Measurements of superficial dose distributions in radiation therapy using translucent cryogel dosimeters

Superficial dose distributions were measured using radiochromic translucent poly(vinyl alcohol) cryogels. The relationship between dose to the skin surface and dose measured with the bolus (cryogel) was established using a series of oblique irradiations. Gafchromic film was placed under the bolus, and the ratio of bolus-film dose was determined for angle ranging from 0o to 90o. The average ratio over 0-67.5 degrees (0.800 ± 0.064) was used as the single correction factor to convert dose in bolus to dose to the skin surface, and applied to bolus measurements of skin dose from head and neck intensity modulated radiation therapy (IMRT) treatments delivered to a RANDO phantom. The resulting dose distributions were compared to film measurements using gamma analysis with a 3%/3mm tolerance and a 10% threshold. The minimum gamma pass rate was 95.2%. This study is the first report on the use of a poly(vinyl alcohol) cryogels based dosimeter to provide an accurate estimation of superficial dose distributions in megavoltage photon beams.