Encrypted login | home

Program Information

Dose Tracking On An MR-Linac for Online QA and Plan Adaptation in Abdominal Organs

M Glitzner

M Glitzner1*, S Crijns1 , B Denis de Senneville1,2 , C Kontaxis1 , F Prins1 , J Lagendijk1 , B Raaymakers1 , (1) University Medical Center Utrecht, Utrecht, The Netherlands, (2) Mathematical Institute of Bordeaux, University of Bordeaux, Talence Cedex, France


SU-E-J-77 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

Recent developments made MRI-guided radiotherapy feasible. Simultaneously performed imaging during dose delivery reveals the influence of changes in anatomy not yet known at the planning stage. When targeting highly motile abdominal organs, respiratory gating is commonly employed in MRI and investigated in external beam radiotherapy to mitigate malicious motion effects. The purpose of the presented work is to investigate anatomy-adaptive dose reconstruction in the treatment of abdominal
organs using concurrent (duplex) gating of an integrated MR-linac modality.

Using navigators, 3D-MR images were sampled during exhale phase, requiring 3s per axial volume (360x260x100mm³, water-selective T1w-FFE). Deformation vector fields (DVF) were calculated for all imaging dynamics with respect to initial anatomy, yielding an estimation of anatomy changes over the time of a fraction. A pseudo-CT was generated from the outline of a reference MR image, assuming a water-filled body. Consecutively, a treatment was planned on a fictional kidney lesion and optimized simulating a 6MV linac in a 1.5T magnetic field. After delivery, using the DVF, the pseudo-CT was deformed and dose accumulated for every individual gating interval yielding the true accumulated dose on the dynamic anatomy during beam-on.

Dose-volume parameters on the PTV show only moderate changes when incorporating motion, i.e. ΔD₉₉(GTV)=0.3Gy with D₉₉(GTV)=20Gy constraints. However, local differences in the PTV region showed underdosages as high as 2.7Gy and overdosages up to 1.4Gy as compared to the optimized dose on static anatomy.

A dose reconstruction toolchain was successfully implemented and proved its potential in the duplex gated treatment of abdominal organs by means of an MR-linac modality. While primary dose constraints were not violated on the fictional test data, large deviations could be found locally, which are left unaccounted for in conventional treatments. Dose-tracking of both target structures and organs at risk using 3D MRI during treatment enables truly adaptive hypofractionated radiotherapy.

Funding Support, Disclosures, and Conflict of Interest: This work was funded by the SoRTS consortium, which includes the industry partners Elekta, Philips and Technolution

Contact Email: