Detection of Local Cancer Recurrence After Stereotactic Ablative Radiation Therapy for Lung Cancer: Physician Performance Versus Radiomic Assessment.

PURPOSE: Stereotactic ablative radiation therapy (SABR) is a guideline-specified treatment option for early-stage lung cancer. However, significant posttreatment fibrosis can occur and obfuscate the detection of local recurrence. The goal of this study was to assess physician ability to detect timely local recurrence and to compare physician performance with a radiomics tool. METHODS AND MATERIALS: Posttreatment computed tomography (CT) scans (n=182) from 45 patients treated with SABR (15 with local recurrence matched to 30 with no local recurrence) were used to measure physician and radiomic performance in assessing response. Scans were individually scored by 3 thoracic radiation oncologists and 3 thoracic radiologists, all of whom were blinded to clinical outcomes. Radiomic features were extracted from the same images. Performances of the physician assessors and the radiomics signature were compared. RESULTS: When taking into account all CT scans during the whole follow-up period, median sensitivity for physician assessment of local recurrence was 83% (range, 67%-100%), and specificity was 75% (range, 67%-87%), with only moderate interobserver agreement (κ = 0.54) and a median time to detection of recurrence of 15.5 months. When determining the early prediction of recurrence within <6 months after SABR, physicians assessed the majority of images as benign injury/no recurrence, with a mean error of 35%, false positive rate (FPR) of 1%, and false negative rate (FNR) of 99%. At the same time point, a radiomic signature consisting of 5 image-appearance features demonstrated excellent discrimination, with an area under the receiver operating characteristic curve of 0.85, classification error of 24%, FPR of 24%, and FNR of 23%. CONCLUSIONS: These results suggest that radiomics can detect early changes associated with local recurrence that are not typically considered by physicians. This decision support system could potentially allow for early salvage therapy of patients with local recurrence after SABR.

Relationship of computed tomography perfusion and positron emission tomography to tumour progression in malignant glioma.

IntroductionThis study aimed to explore the potential for computed tomography (CT) perfusion and 18-Fluorodeoxyglucose positron emission tomography (FDG-PET) in predicting sites of future progressive tumour on a voxel-by-voxel basis after radiotherapy and chemotherapy. MethodsTen patients underwent pre-radiotherapy magnetic resonance (MR), FDG-PET and CT perfusion near the end of radiotherapy and repeated post-radiotherapy follow-up MR scans. The relationships between these images and tumour progression were assessed using logistic regression. Cross-validation with receiver operating characteristic (ROC) analysis was used to assess the value of these images in predicting sites of tumour progression. ResultsPre-radiotherapy MR-defined gross tumour; near-end-of-radiotherapy CT-defined enhancing lesion; CT perfusion blood flow (BF), blood volume (BV) and permeability-surface area (PS) product; FDG-PET standard uptake value (SUV); and SUV:BF showed significant associations with tumour progression on follow-up MR imaging (P < 0.0001). The mean sensitivity (±standard deviation), specificity and area under the ROC curve (AUC) of PS were 0.64 ± 0.15, 0.74 ± 0.07 and 0.72 ± 0.12 respectively. This mean AUC was higher than that of the pre-radiotherapy MR-defined gross tumour and near-end-of-radiotherapy CT-defined enhancing lesion (both AUCs = 0.6 ± 0.1, P ≤ 0.03). The multivariate model using BF, BV, PS and SUV had a mean AUC of 0.8 ± 0.1, but this was not significantly higher than the PS only model. ConclusionPS is the single best predictor of tumour progression when compared to other parameters, but voxel-based prediction based on logistic regression had modest sensitivity and specificity.

Evaluation of image-guidance strategies with helical tomotherapy for localised prostate cancer.

INTRODUCTION: Set-up accuracy of different image-guidance (IG) protocols using reduced imaging frequency was compared with daily IG. Anatomical characteristics were investigated for their potential to help select the suitable IG protocols for individual patients. METHODS: Set-up corrections from 26 prostate cancer patients treated with daily IG on helical tomotherapy were used to simulate IG protocols with reduced imaging frequency, where average set-up corrections from a subset of initial IG sessions were used for subsequent fractions with no IG. Residual set-up error, the difference between the average set-up correction and the actual correction required, was used to evaluate the accuracy of each protocol. Adaptive treatment margins required to encompass these errors were calculated. Body mass index and daily bladder and rectum cross-sectional areas (CSAs) were measured, and their correlations with set-up corrections were evaluated. We also investigated the use of reduced imaging schedules to estimate changes in bladder and rectum CSAs. RESULTS: As expected, residual set-up errors and adaptive treatment margins were effectively reduced with frequent imaging. For the majority of patients (81%), 10 IG sessions were sufficient to reduce residual set-up errors to within the adaptive treatment margins. Daily IG was more suitable than using a reduced IG protocol for a minority of patients (19%) with residual set-up errors that consistently exceeded the margins for >10% of fractions. These patients could be identified with 10 imaging sessions via the analysis of anatomical variations. CONCLUSIONS: The accuracy of modified IG protocols should be validated in the context of institutional practice regarding patient set-up and bowel/bladder preparation.