Imaging and dosimetric errors in 4D PET/CT-guided radiotherapy from patient-specific respiratory patterns: a dynamic motion phantom end-to-end study

Abstract

Effective positron emission tomography/computed tomography (PET/CT) guidance in radiotherapy of lung cancer requires estimation and mitigation of errors due to respiratory motion. An end-to-end workflow was developed to measure patient-specific motion-induced uncertainties in imaging, treatment planning, and radiation delivery with respiratory motion phantoms and dosimeters. A custom torso phantom with inserts mimicking normal lung tissue and lung lesion was filled with [18F]FDG. The lung lesion insert was driven by 6 different patient-specific respiratory patterns or kept stationary. PET/CT images were acquired under motionless ground truth, tidal breathing motion-averaged (3D), and respiratory phase-correlated (4D) conditions. Target volumes were estimated by standardized uptake value (SUV) thresholds that accurately defined the ground-truth lesion volume. Non-uniform dose-painting plans using volumetrically modulated arc therapy (VMAT) were optimized for fixed normal lung and spinal cord objectives and variable PET-based target objectives. Resulting plans were delivered to a cylindrical diode array at rest, in motion on a platform driven by the same respiratory patterns (3D), or motion-compensated by a robotic couch with an infrared camera tracking system (4D). Errors were estimated relative to the static ground truth condition for mean target-to-background (T/Bmean) ratios, target volumes, planned equivalent uniform target doses (EUD), and 2%-2mm gamma delivery passing rates. Relative to motionless ground truth conditions, PET/CT imaging errors were on the order of 10–20%, treatment planning errors were 5–10%, and treatment delivery errors were 5–30% without motion compensation. Errors from residual motion following compensation methods were reduced to 5–10% in PET/CT imaging, < 5% in treatment planning, and < 2% in treatment delivery. We have demonstrated that estimation of respiratory motion uncertainty and its propagation from PET/CT imaging to RT planning, and RT delivery under a dose painting paradigm is feasible within an integrated respiratory motion phantom workflow. For a limited set of cases, the magnitude of errors was comparable during PET/CT imaging and treatment delivery without motion compensation. Errors were moderately mitigated during PET/CT imaging and significantly mitigated during RT delivery with motion compensation. This dynamic motion phantom end-to-end workflow provides a method for quality assurance of 4D PET/CT-guided radiotherapy, including evaluation of respiratory motion compensation methods during imaging and treatment delivery.

Impact of tumour motion compensation and delineation methods on FDG PET‐based dose painting plan quality for NSCLC radiation therapy

“…This may partly be due to bulky tumors being less mobile compared to early stage NSCLC lesions or the motion not being synchronous throughout the whole tumor volume that limits the observed bulk tumor motion. These findings on bulky locally advanced lung cancer tumors differ from prior reports on motion-induced errors for dose painting of small mobile tumors, in which motion-compensated imaging, planning, and delivery substantially reduced errors 30 . Also, patient selection is of paramount importance even for dose painting of small tumors as peaked doses provide superior local control of early stage disease, as demonstrated by stereotactic body radiotherapy of NCSLC 31 .…”

Evaluation of principal component analysis-based data-driven respiratory gating for positron emission tomography

“…Simulations validated by phantom experiments performed by Liu et al35 found that respiratory motion can lead to reductions of around 30% in SUV max for liver and lung lesions, with increases in lesion volumes. Bowen et al36 found respiratory motion applied to a phantom to cause a decrease of 20% in the ratio of hot sphere SUV max to background. In the current study we quantified contrast recovery based on SUV mean rather than SUV max, and found reductions of nearly 50% when comparing motion (without correction) to no motion.…”

A modern review of the uncertainties in volumetric imaging of respiratory‐induced target motion in lung radiotherapy

“…[164][165][166][167][168][169][170][171] 4D PET-CT has also been shown to reduce the risk of underdosing and geographic miss of targets during treatment in comparison to 3D PET-CT. This is due to applying appropriate margins to the motion-compensated images, rather than just a generic target volume margin for 3D PET-CT. [172][173][174] Four dimensional PET-CT has also improved inter-observer agreement in target delineations for lung SBRT volumes, reiterating the benefit of avoiding a geographic miss. 175 Given the very tangible benefits of motion-resolved images of 4D PET-CT, it is still necessary to be cognizant of the prevalent uncertainties of this modality.…”

“…4D PET‐CT has also been shown to reduce the risk of underdosing and geographic miss of targets during treatment in comparison to 3D PET‐CT. This is due to applying appropriate margins to the motion‐compensated images, rather than just a generic target volume margin for 3D PET‐CT 172–174 . Four dimensional PET‐CT has also improved inter‐observer agreement in target delineations for lung SBRT volumes, reiterating the benefit of avoiding a geographic miss 175 …”