SU‐F‐T‐76: Total Skin Electron Therapy: An‐End‐To‐End Examination of the Absolute Dosimetry with a Rando Phantom

Abstract

Purpose:To examine and validate the absolute dose for total skin electron therapy (TSET) through an end‐to‐end test with a Rando phantom using optically stimulated luminescent dosimeters (OSLDs) and EBT3 radiochromic films.Methods:A Varian Trilogy linear accelerator equipped with the special procedure 6 MeV HDTSe‐ was used to perform TSET irradiations using a modified Stanford 6‐dual‐field technique. The absolute dose was calibrated using a Markus ion chamber at a reference depth of 1.3cm at 100 cm SSD with a field size of 36 × 36 cm at the isocenter in solid water slabs. The absolute dose was cross validated by a farmer ion chamber. Then the dose rate in the unit of cGy/Mu was calibrated using the Markus chamber at the treatment position. OSLDs were used to independently verify the dose using the calibrated dose rate. Finally, a patient treatment plan (200 cGy/cycle) was delivered in the QA mode to a Rando phantom, which had 16 pairs of OSLDs and EBT3 films taped onto its surface at different anatomical positions. The doses recorded were read out to validate the absolute dosimetry for TSET.Results:The OSLD measurements were within 7% agreement with the planned dose except the shoulder areas, where the doses recorded were 23% lower on average than those of the planned. The EBT3 film measurements were within 10% agreement with the planned dose except the shoulder and the scalp vertex areas, where the respective doses recorded were 18% and 14% lower on average than those of the planned. The OSLDs gave more consistent dose measurements than those of the EBT3 films.Conclusion:The absolute dosimetry for TSET was validated by an end‐to‐end test with a Rando phantom using the OSLDs and EBT3 films. The beam calibration and monitor unit calculations were confirmed.