Mitigating errors in external respiratory surrogate-based models of tumor position.

Purpose: To investigate the effect of tumor site, measurement precision, tumor-surrogate correlation, training data selection, model design, and interpatient and interfraction variations on the accuracy of external marker-based models of tumor position.

Methods And Materials: Cyberknife Synchrony system log files comprising synchronously acquired positions of external markers and the tumor from 167 treatment fractions were analyzed. The accuracy of Synchrony, ordinary-least-squares regression, and partial-least-squares regression models for predicting the tumor position from the external markers was evaluated.

Inferring positions of tumor and nodes in Stage III lung cancer from multiple anatomical surrogates using four-dimensional computed tomography.

Purpose: To investigate the feasibility of modeling Stage III lung cancer tumor and node positions from anatomical surrogates.

Methods And Materials: To localize their centroids, the primary tumor and lymph nodes from 16 Stage III lung cancer patients were contoured in 10 equal-phase planning four-dimensional (4D) computed tomography (CT) image sets. The centroids of anatomical respiratory surrogates (carina, xyphoid, nipples, mid-sternum) in each image set were also localized.

Investigation of motion sickness and inertial stability on a moving couch for intra-fraction motion compensation.

BACKGROUND. Respiration-induced tumor motion compensation using a treatment couch requires moving the patient at non-trivial speeds. The purpose of this work was to investigate motion sickness and stability of the patient's external surface due to a moving couch with respiration-comparable velocities and accelerations.

Feasibility of small animal cranial irradiation with the microRT system.

Purpose: To develop and validate methods for small-animal CNS radiotherapy using the microRT system.

Materials And Methods: A custom head immobilizer was designed and built to integrate with a pre-existing microRT animal couch. The Delrin couch-immobilizer assembly, compatible with multiple imaging modalities (CT, microCT, microMR, microPET, microSPECT, optical), was first imaged via CT in order to verify the safety and reproducibility of the immobilization method.

Efficient use of continuous, real-time prostate localization.

Recent technological advances make it possible to monitor prostate movement during radiation delivery. Using previously published data from 35 patients who underwent continuous localization during prostate cancer treatment, we simulated various interventions to identify the radiation-gating and patient-repositioning strategies that least prolonged the time to complete the daily treatment. Acceptable response protocols were those that resulted in at least 95% of patients' prostates remaining within the planning margins at least 95% of the time.