Positron emission tomography for assessing local failure after stereotactic body radiotherapy for non-small-cell lung cancer

Abstract

Purpose: We analyzed whether positron emission tomography (PET)/computed tomography standardized uptake values (SUVs) after stereotactic body radiotherapy (SBRT) could predict local recurrence (LR) in non-small-cell lung cancer (NSCLC).

Methods and materials: This study comprised 128 patients with Stage I (n = 68) or isolated recurrent/secondary parenchymal (n = 60) NSCLC treated with image-guided SBRT to 50 Gy over 4 consecutive days; prior radiotherapy was allowed. PET/computed tomography scans were obtained before therapy and at 1 to 6 months after therapy, as well as subsequently as clinically indicated. Continuous variables were analyzed with Kruskal-Wallis tests and categorical variables with Pearson chi-square or Fisher exact tests. Actuarial local failure rates were calculated with the Kaplan-Meier method.

Results: At a median follow-up of 31 months (range, 6-71 months), the actuarial 1-, 2-, and 3-year local control rates were 100%, 98.5%, and 98.5%, respectively, in the Stage I group and 95.8%, 87.6%, and 85.8%, respectively, in the recurrent group. The cumulative rates of regional nodal recurrence and distant metastasis were 8.8% (6 of 68) and 14.7% (10 of 68), respectively, for the Stage I group and 11.7% (7 of 60) and 16.7% (10 of 60), respectively, for the recurrent group. Univariate analysis showed that SUVs obtained 12.1 to 24 months after treatment for the Stage I group (p = 0.007) and 6.1 to 12 months and 12.1 to 24 months after treatment for the recurrent group were associated with LR (p < 0.001 for both). Of the 128 patients, 17 (13.3%) had ipsilateral consolidation after SBRT but no elevated metabolic activity on PET; none had LR. The cutoff maximum SUV of 5 was found to have 100% sensitivity, 91% specificity, a 50% positive predictive value, and a 100% negative predictive value for predicting LR.

Conclusions: PET was helpful for distinguishing SBRT-induced consolidation from LR. SUVs obtained more than 6 months after SBRT for NSCLC were associated with local failure. A maximum SUV greater than 5, especially at more than 6 months after SBRT, should prompt biopsy to rule out LR.

Fig. 1

Maximum standardized uptake value (SUV_max) for lesions with vs. without local recurrence (LR). (A) Distribution of median SUV_max before stereotactic body radiotherapy (SBRT) for patients who did or did not have LR. No difference was found between the group treated for Stage I disease (p = 0.242) and the group treated for recurrent disease (p = 0.355). The box length is the interquartile range. The circles and asterisks are the outliers. The asterisks represent extreme outliers (>3 times the interquartile range). The circles represent outliers with values between 1.5 and 3 times the interquartile range. (B) Changes in median SUV_max over time after SBRT in the group treated for recurrent disease. The solid line indicates standard uptake values (SUVs) for lesions that recurred locally; the dashed line indicates SUVs for lesions that did not. (C) Distribution of median SUV_max at 6.1 to 12 months after SBRT for Stage I disease or recurrent disease for lesions with or without LR. PET = positron emission tomography.

Fig. 2

Stereotactic body radiotherapy plans and axial positron emission tomography (PET)/computed tomography scans obtained before and 6 months after treatment for a patient with a tumor that did recur (A) and for another patient with a tumor that did not recur (B).

Fig. 3

Development of post-treatment consolidation in patients without local recurrence. (A) Median maximum standardized uptake value (SUV_max) and tumor size at various times after stereotactic body radiotherapy (SBRT). (B) Axial positron emission tomography/computed tomography scans and treatment plan illustrate typical post-SBRT consolidation and its resolution over time.