Gelatin 300 bloom type a

The NIPAM gel dosimeter used in this study was provided by the laboratory of the Department of Medical Imaging and Radiological Sciences of Central Taiwan University of Science and Technology (Taichung, Taiwan). The components included deionized water 87%, gelatin (300 Bloom type A, Sigma-Aldrich) 5%, NIPAM (97%, Sigma-Aldrich) 5% as a monomer, bisacrylamide (BIS, Mreck) 3%, and Tetrakis Hydroxymethyl Phosphonium Chloride (THPC, TCI) 5 mM as a deoxidant. To prepare the NIPAM gel dosimeter, we first dissolved gelatin in ionized water and stirred the solution until the gelatin was completely dissolved and fully expanded; the solution was subsequently water heated to 45 ${}^{\circ }$ C and NIPAM and BIS were added as vulcanization agents. Stirring continued until the components were completely mixed. THPC was added to the solution to remove oxygen and stirred until the THPC completely dissolved. The prepared gel dosimeter was wrapped with tin foil to avoid light-induced polymerization, placed in 4 ${}^{\circ }$ C fridge for solidification, and exposed to irradiation within 24 hr after preparation.