Characterisation of 3D-printable thermoplastics to be used as tissue-equivalent materials in photon and proton beam radiotherapy end-to-end quality assurance devices.

OBJECTIVE: To investigate the potential of 3D-printable thermoplastics as tissue-equivalent materials to be used in multimodal radiotherapy end-to-end quality assurance (QA) devices. APPROACH: Six thermoplastics were investigated: Polylactic Acid (PLA), Acrylonitrile Butadiene Styrene (ABS), Polyethylene Terephthalate Glycol (PETG), Polymethyl Methacrylate (PMMA), High Impact Polystyrene (HIPS) and StoneFil. Measurements of mass density (ρ), Relative Electron Density (RED), in a nominal 6MV photon beam, and Relative Stopping Power (RSP), in a 210MeV proton pencil-beam, were performed. Average Hounsfield Units (HU) were derived from CTs acquired with two independent scanners. The calibration curves of both scanners were used to predict average ρ, RED and RSP values and compared against the experimental data. Finally, measured data of ρ, RED and RSP was compared against theoretical values estimated for the thermoplastic materials and biological tissues. MAIN RESULTS: Overall, good ρ and RSP CT predictions were made; only PMMA and PETG showed differences >5%. The differences between experimental and CT predicted RED values were also <5% for PLA, ABS, PETG and PMMA; for HIPS and StoneFil higher differences were found (6.94% and 9.42/15.34%, respectively). Small HUs variations were obtained in the CTs for all materials indicating good uniform density distribution in the samples production. ABS, PLA, PETG and PMMA showed potential equivalency for a variety of soft tissues (adipose tissue, skeletal muscle, brain and lung tissues, differences within 0.19% - 8.35% for all properties). StoneFil was the closest substitute to bone, but differences were >10%. Theoretical calculations of all properties agreed with experimental values within 5% difference for most thermoplastics. SIGNIFICANCE: Several 3D-printed thermoplastics were promising tissue-equivalent materials to be used in devices for end-to-end multimodal radiotherapy QA and may not require corrections in treatment planning systems' dose calculations. Theoretical calculations showed promise in identifying thermoplastics matching target biological tissues before experiments are performed.

ALT in combination with triple-rolled TFL for reconstruction of a complex tendoachilles defect: technical details and rehabilitation regime.

A fit man in his 60s presented with an infected Achilles tendon (AT) following two failed repairs for a traumatic rupture. Initial debridement of necrotic tissue resulted in a large soft tissue defect requiring robust coverage. Following aggressive wound management, an anterolateral thigh flap was elevated with tensor fasciae latae (TFL) which was triple-rolled to provide soft tissue coverage and tendon reconstruction.The flap remained healthy and was monitored with a flow coupler device. Initially, the foot was placed in plantarflexion before gradually increasing the angle to neutral and a thermoplastic splint was used to offload pressure on the flap. Following 1 month of non-weight-bearing, gentle mobilisation began. Three months postoperatively, the patient could walk, had resumed indoor cycling and demonstrated a comparable heel raise with the contralateral side. MRI showed a taut TFL attached to the distal AT and ultrasound showed a smoothly gliding TFL.