Poster — Wed Eve—31: Validation of the Delta4 Phantom for 3‐D Dosimetry of IMRT Plans

Abstract

Modern radiotherapy techniques such as IMRT require time consuming dosimetric quality assurance (QA) for patient plans. ScandiDos (Uppsala, Sweden) has developed the Delta4 measurement system as a tool for efficient, three‐dimensional plan verification. The Delta4 system consists of two orthogonal detector planes, with a total of 1069 p‐type silicon diodes, embedded in an acrylic cylindrical phantom, 22 cm in diameter, 40 cm in length. The Delta4 software can reconstruct 3D dose distributions based upon the measured dose and the imported dose distributions from the planning system. The performance of the Delta4 system for the validation of IMRT plans, with emphasis on the dose measurement accuracy in areas away from the planes of the detectors, has been evaluated. Basic commissioning measurements of the Delta4 include dose linearity, dose rate dependence, angular sensitivity and reproducibility. For performance of IMRT plan validation, a region of interest (ROI) equivalent to a Farmer chamber was created in the plan at locations of high dose and low dose avoidance regions. The planned vs. measured dose for the chamber ROIs, as measured with the Delta4, were compared. To validate the plans, dose measurements were also performed using a cylindrical phantom with a Farmer chamber in the same locations. The Delta4's dose response was found to be linear (), and short term reproducibility is better that 0.15%. Results of the performance testing indicate that the Delta4 is suitable for clinical dosimetry. Comparisons of the Delta4 volumetric dose reconstruction with the dose measured using conventional tools show acceptable agreement.