Toward MR-integrated proton therapy: modeling the potential benefits for liver tumors

Maryam Moteabbed; Julien Smeets; Theodore S Hong; Guillaume Janssens; Rudi Labarbe; John A Wolfgang; Thomas R Bortfeld

doi:10.1088/1361-6560/ac1ef2

Toward MR-integrated proton therapy: modeling the potential benefits for liver tumors

Phys Med Biol. 2021 Sep 23;66(19). doi: 10.1088/1361-6560/ac1ef2.

Authors

Maryam Moteabbed¹, Julien Smeets², Theodore S Hong¹, Guillaume Janssens², Rudi Labarbe², John A Wolfgang¹, Thomas R Bortfeld¹

Affiliations

¹ Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, United States of America.
² Ion Beam Applications, Louvain-La-Neuve, Belguim.

PMID: 34407528
DOI: 10.1088/1361-6560/ac1ef2

Abstract

Magnetic resonance imaging (MRI)-integrated proton therapy (MRiPT) is envisioned to improve treatment quality for many cancer patients. However, given the availability of alternative image-guided strategies, its clinical need is yet to be justified. This study aims to compare the expected clinical outcomes of MRiPT with standard of practice cone-beam CT (CBCT)-guided PT, and other MR-guided methods, i.e. offline MR-guided PT and MR-linac, for treatment of liver tumors. Clinical outcomes were assessed by quantifying the dosimetric and biological impact of target margin reduction enabled by each image-guided approach. Planning target volume (PTV) margins were calculated using random and systematic setup, delineation and motion uncertainties, which were quantified by analyzing longitudinal MRI data for 10 patients with liver tumors. Proton treatment plans were created using appropriate PTV margins for each image-guided PT method. Photon plans with margins equivalent to MRiPT were generated to represent MR-linac. Normal tissue complication probabilities (NTCP) of the uninvolved liver were compared. We found that PTV margin can be reduced by 20% and 40% for offline MR-guided PT and MRiPT, respectively, compared with CBCT-guided PT. Furthermore, clinical target volume expansion could be largely alleviated when delineating on MRI rather than CT. Dosimetric implications included decreased equivalent mean dose of the uninvolved liver, i.e. up to 24.4 Gy and 27.3 Gy for offline MR-guided PT and MRiPT compared to CBCT-guided PT, respectively. Considering Child-Pugh score increase as endpoint, NTCP of the uninvolved liver was significantly decreased for MRiPT compared to CBCT-guided PT (up to 48.4%,p < 0.01), offline MR-guided PT (up to 12.9%,p < 0.01) and MR-linac (up to 30.8%,p < 0.05). Target underdose was possible in the absence of MRI-guidance (D90 reduction up to 4.2 Gy in 20% of cases). In conclusion, MRiPT has the potential to significantly reduce healthy liver toxicities in patients with liver tumors. It is superior to other image-guided techniques currently available.

Keywords: MRiPT; adaptive therapy; image-guidance; liver cancer; proton therapy.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Humans
Liver Neoplasms* / diagnostic imaging
Liver Neoplasms* / radiotherapy
Magnetic Resonance Imaging / methods
Particle Accelerators
Proton Therapy*
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted / methods
Radiotherapy, Image-Guided* / methods
Radiotherapy, Intensity-Modulated* / methods