially ultracentral SBRT are scarce. Most analyses incorporate only peripheral tumors [ 12 , 13 ] or a low number of central tumors [ 14 , 15 ]. Only one retrospective analysis directly compared toxicity due to decrease in PFT parameters between central and peripheral lung tumors [ 16 ].…”