Delivered dose quantification in prostate radiotherapy using online 3D cine imaging and treatment log files on a combined 1.5T magnetic resonance imaging and linear accelerator system

Abstract

Background and purpose: Monitoring the intrafraction motion and its impact on the planned dose distribution is of crucial importance in radiotherapy. In this work we quantify the delivered dose for the first prostate patients treated on a combined 1.5T Magnetic Resonance Imaging (MRI) and linear accelerator system in our clinic based on online 3D cine-MR and treatment log files. Materials and methods: A prostate intrafraction motion trace was obtained with a soft-tissue based rigid registration method with six degrees of freedom from 3D cine-MR dynamics with a temporal resolution of 8.5-16.9 s. For each fraction, all dynamics were also registered to the daily MR image used during the online treatment planning, enabling the mapping to this reference point. Moreover, each fraction's treatment log file was used to extract the timestamped machine parameters during delivery and assign it to the appropriate dynamic volume. These partial plans to dynamic volume combinations were calculated and summed to yield the delivered fraction dose. The planned and delivered dose distributions were compared among all patients for a total of 100 fractions. Results: The clinical target volume underwent on average a decrease of 2.2% ± 2.9% in terms of D99% coverage while bladder V62Gy was increased by 1.6% ± 2.3% and rectum V62Gy decreased by 0.2% ± 2.2%. Conclusions: The first MR-linac dose reconstruction results based on prostate tracking from intrafraction 3D cine-MR and treatment log files are presented. Such a pipeline is essential for online adaptation especially as we progress to MRI-guided extremely hypofractionated treatments.

Technical Challenges of Real-Time Adaptive MR-Guided Radiotherapy

“…A major challenge of real-time adaptive RT is the methodology of real-time dose calculation or reconstruction. Fast et al ( 61 ) proposed a tool for online dose reconstruction which determined the delivered dose based on pre-calculated dose influence data in less than 10 ms. After initial investigations of online dose reconstruction based on 2D cine MR images ( 62 ) and 3D cine MR in addition to treatment log files ( 63 ), recent studies proposed deep learning strategies to empower real-time dose calculation and motion prediction ( 64 , 65 ). Even though proposed for offline planning, methods for deep learning-based dose prediction seem to be promising tools to support real-time dose reconstruction ( 66 , 67 ).…”

Single-fraction prostate stereotactic body radiotherapy: Dose reconstruction with electromagnetic intrafraction motion tracking

“…Consequently, OAR doses in the MER plans should be interpreted with caution. A more accurate dose reconstruction might be obtained by simulating the motion of the prostate only, by shifting the high dose region around it, while keeping the bony structures and the body contours fixed, in an approach similar to the study of Kontaxis et al [36].…”

ESTRO-ACROP recommendations on the clinical implementation of hybrid MR-linac systems in radiation oncology

“…This enables the reconstruction of the delivered dose to be compared with the intended dose delivery for more precise treatment evaluation and/or dose response assessment (e.g. Menten et al [43], Kontaxis et al [44]). These data can be used for off-line adaptation, while in the next step this approach can be used for intra-fraction dose guided adaptation.…”