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Poster — Wed Eve—31: Validation of the Delta 4 Phantom for 3‐D Dosimetry of IMRT Plans
Author(s) -
Zhang TJ,
Norrlinger B,
Islam M
Publication year - 2009
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3244135
Subject(s) - imaging phantom , dosimetry , quality assurance , reproducibility , ionization chamber , nuclear medicine , radiation treatment planning , dose profile , delta , detector , medical physics , physics , medicine , radiation therapy , mathematics , optics , radiology , statistics , external quality assessment , pathology , quantum mechanics , astronomy , ionization , ion
Modern radiotherapy techniques such as IMRT require time consuming dosimetric quality assurance (QA) for patient plans. ScandiDos (Uppsala, Sweden) has developed the Delta 4 measurement system as a tool for efficient, three‐dimensional plan verification. The Delta 4 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 Delta 4 software can reconstruct 3D dose distributions based upon the measured dose and the imported dose distributions from the planning system. The performance of the Delta 4 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 Delta 4 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 Delta 4 , were compared. To validate the plans, dose measurements were also performed using a cylindrical phantom with a Farmer chamber in the same locations. The Delta 4 's dose response was found to be linear ( R 2 = 1 ), and short term reproducibility is better that 0.15%. Results of the performance testing indicate that the Delta 4 is suitable for clinical dosimetry. Comparisons of the Delta 4 volumetric dose reconstruction with the dose measured using conventional tools show acceptable agreement.