title: A Recommendation on How to Analyze In-Room PET for In Vivo Proton Range Verification Using a Distal PET Surface Method.
abstract: We describe the rationale and implementation of a method for analyzing in-room positron emission tomography (PET) data to verify the proton beam range. The method is based on analyzing distal PET surfaces after passive scattering proton beam delivery. Typically in vivo range verification is done by comparing measured and predicted PET distribution for a single activity level at a selected activity line along the beam passage. In the method presented here, we suggest using a middle point method based on dual PET activity levels to minimize the uncertainty due to local variations in the PET activity. Furthermore, we introduce 2-dimensional (2D) PET activity level surfaces based on 3-dimensional maps of the PET activities along the beam passage. This allows determining not only average range differences but also range difference distributions as well as root mean square deviations (RMSDs) for a more comprehensive range analysis. The method is demonstrated using data from 8 patients who were scanned with an in-room PET scanner. For each of the 8 patients, the average range difference was less than 5 mm and the RMSD was 4 to 11 mm between the measured and simulated PET activity level surfaces for single-field treatments. An ongoing protocol at our institution allows the use of a single field for patients being imaged for the PET range verification study at 1 fraction during their treatment course. Visualizing the range difference distributions using the PET surfaces offers a convenient visual verification of range uncertainties in 2D. Using the distal activity level surfaces of simulated and measured PET distributions at the middle of 25% and 50% activity level is a robust method for in vivo range verification.
authors.affiliation: Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA Department of Radiological Science and Research Institute of Health Science, Yonsei University, Wonju, Kangwon, Republic of Korea.
authors.forename: Chul Hee
authors.initials: CH
authors.lastname: Min
authors.affiliation: Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
authors.forename: Xuping
authors.initials: X
authors.lastname: Zhu
authors.affiliation: Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
authors.forename: Kira
authors.initials: K
authors.lastname: Grogg
authors.affiliation: Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
authors.forename: Georges
authors.initials: G
authors.lastname: El Fakhri
authors.affiliation: Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Winey
authors.affiliation: Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA hpaganetti@partners.org.
authors.forename: Harald
authors.initials: H
authors.lastname: Paganetti
mesh_terms: D006801:Humans; D049268:Positron-Emission Tomography / Q000379:methods*; D061766:Proton Therapy / Q000379:methods*; D011522:Protons; D013223:Statistics as Topic / Q000379:methods*
chemical_list: D011522:Protons
keywords: Monte Carlo simulation; distal PET surface; in vivo range; in-room PET; proton therapy