A novel deformable lung phantom with programably variable external and internal correlation

Abstract

Purpose Lung motion phantoms used to validate radiotherapy motion management strategies have fairly simplistic designs that do not adequately capture complex phenomena observed in human respiration such as external and internal deformation, variable hysteresis and variable correlation between different parts of the thoracic anatomy. These limitations make reliable evaluation of sophisticated motion management techniques quite challenging. In this work, we present the design and implementation of a programmable, externally and internally deformable lung motion phantom that allows for a reproducible change in external–internal and internal–internal correlation of embedded markers. Methods An in‐house–designed lung module, made from natural latex foam was inserted inside the outer shell of a commercially available lung phantom (RSD, Long Beach, CA, USA). Radiopaque markers were placed on the external surface and embedded into the lung module. Two independently programmable high‐precision linear motion actuators were used to generate primarily anterior–posterior (AP) and primarily superior–inferior (SI) motion in a reproducible fashion in order to enable (a) variable correlation between the displacement of interior volume and the exterior surface, (b) independent changes in the amplitude of the AP and SI motions, and (c) variable hysteresis. The ability of the phantom to produce complex and variable motion accurately and reproducibly was evaluated by programming the two actuators with mathematical and patient‐recorded lung tumor motion traces, and recording the trajectories of various markers using kV fluoroscopy. As an example application, the phantom was used to evaluate the performance of lung motion models constructed from kV fluoroscopy and 4DCT images. Results The phantom exhibited a high degree of reproducibility and marker motion ranges were reproducible to within 0.5 mm. Variable correlation was observed between the displacements of internal–internal and internal–external markers. The SI and AP components of motion of a specific marker had a correlation parameter that varied from −11 to 17. Monitoring a region of interest on the phantom's surface to estimate internal marker motion led to considerably lower uncertainties than when a single point was monitored. Conclusions We successfully designed and implemented a programmable, externally and internally deformable lung motion phantom that allows for a reproducible change in external–internal and internal–internal correlation of embedded markers.

Development and prospective in‐patient proof‐of‐concept validation of a surface photogrammetry + CT‐based volumetric motion model for lung radiotherapy

“…Any surrogate-based volumetric motion model can be validated so long as there is access to in-room kV fluoroscopy. 49 Whereas, in the case of this patient, the model largely retained its fidelity over multiple fractions, there were instances [Figs. 12(a) and 12(b)] where this correspondence changed.…”

“…Also noteworthy is the fact that our proof‐of‐concept validation strategy is agnostic to the underlying motion model. Any surrogate‐based volumetric motion model can be validated so long as there is access to in‐room kV fluoroscopy …”

Development of a deformable lung phantom with 3D‐printed flexible airways

“…Several research groups have developed deformable lung phantoms since the mid‐2000s . Nioutsikou et al .…”

“…Several research groups have developed deformable lung phantoms since the mid-2000s. [8][9][10][11][12][13][14] Nioutsikou et al 8 constructed a breathing phantom with a deforming lung to investigate the effect of organ and tumor motion that degrades planned dose distributions. This phantom was composed of two solid cylindrical tumors and two accordion-type bottles filled with dampened sponges, which were mounted inside a Perspex thorax-like cavity.…”

“…Gholampourkashi et al constructed a deformable phantom to experimentally verify 4D Monte Carlo simulations; they inserted a removable plug that included an elastic tumor holding dosimeter. Ranjbar et al presented an externally and internally deformable lung phantom. The authors used a commercially available phantom as a shell for the anthropomorphic exterior, and in‐house designed foam with fiducial markers was inserted inside the shell.…”