Real time position management system

Patients performed an inspiration breath-hold using a respiratory monitoring device and feedback system (Varian Real-time Position Management System, Palo Alto, CA). During CT simulation, 3 breath-hold CT scans were obtained for each patient to confirm consistency of the breath-hold. Planning CT images were acquired with 2.5-mm slice thickness. No intravenous or oral contrast was used.
The CTV, defined as the entire stomach, was contoured on breath-hold CT images (planning CT).²¹ An internal CTV was created to encompass the entire stomach on all 3 breath-hold scans. A 0.5- to 1.0-cm margin was added to the internal CTV to create a PTV, at the discretion of the treating physician.
A total radiation dose of 30 Gy, delivered at 1.5 to 2.0 Gy per fraction, was prescribed to cover the PTV. IMRT plans were generated with the Pinnacle treatment planning system (Pinnacle,^{3 (link)} Philips Medical Systems, Fitchburg, WI) using 5 to 7 coplanar 6-MV photon beams. In all plans, >95% of the PTV was covered by the prescription dose. Plans were optimized to deliver the lowest possible dose to adjacent organs at risk (OARs). The bilateral kidney volume receiving 15 Gy was limited to less than one-third (33%).

In general, RT was administered as frontline therapy in cases of H. pylori negative gMALT, or after unsuccessful antibiotics or systemic therapy (ST). When ST was administered, patients were treated with single-agent rituximab or rituximab, cyclophosphamide, doxorubicin, vincristine and prednisone (R-CHOP). All patients underwent CT simulation with four-dimensional (4D) CT or deep-inspiration breath hold (DIBH) after a 4-hour minimum fasting period. DIBH was conducted using a respiratory monitoring device and patient feedback system (Varian Real-time Position Management System, Palo Alto, CA). ISRT planning was utilized with the clinical target volume (CTV) including the stomach alone for stage I disease or stomach and involved lymph nodes (for stage II) according to the International Radiation Oncology Lymphoma Group (ILROG) guidelines (13 (link)). A planning target volume (PTV) margin of 0.5–1.5 cm was used with IMRT for radiation delivery. Daily low-dose CT-on-rails was utilized for image guidance (GE Medical Systems, Milwaukee, WI) (16 (link)). For patients treated in free breathing larger margins of 1.5 cm were generally used. Prescription doses of ≥30 Gy were considered standard-dose and 24 Gy was considered reduced-dose. In general, patients that were treated in late 2014 and beyond received doses of 24 Gy.

We also test our method on a real patient CBCT data with ten respiratory phases. The use of anonymous projection data from this patient was approved by UTSW IRB (082013-008). The data were acquired using a Varian CBCT system. The acquisition protocol parameters were: 120 kVp and 1.6 mAs per projection, a total of 534 projection views (1024 × 768 pixels with a pixel size of 0.388 × 0.388 mm² for each view) evenly distributed in 360°, and acquisition time of 1 min. Each projection was downsampled by a factor of 2 before reconstruction. The source to detector distance was 1500 mm and the source to isocenter distance was 1000 mm. The projection data were sorted into ten phases based on the respiratory signal recorded by Real-time Position Management system (Varian, Inc.). Thirty views per respiratory phase were selected, leading to a total of 300 projection views for 4D reconstruction. The dimensions of reconstructed images were 150 × 150 × 100 with voxel size of 2 × 2 × 2 mm³. We compared the patient images reconstructed by (1) 3D TV; (2) IM4D; (3) SMEIR; and (4) G-SMEIR.