Development of an anthropomorphic phantom of the lower extremities for feasibility studies and verification of total-body irradiation

Background: Total-body irradiation (TBI) is a specialised radiotherapy treatment used alongside chemotherapy to prepare leukaemia patients for stem cell transplants. For commissioning and validation of conformal irradiation techniques, anatomically detailed phantoms of the whole body play an important role. This study aimed to create a cost-effective modular phantom of the lower extremities that can be combined with a commercial torso phantom, thus enabling the optimisation of TBI treatment planning and dose delivery. Methods: We designed a modular leg phantom consisting of five key components: foot, calf, knee, thigh, and hip. Variants of knee and hip allow for both straight and angled leg positions. Inserts for dosimeters are integrated into the knee and hip joints, as well as within femur and fibula. To assess the phantom functionality in TBI, we analysed a currently used static-field technique and studied the feasibility of an intensity-modulated sweeping-beam technique. Results: We employed 3D printing to create hollow structures of bones, pelvis, and legs, which we filled with surrogate materials representing soft tissue and bone marrow. We simulated cortical bone with a gypsum coating. The CT numbers of soft tissue and bone surrogates align accurately with literature data. The material properties remained stable even one-year post-manufacturing, ensuring long-term use of the phantom. First dose verification measurements for the static-field technique show an agreement with the prescribed dose within less than ±10 %. Conclusion: The cost-effective modular phantom can be combined with a commercial torso phantom, allowing for the optimization and verification of various CT-based TBI techniques.