Intraoperative radiotherapy IORT applicators for treatment of small skin lesions a phantom and planning study

Radiation therapy is actively utilized for superficial lesions. External beam radiotherapy for cutaneous lesions utilizes electrons with low transmittance. Conventional electron beam therapy uses Cerrobend blocks for field shaping; however, the Intraoperative Radiotherapy (IORT) applicator offers superior dosimetric characteristics. The dosimetric parameters were measured using 4 and 6 MeV electron beams delivered by a Trilogy linear accelerator, and percent depth dose and lateral dose profiles were compared under the presence of the IORT applicator and Cerrobend block. The dose calculations under various IORT applicator conditions and planning studies were performed using Monte Carlo simulation. Treatment plans for three sites were evaluated in terms of coverage of the planning target volume, dose to the surrounding normal tissue, and beam-on time for two treatment modalities. The results of the measured and calculated dosimetric parameters correspond. Scattered electrons along the IORT applicators resulted in shorter dmax and R50 and sharper penumbras compared to the blocks. Oblique IORT applicators also maintained sharp penumbras. Treatment-plan analysis indicated significant reductions in normal tissue dose using the IORT applicator. Implementing IORT in clinical practice requires deliberation of extended beam-on times and associated patient safety protocols; however, the potential benefits regarding dose distribution warrant further optimization in clinical use.