Transitional changes of spacer materials used in carbon-ion radiation therapy.

Purpose: To evaluate the imaging findings and transitional changes in spacer materials used in carbon-ion radiation therapy MATERIALS: Medical records were retrospectively reviewed, and the maximum thickness, volume, and CT value of spacers were calculated from CT scans. Procedure-related complications were recorded.

Results: A spacer was surgically placed in six patients in retroperitoneal, presacral, or peritoneal sites. The spacer material was polyglycolic acid (PGA) in four patients and expanded polytetrafluoroethylene (ePTFE) in two patients. The thickness of PGA spacers showed no changes in any patients within 4 weeks, but increased within 6 weeks in one patient and was unchanged or decreased in the remaining patients. PGA spacer volume decreased gradually after placement in three of four patients; this was observed at 4 months in two patients and at 6 months in one patient. The mean CT value of PGA spacers was 83 HU just after placement, and decreased gradually thereafter. Air was seen in the PGA spacers of two patients. Neither ePTFE spacer showed volume changes over time, and the mean CT value was low (mean, -53.7 HU) just after placement but increased rapidly to 145 HU at 2 months.

Conclusion: Spacer imaging findings may vary according to type and may change over time. Familiarity with these features is beneficial for diagnostic radiologists.