Experimental lens-sparing optimization in therapeutic orbital irradiation with electron beams.

There has been a number of approaches in the literature for therapeutic malignant and benign orbital irradiation. All techniques intend to deliver a homogenous dose to the orbital and retroorbital target volume while sparing the lens of excessive dose. In this experimental lens-sparing study, 4 MeV and 12 MeV anterior electron irradiation has been used with cerrobend shielding circular blocks of varying diameter and thickness placed on a thin Mylar at the distal tip of the electron applicator to spare the lens. The first phase of the study in water phantom has been designed to determine the shield thickness and diameter constant for 4 MeV and 12 MeV electron beams. After optimizing the lens dose by water phantom, the second phase of our study has been designed to measure doses at lens and other specific localizations in randophantom under same conditions with 4 MeV and 12 MeV electron beams. By this technique lens accumulated 18.56% of prescribed dose and lateral aspects of the lens received 44.59% of the prescribed dose in 4 MeV electron irradiation, whereas this was 13.86% and 44.80%, respectively in 12 MeV electron irradiation. The technique used is found to be an extremely simple and effective technique allowing an easier setup with excellent dose distribution characteristics with lens sparing applicable to orbital irradiation practice.