Technical Note: Dosimetric characterization of the dynamic beam flattening MLC sequence on a ring shaped, Jawless Linear Accelerator with double stacked MLC

Abstract

Purpose To characterize the dosimetric features and limitations of the dynamic beam flattening (DBF) on the Halcyon 2.0 linear accelerator (Varian Medical Systems). Methods A predefined multi‐leaf collimator (MLC) sequence was introduced and used to flatten the 6 MV flattening filter free (FFF) beam on the Halcyon 2.0. Dosimetric characterizations of the flattened beams, including beam flatness, symmetry, percent depth dose (PDD), output factor and MU linearity, were investigated. Flatness and symmetry were obtained from profile measurements with both radiographic films (EDR2) and a two dimensional ion‐chamber array (IC Profiler, Sun Nuclear Corporation). MU linearity, output factors, and PDDs were measured in a water tank with a CC13 ion chamber (Scanditronix Wellhöfer, Nuremburg, Germany). In addition, the effect of the DBF sequence on 3D plan quality was evaluated by creating DBF plans for a 4‐field box rectum and an AP/PA spine plan. Patient specific QA was performed on these plans. Results At 100 cm SSD and 10 cm depth, a flatness of <3% was observed on both transversal and radial profiles for all square field sizes ≥10 cm with DBF. For both larger and smaller field sizes the flatness showed a tendency to increase as the fields got bigger or smaller, respectively. Similar trends in flatness were observed at all depths measured. All measured output factors for square field sizes ≥5 cm were within 1% of the TPS prediction. Linearity was ≤2.02% for all measurements. For both treatment sites, the MD judged the plans created for the Halcyon without the use of DBF not to be clinically acceptable, however considered both the TrueBeam plan and the Halcyon plan with the DBF sequence to be clinically acceptable. Conclusions The DBF sequence on the Halcyon and its characteristics were investigated. The analysis indicates that the DBF sequence can be used on the Halcyon to generate clinically acceptable 3D treatment plans.

Comprehensive validation of halcyon 2.0 plans and the implementation of patient specific QA with multiple detector platforms

“…Halcyon 2.0 contains a fixed MLC sequence that flattens the 6FFF beam by sweeping the proximal MLCs while the beam is delivering dose to provide a flattened beam profile (dynamically flattened beam, DFB). [12][13][14] The distal MLCs define the treatment field.…”

Initial Clinical Experience Treating Patients With Lung Cancer on a 6MV-Flattening-Filter-Free O-Ring Linear Accelerator

“…Halcyon™ (Varian Medical Systems, Palo Alto, CA, USA), a novel 6 megavolt (MV)-flatteningfilter-free (6X-FFF) O-ring gantry linac, was built to administer RT with greater speed and throughput than a C-arm linac (CAL), with some similarities to TomoTherapy (Accuray, Sunnyvale, CA, USA) [14]. Published reports of 6X-FFF O-ring linacs (ORL) are largely limited to pre-clinical planning studies, and have demonstrated similar plan quality with faster calculated treatment times for 6X-FFF ORLs versus CALs [14][15][16][17][18][19]. Reports of the clinical use of a 6X-FFF ORL to date have been limited to breast cancer [20], gynecologic cancers [12], and malignant pleural mesothelioma (MPM) [21], and have demonstrated fast treatment times and high throughput with the 6X-FFF ORL compared to CALs, with comparable plan quality, toxicity, and early disease-control.…”

Dosimetric performance evaluation of the Halcyon treatment platform for stereotactic radiotherapy: A pooled study

“…The results indicate that the Halcyon can perform reference dosimetry without a specialized chamber or lead filtering chamber and is well suited for resource-limited units. Bollinger et al [12] studied the dosimetric features and limitations of the dynamic flattening beam on the Halcyon 2.0 and found that the transversal and radial profiles of ≥10 cm square fields were observed with <3% flatness under the conditions of 100 cm SSD and 10 cm water depth. The positioning accuracy of MLC, gantry angle, and couch shift were within 0.05 mm, 0.02°, and 0.03 mm, respectively.…”