Two-and-a-half-year clinical experience with the world's first magnetic resonance image guided radiation therapy system

Abstract

Purpose: Magnetic resonance image guided radiation therapy (MR-IGRT) has been used at our institution since 2014. We report on more than 2 years of clinical experience in treating patients with the world's first MR-IGRT system.

Methods and materials: A clinical service was opened for MR-IGRT in January 2014 with an MR-IGRT system consisting of a split 0.35T magnetic resonance scanner that straddles a ring gantry with 3 multileaf collimator-equipped 60Co heads. The service was expanded to include online adaptive radiation therapy (ART) MR-IGRT and cine gating after 6 and 9 months, respectively. Patients selected for MR-IGRT were enrolled in a prospective registry between January 2014 and June 2016. Patients were treated with a variety of radiation therapy techniques including intensity modulated radiation therapy and stereotactic body radiation therapy (SBRT). When applicable, online ART was performed and gating on sagittal 2-dimensional cine MR was used. The charts of patients treated with MR-IGRT were reviewed to report on the clinical and treatment characteristics of the initial patients who were treated with this novel technique.

Results: A total of 316 patients have been treated with the MR-IGRT system, which has been integrated into a high-volume clinic. The cases were most commonly selected for improved soft tissue visualization, ART, and cine gating. Seventy-six patients were treated with 3-dimensional conformal radiation therapy, 146 patients with intensity modulated radiation therapy, and 94 patients with SBRT. The most commonly treated disease sites were the abdomen (28%), breast (26%), pelvis (22%), thorax (19%), and head and neck (5%). Sixty-seven patients were treated with online ART over a total of 244 adapted fractions. Cine treatment gating was used for a total of 81 patients.

Conclusions: MR-IGRT has been successfully implemented in a high-volume radiation clinic and provides unique advantages in the treatment of a variety of malignancies. Additional clinical trials are in development to formally evaluate MR-IGRT in the treatment of multiple disease sites with techniques such as SBRT and ART.

Figures

Figure 1

Anatomical site of treatment with magnetic resonance image guided radiation therapy.

Figure 2

Example anatomy for commonly treated disease sites, including gross tumor volumes and planning target volumes in blue and lime and relevant organs-at-risk in purple and orange. Sites include (a) intrahepatic cholangiocarcinoma, (b) early stage breast cancer, (c) bladder cancer, (d) central thorax malignancy, (e) adrenal metastases, (f) locally advanced pancreatic cancer, (g) postoperative prostate cancer, and (h) gastric mucosa-associated lymphoid tissue lymphoma.

Figure 3

Workflow of common disease sites and clinical scenarios in which key features of magnetic resonance image guided radiation therapy are indicated. GU, genitourinary; H&N, head and neck; LAPC, locally advanced pancreatic cancer; liver, primary liver cancer.

Figure 4

Clinical decision flowchart for using magnetic resonance image guided radiation therapy for (a) unresectable pancreatic/liver primary or oligometastatic abdominal malignancy and (b) early stage breast cancer.

Figure 5

(a) Magnetic resonance–based, adaptive plan for fraction 1 met all organ-at-risk constraints based on daily set-up anatomy from fraction 1. (b) Application of the fraction 1 plan to the fraction 2 magnetic resonance image of a patient with a pancreatic tumor (blue color wash) resulted in a violation of the hard duodenal (green color wash) and small bowel (lime color wash) constraints. (c) Daily adaptive planning for fraction 2 achieved resolution of the organ-at-risk constraint violation to the duodenum and small bowel while preserving target volume coverage.

Figure 6

Magnetic resonance real-time cine image with (a, c) the target within the specified gating margin and the beam turned on and (b, d) >10% of the target located outside of the specified gating margin and the beam turned off. Patient 1 had oligometastatic rectal cancer and underwent stereotactic body radiation therapy to a solitary thorax lesion. Patient 2 had a history of stage IIIA non-small cell lung cancer with solitary adrenal metastasis and underwent stereotactic body radiation therapy.