Abstract
Purpose: Verification of patient-specific proton stopping powers obtained in the patient’s treatment position can be used to reduce the distal and proximal margins needed in particle beam planning. Proton radiography can be used as a pretreatment instrument to verify integrated stopping power consistency with the treatment planning CT. Although a proton radiograph is a pixel by pixel representation of integrated stopping powers, the image may also be of high enough quality and contrast to be used for patient alignment. This investigation quantifies the accuracy and image quality of a prototype proton radiography system on a clinical proton delivery system. Methods: We have developed a clinical prototype proton radiography system designed for integration into efficient clinical workflows. We tested the images obtained by this system for water-equivalent thickness (WET) accuracy, image noise, and spatial resolution. We evaluated the WET accuracy by comparing the average WET and rms error in several regions of interest (ROI) on a proton radiograph of a custom peg phantom. We measured the spatial resolution on a CATPHAN Line Pair phantom and a custom edge phantom by measuring the 10% value of the modulation transfer function (MTF). In addition, we tested the ability to detect proton range errors due to anatomical changes in a patient with a customized CIRS pediatric head phantom and inserts of varying WET placed in the posterior fossae of the brain. We took proton radiographs of the phantom with each insert in place and created difference maps between the resulting images. Integrated proton range was measured from an ROI in the difference maps. Results: We measured the WET accuracy of the proton radiographic images to be ±0.2 mm (0.33%) from known values. The spatial resolution of the images was 0.6 lp/mm on the line pair phantom and 1.13 lp/mm on the edge phantom. We were able to detect anatomical changes producing changes in WET as low as 0.6 mm. Conclusion: The proton radiography system produces images with image quality sufficient for pretreatment range consistency verification.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 2271-2278 |
| Number of pages | 8 |
| Journal | Medical Physics |
| Volume | 48 |
| Issue number | 5 |
| DOIs | |
| State | Published - May 2021 |
Funding
This work used resources of the Center for Research Computing and Data at Northern Illinois University and resources at Northwestern Medicine Chicago Proton Center. The authors thank Reinhard Schulte, MD from Loma Linda University for reviewing and commenting on this paper. We also thank Nick Detrich from Ion Beam Applications for his work to create control software to deliver proton spot patterns at the correct intensity and energies required by the radiography system. In addition, we thank Igor Polnyi for his help assembling the detector and assisting during data collection. This work was sponsored by the National Cancer Institute of the National Institutes of Health contract numbers R44CA203499 and R44CA243939, the US Department of the Army contract number W81XWH-10-1-0170, and the US Department of Energy contract number DE-SC0005135. The US Army Medical Research Acquisition Activity, 820 Chandler Street, Fort Detrick MD 21702-5014 is the awarding and administering acquisition office for contract number W81XWH-10-1-0170. The content in this article does not necessarily reflect the position or policy of the Government, and no official endorsement should be inferred.
Keywords
- proton imaging
- proton radiography
- proton range error
- proton therapy
ASJC Scopus subject areas
- Biophysics
- Radiology Nuclear Medicine and imaging