Roeske, John C.

Abstract Background Markerless tumor tracking (MTT) using single‐energy (SE) kilovoltage (kV) imaging has been proposed as a technique for lung tumor motion management. However, bony structures can obscure the tumor and make tracking challenging. Dual‐energy (DE) subtraction imaging can suppress the bone and therefore enhance tumor visibility, potentially improving tracking accuracy. Purpose To develop a machine learning model that predicts the reliability of MTT for SE and DE imaging using phantom and patient data. Methods Images were collected at high and low energy (120/60 kV) using fast‐kV switching on dynamic thorax phantom with 5–15 diameter targets and 20 lung cancer patients, including one patient with two tumor locations. DE images were then generated off‐line using weighted logarithmic subtraction. Separately, a template‐based tracking algorithm was used to track the tumor on both phantom and patient images. For phantom data, the ground truth (GT) was defined by the cos 4 waveform programmed into the motion controller. Since the GT was unknown for patient data, it was estimated using a Kalman filter and further refined using visual inspection. The tracking success rate (TSR) was subsequently calculated. Based on TSR, patients were stratified into three tracking groups: good, moderate, and poor. A logistic regression (LR) model was implemented with tracking features, including match score, peak to side‐peak ratio (PSR), x ‐ and y ‐velocity. To address the distribution differences between phantom and patient data, a domain indicator and interaction features were also incorporated. The model was trained on phantom and 17 patient data using leave‐one‐out cross‐validation, and its performance was evaluated on three held‐out patients, one from each tracking group. Separate LR models were developed for each imaging modality, resulting in SE‐LR and DE‐LR models. For each held‐out patient, the confusion matrix, sensitivity, and specificity were reported. Results For both SE‐LR and DE‐LR models, PSR has the largest coefficient value, indicating that it is the most influential factor when determining the reliability of tracking. At a specificity of 95%, the DE‐LR model achieved significantly higher sensitivity than the SE‐LR model (0.908 vs. 0.731, p < 0.01 for phantom data and 0.657 vs. 0.589, p < 0.01 for patient data). In the three held‐out patients, the DE‐LR model outperformed the SE‐LR model across all metrics. The largest gains were found in the patient with good tracking quality. Conclusions The proposed LR models successfully predicted the reliability of SE‐ and DE‐MTT. Across phantom and patient datasets, the DE‐LR model consistently demonstrated improved performance compared with the SE‐LR model, suggesting that DE imaging may be beneficial for MTT applications.

Purpose To report a multicenter experience treating anal canal cancer patients with concurrent chemotherapy and intensity-modulated radiation therapy (IMRT). Patients and Methods From October 2000 to June 2006, 53 patients were treated with concurrent chemotherapy and IMRT for anal squamous cell carcinoma at three tertiary-care academic medical centers. Sixty-two percent were T1-2, and 67% were N0; eight patients were HIV positive. Forty-eight patients received fluorouracil (FU)/mitomycin, one received FU/cisplatin, and four received FU alone. All patients underwent computed tomography–based treatment planning with pelvic regions and inguinal nodes receiving a median of 45 Gy. Primary sites and involved nodes were boosted to a median dose of 51.5 Gy. All acute toxicity was scored according to the Common Terminology Criteria for Adverse Events, version 3.0. All late toxicity was scored using Radiation Therapy Oncology Group criteria. Results Median follow-up was 14.5 months (range, 5.2 to 102.8 months). Acute grade 3+ toxicity included 15.1% GI and 37.7% dermatologic toxicity; all acute grade 4 toxicities were hematologic; and acute grade 4 leukopenia and neutropenia occurred in 30.2% and 34.0% of patients, respectively. Treatment breaks occurred in 41.5% of patients, lasting a median of 4 days. Forty-nine patients (92.5%) had a complete response, one patient had a partial response, and three had stable disease. All HIV-positive patients achieved a complete response. Eighteen-month colostomy-free survival, overall survival, freedom from local failure, and freedom from distant failure were 83.7%, 93.4%, 83.9%, and 92.9%, respectively. Conclusion Preliminary outcomes suggest that concurrent chemotherapy and IMRT for anal canal cancers is effective and tolerated favorably compared with historical standards.