The Effectiveness of Proton Beam Therapy for Liver Metastatic Lesions in Colorectal Cancer Patients

Abstract

<h3>Purpose/Objective(s)</h3> The purpose of this study was to evaluate the efficacy and safety of proton beam therapy (PBT) for liver metastatic (LM) lesion in colorectal cancer (CRC) patients. <h3>Materials/Methods</h3> Consecutive CRC patients who underwent PBT for ≤3 LM lesions from 2009 to 2018 were isolated from our institutional database. Patients with extrahepatic metastatic lesions were excluded. The effectiveness was assessed based on the local control (LC), overall survival (OS) and progression-free survival (PFS) rates. The LC, OS and PFS rates were calculated using the Kaplan–Meier method and log-rank test. Factors that may be related to LC, such as tumor size, fraction size, BED₁₀ and the distance from the lesion to the most recently involved intestinal tract were investigated. The cut-off values were estimated using the ROC curve and AUC. P-values below 0.05 were consider significant. Adverse events were described according to CTCAE ver 5.0. <h3>Results</h3> This study included 23 men and 18 women whose median age was 66 years (24 - 87 years). Sixty-three lesions were enrolled. The most frequent dosage was 72.6 Gy (RBE) /22fr. The median lesion size, fraction size, BED₁₀, the distance between LM lesion and adjacent were 30 mm (9-103 mm), 3.3 Gy(RBE)/fr (2-8 Gy(RBE)/fr),105.6 Gy(RBE) (72-154.7 Gy(RBE)), 42.4mm (0-147mm), respectively. The median follow-up period was 27.6 months (5.2-84.7 months). As of November 2020, 20 patients died (including one of intercurrent disease death). The 3-year LC, OS and PFS rates were 54.9%, 61.6%, and 16.7%, respectively. Twenty-three lesions were local recurrence which of five lesions were surgically removed and one lesion was re-irradiated with PBT. Both re-treatments after PBT were performed safely and without complications. Distant metastasis occurred in 24 patients. The most common site of distant metastasis was the lung with 11 patients. Any statistically significant LC related factors were not found. However, the P-value for tumor size was the smallest, P=0.0665. The 2-year LC rates in the group with less than 14.1 mm and the larger group were 100% and 50%, respectively. and 50%, respectively. No grade ≥3 adverse events were observed. No patients experienced liver failure in the acute or late phase. The only acute adverse event was one cases of G2 dermatitis radiation. The only late adverse effect was three cases of G1 radiation-induced rib fracture. <h3>Conclusion</h3> PBT might be a treatment option for patients with liver metastasis of CRC. Tumor size tended to be associated with local control rates.