RefleXion Presents New Evidence for Its X1 Machine at AAPM 2020

By Dr. Sean Shirvani

For almost a decade, RefleXion has been collaborating with its scientific partners to generate evidence for biology-guided radiotherapy* (BgRT). Our vision to reveal cancer as never before and offer a new treatment modality rests on our ability to validate machine components, ensure functional quality and demonstrate the feasibility for new ways of delivering radiotherapy. In the last year alone, RefleXion has more than doubled the scientific evidence that supports future X1 applications.

In addition to the new treatment mode of BgRT, our machine is also designed to be a workhorse for the radiotherapy clinic and deliver excellent IMRT/SBRT/SRS. The abstracts presented at the American Association of Physicists in Medicine (AAPM) 2020 Annual Meeting focused on these technical capabilities of the RefleXion™ X1 for these workhorse functions.

One presentation focused on the results of evaluation tests to benchmark the X1 machine’s mechanical performance. The X1 employs a novel architecture with linac, kVCT and PET subsystems in the same treatment gantry. The testing used the applicable aspects of AAPM TG-148 and AAPM TG-142 methodologies to demonstrate that the X1 machine’s architecture was able to meet the expected mechanical and beam performance requirements outlined in AAPM TG-148 and AAPM TG-142 reports.

A second presentation focused on the X1 machine’s intensity modulated radiation therapy (IMRT) performance following AAPM’s TG-119 methodology. The TG-119 tests demonstrated that the X1 treatment planning system (TPS) was able to create IMRT treatment plans that met the expected goals as outlined in AAPM TG-119, and that these plans were successfully delivered on the X1 machine to within the desired accuracy. These results are significant because they offer evidence that the X1 machine meets the rigorous standards for delivery of IMRT.

Presenters shared the results of the evaluation of Patient Plan QA performance for multiple treatment plans: three clinical cases (IMRT prostate bed, SBRT lung and SRS brain) and five mock cases (C1: multitarget, C2: mock prostate, C3: mock head/neck, C4: C-shape easy and C5: C-shape hard). The Patient QA versions of these plans were created, where the expected dose is calculated assuming the plan is delivered into an ArcCHECK (AC) dosimetry device instead of the patient. The experimental results showed that the Patient Plan QA in the IMRT, SBRT and SRS modes of the X1 machine is robust and passed patient-specific QA dosimetric goals outlined in the AAPM TG-119 report.

Using seven test cases, RefleXion tested the use of ArcCHECK as a dosimetry tool for use with the X1 machine’s novel ring-based architecture. All seven test cases passed the test criteria, which validated the use of AC as a dosimetry tool for use with the X1 machine’s novel ring-based architecture. In a separate evaluation, the X1 machine’s IMRT and SBRT performance using ArcCHECK was evaluated using five test cases. All IMRT and SBRT test cases met or exceeded the Gamma Index passing rate of at least 90% of the measurement points met or exceeded the 3%/3 mm criteria.

RefleXion also presented on the imaging performance of a fully integrated fast-rotation kV-energy fan-beam CT (kV-FBCT) scanner in a radiotherapy machine. RefleXion’s X1 machine is among the first linear accelerators to integrate a 16-slice kV-FBCT scanner for patient alignment and target localization. The kV-FBCT is located on the gantry ring of the radiotherapy machine. In this AAPM presentation, the first report of the kV-FBCT performance of the RefleXion X1 machine, indicating high image quality for radiotherapy localization and possible treatment adaptation based upon intra-course CT information was presented. Future testing will focus on assessing imaging performance in the setting of target motion.

Lastly, RefleXion validated the performance of the X1 machine’s Treatment Planning system (TPS) following the testing methodology outlined in IAEA-TECDOC-1540: Specification and Acceptance Testing of Radiotherapy Treatment Planning Systems. RefleXion developed static field plans for each of the tests on the X1 TPS; the resulting RTDOSE DICOM files were exported for comparison to measurements. A commercially available water phantom and solid slab materials were used to simulate water, bone and lung for making dose measurements. These tests demonstrated that dose calculations were accurate and consistent between the X1 TPS and physical measurements of the 6MV photon beam in a variety of test conditions.

This research highlights the strong technical foundation of the X1 and underpins the commitment of RefleXion Medical to achieving and surpassing industry standards for the delivery of quality radiotherapy treatments. These features make the X1 an exceptional choice for current modes of radiotherapy delivery including IMRT, SBRT, and stereotactic radiosurgery.

*The RefleXion™ X1 is cleared for SBRT/SRS/IMRT treatments. BgRT is limited by U.S. law to Investigational use.