Author: Soon N. Huh, Perry B. Johnson, Jiyeon Park, Ryan Stevens 👨🔬
Affiliation: University of Florida Health Proton Therapy Institute, UF Health Proton Therapy Institute, UFHPTI 🌍
Purpose:
Cone-beam computed tomography (CBCT) doses shall be limited for pediatric patients in clinical settings. Device called Filtimator (filter+collimator) was custom designed to reduce setup CBCT radiation doses, improving image quality in region-of-interest (ROI) for pediatric patients receiving proton therapy using IBA Proteus-Plus and Proteus-One machines.
Methods:
Fabricated filtimator mounts directly to Proteus-One X-ray tube and ground-rolling-floor (GRF) for Proteus-Plus. Attachment and detachment is safely optimized using two sets of magnets and suction-cups coupled contact switches. Two collimator regions (peripheral) consist of copper sheets in incremental thicknesses 0.1mm-2.5mm. Central filter region consists of differing thickness copper, composing filter+collimator regions (ranging 1.0-2.5mm sheets) in peripheral registration region and ROI (0.6mm thickness) with beam center of ~0.6mm Cu increasing average energy (80-100KVp) in ROI region, also reducing scattered radiation for acquiring higher signal-to-noise ratio (SNR) in ROI region. Filtimator can be moved superior/inferior direction defining any ROI region. Maximum Cu thickness (2-3mm) determines image fusion ROI. House-made software (median and Wiener) remove statistical noise due to lower dose.
Results:
For most cases, ROI of 5cm field size at central region is sufficient. 100kVp protocol plus filtimator reduces dose ten-fold, bony artefacts, and improves image quality (CNR). Adult and pediatric phantoms were used to estimate imaging quality. Catphan-604 was used to evaluate imaging quality resolution and SNR. “Isocenter-shift” technique, in addition to filtimator, removes artefacts from hardware, e.g. Omaya reservoir. Dose reduction to optic pathways can be implemented using secondary shielding from filtimator.
Conclusion:
Ultra-low-dose CBCT for pediatric cancer patients can be implemented without major changes to imaging system. The concept “As-low-as-technically-achievable: ALATA” so that we could use daily CBCT for setup. Filtimator’s clinical application is possibly the near future. Filtimator may be rotated, reducing dose (factor of 8) to anterior part of body, such as small bowels for CSI or spine treatments.