Prostate HDR Treatment End-to-End Testing with In-House Fabricated 16 Mm EBT4 Radiochromic Film Discs
Abstract
Purpose
To develop and evaluate an end-to-end testing procedure for catheter-based prostate HDR treatments using in-house fabricated 16 mm EBT4 radiochromic film, refining a previously described OSLD-based methodology.
Methods
A CAD-designed, 3D-printed treatment grid assembly was developed to reproducibly position 16mm radiochromic film discs at fixed locations between simulation and irradiation. The assembly replicates a clinical prostate HDR grid and positions film discs >3 cm from the expected 100% isodose lines to minimize steep dose gradients. The phantom, containing treatment catheters and film discs, was submerged in water and CT simulated using dummy discs, which were replaced with calibrated film prior to treatment. Film disc centers were identified using CT re-slicing and optimized window/level settings. Novel integrated air-ring markers within the phantom facilitated accurate localization of the film plane for dose point selection. Film calibration was performed using a 6MV linac. End-to-end testing included: (1) CT simulation with dummy discs and fifteen 240-mm sharp plastic catheters, (2) treatment planning to a simulated prostate HR-CTV, (3) irradiation in water, and (4) flatbed scanning using freely available software analysis and application of dose calibration correction.
Results
With complex treatment geometry and identification of the center of the radiochromic film discs to find the dose in the treatment planning system, agreement between planned and measured dose was within 3%.
Conclusion
End-to-end testing that closely replicates clinical prostate HDR treatments can be accurately performed using a custom 3D-printed assembly, patient catheters, and EBT4 film. This refined approach updates our prior OSLD-based methodology and demonstrates good dosimetric agreement.