ADAM a Breathing Anthropomorphic Phantom for Quality Assurance of Respiratory Motion-Management Techniques in Radiation Therapy

Purpose: Different dose planning/delivering solutions have been proposed to deliver dose to moving targets. The complexity of the proposed strategies needs accurate quality assurance tests which are capable of highlighting potential challenges behind each of them. For this purpose has been developed ADAM (Anthropomorphic Dynamic breAthing Model) a phantom capable of simulating realistic patient breathing. ADAM and some tests describing its performances are here presented. Methods: ADAM is a thorax phantom composed by an external bodywork made with a 3D printer. It contains lungs, with embedded inserts simulating lung tumours (LTs), ribs and spine and it is made of materials that reproduce human tissue Hounsfield Unit. The two mobile lungs can be opened to host Gafchromic films. Around one LT 6 small tin markers have been included to test markers guided tracking procedure. Moreover a fillable glass sphere has been inserted in one lung to evaluate the impact of breathing patterns on 4D-CT phase reconstruction. An Arduino programmable board drives lungs along elliptical or linear pre-programmed paths with symmetrical and asymmetrical inhale and exhale phase, while the phantom chest wall moves up and down. Maximum motion amplitude is 12 mm; period ranges between 4.4 and 12 s. ADAM performances were assessed considering: LTs position repeatability, LTs motion repeatability and LT-to-surface motion correlation. Results: The phantom can generate repeatable motion patterns with symmetrical and asymmetrical breathing pattern. Repeatability of thorax and LTs amplitude was less than 0.5 mm, over 60 min, and less than 1mm over a day, after resetting motors each time before use. Maximum and mean LT repositioning reproducibility inside the phantom thorax was 0.9 mm and 0.7+0.2 mm respectively. Good correlation between tumor and surface motion was found with R=0,9992. Conclusion: ADAM demonstrates suitable performances to test respiratory gating and tumor tracking devices used to treat moving lesions.