Delta-radiomics features for the prediction of patient outcomes in non-small cell lung cancer

Radiomics is the use of quantitative imaging features extracted from medical images to characterize tumor pathology or heterogeneity. Features measured at pretreatment have successfully predicted patient outcomes in numerous cancer sites. This project was designed to determine whether radiomics features measured from non–small cell lung cancer (NSCLC) change during therapy and whether those features (delta-radiomics features) can improve prognostic models. Features were calculated from pretreatment and weekly intra-treatment computed tomography images for 107 patients with stage III NSCLC. Pretreatment images were used to determine feature-specific image preprocessing. Linear mixed-effects models were used to identify features that changed significantly with dose-fraction. Multivariate models were built for overall survival, distant metastases, and local recurrence using only clinical factors, clinical factors and pretreatment radiomics features, and clinical factors, pretreatment radiomics features, and delta-radiomics features. All of the radiomics features changed significantly during radiation therapy. For overall survival and distant metastases, pretreatment compactness improved the c-index. For local recurrence, pretreatment imaging features were not prognostic, while texture-strength measured at the end of treatment significantly stratified high- and low-risk patients. These results suggest radiomics features change due to radiation therapy and their values at the end of treatment may be indicators of tumor response.

Stereotactic ablative radiotherapy for adrenal gland metastases: Factors influencing outcomes, patterns of failure, and dosimetric thresholds for toxicity

PURPOSE

We report our single-institution experience with stereotactic ablative radiotherapy (SABR) for adrenal metastasis and identify factors influencing outcomes, patterns of failure, and dosimetric thresholds for toxicity.

METHODS AND MATERIALS

We identified patients with adrenal metastases treated with SABR from 2009 to 2015. Toxicity was evaluated with Common Terminology Criteria for Adverse Events v4.0. Local failures were categorized as in-field, marginal, or out-of-field. New or progressive disease outside the treated adrenal gland was considered distant failure. Survival and time to local and distant failure were estimated by the Kaplan-Meier method. Prognostic factors were evaluated with a Cox proportional hazards model. Fisher's exact tests were used to compare toxicity between dosimetric thresholds.

RESULTS

Forty-three patients with 49 adrenal metastases (84% from lung) were treated with SABR to a median prescribed dose of 60 Gy in 10 fractions. Median overall survival time was 19 months, and 1- and 2-year rates were 65% and 42%, respectively. Bilateral adrenal metastases were associated with worse overall survival (P = .01). Median progression-free survival (PFS) time was 6 months, with most progressions being distant failure (most often to brain or bone). PFS was better in patients with a solitary adrenal metastasis (P = .03). Median time to local failure was not reached; the 1-year freedom from local failure rate was 74%. Nine failures were in field and 1 was marginal; no local failures occurred in lesions treated with biologically equivalent doses of >100 Gy. No patient experienced grade 3-5 toxicity. Low-grade gastrointestinal toxicity was common, but grade 2 toxicity was avoided in patients with a maximum stomach-bowel point dose of ≤50 Gy (P = .03). Low-grade adrenal insufficiency was common with bilateral treatment.

CONCLUSION

SABR was well tolerated and resulted in good 1-year local control; PFS was promising for patients with solitary metastases. Low-grade toxicity was common, but can be minimized with strict dosimetric constraints.

Can radiomics features be reproducibly measured from CBCT images for patients with non-small cell lung cancer?

PURPOSE

Increasing evidence suggests radiomics features extracted from computed tomography (CT) images may be useful in prognostic models for patients with nonsmall cell lung cancer (NSCLC). This study was designed to determine whether such features can be reproducibly obtained from cone-beam CT (CBCT) images taken using medical Linac onboard-imaging systems in order to track them through treatment.

METHODS

Test-retest CBCT images of ten patients previously enrolled in a clinical trial were retrospectively obtained and used to determine the concordance correlation coefficient (CCC) for 68 different texture features. The volume dependence of each feature was also measured using the Spearman rank correlation coefficient. Features with a high reproducibility (CCC > 0.9) that were not due to volume dependence in the patient test-retest set were further examined for their sensitivity to differences in imaging protocol, level of scatter, and amount of motion by using two phantoms. The first phantom was a texture phantom composed of rectangular cartridges to represent different textures. Features were measured from two cartridges, shredded rubber and dense cork, in this study. The texture phantom was scanned with 19 different CBCT imagers to establish the features' interscanner variability. The effect of scatter on these features was studied by surrounding the same texture phantom with scattering material (rice and solid water). The effect of respiratory motion on these features was studied using a dynamic-motion thoracic phantom and a specially designed tumor texture insert of the shredded rubber material. The differences between scans acquired with different Linacs and protocols, varying amounts of scatter, and with different levels of motion were compared to the mean intrapatient difference from the test-retest image set.

RESULTS

Of the original 68 features, 37 had a CCC >0.9 that was not due to volume dependence. When the Linac manufacturer and imaging protocol were kept consistent, 4-13 of these 37 features passed our criteria for reproducibility more than 50% of the time, depending on the manufacturer-protocol combination. Almost all of the features changed substantially when scatter material was added around the phantom. For the dense cork, 23 features passed in the thoracic scans and 11 features passed in the head scans when the differences between one and two layers of scatter were compared. Using the same test for the shredded rubber, five features passed the thoracic scans and eight features passed the head scans. Motion substantially impacted the reproducibility of the features. With 4 mm of motion, 12 features from the entire volume and 14 features from the center slice measurements were reproducible. With 6-8 mm of motion, three features (Laplacian of Gaussian filtered kurtosis, gray-level nonuniformity, and entropy), from the entire volume and seven features (coarseness, high gray-level run emphasis, gray-level nonuniformity, sum-average, information measure correlation, scaled mean, and entropy) from the center-slice measurements were considered reproducible.

CONCLUSIONS

Some radiomics features are robust to the noise and poor image quality of CBCT images when the imaging protocol is consistent, relative changes in the features are used, and patients are limited to those with less than 1 cm of motion.