Dosimetric validation of a magnetic resonance image gated radiotherapy system using a motion phantom and radiochromic film.

Journal Article (Journal Article)

PURPOSE: Magnetic resonance image (MRI) guided radiotherapy enables gating directly on the target position. We present an evaluation of an MRI-guided radiotherapy system's gating performance using an MRI-compatible respiratory motion phantom and radiochromic film. Our evaluation is geared toward validation of our institution's clinical gating protocol which involves planning to a target volume formed by expanding 5 mm about the gross tumor volume (GTV) and gating based on a 3 mm window about the GTV. METHODS: The motion phantom consisted of a target rod containing high-contrast target inserts which moved in the superior-inferior direction inside a body structure containing background contrast material. The target rod was equipped with a radiochromic film insert. Treatment plans were generated for a 3 cm diameter spherical planning target volume, and delivered to the phantom at rest and in motion with and without gating. Both sinusoidal trajectories and tumor trajectories measured during MRI-guided treatments were used. Similarity of the gated dose distribution to the planned, motion-frozen, distribution was quantified using the gamma technique. RESULTS: Without gating, gamma pass rates using 4%/3 mm criteria were 22-59% depending on motion trajectory. Using our clinical standard of repeated breath holds and a gating window of 3 mm with 10% target allowed outside the gating boundary, the gamma pass rate was 97.8% with 3%/3 mm gamma criteria. Using a 3 mm window and 10% allowed excursion, all of the patient tumor motion trajectories at actual speed resulting in at least 95% gamma pass rate at 4%/3 mm. CONCLUSIONS: Our results suggest that the device can be used to compensate respiratory motion using a 3 mm gating margin and 10% allowed excursion results in conjunction with repeated breath holds. Full clinical validation requires a comprehensive evaluation of tracking performance in actual patient images, outside the scope of this study.

Full Text

Duke Authors

Cited Authors

  • Lamb, JM; Ginn, JS; O'Connell, DP; Agazaryan, N; Cao, M; Thomas, DH; Yang, Y; Lazea, M; Lee, P; Low, DA

Published Date

  • May 2017

Published In

Volume / Issue

  • 18 / 3

Start / End Page

  • 163 - 169

PubMed ID

  • 28436094

Pubmed Central ID

  • PMC5689863

Electronic International Standard Serial Number (EISSN)

  • 1526-9914

Digital Object Identifier (DOI)

  • 10.1002/acm2.12088


  • eng

Conference Location

  • United States