PLA as a suitable 3D printing thermoplastic for use in external beam radiotherapy.

The purpose of this paper is to investigate the tissue equivalence and radiological properties of Polylactic Acid (PLA) to determine if this material is suitable for use as a 3D printing thermoplastic for radiotherapy applications. Profiles and percentage depth-dose measurements (PDDs) were analysed for photon and electron modalities with PLA samples (~ 1.25 g/cm3) to determine material dosimeteric characteristics. Beam profiles and PDDs from treatment planning system (TPS) simulations, water tank measurements and radiochromic film measurements were compared. Tissue equivalence was determined through CT scanning several PLA samples and measuring the Hounsfield units (HUs) to determine relative electron density (RED), mass density and mass attenuation, these results were compared to several commercial tissue phantoms with varying properties. Geometric accuracy was tested by comparing digitally planned dimensions to physical and CT image measurements. Finally, resistance to radiation damage was tested by exposing PLA samples to several thousand monitor units (MUs) over several weeks and inspecting for damage. It was determined that PLA is a safe and effective thermoplastic for use as a patient specific bolus for both electron and photon treatment modalities. The material properties have been characterised and can be accurately modelled in the MONACO TPS.