A novel 4D-phantom for evaluation of PET/CT-guided radiotherapy

Ziel/Aim:

Tumor movement has always challenged cancer treatment and modern radiotherapy includes the compensation of organ movement induced inaccuracies, both in therapy planning and delivery. Tumor- and organ movements also affect quantitative accuracy for diagnostic purposes. Phantom studies are important to estimate the intensity of these uncertainties. Main objective of the presented project was to develop a 4D-phantom that can be equipped with tumor, which can be moved on highly reproducible 3D-trajectories. The phantom should be usable within an end-to-end workflow to measure motion-induced uncertainties in imaging, treatment planning, and radiation delivery.

Methodik/Methods:

A 3-dimensional mechanics equipped with three pneumatically driven axes was constructed to accurately reproduce the breathing-induced motion of lung tumors. A control-oriented model that describes the robot kinematics and a cascaded flatness-based control approach is implemented on a real time system, warranting highly reproducible and individualized trajectories of breathing-induced motion of a tumor model. Based on the work by Seppenwoolde et al [1] a mathematical model for the description of the 3-dimensional motion of the tumor model has been described. 4D PET/CT scans of the new phantom with different respiratory motion patterns were acquired and end-to-end test were performed; from PET/CT scanning to transferring data to the planning system, target volume delineation and test of 4D-plans.

Ergebnisse/Results:

The phantom was easily implemented into PET/CT-imaging (Philips Gemini TF 16) and treatment environment (Brainlab VERO). The designed mechanics has a working range of up to 6 cm in all three directions, enabling the realization of complex 3D movements. The absolute position errors for the desired trajectories of the tumor model are approx. 1 mm, enabling the exact replication of trajectories during imaging and treatment validation.

Schlussfolgerungen/Conclusions:

The novel 4D-phantom mimics the complex movement of tumors due to respiratory motion. Obtained 4D PET/CT scans are suitable for quality assurance of 4D-radiotherapy, to test segmentation algorithms and the validation of treatment planning and delivery, both for 3D and 4D plans.

Literatur/References:

[1] Seppenwoolde Y et al. Int J Radiat Oncol Biol Phys. 2002 Jul 15;53(4):822 – 34.