Exhibit Hall | Forum 5
Purpose: It is highly desirable to measure the proton beam-range with a fraction of therapeutic beams (intra-beam) within a single treatment session and guide an on-line adaptive therapy based on measured range-shift. We used a newly developed on-line brain PET to experimentally investigate the feasibility of such proton-induced positron activity-range (AR) measurement with low dose and short acquisition time.
Methods: The PET with ~32cm trans-axial and ~6.4cm axial field-of-view was used to measure ARs generated from scanning-beam proton radiations to a head-neck Stereotactic-End-to-End-Verification (STEEV) phantom and a Lucite cylinder inserted inside a 16x16x16 cubic cm water tank. ARs were measured with different pristine beam energies, doses, acquisition times, and extra Lucite sheets inserted between the beam nozzle and the phantom for altering the beam pathlength. To the purpose of fast on-line imaging, no data corrections except energy and timing windows were applied. Beam ranges and doses were measured with Gafchromic EBT films for reference.
Results: With 105.2MeV beam energy, ARs with 60s PET acquisition time immediately after the proton radiation of 20MU (~6Gy) high dose or 1MU (~0.3Gy) low dose were 62.4mm or 62.0mm (standard deviation STD=1.0mm) from Lucite phantom, and 63.3mm or 62.2mm (STD=2.85mm) from STEEV phantom. ARs measured with different beam energies and different inserted Lucite sheet thicknesses were fitted well to expected curves. Different methods were applied to improve the measurement accuracy and precision that include the optimization of image reconstruction, noise rejection, and minimizing PET background activity, etc.
Conclusion: Initial phantom studies demonstrated the feasibility of intra-beam range measurement with on-line PET imaging. Ongoing study focuses on further improving the AR measurement accuracy and conducting studies on range-guided adaptive proton therapy.
Funding Support, Disclosures, and Conflict of Interest: This study was partially supported by NIH funding 1R01CA218402.