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

Abstract

Three-dimensional (3D) conformal radiation therapy is the standard technique used for adjuvant breast radiation. We report the clinical use of a novel 6-MV flattening-filter-free O-ring linear accelerator (6X-FFF ORL) for breast cancer that may improve upon 3D conformal radiation therapy with its higher dose rate and faster rotation and leaf speed than traditional C-arm gantries. Methods and Materials: We retrospectively identified consecutive women with breast cancer who underwent surgery followed by radiation therapy to the breast or chest wall on Halcyon (Varian Medical Systems, Palo Alto, CA), a novel 6X-FFF ORL. We report their clinicopathologic information, radiation therapy details, acute toxicities, dose-volume histogram data, couch corrections, and treatment times. Results: Thirty-four women were treated for breast cancer on a 6X-FFF ORL between February 2018 and September 2018. All patients underwent lumpectomy (92%) or mastectomy (8%). Tumors were left sided in 44% and bilateral in 9%, and 9% included comprehensive nodal radiation therapy. Twelve percent of patients were treated prone and 29% with deep-inspiration breath hold. Standard target and normal-tissue constraints were met in nearly all plans. The 3D vector couch correction average was 0.77 AE 0.05 cm. The mean beam-on time was 2.0 AE 0.3 minutes, and mean treatment time from start of imaging to beam-off was 4.4 AE 0.4 minutes. Grade 2 dermatitis, fatigue, and breast pain occurred in 18%, 9%, and 3% of patients, respectively. Conclusions: In this first clinical report of breast radiation therapy with a 6X-FFF ORL, treatment was versatile and fast for complex setups and techniques, with acceptable toxicity and organ-at-risk doses. Thus, a 6X-FFF ORL can increase throughput or reduce length of day compared with a conventional C-arm linear accelerator in departments with a busy breast service.

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

“…As expected, larger field sizes resulted in increased surface dose as well as a slower dose fall off past dmax. The beam quality was recorded following TG-51 guidelines as %dd (10) . 18 The beam was not filtered with lead for these measurements however Lloyd et al has shown this to impact the measured %dd(10) by less than 0.7% on the Halcyon.…”

“…Having validated the physical performance of the DBF, simple 3D treatment plans with AP/PA and 4‐field box techniques were created for clinical evaluations. Prior studies have looked into planning on the Halcyon however have not investigated the sites presented and did not investigate the impact of the DBF to the same depth as this study …”

“…Prior studies have looked into planning on the Halcyon however have not investigated the sites presented and did not investigate the impact of the DBF to the same depth as this study. [8][9][10] 2. MATERIALS AND METHODS…”

Per-Fraction Positional and Dosimetric Performance of Prone Breast Tangential Radiotherapy Assessed with Daily Rapid Kilo-voltage Cone Beam Computed Tomography: Key Statistics, Predictors, and Recommendations

“…Halcyon™ v2.0 (Varian Medical Systems, Palo Alto, CA) is a commercially available 6MV attening-lterfree O-ring linear accelerator that provides rapid daily kV CBCT image guidance for tangential WBRT. The O-ring design reduces the risk of collisions and enables higher gantry rotation speed for faster CBCT imaging, which demonstratively improved patient throughput in many clinical sites including whole breast [8,9]. Compared to C-arm linacs, Halcyon v2.0 CBCT acquisition is faster (17-42 seconds versus 60 seconds), even after taking into account reconstruction duration for iterative CBCT, or iCBCT [10], which results in a better contrast-to-noise ratio.…”

Treatment Planning Comparison of Volumetric Modulated Arc Therapy With Trilogy and Halcyon for Bilateral Breast Cancer 

“…Halcyon has many differences from conventional C-arm LINACs, such as jawless, dual-layer multi-leaf collimator (MLC), faster gantry rotation and daily image guided radiotherapy (IGRT). Comparable dose distribution and excellent delivery e ciency have been shown on Halcyon in radiotherapy for head and neck, brain, unilateral breast, and cervical cancers [3][4][5][6][7]. Trilogy is a conventional C-arm LINAC with jaw and Millennium MLC.…”