A patient-specific quality assurance study on absolute dose verification using ionization chambers of different volumes in RapidArc treatments

Kumar, S.A. Syam; Sukumar, Prabakar; Pothapregada, Sriram; Rajasekaran, Dhanabalan; Aketi, Srinu; Nagarajan, Vivekanandan

doi:10.1016/j.meddos.2012.04.001

Cited by 14 publications

(11 citation statements)

References 35 publications

(21 reference statements)

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“…for the difference between measured and calculated dose for head and neck tumors. Syam Kumar et al 15 reported also that a 0.6 cm 3 ionization chamber gave 2.23% of the measured isocenter absolute dose which was comparable to the calculated plan. In the present results the differences may reach a maximum of 9% for an individual field.…”

Section: Verisoft Softwaresupporting

confidence: 57%

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Dose verification of intensity modulated radiotherapy in head and neck tumors

Elawady

Attalla

Elshemey

et al. 2014

Int J Cancer Ther Oncol

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Purpose: To evaluate the agreement between measured and calculated doses for head and neck tumors using different gamma criteria and to establish quality assurance protocol for the delivery of IMRT in The National Cancer Institute in Cairo. Methods: The dose is calculated for 30 patients using CMS Treatment Planning System. The ionization chamber (0.6 cm 3 Farmer type) is used for point dose measurements. The 2D-array (PTW 729) and GafChromic films (EBT2) are used for 2D graphical dose distribution. Four different gamma criteria of dose difference (DD) and distance to agreement (DTA) (3%/3 mm, 3%/5 mm, 4%/4 mm and 5%/5 mm DD / DTA) are selected. These criteria are evaluated while suppressing the dose of 10%, 20% or 30% from dose distribution. Results: Point dose evaluations using the ion chamber ranged from-2.6% to 3.7% (mean and standard deviation of 0.46 ± 1.7). Significant differences are observed between the films and 2D-array for all criteria except the 3%/5 mm criteria (96.89 ± 2.2% vs. 94.81 ± 4.2% (p < 0.01)). Conclusion: Differences may exceed about 3% when the ionization chamber is present in steep dose gradient regions. The present results suggest the gamma criteria of 3%/5 mm as the most suitable criteria for IMRT quality assurance. This gamma criterion of 3%/5 mm favorably exceeds 95% in case of maximum dose while suppressing the dose of 20%.The use of 2D-array can reduce the IMRT QA workload.

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Section: Verisoft Softwaresupporting

confidence: 57%

“…The same observation is reported by several authors. 15,18,19,20 FIG. 1: Examples of relative difference in dose values between measured dose using 0.6 cm 3 ionization chamber and calculated dose using XiO TPS.…”

Section: Verisoft Softwarementioning

confidence: 99%

Dose verification of intensity modulated radiotherapy in head and neck tumors

Elawady

Attalla

Elshemey

et al. 2014

Int J Cancer Ther Oncol

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“…Under such a complex dose distribution, large-volume ionization chambers, which are less sensitive to geometrical errors, would be effective for dose difference evaluations. A previous report involving a Farmer chamber (sensitive volume of 0.6 cm 3 ) indicated that this chamber reduced variations in dose differences to a greater extent when compared with small-volume detectors such as the PinPoint ionization chamber [23]. In this situation, measured and calculated doses are compared with volume-averaged doses to account for the effect of volume averaging.…”

Section: Discussionmentioning

confidence: 99%

A robust measurement point for dose verification in delivery quality assurance for a robotic radiosurgery system

Kurosu

Sumida

Shiomi

et al. 2016

Journal of Radiation Research

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In this CyberKnife® dose verification study, we investigated the effectiveness of the novel potential error (PE) concept when applied to the determination of a robust measurement point for targeting errors. PE was calculated by dividing the differences between the maximum increases and decreases in dose distributions by the original distribution after obtaining the former by shifting the source-to-axis and off-axis distances of each beam by ±1.0 mm. Thus, PE values and measurement point dose heterogeneity were analyzed in 48 patients who underwent CyberKnife radiotherapy. Sixteen patients who received isocentric dose delivery were set as the control group, whereas 32 who received non-isocentric dose delivery were divided into two groups of smaller PE (SPE) and larger PE (LPE) by using their median PE value. The mean dose differences (± standard deviations) were 1.0 ± 0.9%, 0.5 ± 1.4% and 4.1 ± 2.8% in the control, SPE and LPE groups, respectively. We observed significant correlations of the dose difference with the PE value (r = 0.582, P < 0.001) and dose heterogeneity (r = 0.471, P < 0.001). We concluded that when determining a robust measurement point for CyberKnife point dose verification, PE evaluation was more effective than the conventional dose heterogeneity-based method that introduced optimal measurement point dose heterogeneity of <10% across the detector.

