OC-0533: ADAM: a breathing phantom for testing radiotherapy treatment on moving lesions

Purpose or Objective Dose delivery to moving targets can be approached following different strategies. For stereotactic radiotherapy treatments motion-encompassing methods, respiratory-gating techniques and respiration- synchronized techniques permit the treatment during lesions motion using different dose planning/delivering solutions. In all cases the complexity of the proposed methods needs the development of solutions for accurate Quality Assurance tests as stated also by AAPM TG76. For this purpose we developed a new phantom: ADAM (Anthropomorphic Dynamic breAthing Model), capable of simulating realistic patient movements. The phantom and some preliminary tests showing ADAM performances are here presented. Material and Methods ADAM is a 3D printed anthropomorphic phantom created using a real patient CT data. The central portion of the torso contains lungs and ribs and is made of materials mimicking human tissue Hounsfield Unit. The lungs are shaped thus to host four water equivalent inserts (WEI) that simulate lung lesions and a fillable QA sphere (QAS) to test reconstruction performances of 4D scanners. Films can be inserted between two WEIs and a specific housing for a diamond detector has been drilled into one WEI. 6 small tin markers have also been included near the fourth WEI to test markers guided tracking procedure. The anterior part of the phantom moves up and down in sync with lungs movements driven by an Arduino programmable board hosted in the caudal phantom portion. Elliptical paths (axes up to 2cm), pre-programmed in the microcontroller , and patient specific respiratory movements, programmable by users, can be chosen on the LCD screen placed on the caudal extremity of the phantom. Preliminary tests were performed to assess Adam usability and its performances in terms of HU, WEI motion repeatability and lungs-to-surface motion correlation. Finally a VMAT plan, to deliver 18Gy to one internal WEI, was planned on an average reconstructed 4DCT data set and delivered to ADAM. Dose was prescribed to 95% of the PTV = ITV (encompassing all motion and delineated on MIP) + 5 mm margin. The delivered dose distribution, measured with a Gafchromic EBT3 film, was overlapped on the WEI to assess moving target dose coverage. Results In Figure 1 ADAM and some internal details, as appear in CT images, are presented. CT acquisitions demonstrate realistic human tissues HU values: -860±37, 77±30, 83±20, 1098±84 respectively for lung, thorax soft tissue, WEI and bone. The absence of artifacts of reconstructed QAS and WEIs in all phases, demonstrate lungs-to-surface motion correlation. Movement tests show a long (20 days) and short-term (30min) amplitude repeatability <1 mm along both axes. In Figure 2 measured dose distribution delivered to a moving target is shown together with the QAS volume measured in static CT and in some 4DCT reconstructed. Conclusion ADAM demonstrates suitable performances to test instruments and methods used to treat moving lesions.