A phantom for prostate cancer brachytherapy has a prostate tissue phantom shaped like a real prostate gland, a perineal tissue phantom surrounding the prostate tissue phantom, a skin tissue phantom separating the perineal tissue phantom from an outside environment, and an enclosure. The prostate tissue phantom is a polyvinyl alcohol cryogel (PVA-C) having undergone 3-5 freeze-thaw cycles and having 10-20% w/w PVA in a solvent (e.g. water), 4-8% w/w oil and an amount of acoustic scattering particles to ultrasonically distinguish the prostate-tissue phantom from its surroundings. The perineal tissue phantom is a PVA-C having undergone 1-2 freeze-thaw cycles and having 10-20% w/w PVA in a solvent, 4-8% w/w oil and an amount of acoustic scattering particles to ultrasonically distinguish the perineal tissue phantom from its surroundings. The skin tissue phantom is a PVA-C having undergone at least 6 freeze-thaw cycles and having 15-25% w/w PVA in a solvent. The phantom mimics the imaging and mechanical properties of the prostate and surrounding tissues, providing a realistic phantom for prostate cancer brachytherapy.