Application of 3D Gel Dosimetry as a Quality Assurance Tool in Functional Leksell Gamma Knife Radiosurgery

Abstract

Highly precise dose delivery to the target (tumor or cancerous tissue) is a key point whenbrain diseases are treated applying recent stereotactic techniques: intensity-modulated, image-guidedradiotherapy, volumetric modulated arc therapy, Gamma knife radiosurgery. The doses in onesingle shot may vary between tens and hundreds of Gy and cause significant cell/tissue/organdamages. This indicates the need for implementation of quality assurance (QA) measures whichare realized performing treatment dose verification with more than one calibrated quality assurancemethod or tool, especially when functional radiosurgery with a high dose (up to 40 Gy in ourcase) shall be delivered to the target using small 4 mm collimator. Application of two dosimetrymethods: radiochromic film dosimetry using RTQA2 and EBT3 films and dose gel dosimetry usingmodified nPAG polymer gels for quality assurance purposes in stereotactic radiosurgery treatmentsusing Leksell Gamma Knife© Icon™ facility is discussed in this paper. It is shown that due to theirpolymerization ability upon irradiation nPAG gels might be potentially used as a quality assurancetool in Gamma knife radiosurgery: they indicate well pronounced linear dose response in hypofractionated(up to 10 Gy) dose range and are sensitive enough to irradiation dose changes with ahigh (at least 0.2 mm) spatial resolution. Dose assessment sensitivity of gels depends on parametersof a dose evaluation method (optical or magnetic resonance imaging), however, is similar to thisestimated using film dosimetry, which is set as a standard dosimetry method for dose verificationin radiotherapy.