Abstract
Two‐dimensional array dosimeters are commonly used to perform pretreatment quality assurance procedures, which makes them highly desirable for measuring transit fluences for in vivo dose reconstruction. The purpose of this study was to determine if an in vivo dose reconstruction via transit dosimetry using a 2D array dosimeter was possible. To test the accuracy of measuring transit dose distribution using a 2D array dosimeter, we evaluated it against the measurements made using ionization chamber and radiochromic film (RCF) profiles for various air gap distances (distance from the exit side of the solid water slabs to the detector distance; 0 cm, 30 cm, 40 cm, 50 cm, and 60 cm) and solid water slab thicknesses (10 cm and 20 cm). The backprojection dose reconstruction algorithm was described and evaluated. The agreement between the ionization chamber and RCF profiles for the transit dose distribution measurements ranged from ‐0.2%~ 4.0% (average 1.79%). Using the backprojection dose reconstruction algorithm, we found that, of the six conformal fields, four had a 100% gamma index passing rate (3%/3 mm gamma index criteria), and two had gamma index passing rates of 99.4% and 99.6%. Of the five IMRT fields, three had a 100% gamma index passing rate, and two had gamma index passing rates of 99.6% and 98.8%. It was found that a 2D array dosimeter could be used for backprojection dose reconstruction for in vivo dosimetry.PACS number: 87.55.N‐
Highlights
Intensity-modulated radiation therapy (IMRT) allows the dose distribution to be shaped to the target while avoiding normal structures by using an intensity-modulated beam produced with a multileaf collimator (MLC)
The radiochromic film (RCF) showed that the central axis (CAX) percent dose difference and the average difference ranged from -2.8% to -1.0% and 0.5% (1σ = 1.9%) to 3.1% (1σ = 2.6%), respectively
The transit dosimetry using the MapCHECK 2D array dosimeter produced very similar results to those reported by others using amorphous silicon electronic portal imaging device (EPID) systems even though the device was not utilized in its original design
Summary
Intensity-modulated radiation therapy (IMRT) allows the dose distribution to be shaped to the target while avoiding normal structures by using an intensity-modulated beam produced with a multileaf collimator (MLC). Létourneau et al[13] and Jursinic and Nelms[12] reported that the MapCHECK had a linear dose response and that all diodes were calibrated to within ± 1% of each other (mostly within ± 0.5%) They reported that MapCHECK readings were reproducible to within a maximum standard deviation (SD) of ± 0.15%, and noted a temperature dependence of 0.57%/°C, which should be taken into account for absolute dosimetric measurement. Both Spezi et al[17] and Herzen et al[15] showed 1% discrepancy when compared against an ionization chamber using MatriXX 2D array dosimeter. Poppe et al[20] reported 2D-ARRAY dosimeter could detect a 2 mm MLC misalignment in terms of dose difference of 5% to 15%, when compared to the non-misaligned MLC
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