Dose verification of helical tomotherapy intensity modulated radiation therapy planning using 2D-array ion chambers

Abstract

Purpose:To investigate the clinical usage of dose verification of Helical Tomotherapy plans by using 2D-array ion chambers, and to develop an efficient way to validate the dose delivered for the patients during treatments.Materials and Methods:A pixel-segmented ionisation chamber device, IMRT MatriXX™ and Multicube™ phantom from IBA were used on ten selected Tomotherapy IMRT/IGRT head and neck plans in this study. The combined phantom was set up to measure the dose distribution from coronal and sagittal planes. The setup of phantom was guided for verifying the correction position by pre-treatment Tomotherapy MVCT images. After the irradiation, the measured dose distributions of coronal and sagittal planes were compared with those from calculation by the planning system for cross verification. The results were evaluated by the absolute and relative doses as well as Gamma (γ) function. The feasibility of the different measuring methods was studied for this rotational treatment technique.Results:The dose distributions measured by the MatriXX 2D array were in good agreements with plans calculated by Tomotherapy planning system. The discrepancy between the measured dose and predicted dose in the selected points was within ±3%. In the comparison of the pixel-segmented ionisation chamber versus treatment planning system using the 3 mm/3% γ-function criteria, the mean passing rates of 2 mm dose grid with γ-parameter ≤1 were 97.37% and 96.91%, in two orthogonal planes (coronal and sagittal directions), respectively.Conclusion:MatriXX with Multicube is a new system created for rotational delivery quality assurance (QA) and found to be reliable to measure both absolute dose and relative dose distributions, simultaneously. It achieves the goal of an efficient and accurate dosimetry validation method of the helical delivery pattern for the Helical Tomotherapy IMRT planning.

Clinical implementation of Dosimetry Check™ for TomoTherapy® delivery quality assurance

“…For TomoTherapy ® ‐based intensity‐modulated radiotherapy (IMRT), the current delivery quality assurance (DQA) process consists of comparing measured versus calculated doses in a phantom using an ionization chamber and a film or using detector array devices . These devices have generally provided such accurate DQA results in terms of low absolute dose difference or high gamma pass rate.…”

Characterisation of Silicon Diode Arrays for Dosimetry in External Beam Radiation Therapy

“…Studies from Bhardwaj et al and Xu et al [9][12] explore the performances of 2D array of cubic ionization chambers with 5 mm pitch in intensity modulated radiotherapy (IMRT) and Helical Tomotherapy (a form of IMRT comprised of 'slice-by-slice' delivery of radiation), respectively. The array shows excellent performance in terms of dose distribution reconstruction for regular field size beams (from 4 cm x 4 cm and above) but the authors posit a need to observe care in penumbra region analysis and measurement due to the limited spatial resolutions for the device for smaller field sizes [9] [12].…”

Filmless methods for quality assurance of Tomotherapy using ArcCHECK

“…12,14 However, film QA using EDR2 has been reported to be easily affected by the development process which introduces uncertainty to the calibration curve. 15,16 Devices with 2D arrays also have successful applications in helical Tomotherapy QA 17,18 despite the possible limitation due to its directional dependency. 19,20 The ArcCHECK (Sun Nuclear, Melbourne, FL, Australia), a cylindrical acrylic phantom with an array of spirally arranged diode detectors, has been found to be well suited for QA of VMAT, IMRT, and Tomotherapy, [21][22][23][24][25][26][27] since the cylindrical design of Arc-CHECK removes rotational dependence of the detectors.…”