RESUMEN
Different planning and treatment systems for intracranial stereotactic radiosurgery available in the Netherlands are compared. The systems for intracranial radiosurgery include: Gamma Knife, Cyberknife, Novalis, and Tomotherapy. Electronic data of 5 patients was transferred to all participating centres and treatment plans were generated according to 2 different prescription protocols. For this study, plans were also generated for a conventional linac. Even systems with a high resolution (Gammaknife and Novalis) have conformity indices in violation with RTOG guidelines (CI > 2.5) when target volumes of <0.5 cc are treated. For medium sized targets (0.5-1 cc) all systems performed reasonably well, but for the different systems a large range of conformity indices was seen (1.1 to 3.7). The differences are partly system dependent but depend also on specific planning choices made. For larger target volumes (> 1 cc), all systems perform well. The workload of the different techniques was comparable although the treatment times were usually longer for Gamma Knife radiosurgery. We conclude that small targets should be treated by dedicated systems, larger volumes (> 0.5-1 cc) can also be treated using conventional treatment systems equipped with a MLC.
Asunto(s)
Neoplasias Encefálicas/cirugía , Radiocirugia/métodos , Terapia Asistida por Computador/métodos , Adulto , Anciano , Femenino , Humanos , Masculino , Persona de Mediana Edad , Países Bajos , Guías de Práctica Clínica como AsuntoRESUMEN
In a previous paper the calibration of an isotropic light detector in clear media was described and validated. However, in most applications the detector is used to measure light distribution in turbid (scattering) media, that is, in tissues or tissue equivalent optical phantoms. Despite its small diameter (typically 0.8 mm), inserting the detector in a turbid medium may perturb the light distribution and change the fluence rate at the point of measurement. In the present paper we estimate the error in the fluence rate measured by a detector in turbid media after calibration in a clear medium (air), using an optical phantom and detector bulbs of different optical properties. The experimental results are compared with calculations using the diffusion approximation to the transport equation in a spherical geometry. From measurements in optical phantoms and the results of the calculations it appears that introduction of the detector into a water-based turbid medium with refractive index, absorption- and scattering coefficients different from those of the detector bulb may require corrections to the detector response of up to 10-15%, in order to obtain the true fluence rate in that medium. The diffusion model is used to explore the detector response in a number of tissues of interest in photodynamic therapy, using tissue optical properties from the literature. Based on these model calculations it is estimated that in real tissues the fluence rate measured by the detector is up to 3% below the true value.