A.R. Yeung

Evaluation of kV cone-beam ct performance for prostate IGRT: a comparison of automatic grey-value alignment to implanted fiducial-marker alignment.

Purpose: Cone-beam computed tomography (CBCT) is a new image-guided radiation therapy (IGRT) technique for patient alignment in radiotherapy. The CBCT x-ray volume imaging system from Elekta allows for a variety of alignment methods. The aim of this study is to assess the accuracy of soft-tissue-based automatic alignment as compared with manual alignment using intraprostatic fiducials. Methods and Materials: All patients were treated on an Elekta Synergy S linear accelerator with kilovoltage CBCT. All alignments were performed using the x-ray volume imaging system and associated software. Automatic alignment with gray-value-based registration and manual alignment to fiducial markers were performed. Transitional corrections along each axis as well as 3-dimensional vectors were compared with evaluate the accuracy of gray-value-based registration compared with fiducials. Results: The distribution of the 3-dimensional vectors between gray-value and fiducial registrations demonstrated notable differences. The mean summed vector was 0.75 cm, with a standard deviation (SD) of 0.52 cm and range from 0.04 to 2.06 cm. There was minimal difference along the lateral direction, with a mean ± SD of −0.02 cm ± 0.13 cm. However, there were large discrepancies along the superior-inferior and anterior-posterior direction alignments, with mean ± SD values of −0.55 ± 0.48 cm and −0.31 ± 0.43 cm, respectively. Conclusions: CBCT with soft-tissue-based automatic corrections is not an accurate alignment compared with manual alignment to fiducial markers for prostate IGRT. We have concluded that a daily manual alignment to fiducials is one of the most reliable methods to maintain accuracy in prostate IGRT.

The Effect of Intravenous Contrast on Photon Radiation Therapy Dose Calculations for Lung Cancer

Objective:The aim of this study was to evaluate the effect of intravenous contrast-enhanced computed tomography (CT) scans on the photon radiation dose calculations for lung cancer treatment planning. Materials and Methods:Nonionic iodinated intravenous contrast (Iohexol) was administered during the treatment planning CT scan of 9 patients with node-positive non–small-cell lung cancer (NSCLC). The potential effect of intravenous contrast was studied by changing the density of the contrast-enhanced vessels. A total of 9 patients were treated in this study: 5 patients with intensity-modulated radiation therapy (IMRT), and 4 patients with three-dimensional (3D) conformal radiation therapy. A treatment plan was generated from an unmanipulated “normal contrast” planning scan. The same planning parameters were then applied to a “no contrast” planning scan. The effect of intravenous contrast was quantified by calculating the percent change of dose in a variety of target and normal structures. To evaluate a worst-case scenario, the comparison between “normal contrast” and “no contrast” planning scans was repeated, assigning each vessel the artificial high density of 1.3 g/cm3. Results:Dose differences between the planning image set using intravenous contrast and the image set without contrast were less than 2.5% for planning target volumes. A worst-case scenario in which normal contrast was overridden with an artificially high density of 1.3 g/cm3 led to small dose differences of less than 3%. Conclusions:Planning lung radiation therapy treatment using CT scans that contain intravenous contrast does not result in clinically significant errors in dose delivery.

Proton Therapy for Prostate Cancer Treatment Employing Online Image Guidance and an Action Level Threshold

Purpose:The ability to determine the accuracy of the final prostate position within a determined action level threshold for image-guided proton therapy is unclear. Materials and Methods:Three thousand one hundred ten images for 20 consecutive patients treated in 1 of our 3 proton prostate protocols from February to May of 2007 were analyzed. Daily kV images and patient repositioning were performed employing an action-level threshold (ALT) of ≥2.5 mm for each beam. Isocentric orthogonal x-rays were obtained, and prostate position was defined via 3 gold markers for each patient in the 3 axes. Results:To achieve and confirm our action level threshold, an average of 2 x-rays sets (median 2; range, 0–4) was taken daily for each patient. Based on our ALT, we made no corrections in 8.7% (range, 0%–54%), 1 correction in 82% (41%–98%), and 2 to 3 corrections in 9% (0–27%). No patient needed 4 or more corrections. All patients were treated with a confirmed error of <2.5 mm for every beam delivered. After all corrections, the mean and standard deviations were: anterior-posterior (z): 0.003 ± 0.094 cm; superior-inferior (y): 0.028 ± 0.073 cm; and right-left (x) −0.013 ± 0.08 cm. Conclusion:It is feasible to limit all final prostate positions to less than 2.5 mm employing an action level image-guided radiation therapy (IGRT) process. The residual errors after corrections were very small.

Outpatient Palliative Care Needs of Metastatic Cancer Patients Treated With Radiation Therapy

Accumulated Tumor Volume Threshold Correlates With Neurologic Outcomes in Patients With Brain Metastases Treated With Radiosurgery R.L. Hong, I.K. Kim, R. Starke, D. McRae, G. Cernica, N.M. Nasr, A. Caputy, and J. Sherman; George Washington University School of Medicine, Washington, DC, Virginia Hospital Center, Arlington, VA, University of Virginia Department of Neurosurgery, Charlottesville, VA, Virginia Hospital Center, Arlington, VA