AbstractID: 9353 Title: 3D MAGIC Gel Dosimetry for Verifying Proton Patch Fields
Abstract
Purpose: Patching fields is a technique for combining multiple charged particle beams to
treat a target volume that wraps around a critical structure such as the spinal cord. Typically, the penetration of one beam is adjusted by a milled bolus such that its distal edge
abuts exactly the lateral edge of another beam. Verification of the delivered dose along
the patch surface (junction) is difficult because of the three-dimensional nature of the
target and heterogeneities. 3D-gel dosimetry could verify proper patching in phantom
test cases.
Method: A cylindrical phantom filled with MAGIC gel, XCT scanned, and a target
volume drawn. A treatment plan was developed in which the target was divided into two
sub-volumes. A single proton beam was designed for each sub-volume, apertures and
boluses manufactured, and the phantom treated. A MRI scan was performed, the signal
distribution converted to dose and the dose distribution compared with the treatment plan.
Results: The MRI of the MAGIC gel showed the patch surface between the two fields.
Dose at the junction was 12 - 15% higher than the treatment planning simulation, which
indicated a 17 - 19%. The positions of the MRI isodose curves were within 1 mm of the
curves calculated by the treatment planning system as referenced to phantom fiducials.
Conclusion: This work demonstrates the potential of MAGIC gel for use in visualizing
proton therapy dose distributions. Understanding these distributions is extremely
important when designing 3D, multi-beam combinations around critical structures.