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

Abstract

Purpose Radiation therapy (RT) is commonly used in the treatment of gynecologic cancers. Intensity-modulated RT (IMRT) has been shown to reduce gastrointestinal toxicity compared with 2-dimensional and 3-dimensional RT modalities. We report the initial clinical experience using IMRT for gynecologic cancers with a novel 6MV flattening filter free O-ring linear accelerator (6X-FFF ORL). Methods and Materials We retrospectively identified consecutive women with uterine or cervical cancer who received pelvic RT on Halcyon (Varian Medical Systems, Palo Alto, CA), a novel 6X-FFF ORL. We report their clinicopathologic data, RT details, early disease-control outcomes, acute toxicities, dose-volume histogram data, couch corrections, and treatment times. Results Seventeen women received RT on a 6X-FFF ORL for uterine cancer (76%) or cervical cancer (24%) between January 2017 and September 2019. RT was delivered postoperatively (82%) or to intact disease (18%), to a median dose of 50.4 Gy (range, 19.8-55.0 Gy) in 25 fractions (range, 11-28), with 12% receiving extended-field RT and 65% receiving chemotherapy. Target and organ-at-risk constraints were met in all plans. The 3-dimensional vector couch correction average was 0.90 ± 0.37 cm. The mean beam-on time was 2.9 ± 0.4 min and mean treatment time, from imaging start to beam-off, was 3.6 ± 0.4 min. Grade 2 fatigue, anorexia, diarrhea, bloating, and nausea occurred in 41%, 12%, 12%, 6%, and 6% of patients, respectively. There were no grade ≥3 toxicities. Conclusions In the initial clinical report of pelvic RT for gynecologic cancers using a 6X-FFF ORL, the linac showed versatility in treatment; comparability to flattening-filtered IMRT for early disease-control, toxicity, and dosimetry; and treatment speed that compared favorably to IMRT on a C-arm gantry. Accordingly, a 6X-FFF ORL may increase throughput or reduce day length in departments with high gynecologic cancer volumes, without compromising clinical outcomes.

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

“…While prior reports have shown short treatment times and high throughput for patients treated on a 6X-FFF ORL for breast cancer [ 20 ], gynecologic cancers [ 12 ], and MPM [ 21 ], our report is the first clinical report of TRT using this linac for LC, and showed similar results. Quick treatments may improve the patient experience, as treatment tables are often uncomfortable, and maintaining immobility for prolonged periods of time may be difficult, particularly in patients with LC, many of whom may be elderly, frail, and/or have underlying pulmonary and cardiovascular co-morbidities.…”

“…To the best of our knowledge, no published beam-on plus CBCT or total in-room time data for TRT exist. As a means of comparison, mean beam-on plus CBCT and total in-room times for 6X-FFF ORL breast RT (4.4 ± 0.4 min and 12.4 ± 0.5 min, respectively) [ 20 ] and pelvic RT (3.6 ± 0.4 min and 10.8 ± 1.4 min, respectively) are provided [ 12 ]. While the total in-room time qualitatively appears longer than the breast and pelvic experiences, it is important to note that those experiences excluded prolonged outlier treatment times that were due to non-linac-related externalities including physician availability for on-board imaging approval, transport staff availability, bladder-filling troubleshooting, and interlock issues requiring physics override.…”

“…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.…”

“…IMRT has been shown to reduce high-grade RT pneumonitis and cardiac dose in patients receiving TRT for Stage III non-small cell LC (NSCLC) compared to 3D-CRT, with comparable survival and disease-control, suggesting its role as a standard of care [ 11 ]. VMAT, a subtype of IMRT, is delivered in dynamic, continuous arcs that allow for reduced RT treatment times compared to static-field IMRT [ 12 ]. Further, static-field IMRT and VMAT may be administered using a flattening-filter-free (FFF) linear accelerator (linac), which can increase dose rate, and decrease head scatter and penumbra in comparison to flattening-filtered (FF) RT [ 13 ].…”

Initial clinical experience treating patients with palliative radiotherapy for malignant pleural mesothelioma on the HalcyonTM linear accelerator

“…Pre-clinical treatment planning studies comparing RT on Halcyon TM to RT on CALs in head-and-neck cancer (9,11,12), pediatric cancers (13), prostate cancer (12), breast cancer (12,14,15), and stereotactic RT (11,16) showed overall similar plan quality and faster calculated treatment times with Halcyon TM . Aside from reports of the use of Halcyon TM to treat patients with breast cancer and gynecologic cancers showing fast beam-on, treatment, and in-room times for patients, with comparable OAR doses and toxicity to breast and pelvic RT on CALs (17,18), reports of the clinical use of Halcyon TM are limited.…”