Photothermographic material and image forming method

An image forming method, which is an X-ray image forming method using a photothermographic material comprising, on at least one side of a support, an image forming layer comprising at least a photosensitive silver halide, a non-photosensitive silver salt of a fatty acid, a reducing agent, and a binder, wherein the photosensitive silver halide has an average silver iodide content of 40 mol % or higher, and the photothermographic material comprises an acetylene compound represented by the following formula (II) or a salt thereof:

• wherein R2 represents a substituted or unsubstituted alkyl group, aryl group, or heterocyclic group;
• R3 represents a hydrogen atom or a substituent substituting for a hydrogen atom on a benzene ring;
• n1 represents an integer of 1;
• and n2 represents an integer of from 0 to 4;
• wherein the image forming method comprises:
• 1) bringing the photothermographic material into contact with a fluorescent intensifying screen;
• 2) imagewise exposing the photothermographic material with X-rays to record a latent image on the photothermographic material;
• and
• 3) thermally developing the photothermographic material at a temperature of 107° C. to 140° C. to convert the latent image into a visible image by thermal development.