**2. Medical application of nonwoven fabric spacers**

Nonwoven fabric is a fabric-like material manufactured from long fibers bonded together by chemical, mechanical, heat, or solvent treatment. The performance characteristics of nonwoven fabrics vary according to the material components and the manufacturing process. A charac‐ teristic of nonwoven fabrics is not to have directionality for strength or growth. In addition, specific features of nonwoven fabrics include "water absorbency," "chemical resistance," "breathability," "abrasion resistance," and "flexibility." These characteristics of nonwoven fabrics support their use as surgical gowns and hats, masks, drapes, water-absorbing mats, and machine covers. The GORE-TEX sheet is a waterproof, breathable fabric membrane and has been widely used in permanent implants, including the artificial blood vessel, for many years. The GORE-TEX sheet was the first nonwoven fabric to be applied as a spacer in the field of particle therapy [10–12] (Figure 1). The use of this spacer allows the application of particle therapy in cases in which particle therapy may result in severe incurable damage to adjacent organs. However, although the GORE-TEX spacer is useful during the period of particle therapy, it becomes a foreign body after the therapy [12]. Problems related to the ongoing presence of the spacer may be avoided by removal during a second surgery, but repeated operations might be a risk for the patient.
