Lung radiotherapy verification with a 3D printed thorax phantom and an ionisation chamber array

In this study, a 3D printing error inspired the development of a novel method for using a sagittally-sliced 3D printed thorax phantom to perform dosimetric verifications of lung radiotherapy treatment methods using a 2D ionization chamber array. A full-size thorax model was designed for 3D printing with multiple tissue densities including lung and bone and printed as a series of 2.4 cm sagittal slices using a Raise 3D Pro dual nozzle printer (Raise 3D Technologies Inc, Irvine, USA). An error introduced midway through printing resulted in one half of the phantom being printed at unrealistically high densities. A method was therefore devised whereby the entire phantom was used to plan two lung treatments, one conventionally fractionated and one hypo-fractionated, which were then verified via measurements using an Octavius 729 ionisation chamber array (PTW-Freiburg GmbH, Freiburg, Germany) in combination with several correctly-printed slices of the phantom. The measurements allowed dose distributions in planes through the target, adjacent to the target and at the location key of organs at risk to be verified, for both treatment plans. This method has the potential to be adapted for use with other phantoms and other dosimetry arrays to allow efficient evaluation of future treatment techniques.