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“…In the literature, alternative calibration methods have been suggested which employ a small‐volume ion chamber for MOSFET calibration, e.g. as in Brady and Kaufman's work on calibration in air and in a scattering medium . Such calibration methods have been limited to in‐field (i.e.…”

Section: Methodsmentioning

confidence: 99%

“…Due to MOSFET energy dependence of about 10% in the 40–120 kVp range, calibration has to be performed for each tube voltage of interest. Ionization chambers (“ion chambers”) are considered to be the “gold standard” for radiation dose measurements due to their precision and linearity of response. Various MOSFET calibration methods, which use ion chambers, are reported in the literature.…”

Section: Introductionmentioning

confidence: 99%

Calibration and error analysis of metal‐oxide‐semiconductor field‐effect transistor dosimeters for computed tomography radiation dosimetry

et al. 2017

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Purpose Metal-oxide-semiconductor field-effect transistors (MOSFETs) serve as a helpful tool for organ radiation dosimetry, and their use has grown in computed tomography (CT). While different approaches have been used for MOSFET calibration, those using the commonly-available 100 mm pencil ionization chamber have not incorporated measurements performed throughout its length, and moreover no previous work has rigorously evaluated the multiple sources of error involved in MOSFET calibration. In this paper we propose a new MOSFET calibration approach to translate MOSFET voltage measurements into absorbed dose from CT, based on serial measurements performed throughout the length of a 100 mm ionization chamber, and perform an analysis of the errors of MOSFET voltage measurements and four sources of error in calibration. Methods MOSFET calibration was performed at two sites, to determine single calibration factors for tube potentials of 80, 100, and 120 kVp, using a 100 mm long pencil ion chamber and a cylindrical computed tomography dose index (CTDI) phantom of 32 cm diameter. The dose profile along the 100 mm ion chamber axis was sampled in 5 mm intervals by nine MOSFETs in the nine holes of the CTDI phantom. Variance of the absorbed dose was modeled as a sum of the MOSFET voltage measurement variance and the calibration factor variance, the latter being comprised of three main subcomponents: ionization chamber reading variance, MOSFET-to-MOSFET variation and a contribution related to the fact that the average calibration factor of a few MOSFETs was used as an estimate for the average value of all MOSFETs. MOSFET voltage measurement error was estimated based on sets of repeated measurements. The calibration factor overall voltage measurement error was calculated from the above analysis. Results Calibration factors determined were close to those reported in the literature and by the manufacturer (∼ 3mV/mGy), ranging from 2.87 to 3.13 mV/mGy. The error σV of a MOSFET voltage measurement was shown to be proportional to the square root of the voltage V: σV=cV where c = 0.11 mV. A main contributor to the error in the calibration factor was the ionization chamber reading error with 5% error. The usage of a single calibration factor for all MOSFETs introduced an additional error of about 5-7%, depending on the number of MOSFETs that were used to determine the single calibration factor. The expected overall error in a high dose region (∼30 mGy) was estimated to be about 8%, compared to 6% when an individual MOSFET calibration was performed. For a low-dose region (∼3 mGy) these values were 13% and 12%. Conclusions A MOSFET calibration method was developed using a 100 mm pencil ion chamber and a CTDI phantom, accompanied by an absorbed dose error analysis reflecting multiple sources of measurement error. When using a single calibration factor, per tube potential, for different MOSFETs, only a small error was introduced into absorbed dose determinations, thus supporting the use of such a calibration factor for experim...

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A patient-specific quality assurance study on absolute dose verification using ionization chambers of different volumes in RapidArc treatments

Cited by 14 publications

References 35 publications

Dose verification of intensity modulated radiotherapy in head and neck tumors

Dose verification of intensity modulated radiotherapy in head and neck tumors

A robust measurement point for dose verification in delivery quality assurance for a robotic radiosurgery system

Calibration and error analysis of metal‐oxide‐semiconductor field‐effect transistor dosimeters for computed tomography radiation dosimetry

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