Particle beam therapy versus photon radiotherapy for extrahepatic biliary cancer—systemic review and meta-analysis

Particle beam therapy (PT) is a potentially promising approach to the treatment of extrahepatic biliary cancer (EBC) because of its unique dose distribution using the Bragg peak. However, the superiority of PT to photon radiotherapy (XT) remains unclear. Therefore, we conducted a systematic review and meta-analysis to compare PT and XT for the treatment of EBC. The primary endpoint was overall survival (OS), which was pooled using a random-effects model. Nine articles comprising a total of 1558 patients (seven XT articles, n = 1488 patients; two PT articles, n = 70 patients) were screened. In addition, we compared the outcomes of XT and PT with the outcomes available from a prospective data registry (proton-net). The 1-year OS probability rates were 55, 65 and 72% for the XT group, PT group and PT registry, respectively. The 2-year OS probability rates were 26, 38 and 38% for the XT group, PT group and PT registry, respectively. The 3-year OS probability rates were 12, 35 and 18% for the XT group, PT group and PT registry, respectively. Although the difference between the 1-year OS rates of the XT group and PT registry was statistically significant, no other significant superiority was observed among these groups. In conclusion, the efficacy of PT was not superior to that of XT during this meta-analysis.