Automated prediction of dosimetric eligibility for hypofractionated prostate radiotherapy.

Clinical implementation of hypofractionated prostate radiotherapy (PROFIT trial, NCT003046759) represents an opportunity to significantly reduce the burden of treatment on the patient and clinic. However, efficacy was only demonstrated among the patient demographic who could meet the trial dose constraints and so it is necessary to emulate this triage step in clinical practice. The purpose of this study was to build a convenient tool to address the challenge of determining patient eligibility for hypofractionated treatment within the clinic. The tool was implemented within the EclipseTM treatment planning system using the scripting environment. Prior to planning a new case, the script computes and displays in a plot the fractional overlap of rectal and bladder wall with the planning target volume. Radial decision boundaries separate the plot into three zones and the new case is then classified as "feasible", "uncertain", or "not feasible". The radial decision boundaries were derived from a retrospective analysis of the overlap values and dosimetric eligibility of 150 patients with intermediate risk prostate cancer. Two-fold cross validation with repetitions demonstrated an average prediction accuracy of over 90%. The tool has been integrated into our clinical planning workflow to enable early identification of the need for planning consults and rapid a-priori determination of dosimetric eligibility for hypofractionated radiotherapy. The tool can be readily adopted by other centres since the underlying metrics can be evaluated without scripting if desired.

A method to analyze the cord geometrical uncertainties during head and neck radiation therapy using cone beam CT.

We developed a method to analyze quantitatively the residual cord geometrical uncertainties after image registration during head and neck radiation therapy by using sequential cone beam CT (CBCT). The geometrical centroid line of cervical spinal canal was computed to serve as a cord surrogate. We found that the cord motions were non-uniform from C1 to C6, and that the patterns of motion were variable across patients. This method has potential applications in monitoring cord setup accuracy and in designing treatment margins.

Calcifications are potential surrogates for prostate localization in image-guided radiotherapy.

PURPOSE: To investigate the feasibility of using calcifications as surrogates for the prostate position during cone-beam computed tomography (CBCT) image-guided radiotherapy. METHODS AND MATERIALS: The twice-weekly CBCT images taken during the treatment course of 4 patients were retrospectively studied for the stability of the calcifications. The geometric center of three fiducial markers was used as the reference. The planning CT images of 131 prostate patients recently treated with external beam radiotherapy at our center were reviewed to estimate the calcification occurrence rate. Analysis was conducted using the Varian Eclipse treatment planning system. Two patients were treated using prostate calcifications as the landmark in on-line registration. Both the Varian standard and the low-dose CBCT modes were used for imaging. RESULTS: The calcifications were found to be stable during the treatment course. At the 95% confidence interval, the difference between the distance from an identified calcification to the fiducial markers on CBCT and the distance on the planning CT scans was 0.2 +/- 2.0 mm, 0.8 +/- 2.2 mm, and 0.4 +/- 2.4 mm in the left-right, anteroposterior, and superoinferior direction, respectively. Of the 131 patients, 46 (35%) had well-defined calcifications either inside the prostate or near the borders. Our experience in treating the first 2 patients demonstrated that the calcifications are easily distinguished on low-dose scans and that calcification registration can be precisely performed. CONCLUSION: The results of our study have shown that calcifications can be reliable markers of prostate position and allow for precise image guidance with a low-imaging dose. With this approach, potentially about one-third of prostate patients could benefit from precise image guidance without the invasive use of markers.