High Resolution and High Accuracy Measurements of Small Radiosurgery Fields with a Homogeneous Detector Array
Abstract
Purpose
Measuring dose from small fields delivered by dedicated radiosurgery devices like the Gamma Knife can be challenging and time consuming. It usually required a combination of films and point detectors (diodes, micro-ion chamber). Our goal is to facilitate radiosurgery measurements by using a 7-points plastic scintillation detector (PSD) array that can be inserted in conventional phantoms to simultaneously measure the outputs and profiles of even the smallest field sizes.
Methods
Measurements were performed using a 7-points PSD array from Medscint, read using the Hyperscint scintillation dosimetry platform. Each point has a sensitive volume of 1 mm diameter by 1 mm length. A holder compatible with the solid water Gamma Knife dosimetry phantom was printed in nylon-12. Detectors were placed on a single line and spaced 2 mm center-to-center, spanning a length of 12 mm. Irradiations were carried with the Leksell Gamma Knife Perfexion with spherical field sizes of 4 mm to 16 mm as well as with an asymmetrical 4 mm field with a blocked sector and a15 shots clinical plan.
Results
The 3D printed holder density was homogeneous with a density of 0.95 g/cc. PSD measurements were highly reproducible with relative standard deviation better than 0.3% for all probes (0.07-0.27%) at 200 cGy. Measurement profiles were all in excellent agreement with reference data with an average absolute difference of 0.55% and 1.6% for the 4 mm and asymmetrical 4 mm profiles respectively. High resolution profiles and 2D maps with measurements every 0.5 mm where also obtained by scanning the array in the X-Z plane.
Conclusion
PSD array is ideal for simultaneous measurement of both output factor and profile with high precision and accuracy. High sampling resolution can be achieved by scanning the array which is faster than film measurement that require lengthy calibration, optical scanning and processing.