Treatment planning system commissioning of the first clinical biology‐guided radiotherapy machine

Abstract

Purpose The RefleXion X1 is a novel radiotherapy machine designed for image‐guided radiotherapy (IGRT) and biology‐guided radiotherapy (BgRT). Its treatment planning system (TPS) generates IMRT and SBRT plans for a 6MV‐FFF beam delivered axially via 50 firing positions with the couch advancing every 2.1 mm. The purpose of this work is to report the TPS commissioning results for the first clinical installation of RefleXion™ X1. Methods CT images of multiple phantoms were imported into the RefleXion TPS to evaluate the accuracy of data transfer, anatomical modeling, plan evaluation, and dose calculation. Comparisons were made between the X1, Eclipse™, and MIM™. Dosimetric parameters for open static fields were evaluated in water and heterogeneous slab phantoms. Representative clinical IMRT and SBRT cases were planned and verified with ion chamber, film, and ArcCHECK@ measurements. The agreement between TPS and measurements for various clinical plans was evaluated using Gamma analysis with a criterion of 3%/2 mm for ArcCHECK@ and film. End‐to‐end (E2E) testing was performed using anthropomorphic head and lung phantoms. Results The average difference between the TPS‐reported and known HU values was −1.4 ± 6.0 HU. For static fields, the agreements between the TPS‐calculated and measured PDD10, crossline profiles, and inline profiles (FWHM) were within 1.5%, 1.3%, and 0.5 mm, respectively. Measured output factors agreed with the TPS within 1.3%. Measured and calculated dose for static fields in heterogeneous phantoms agreed within 2.5%. The ArcCHECK@ mean absolute Gamma passing rate was 96.4% ± 3.4% for TG 119 and TG 244 plans and 97.8% ± 3.6% for the 21 clinical plans. E2E film analysis showed 0.8 mm total targeting error for isocentric and 1.1 mm for off‐axis treatments. Conclusions The TPS commissioning results of the RefleXion X1 TPS were within the tolerances specified by AAPM TG 53, MPPG 5.a, TG 119, and TG 148. A subset of the commissioning tests has been identified as baseline data for an ongoing QA program.

First-Year Experience of Stereotactic Body Radiation Therapy/Intensity Modulated Radiation Therapy Treatment Using a Novel Biology-Guided Radiation Therapy Machine

“…Simiele et al reported on the results of the commissioning of the X1 TPS. 8 The results showed that the TPS met the specified tolerances for dose calculation accuracy and data transfer for targets >1.5 cm in diameter. The end-to-end testing showed small targeting errors for both isocentric and off-axis treatments.…”

“…Our previous phantom study found the presence of an interplay effect when treating targets moving along the direction of table motion. 8 To prevent the interplay effect, only tumors with an amplitude of motion of <2 cm are treated based on the motion-inclusive target volume. During treatment, a slow couch speed CT scan is acquired to maintain the target motion information and enable accurate patient positioning.…”

IMRT and SBRT Treatment Planning Study for the First Clinical Biology-Guided Radiotherapy System

“…The quality assurance for all tested plans passed gamma 3%/2 mm criteria as described in a related X1 TPS commissioning manuscript. 6…”

“…The first clinical RefleXion X1 system was recently installed at our institution, commissioned [6][7][8] , and is currently in clinical use for IMRT and SBRT since May 2021. This work is the first treatment planning study investigating the capabilities of the clinical X1 TPS to determine the achievable plan quality for various common treatment sites including conventionally fractionated lung, head-and-neck, prostate, anus, brain, and lung SBRT.…”

Evaluation of fan-beam kilovoltage computed tomography image quality on a novel biological-guided radiotherapy platform

“…A recently designed radiotherapy platform has incorporated an on-board kV fan-beam CT (kVCT) and Positron Emission Tomography (PET) system into a ring-shaped gantry that can provide both anatomical and functional images [8] . A few studies on this novel radiotherapy platform have been reported regarding the initial machine commissioning [9] , the characteristics of the PET imaging system performance [10] , treatment planning experiences [11] , [12] as well as a detailed clinical workflow for using this system for biology-guided radiotherapy [13] . However, the imaging performance of the kVCT system has not been investigated.…”