Evaluation and commissioning of a surface based system for respiratory sensing in 4D CT.

The purpose of this study is to assess the temporal and reconstruction accuracy of a surface imaging system, the GateCT under ideal conditions, and compare the device with a commonly used respiratory surrogate: the Varian RPM. A clinical CT scanner, run in cine mode, was used with two optical devices, GateCT and RPM, to detect respiratory motion. A radiation detector, GM-10, triggers the X-ray on/off to GateCT system, while the RPM is directly synchronized with the CT scanner through an electronic connection. Two phantoms were imaged: the first phantom translated on a rigid plate along the anterior-posterior (AP) direction, and was used to assess the temporal synchronization of each optical system with the CT scanner. The second phantom, consisting of five spheres translating 3 cm peak-to-peak in the superior-inferior direction, was used to assess the quality of rebinned images created by GateCT and RPM. Calibration assessment showed a nearly perfect synchronization with the scanner for both the RPM and GateCT systems, thus demonstrating the good performance of the radiation detector. Results for the volume rebinning test showed discrepancies in volumes for the 3D reconstruction (compared to ground truth) of up to 36% for GateCT and up to 40% for RPM. No statistical difference was proven between the two systems in volume sorting. Errors are mainly due to phase detection inaccuracies and to the large motion of the phantom. This feasibility study assessed the consistency of two optical systems in synchronizing the respiratory signal with the image acquisition. A new patient protocol based on both RPM and GateCT will be soon started.

Comparison of target registration errors for multiple image-guided techniques in accelerated partial breast irradiation.

PURPOSE: External beam accelerated partial breast irradiation requires accurate localization of the target volume for each treatment fraction. Using the concept of target registration error (TRE), the performance of several methods of target localization was compared. METHODS AND MATERIALS: Twelve patients who underwent external beam accelerated partial breast irradiation were included in this study. TRE was quantified for four methods of image guidance: standard laser-based setup, kilovoltage imaging of the chest wall, kilovoltage imaging of surgically implanted clips, and three-dimensional surface imaging of the breast. The use of a reference surface created from a free-breathing computed tomography scan and a reference surface directly captured with three-dimensional video imaging were compared. The effects of respiratory motion were also considered, and gating was used for 8 of 12 patients. RESULTS: The median value of the TRE for the laser, chest wall, and clip alignment was 7.1 mm (n=94), 5.4 mm (n=81), and 2.4 mm (n=93), respectively. The median TRE for gated surface imaging based on the first fraction reference surface was 3.2 mm (n=49), and the TRE for gated surface imaging using the computed tomography-based reference surface was 4.9 mm (n=56). The TRE for nongated surface imaging using the first fraction reference surface was 6.2 mm (n=25). CONCLUSIONS: The TRE of surface imaging using a reference surface directly captured with three-dimensional video and the TRE for clip-based setup were within 1 mm. Gated capture is important for surface imaging to reduce the effects of respiratory motion in accelerated partial breast irradiation.

Boron neutron capture therapy: cellular targeting of high linear energy transfer radiation.

Boron neutron capture therapy (BNCT) is based on the preferential targeting of tumor cells with (10)B and subsequent activation with thermal neutrons to produce a highly localized radiation. In theory, it is possible to selectively irradiate a tumor and the associated infiltrating tumor cells with large single doses of high-LET radiation while sparing the adjacent normal tissues. The mixture of high- and low-LET dose components created in tissue during neutron irradiation complicates the radiobiology of BNCT. Much of the complexity has been unravelled through a combination of preclinical experimentation and clinical dose escalation experience. Over 350 patients have been treated in a number of different facilities worldwide. The accumulated clinical experience has demonstrated that BNCT can be delivered safely but is still defining the limits of normal brain tolerance. Several independent BNCT clinical protocols have demonstrated that BNCT can produce median survivals in patients with glioblastoma that appear to be equivalent to conventional photon therapy. This review describes the individual components and methodologies required for effect BNCT: the boron delivery agents; the analytical techniques; the neutron beams; the dosimetry and radiation biology measurements; and how these components have been integrated into a series of clinical studies. The single greatest weakness of BNCT at the present time is non-uniform delivery of boron into all tumor cells. Future improvements in BNCT effectiveness will come from improved boron delivery agents, improved boron administration protocols, or through combination of BNCT with other modalities.

Analysis of setup uncertainties for extremity sarcoma patients using surface imaging.

PURPOSE: Proper positioning of patients with extremity sarcoma tumors can be challenging. A surface imaging technique was utilized to quantify the setup uncertainties for sarcoma patients and to assess whether surface imaging could improve the accuracy of patient positioning. METHODS AND MATERIALS: Pretreatment and posttreatment 3-dimensional (3D) surface images were obtained for 16 patients and 236 treatments. Offline surface registration was performed to quantify interfraction and intrafraction setup errors, and the required planning target volume (PTV) margins were calculated. Setup differences were also assessed using root mean square (RMS) error analysis. RESULTS: For intrafraction variation, the mean 3D vector shift was 2.1 mm, and the systematic and random errors were 1.3 mm or less. When using a reference surface from the first fraction, the mean interfraction setup variation (3D vector shift) was 7.6 mm. Systematic and random errors were 3-4 mm in each direction. When using a computed tomographic based reference surface, the mean 3D vector shift was 9.5 mm. Systematic and random errors ranged from 3.1 to 7.9 mm. The required PTV margins were 1.0 cm, 1.2 cm, and 1.3 cm in the anterior-posterior, superior-inferior, and lateral directions, respectively. The mean (standard deviation) RMS errors for the uncorrected position were 4.7 mm (1.9 mm) and were reduced to 2.2 mm (0.8 mm) and 1.7 mm (0.8 mm), for 4 degree of freedom (DOF) and 6 DOF surface alignment, respectively. CONCLUSIONS: Intrafraction motion is small. Interfraction motion can exceed typical PTV margins and daily imaging should be utilized to reduce setup variations. Surface imaging may reduce setup errors and is a feasible technique for daily image guidance.

A voluntary breath-hold treatment technique for the left breast with unfavorable cardiac anatomy using surface imaging.

PURPOSE: Breath-hold (BH) treatments can be used to reduce cardiac dose for patients with left-sided breast cancer and unfavorable cardiac anatomy. A surface imaging technique was developed for accurate patient setup and reproducible real-time BH positioning. METHODS AND MATERIALS: Three-dimensional surface images were obtained for 20 patients. Surface imaging was used to correct the daily setup for each patient. Initial setup data were recorded for 443 fractions and were analyzed to assess random and systematic errors. Real time monitoring was used to verify surface placement during BH. The radiation beam was not turned on if the BH position difference was greater than 5 mm. Real-time surface data were analyzed for 2398 BHs and 363 treatment fractions. The mean and maximum differences were calculated. The percentage of BHs greater than tolerance was calculated. RESULTS: The mean shifts for initial patient setup were 2.0 mm, 1.2 mm, and 0.3 mm in the vertical, longitudinal, and lateral directions, respectively. The mean 3-dimensional vector shift was 7.8 mm. Random and systematic errors were less than 4 mm. Real-time surface monitoring data indicated that 22% of the BHs were outside the 5-mm tolerance (range, 7%-41%), and there was a correlation with breast volume. The mean difference between the treated and reference BH positions was 2 mm in each direction. For out-of-tolerance BHs, the average difference in the BH position was 6.3 mm, and the average maximum difference was 8.8 mm. CONCLUSIONS: Daily real-time surface imaging ensures accurate and reproducible positioning for BH treatment of left-sided breast cancer patients with unfavorable cardiac anatomy.