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Table 2 Motion-managed and PET/CT-guided radiotherapy components

From: Challenges and opportunities in patient-specific, motion-managed and PET/CT-guided radiation therapy of lung cancer: review and perspective

Approaches Advantages Disadvantages Comments
Abdominal displacement markers Clinical feasibility Insensitive to small abdominal displacements Indicated for most patients. Use patient-specific block position, camera aperture and brightness to maximize detectable abdominal displacement
Lung volume spirometer Stronger correlation to internal target motion Patient coaching complexity Indicated in patients with small abdominal displacements
Fiducial implants Direct image of internal target motion Invasive procedure and subsequent migration Indicated in patients with accessible lesions when other respiratory signal surrogates not indicated
Image segmentation of diaphragm ROI Non-invasive measure of respiratory motion Challenges associated with deformable registration across phases Ensure phase-sorted images not undersampled through sufficient projections or reliable undersampled image reconstruction algorithms
Deep inspiration breath hold Clinical feasibility Lack of reproducibility and temporal inefficiency Indicated in patients with sufficient lung function to allow for reliable breath hold under audiovisual coaching
Active Breathing Control Reduction of motion envelope Lung function requirement to permit forced breath hold Determine patient-specific lung volume for breath hold (50–80% of max)
Abdominal compression Reduction of abdominal displacement Upper lobe lesions subject to motion in non-diaphragmatic breathers Indicated in diaphragmatic breathers with additional measurement of residual motion when possible to enact tolerance criteria
Static PET/CT Reproducibility Motion-blurred image Indicated for low amplitude motion lesions (e.g. upper lobe, chest wall attached)
Static prospectively gated PET/CT Suppression of motion blurring without loss of SNR Temporal inefficiency Use in conjunction with ABC for patients with random breathing pattern that can achieve sufficient lung volume
Dynamic motion-tracked PET/CT Better representation of target motion Challenge to reproduce correlation at treatment Use in conjuction with RF block, spirometer, fiducials, or image segmentation over all phases of breathing cycle for patients with periodic breathing
Phase-averaged PET/CT Robust low noise image Reduced contrast and quantitative accuracy without motion information Evaluate helical CT to determine whether to use phase-averaged PET or motion-compensated PET/CT
Maximum Intensity Projection PET/CT Represents high confidence interval of motion envelope PET image SNR reduced to equivalent counts for single phase Weight intensity projection distribution across respiratory phases to improve SNR while maintaining motion envelope confidence interval
Quiescent period gated PET/CT Variance reduction from motion over reproducible phase bin Image quality dependent on fractional counts within quiescent window Patient-specific gating window based on either relative displacement amplitude or absolute phase
Multiphase PET/CT Motion compensated images with little information loss Requires sufficient correlation between respiratory signal and target motion Optimize number of phases and phase bin sizes as function of lesion size, location, motion amplitude
Manual contour Patient-specific target delineation Inter-observer variability in target definition Useful as higher order correction to target definition following automated techniques
Absolute/relative threshold Clinical feasibility Uncertainty in threshold due to noise or variation in backround uptake Validate threshold-defined targets as prognostic factors of treatment outcome in abdominothoracic cancer patients
Confidence interval Target motion margins weighted by spatiotemporal likelihood map Limited to single target envelope by ignoring phase-specific information Establish relevant confidence interval criteria based on MIP or motion-weighted intensity projection to build dose volume relationship for fixed normal tissue integral dose
Phase adaptive threshold ROI specific to different phases of target motion Complexity of threshold determination for all phases Validate phase-adapted threshold-defined targets against known target parameters in motion phantoms
Phase adaptive stochastic segmentation Robust to image noise and heterogeneities Dependent on initialization conditions and susceptible to statistical variation Validate in motion phantoms followed by comparison of prognostic value to phase-averaged targets
Single plan from ROI Clinical feasibility Single plan may require frequent adaptation during treatment course Indicated in patients with fewer normal tissue tolerance constraints that allow for sufficient target dose
Single plan from optimal margin target definition Single plan feasibility with motion-compensated target definition Reduced delivery degrees of freedom compared to phase-adapted plan Indicated in patients whose single plan normal tissue constraints do not allow for sufficient target dose
Phase-adapted plan Physical/biological advantages to differential delivery across phases No consensus on weighting scheme for phase fluence maps Indicated in patients whose single motion-compensated plan normal tissue constraints do not allow for sufficient target dose
Single plan to static phantom Clinical feasibility Ignores impact of motion on clinical deliverability of treatment plan Baseline measure of plan deliverability prior to motion uncertainties
Single plan to patient-specific motion phantom Accounts for realistic motion trajectories Plan deliverability limited by motion Plans that fail QA due to motion should be replanned on individual phases
Phase-adapted plan to patient-specific motion phantom Characterize deliverability of phase-correlated plan Higher sensitivity to phantom setup and dosimeter measurement uncertainties Ensure precise and accurate setup of phantom and sufficient spatiotemporal resolution of dosimeters
IGRT Clinical feasibility Reliant on motion control or static lesion to maximize delivery efficacy Daily imaging to verify target motion envelope within PTV
Respiratory-gated IGRT Compromise between delivery reproducibility and treatment efficacy Temporal inefficiency Ensure gating window provides sufficient target coverage to phase gate-matched PTV through daily imaging and respiratory signal measurement
Respiratory-tracked IGRT Advanced delivery optimized to complete target motion trajectory Requires accurate and precise motion prediction algorithm to account for delivery system latency Ensure correlation between imaged target trajectory and planned phase-correlated target trajectory
Planned adaptive treatment Adapt to morphological and biological changes during RT Adapted plan does not account for changes in image signal due to motion Establish criteria for adapting plan that include uncertainties in imaging signal change due to motion
Planned phase-adaptive treatment Adapt to motion-compensated morphological and biological changes during RT Challenge of re-planning from mid Tx motion-compensated PET/CT or from on-board imager alone Determine disease and site-specific criteria for adapting plan based on PET/CT or on-board imager