First report of retroperitoneal rhabdomyosarcoma treated with space-making particle therapy for preservation of renal function.

Space-making particle therapy, which consists of surgical placement of a spacer followed by particle therapy, has become a solution to the problem of normal organs being exposed to a high radiation dose. A bioabsorbable spacer is particularly suitable for this purpose, but is not widely used. Surgical placement of a spacer is performed mostly to protect the digestive tract, but can also be used to protect the kidneys. Therefore, we have been interested in the use of space-making particle therapy to preserve renal function. A 14 month-old boy with intermediate-risk retroperitoneal rhabdomyosarcoma underwent surgery with placement of a bioabsorbable spacer following neoadjuvant chemotherapy and then received proton beam therapy of 41.4 Gy (relative biological effectiveness) in 23 fractions. In the 41 months since PBT, he has survived without local recurrence or signs of renal impairment. This report describes the first-ever case of surgical placement of a bioabsorbable spacer with the aim of preserving renal function during proton beam therapy. Space-making particle therapy is an innovative solution for peritoneal tumors adjacent to the kidneys.