Stereotactic MR-guided online adaptive radiation therapy (SMART) for the treatment of liver metastases in oligometastatic patients: initial clinical experience

Abstract

Purpose We aimed to present our initial clinical experience on the implementation of a stereotactic MR-guided online adaptive radiation therapy (SMART) for the treatment of liver metastases in oligometastatic disease. Materials and Methods Twenty-one patients (24 lesions) with liver metastasis treated with SMART were included in this retrospective study. Step-and-shoot intensity-modulated radiotherapy technique was used with daily plan adaptation. During delivery, real-time imaging was used by acquiring planar magnetic resonance images in sagittal plane for monitoring and gating. Acute and late toxicities were recorded both during treatment and follow-up visits. Results The median follow-up time was 11.6 months (range, 2.2 to 24.6 months). The median delivered total dose was 50 Gy (range, 40 to 60 Gy); with a median fraction number of 5 (range, 3 to 8 fractions) and the median fraction dose was 10 Gy (range, 7.5 to 18 Gy). Ninety-three fractions (83.7%) among 111 fractions were re-optimized. No patients were lost to follow-up and all patients were alive except one at the time of analysis. All of the patients had either complete (80.9%) or partial (19.1%) response at irradiated sites. Estimated 1-year overall survival was 93.3%. Intrahepatic and extrahepatic progression-free survival was 89.7% and 73.5% at 1 year, respectively. There was no grade 3 or higher acute or late toxicities experienced during the treatment and follow-up course. Conclusion SMART represents a new, noninvasive and effective alternative to current ablative radiotherapy methods for treatment of liver metastases in oligometastatic disease with the advantages of better visualization of soft tissue, real-time tumor tracking and potentially reduced toxicity to organs at risk.

Multi-Institutional Outcomes of Stereotactic Magnetic Resonance Image Guided Adaptive Radiation Therapy With a Median Biologically Effective Dose of 100 Gy10 for Non-bone Oligometastases

“…Henke et al also published results of a phase 1 trial of SMART for ovarian OM showing that dose escalation was safe. 26 Ugurluer et al 19 evaluated SMART in 21 patients treated to 24 liver metastases to a median total dose of 50 Gy in 5 fractions (BED = 100 Gy 10 ) and 83.7% of fractions were reoptimized; no grade 3+ toxicity was reported. In our study, there was no reported grade 3 or higher toxicity despite the median prescribed BED of 100 Gy 10 , adding to the evidence suggesting that SMART is an ideal strategy to deliver ablative dose even to lesions in challenging anatomic locations, such as lymph nodes in the abdomen and pelvis.…”

“…The feasibility of stereotactic magnetic resonance-guided adaptive radiation therapy (SMART) has been demonstrated for tumors in the chest, abdomen, and pelvis. 13 , 14 , 15 , 16 , 17 , 18 , 19 However, most of the supporting literature consists of small retrospective and phase 1 trials. The intent of this analysis was to evaluate multi-institutional outcomes of SMART for OM to better understand the benefits of this novel technology.…”

MR-guided adaptive versus ITV-based stereotactic body radiotherapy for hepatic metastases (MAESTRO): a randomized controlled phase II trial

“…MRgRT with its technical innovations of real-time imaging, gating and online on-table adaption is believed to improve hepatic SBRT. First publications on MR-guided SBRT of liver lesions show promising results [ 39 , 40 , 46 – 52 ]. With a maximum of 21 patients with liver metastases per study and no randomized controlled trials (RCT), high-level evidence is still missing.…”

“…Up to now, studies for MRgRT of hepatic lesions are scarce with mainly retrospective analyses, observational studies and small case series, limited to a maximum of 21 patients with liver metastases per study [ 39 , 40 , 46 – 52 ]. However, MRgRT is very staff-intense and time-consuming compared to standard CT-guided hepatic SBRT [ 53 , 54 ].…”

Compact bunker shielding assessment for 1.5 T MR-Linac

“…The magnetic resonance-guided linear accelerator (MR-Linac), a linear accelerator and MRI scanner combination, is a recent medical development. It offers high-resolution real time MR imaging during treatment 10 – 13 . Similar to conventional MRI, MR images acquired via MR-Linac are affected by the electromagnetic noise of nearby geomagnetic fields and electronic devices.…”