Purpose: Total skin electron therapy (TSET) with single-field rotational technique was commissioned based on point dose measurement on phantom. A large number of OSLDs were routinely used to spot check the calculated planned dose for each treatment and identify hot/cold spots, which is labor intensive and time consuming. Monte Carlo (MC) calculation is expected to provide whole body skin dose for TSET to improve TSET planning and achieve better dose distribution.
Methods: Rotational TSET technique was commissioned for Varian Linac with custom made flattening filter. TOPAS MC simulation was performed on a dual-core workstation (Xeon E5-2600, 32GB Ram) and calibrated to match the commission PDD and profile data. The MC calculation was then compared to in vivo measurement.
Results: The TSET output at nominal SSD of 380cm and depth of 10mm was determined as 0.0756cGy/MU by ion chamber and OSLD. The output of rotational TSET(R-TSET) technique was measured as 0.0289cGy/MU by Nanodots. Using custom made flattening filter (Rad. Product. Designs Inc), a field uniformity of better than 5% was achieved over 60cm x 180cm field, in agreement with AAPM TG30 guidelines. In vivo measurements verified the accuracy of MU calculation for TSET. The hot spots appeared at patient extremities due to lack of self-shielding. The cold spots were found to be on top of scalp, top of shoulder, inner side of elbows, perineum and breast fold where the sites were either indirectly radiated or shielded by patient body. MC simulation verified the skin dose distribution of R-TSET.
Conclusion: The rotational TSET was commissioned and successfully treated 6 patients. The MC simulation verified the in vivo measurements and will be applied to improved the design of TSET applicators to reduce the hot/code spots as well as the usage of OSLDs.