Magnetic Resonance Imaging-Guided Adaptive Radiotherapy for Colorectal Liver Metastases

Abstract

Technological advances have enabled well tolerated and effective radiation treatment for small liver metastases. Stereotactic ablative radiation therapy (SABR) refers to ablative dose delivery (>100 Gy BED) in five fractions or fewer. For larger tumors, the safe delivery of SABR can be challenging due to a more limited volume of healthy normal liver parenchyma and the proximity of the tumor to radiosensitive organs such as the stomach, duodenum, and large intestine. In addition to stereotactic treatment delivery, controlling respiratory motion, the use of image guidance, adaptive planning and increasing the number of radiation fractions are sometimes necessary for the safe delivery of SABR in these situations. Magnetic Resonance (MR) image-guided adaptive radiation therapy (MRgART) is a new and rapidly evolving treatment paradigm. MR imaging before, during and after treatment delivery facilitates direct visualization of both the tumor target and the adjacent normal healthy organs as well as potential intrafraction motion. Real time MR imaging facilitates non-invasive tumor tracking and treatment gating. While daily adaptive re-planning permits treatment plans to be adjusted based on the anatomy of the day. MRgART therapy is a promising radiation technology advance that can overcome many of the challenges of liver SABR and may facilitate the safe tumor dose escalation of colorectal liver metastases.

MRI-LINAC: A transformative technology in radiation oncology

“…This technique allows for better visualization of soft tissue, real-time tumor tracking, motion management (during the breathing cycle) via deep inspiration breath holding techniques (to allow for smaller target volumes), and adaptive planning (to improve target dosing while limiting dose to radiosensitive organs [that move with the respiratory cycle and change their juxtaposition daily] in line with recommended dose constraint guidelines) (74,80). Although the normal organ constraints come from retrospective series, CT based planning (that assumes mobile structures remain in the same position throughout treatment), and animal studies, some have posited that radiation toxicity risks may be overestimated, the dose constraints too conservative, and the tumor unnecessarily underdosed (to meet the dose constraints) in patients treated with MRI guided adaptive radiotherapy (81). Thus, through a combination of raising the tolerance for normal organs at risk and reducing the margins delivered through MRI guidance, the overall dose to the tumor could be substantially increased or improved (82).…”

Local Treatments in the Unresectable Patient with Colorectal Cancer Metastasis: A Review from the Point of View of the Medical Oncologist

“…This allows for better monitoring for in-treatment changes in position of the lesion to treat. Additionally, it allows for a better delimitation of tumors in the liver [ 133 ]. For liver metastases, fiducial placement is usually used to improve correct treatment delivery.…”

“…For liver metastases, fiducial placement is usually used to improve correct treatment delivery. In MR-guided SBRT, no fiducials are needed, avoiding an unnecessary invasive procedure [ 133 ]. Apart from the treated lesion, a margin of 5 mm of normal tissue is usually added.…”

The Prognostic and therapeutic value and clinical implications of fibroblast activation protein-α as a novel biomarker in colorectal cancer

“…Additionally, 25–50% of patients will suffer from metastatic CRC (mCRC) over time [ 6 ]. Compared to localized CRC, the 5-year survival rate of mCRC is low at 14–20% [ 7 , 8 ].…”