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.
Highlights
Colorectal cancer commonly metastasizes to the liver and can often be localized there
Re-analysis of the Intergroup 0114 study noted an improvement in overall survival (OS) in rectal cancer patients with isolated metastatic disease treated with surgical resection as compared to no surgical resection (5 year OS 27% vs. 6%, p < 0.001) [14]
EORTC 40004 demonstrated improved progression-free survival (PFS) and OS for radiofrequency ablation (RFA), as compared to systemic chemotherapy, in a randomized phase II trial for colorectal cancer patients with surgically unresectable disease limited to the liver [18,19]
Summary
Colorectal cancer commonly metastasizes to the liver and can often be localized there. The 5-year OS was significantly longer for patients who underwent both liver and lung resections than those who did not undergo lung resection for pulmonary metastases (74% vs 42%, p = 0.05) [11] These data, when taken together, demonstrate that for selected patients with oligometastatic CRC surgical metastasectomy can dramatically alter disease progression. EORTC 40004 demonstrated improved PFS and OS for radiofrequency ablation (RFA), as compared to systemic chemotherapy, in a randomized phase II trial for colorectal cancer patients with surgically unresectable disease limited to the liver [18,19]. While 4.5% of patients in the SABR group had grade 5 treatment-related adverse events, the 5-year OS rate was 17.7% in the control arm as compared to 42.3% in the SABR arm [26] Given these data, the use of SABR has gained popularity as ~70% of radiation oncologists reported using SABR for the treatment of oligometastatic disease [27]
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