Presenter: Kazuki Terashima Presenter's Affiliation: Hyogo Ion Beam Medical Center, Department of Radiology, Tatsuno, Japan
The liver is inherently sensitive to radiation therapy, thus limiting the use of external beam photon therapy in treating primary tumors and isolated metastases.
The unique physical properties of proton and heavy ion particles - allowing for increased deposition of dose within the target while sparing adjacent normal tissues - have led to increased application of particle therapy in liver tumors.
The radiobiologic advantages of carbon ion therapy, including increased LET and RBE, may provide further benefit in controlling tumors within the liver.
The purpose of this study was to evaluate the clinical differences between proton and carbon ion therapies for metastatic liver tumors.
The study included 47 patients with 51 metastatic liver lesions treated between January 2003 and January 2009.
Primary tumors were majority colorectal (26), as well as gastric (5), and other (17).
Tumor size ranged from 0.8 cm to 8.0 cm, with a median size of 3.1 cm.
24 patients received proton therapy and 27 patients received carbon ion therapy
All patients received 56-68 Gy(RBE) in 8 fractions.
Overall survival, recurrence-free survival, distant metastasis, and local control rates were evaluated with Kaplan-Meier curves.
Acute and late morbidities were assessed by Common Terminology Criteria for Adverse Events (CTCAE) version 3.0.
Median follow-up was 19.1 months, ranging from 4.1 – 58.7 months.
1, 2, and 3 year overall survival rates did not differ significantly and were respectively for proton therapy 81.8%, 47.3%, and 13.5%, and for carbon ion therapy, 87.8%, 70% and 60% (p = 0.13)
There were similarly no differences in 1-year recurrence free survival rates.
1 and 2 year local control rates 78.9% and 65.7% in the proton group and 64.5% and 42.2% in the carbon group (p=0.51)
Only one grade 3 acute reaction was observed - an acute elevation in transaminases
A single grade 4 late toxicity was recorded, radiation dermatitis.
There were no statistically significant differences in clinical outcomes between proton and carbon ion therapy in this retrospective analysis.
Randomized controlled trials are planned to confirm these findings.
The treatment of oligometastatic disease is an ever-expanding field and of particular interest in the setting of isolated liver metastasis.
The potential application of the physical and biologic properties of particle therapy with successful clinical outcome is therefore of continued future importance.
This study is limited by its relatively small number of patients and retrospective, nonrandomized nature. A prospective randomized trial which the author's express an intention to pursue, if completed, should further clarify whether the increased LET and RBE of carbon ion therapy translates to a clinical benefit in the treatment of primary or metastatic liver tumors.