Mechanical and dose delivery accuracy evaluation in radiosurgery using polymer gels

Abstract

The polymer gel–magnetic resonance imaging (MRI) dosimetry technique was used to evaluate the mechanical and dose delivery accuracy in Leksell gamma‐knife stereotactic radiosurgery for the treatment of multiple targets. Two different polymer gel dosimeter formulations reported in the literature were prepared in‐house. A plan for the treatment of four brain metastases (targets) was generated. It involved the delivery of four 8‐mm collimator shots using different prescription isodose lines and different prescription doses for each target, keeping the maximum dose constant for all targets. A sample of each gel formulation was irradiated using a custom‐made phantom with an experimental procedure capable of testing the increased nominal mechanical accuracy of stereotactic radiosurgery. The irradiated dosimeters were evaluated using a clinical 1.5 T MR imager. Result manipulation in 3D allowed for the determination of the mechanical accuracy in the delivery of each shot through the comparison of measured versus planned shot center coordinates. Dose delivery accuracy was also evaluated by comparison of maximum dose values measured at the center of each shot as well as dose distribution measurements, with corresponding treatment‐planning calculations. Polymer gel dosimetry was found capable of verifying the complete chain of radiosurgery treatment in gamma‐knife applications involving the irradiation of multiple targets.PACS numbers: 87.53.Dq, 87.53.Ly, 87.53.Xd

MRI‐based polymer gel dosimetry for validating plans with multiple matrices in Gamma Knife stereotactic radiosurgery

“…An important question is the validity of the multiple matrix method, in particular, with older versions of LGP, in terms of the dose prescription to multiple targets scattered over the multiple matrices. To answer this question, Sandilos et al (9) recently used polymer gel dosimetry. In their study, dose delivery accuracy was evaluated by comparing measured dose distributions with corresponding calculations.…”

Investigating potential physicochemical errors in polymer gel dosimeters

“…This may indicate that R 2 values in calibration vials were smaller compared to the phantoms, suggesting that polymerization was slightly inhibited in these vials by some oxygen infiltration. Sandilos et al (2006) observed a 9% underestimation in their measurements with anoxic PABIC and VIPAR dosimeters and attributed that to the attenuation of the Plexiglas phantom walls. However, while the dosimetry was done with a Perspex phantom, they used glass vials for calibration; therefore it is also possible that the gel in the calibration vials was less affected by oxygen infiltration than the gel in the Plexiglas phantom and the observed discrepancies originated from differences in oxygen contamination between calibration vials and dosimeters.…”

Geant4 based dosimetry evaluation for gamma knife using different phantom materials

“…These definitions; While creating the basic geometric structure, the collimator head and dimensions that ensure the exact fit of the model are defined. Geometric definitions of other objects are made similarly [16].…”