SU‐FF‐T‐398: Commissioning a 5 Mm Circular Cone for Linac‐Based Stereotactic Radiosurgery Using MicroMOSFET and Polymer Gel

Abstract

Purpose: The accuracy of measured small cone parameters is important in the treatment of certain disorders like trigeminal neuralgia, where a single large dose is delivered via a small cone. The purpose of this presentation is to identify practical dosimeters for commissioning the cone accurately and efficiently in a community clinic. Method and Materials: Relative output factors for 5, 12.5, and 15 mm cones were measured using microMOSFET, Kodak EDR2 film, and TLD microcubes. TMRs for the 5 mm cone were measured using microMOSFET and BANG®polymer gel. OARs for the 5 mm cone were measured using radiographic and radiochromic films. Results: The output factor for the 5 mm cone measured with microMOSFET was 0.654 for a 6 MV beam and agreed with data published elsewhere. MicroMOSFET measurements agreed with EDR2 film and TLD microcubes measurements within 4.3% and 3.2% respectively for the 5 mm cone. All techniques were within 2.5% agreement for the 12.5 and 15 mm cones. TMR values measured with microMOSFET and polymer gel agreed within 3%. Radiographic and radiochromic film off‐axis ratio measurements showed differences not exceeding 1% above the 10% relative dose level. The measurements were verified using a MD Anderson Cancer Center phantom for a single static beam and polymer gel for a clinical set of three arcs. The doses reported by the institution and MDACC at dmax and 7.5 cm depth agreed within 4% and 3% respectively. The volumetric doses between the treatment planning system and the polymer gel were within 4%. Conclusion: The overall precision and accuracy of microMOSFET‐based measurement techniques are clinically acceptable. The microMOSFET is a feasible alternative with some advantages to TLD microcubes for dosimetric measurements of very small cones and fields. The polymer gel was found to be the only commercially available 3D‐dimensional verification dosimeter for these cones.