Purpose: To design a high throughput respiratory motion QA system using portal dosimetry (PD) and customizable tumor with 3D printing.
Methods: The design is divided into the stage control and tumor printing part. A closed-loop stages was assembled and the tumor was mounted on a rod attached to the stage and driven in the Sup-inf direction. The stage can be programmed to move with variable amplitude, period or according to patient’s breathing curve. 3D printing was used to build customizable tumor to provide realistic representation of the treated tumor. Different PLA fill patterns and percentages were optimized to obtain a HU of close to zeros and the shortest printing time. The set-up was tested with an actual treatment plan comparing the static and moving phantom. Spherical tumors with 2 cm and 4 cm diameter were used for this testing. Gamma passing rate was used to quantify the dose agreement between static and moving phantom.
Results: A linear pattern with 80% in-fill yields the shortest printing time and gives a HU closest to 0. A maximum HU of about 100 is achievable with PLA material. A moving phantom does blurs out the portal dose and causes a disagreement between the dose distribution between the static and moving phantom. A smaller tumor gives a gamma passing rate of 97% while a larger tumor gives a smaller passing rate of 94% with a 2%/2mm criteria.
Conclusion: Appreciable dose difference between moving and static phantom with 4 cm and 2 cm water equivalent tumor phantom can be detected with portal dosimetry. Further work is underway to test the system with phase gating and determine the sensitivity of detecting breathing curve discrepancy and dose degradation due to motion interplay.
Funding Support, Disclosures, and Conflict of Interest: SingHealth Duke-NUS AM & NHIC Joint MedTech Grant (SHF-NHIC/JMT006/2020)