Initial validation of proton dose calculations on SPR images from DECT in treatment planning system

• Type of Material: Article
• Authors: Sina Mossahebi, University of Maryland School of Medicine; Pouya Sabouri, Miami Cancer Institute; Haijian Chen, Emory University; Michelle Mundis, Maryland Proton Treatment Center; Matthew O'Neil, Associates Medical Physics; Paul Maggi, University of Maryland School of Medicine; Jerimy C Polf, University of Maryland School of Medicine
• Language: English
• Date: 2021-09-01
• Publisher: International Journal of Particle Therapy
• Publication Version: Final Published Version
• Copyright Statement: © 2020 The Author(s)
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.14338/IJPT-XX-000XX.1
• Title of Journal or Parent Work: International Journal of Particle Therapy
• Volume: 7
• Issue: 2
• Start Page: 51
• End Page: 61
• Grant/Funding Information: The authors have no funding to disclose.
• Keywords: proton therapy; range uncertainty; dual energy CT; stopping power ratio; treatment planning
• Research Categories: Biology, Radiation; Health Sciences, Oncology

Abstract

Purpose: To investigate and quantify the potential benefits associated with the use of stopping-power-ratio (SPR) images created from dual-energy computed tomography (DECT) images for proton dose calculation in a clinical proton treatment planning system (TPS). Materials and Methods: The DECT and single-energy computed tomography (SECT) scans obtained for 26 plastic tissue surrogate plugs were placed individually in a tissue-equivalent plastic phantom. Relative-electron density (qe) and effective atomic number (Zeff) images were reconstructed from the DECT scans and used to create an SPR image set for each plug. Next, the SPR for each plug was measured in a clinical proton beam for comparison of the calculated values in the SPR images. The SPR images and SECTs were then imported into a clinical TPS, and treatment plans were developed consisting of a single field delivering a 10 3 10 3 10-cm3 spread-out Bragg peak to a clinical target volume that contained the plugs. To verify the accuracy of the TPS dose calculated from the SPR images and SECTs, treatment plans were delivered to the phantom containing each plug, and comparisons of point-dose measurements and 2-dimensional c-analysis were performed. Results: For all 26 plugs considered in this study, SPR values for each plug from the SPR images were within 2% agreement with measurements. Additionally, treatment plans developed with the SPR images agreed with the measured point dose to within 2%, whereas a 3% agreement was observed for SECT-based plans. c-Index pass rates were. 90% for all SECT plans and. 97% for all SPR image-based plans. Conclusion: Treatment plans created in a TPS with SPR images obtained from DECT scans are accurate to within guidelines set for validation of clinical treatment plans at our center. The calculated doses from the SPR image-based treatment plans showed better agreement to measured doses than identical plans created with standard SECT scans.