Percent Depth Dose (PDD) and Tissue‑Air Ratio (TAR) Measurements Using an Acrylic Phantom and 3D‑Printed Ion Chamber Holders
Abstract
Purpose
This study aimed to generate system-specific Percent Depth Dose (PDD) and Tissue‑Air Ratio (TAR) curves using an acrylic slab phantom and custom 3D‑printed ion‑chamber holders.
Methods
Ion‑chamber holders were designed to hold the Radcal 10X5‑6 ion chamber and 10A96 adapter. It was 3D printed using PLA filament. Two phantom holders with infill densities of 15% and 50% (masses: 509 g and 1216 g, respectively) were printed. The phantom consisted of eight acrylic slabs, each measuring 251 mm × 251 mm × 25 mm. The ion-chamber inside a phantom holder was positioned at depths from 0 to 20 cm in 2.5‑cm increments. For each depth, exposures were measured at nine tube potentials (60–140 kVp). Both infill‑density holders were used for all measurements. In‑air exposure and half‑value layer (HVL) measurements were also performed for the nine kVp settings. All measurements were acquired in a radiographic room with a source‑to‑image distance (SID) of 40 in (101.6 cm), and the beam was collimated to the top surface of the phantom.
Results
Relative to the 15%‑infill holder, the 50%‑infill holder produced higher measured exposures with an average difference below 4%. PDD curves were generated for depths from 0 to 20 cm at each kVp. Linear attenuation coefficients derived from the PDD data ranged from 0.215 cm⁻¹ at 60 kVp to 0.155 cm⁻¹ at 140 kVp. The corresponding HVLs for each kVp were also estimated. TAR curves (exposure in phantom relative to exposure in air) were also determined. For a given depth, TAR increased with kVp, whereas for a fixed kVp, TAR decreased with increasing depth.
Conclusion
PDD and TAR curves were successfully obtained using 3D‑printed ion‑chamber holders and an acrylic phantom. These datasets will support future system specific fetal and organ dose estimation efforts.