Commissioning and Clinical Implementation of a Sliding Gantry CT Scanner Installed in an Existing Treatment Room and Early Clinical Experience for Precise Tumor Localization

Abstract

The primary objective of the present study is to demonstrate that a unique computed tomography (CT)-linear accelerator combination can be used to reduce uncertainties caused by organ motion and setup inaccuracy. The acceptance, commissioning, and clinical implementation of a sliding gantry CT scanner installed in an existing linear accelerator room are reported in this paper. A Siemens CT scanner was installed directly opposite to an existing accelerator. The scanner is movable on a pair of horizontal rails mounted parallel to the longitudinal axis of the treatment couch replaced with a carbon fiber tabletop. Acceptance and commissioning of the CT scanner were verified with phantom studies. For clinical implementation, quality assurance (QA) procedures have been instituted to ensure the integrity of the CT gantry axis alignment and the accuracy of its movement using a phantom designed in house. A clinical example employing the CT-Linac combination to correct the isocenter positioning caused by organ motion and setup inaccuracy was presented for a prostate irradiation. Dose calculations were performed to study the effects on tumor coverage without the adjustments of the isocenter. A summary of the isocenter adjustments for the first 30 patients is also presented. The geometric accuracy of the CT scanner is < or =1 mm. An isocenter deviation of > or =2 mm from the original plan can be detected. For the clinical example of a prostate patient, the average movement of the prostate gland was found to be approximately 3mm in the anterior-posterior (AP/PA) direction and 5 mm in the cephalic-caudal direction. Variations in the isocenter position may result in underdosage of the PTV if correction is not made for the change in the isocenter position. Our experience with the first 30 patients indicates that while the left-right adjustment of the isocenter is minimal, in the AP/PA direction, about 33% of treatments required an adjustment of 3-5 mm, and about 18% required a 5.1-mm to 10-mm adjustment. In the caudal-cephalic direction, about 26% required an adjustment of 3-5 mm, and 8% required a 5.1-mm to 10-mm adjustment. Retrofitting a CT scanner in an existing linear accelerator room requires careful planning and well-coordinated efforts from all personnel involved. Special QA procedures are needed to ensure the mechanical integrity and imaging accuracy of the CT scanner. A CT scan of the patient prior to irradiation provides valuable information on organ motion. Any deviations from treatment plan can be corrected before dose delivery. Significant deviation from the planning isocenter may occur due to daily variations in the rectal filling. The CT-Linac combination has significant implications for the treatment of prostate cancer.

Evaluation of interfraction patient setup errors for image-guided prostate and head-and-neck radiotherapy using kilovoltage cone beam and megavoltage fan beam computed tomography

“…[6][7][8][9][10][11] Commonly used in-room X-ray imaging technologies for IGRT includes: kilovoltage, megavoltage cone beam computed tomography (KVCBCT and MVCBCT) and fan beam computed tomography (such as KVFBCT and MVFBCT). [12][13][14][15][16][17][18] The Elekta Oncology Systems Synergy medical linear accelerator is among the first commercially available treatment units with integrated KVCBCT system implementing X-ray-based volumetric imaging system (XVI, Elekta Oncology Systems, Norcross, GA, USA) capable of acquiring patient images in the treatment position. Interfraction displacements can be quantified and adjusted using KVCBCT so that daily treatment dose can be accurately delivered.…”

Accuracy of finite element model‐based multi‐organ deformable image registration

“…As more pretreatment imaging ͑i.e., PET, 1-4 MRS, [5][6][7][8] 4D CT, [9][10][11][12] and MR [13][14][15][16][17] ͒ becomes integrated into the treatment planning process and full three-dimensional ͑3D͒ imageguidance ͑i.e., kV and MV cone-beam, 18-23 tomotherapy, [24][25][26] and conventional CT͒, [27][28][29] becomes part of the treatment delivery the need for a deformable image registration technique becomes more apparent. In addition to being accurate and efficient, the image registration technique must include deformable alignment, allow various regions of interest to behave differently, and maintain the geometric integrity of regions of interest that are presented differently on different imaging modalities.…”

Dosimetric implications of two registration based patient positioning methods in prostate image guided radiation therapy (IGRT)

“…1,2 A number of correctional strategies including implanted fiducials [3][4][5] and on-line three-dimensional (3D) computed tomography (CT) imaging [6][7][8][9] have been developed and clinically implemented. Although both methods provide daily image guidance, the latter is advantageous in that it allows for the evaluation of daily delivered doses.…”