PMID- 33125725 OWN - NLM STAT- MEDLINE DCOM- 20210514 LR - 20210514 IS - 2473-4209 (Electronic) IS - 0094-2405 (Linking) VI - 48 IP - 1 DP - 2021 Jan TI - openPR - A computational tool for CT conversion assessment with proton radiography. PG - 387-396 LID - 10.1002/mp.14571 [doi] AB - PURPOSE: One of the main sources of uncertainty in proton therapy is the conversion of the Hounsfield Units of the planning CT to (relative) proton stopping powers. Proton radiography provides range error maps but these can be affected by other sources of errors as well as the CT conversion (e.g., residual misalignment). To better understand and quantify range uncertainty, it is desirable to measure the individual contributions and particularly those associated to the CT conversion. METHODS: A workflow is proposed to carry out an assessment of the CT conversion solely on the basis of proton radiographs of real tissues measured with a multilayer ionization chamber (MLIC). The workflow consists of a series of four stages: (a) CT and proton radiography acquisitions, (b) CT and proton radiography registration in postprocessing, (c) sample-specific validation of the semi-empirical model both used in the registration and to estimate the water equivalent path length (WEPL), and (d) WEPL error estimation. The workflow was applied to a pig head as part of the validation of the CT calibration of the proton therapy center PARTICLE at UZ Leuven, Belgium. RESULTS: The CT conversion-related uncertainty computed based on the well-established safety margin rule of 1.2 mm + 2.4% were overestimated by 71% on the pig head. However, the range uncertainty was very much underestimated where cavities were encountered by the protons. Excluding areas with cavities, the overestimation of the uncertainty was 500%. A correlation was found between these localized errors and HUs between -1000 and -950, suggesting that the underestimation was not a consequence of an inaccurate conversion but was probably rather due to the resolution of the CT leading to material mixing at interfaces. To reduce these errors, the CT calibration curve was adapted by increasing the HU interval corresponding to the air up to -950. CONCLUSION: The application of the workflow as part of the validation of the CT conversion to RSPs showed an overall overestimation of the expected uncertainty. Moreover, the largest WEPL errors were found to be related to the presence of cavities which nevertheless are associated with low WEPL values. This suggests that the use of this workflow on patients or in a generalized study on different types of animal tissues could shed sufficient light on how the contributions to the CT conversion-related uncertainty add up to potentially reduce up to several millimeters the uncertainty estimations taken into account in treatment planning. All the algorithms required to perform the workflow were implemented in the computational tool named openPR which is part of openREGGUI, an open-source image processing platform for adaptive proton therapy. CI - (c) 2020 American Association of Physicists in Medicine. FAU - Deffet, Sylvain AU - Deffet S AD - Institute of Information and Communication Technologies, Universite catholique de Louvain, Louvain-La-Neuve, 1348, Belgium. FAU - Cohilis, Marie AU - Cohilis M AD - Center of Molecular Imaging, Radiotherapy and Oncology, Institut de Recherche Experimentale et Clinique (IREC), Universitecatholique de Louvain, Louvain-La-Neuve, 1348, Belgium. FAU - Souris, Kevin AU - Souris K AD - Center of Molecular Imaging, Radiotherapy and Oncology, Institut de Recherche Experimentale et Clinique (IREC), Universitecatholique de Louvain, Louvain-La-Neuve, 1348, Belgium. FAU - Salvo, Koen AU - Salvo K AD - Department of Oncology, Katholieke Universiteit Leuven, Leuven, 3000, Belgium. FAU - Depuydt, Tom AU - Depuydt T AD - Department of Oncology, Katholieke Universiteit Leuven, Leuven, 3000, Belgium. AD - Department of Radiation Oncology, University Hospitals Leuven, Leuven, 3000, Belgium. FAU - Sterpin, Edmond AU - Sterpin E AD - Center of Molecular Imaging, Radiotherapy and Oncology, Institut de Recherche Experimentale et Clinique (IREC), Universitecatholique de Louvain, Louvain-La-Neuve, 1348, Belgium. AD - Department of Oncology, Laboratory of Experimental Radiotherapy, Katholieke Universiteit Leuven, Leuven, 3000, Belgium. FAU - Macq, Benoit AU - Macq B AD - Institute of Information and Communication Technologies, Universite catholique de Louvain, Louvain-La-Neuve, 1348, Belgium. LA - eng GR - Fonds europeen de developpement regional (FEDER)/ GR - 7450517F/Fonds National pour la Recherche Scientifique F.R.S-FNRS/ GR - 8090/MECATECH/BIOWIN/ PT - Journal Article DEP - 20201121 PL - United States TA - Med Phys JT - Medical physics JID - 0425746 RN - 0 (Protons) SB - IM MH - Animals MH - Calibration MH - Humans MH - Phantoms, Imaging MH - *Proton Therapy MH - *Protons MH - Radiography MH - Radiotherapy Planning, Computer-Assisted MH - Swine MH - Tomography, X-Ray Computed OTO - NOTNLM OT - CT calibration OT - multilayer ionization chamber OT - particle imaging OT - proton radiography OT - range uncertainty EDAT- 2020/10/31 06:00 MHDA- 2021/05/15 06:00 CRDT- 2020/10/30 17:15 PHST- 2020/06/08 00:00 [received] PHST- 2020/08/20 00:00 [revised] PHST- 2020/10/15 00:00 [accepted] PHST- 2020/10/31 06:00 [pubmed] PHST- 2021/05/15 06:00 [medline] PHST- 2020/10/30 17:15 [entrez] AID - 10.1002/mp.14571 [doi] PST - ppublish SO - Med Phys. 2021 Jan;48(1):387-396. doi: 10.1002/mp.14571. Epub 2020 Nov 21.