PV QA 4 - Poster Viewing Q&A 4
Purpose/Objective(s):Larger tumors are associated with decreased local control in non-small cell lung cancer (NSCLC) treated with conventional radiotherapy. Although multiple studies characterize dose-response relationships in the setting of NSCLC treated with SBRT, fewer studies evaluate diameter-response. Furthermore, given the preponderance of bidimensional reporting of tumor volumes in CT chest radiology, as influenced by Response Evaluation Criteria in Solid Tumors (RECIST) criteria, existing database studies may limit measurements, and thus prognostic sensitivity, to the axial plane. We hypothesized that higher 3-dimensional maximum tumor diameter (MTD) is associated with locoregional and distant recurrence.
Materials/Methods:We retrospectively reviewed outcomes for patients with localized NSCLC treated at our institution between 2008 and 2017. MTD was measured using CT images for radiation planning and taken as the largest tumor diameter on axial, sagittal, and coronal planes. Endpoints included overall survival (OS), primary tumor failure (PTF), ; lobar failure (LF), defined as recurrence within the same lobe as but outside of the treatment volume of the treated tumor; regional nodal failure (RF; defined as recurrence in regional N1-N3 nodes), and distant metastasis (DM). Cox regression was used to test association between endpoints and MTD, which was dichotomized as high and low by the median.
Results:A total of 222 patients and 236 treated tumors were included. Median follow up was 14.3 months. Median age was 72 (range 49-92). Males comprised 57.7% (128) of the cohort and females comprised 42.3% (94). The majority of tumors were early-stage, with 172 (72.9%) T1 and 48 (20.3%) T2 tumors. A small minority of tumors (10 (4.2%) T3 and 6 (2.5%) T4) were included due to multiple nodules thought to be of the same primary. Adenocarcinomas, squamous cell carcinomas, and undifferentiated/unspecified NSCLC represented 52.7% (145), 36.7% (101), and 10.5% (30) of the cohort, respectively. Median SBRT total dose, dose per fraction, and number of fractions was 50 Gy, 10 Gy/fraction, and 5 fractions, respectively. Median MTD for patients was 2.5 cm (range 0.6 to 8.5). Cox regression analysis indicated higher MTD was significantly associated with PTF (HR 7.5; 95% CI 2.2-25.5, p=.001), LF (HR=3.3; 95% CI 1.5-7.5, p=.003) and DM (HR=7.2; 95% CI 2.818.6, p<.001). There was a trend toward significance with regard to OS (HR=1.4; 95% CI .95-2.05, p=.09) and RF (HR=1.74; 95% CI .89-3.23, p=.11).
Conclusion:Three-dimensional MTD is associated with increased risk of local recurrence and distant metastasis after SBRT for localized NSCLC and may be useful in predicting treatment response. These findings require validation using a large, independent data set.
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