Proton dose calculation on scatter‐corrected CBCT image: Feasibility study for adaptive proton therapy

• Published in: Medical physics (Lancaster) 2015-08, Vol.42 (8), p.4449-4459
• Main Authors: Park, Yang‐Kyun, Sharp, Gregory C., Phillips, Justin, Winey, Brian A.
• Format: Article
• Language: English
• Subjects: 60 APPLIED LIFE SCIENCES; Accelerators; adaptive; ALGORITHMS; ANIMAL TISSUES; Biological material, e.g. blood, urine; Haemocytometers; Calibration; Computed tomography; Computerised tomographs; computerised tomography; COMPUTERIZED TOMOGRAPHY; cone beam; Cone beam computed tomography; Cone-Beam Computed Tomography - instrumentation; Cone-Beam Computed Tomography - methods; CORRECTIONS; Digital computing or data processing equipment or methods, specially adapted for specific applications; Dose‐volume analysis; dosimetry; Dosimetry/exposure assessment; FEASIBILITY STUDIES; graphics processing units; Humans; Image data processing or generation, in general; IMAGE PROCESSING; image reconstruction; LINEAR ACCELERATORS; Male; Medical image artifacts; medical image processing; Medical image reconstruction; Medical treatment planning; Models, Biological; phantoms; Phantoms, Imaging; Processor architectures; Processor configuration, e.g. pipelining; PROSTATE; Prostatic Neoplasms - diagnostic imaging; Prostatic Neoplasms - radiotherapy; PROTON BEAMS; proton therapy; Proton Therapy - instrumentation; Proton Therapy - methods; Protons; RADIATION DOSES; RADIATION PROTECTION AND DOSIMETRY; radiation therapy; Radiation Therapy Physics; Radiometry - methods; RADIOTHERAPY; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted - methods; Reconstruction; scatter correction; Scattering, Radiation; Scintigraphy; Tissue response; Water; X-Rays; X‐ray scattering
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.4923179

Purpose: To demonstrate the feasibility of proton dose calculation on scatter‐corrected cone‐beam computed tomographic (CBCT) images for the purpose of adaptive proton therapy. Methods: CBCT projection images were acquired from anthropomorphic phantoms and a prostate patient using an on‐board imaging system of an Elekta infinity linear accelerator. Two previously introduced techniques were used to correct the scattered x‐rays in the raw projection images: uniform scatter correction (CBCTus) and a priori CT‐based scatter correction (CBCTap). CBCT images were reconstructed using a standard FDK algorithm and GPU‐based reconstruction toolkit. Soft tissue ROI‐based HU shifting was used to improve HU accuracy of the uncorrected CBCT images and CBCTus, while no HU change was applied to the CBCTap. The degree of equivalence of the corrected CBCT images with respect to the reference CT image (CTref) was evaluated by using angular profiles of water equivalent path length (WEPL) and passively scattered proton treatment plans. The CBCTap was further evaluated in more realistic scenarios such as rectal filling and weight loss to assess the effect of mismatched prior information on the corrected images. Results: The uncorrected CBCT and CBCTus images demonstrated substantial WEPL discrepancies (7.3 ± 5.3 mm and 11.1 ± 6.6 mm, respectively) with respect to the CTref, while the CBCTap images showed substantially reduced WEPL errors (2.4 ± 2.0 mm). Similarly, the CBCTap‐based treatment plans demonstrated a high pass rate (96.0% ± 2.5% in 2 mm/2% criteria) in a 3D gamma analysis. Conclusions: A priori CT‐based scatter correction technique was shown to be promising for adaptive proton therapy, as it achieved equivalent proton dose distributions and water equivalent path lengths compared to those of a reference CT in a selection of anthropomorphic phantoms.