3609 - Impact of Dosimetric Factors on Rib Fracture (RF) and Chest Wall (CW) Pain (CWP) in Ultra-Peripheral Lung Tumors (UPLT) Treated with Stereotactic Body Radiation Therapy (SBRT)
Presenter(s)
N. Sathi1, L. Garlick2, R. Alden1, D. Linder3, A. Panjwani4, A. Thakurdyal1, D. Wang1, J. A. Bogart5, and M. D. Mix1; 1SUNY Upstate Medical University, Syracuse, NY, 2Florida Atlantic University College of Medicine, Boca Raton, FL, 3Stony Brook University Hospital, Stony Brook, NY, 4Nassau University Medical Center, East Meadow, NY, 5SUNY Upstate Medical Center, Syracuse, NY
Purpose/Objective(s): SBRT is a curative option for early-stage non-small cell lung cancer (NSCLC), and risk of CWP/RF is prominent for UPLT. This analysis sought to evaluate the incidence of CWP/RF in this population and the potential impact of dosimetric factors.
Materials/Methods: Single institution data from those with UPLT treated with SBRT between 2007 and 2022 were abstracted and maintained in an IRB-approved database. UPLT was defined by direct PTV overlap with the rib or CW. Toxicity was graded (GX) with CTCAE v5. Maximum point dose (MPD) and volumes receiving specified doses (VX) were correlated with CWP/RF using univariate analysis (UVA) and multivariate cox regression analysis (MVA). Kaplan Meier method was used for actuarial estimates.
Results: 315 UPLT in 306 patients were included. Median tumor size was 2 cm (0.6 – 6.2). IMRT was used in 95%, and prescription dose to PTV was 27-60 Gy in 1-5 fractions (median 60 Gy in 5). Most received 5 fractions (80%). After median follow up of 37.8 months (mo), 3 year local tumor control and overall survival were 88% and 51% respectively. The crude rate of CWP was 13% (97.5% G1, 2.5% G2) and the rate of RF was 6% (89% G1,11% G2). The median time to CWP was 7.8 mo and median time to rib fracture 19.1 mo. On MVA: rib V32 > 2.8 cc and rib MPD 57-62 Gy predicted for CWP (Hazard Ratio (HR) of 2.9 (p= 0.045) and 2.0 (p = 0.029), respectively). Rib MPD and V32 were predictive for RF on UVA, but not MVA. CWP was not associated with CW MPD, or V30/V40/V50/V60. RF was not associated with CW MPD, V50, or V60. When analyzing for either CWP or RF, Rib MPD and V32 remained significant on MVA, with HR of 2.4 (p=0.003) and 2.7 (p=0.03), respectively.
Conclusion: The optimal balance between prescription dose intensity and R/CW sparing remains poorly defined. Both volumetric and maximum point dose factors may be associated with CWP/RF. However, the incidence of R/CW toxicity is modest even among UPLT and severity is generally mild. These findings support continued prioritization of tumor coverage over R/CW sparing. However, a 5-fraction regimen with restrained heterogeneity to limit MPD of R/CW may represent an ideal approach with consideration of limiting rib V32 and MPD.