DIFFERENCE BETWEEN RADIOTHERAPY QUALITY ASSURANCE DEVICES ( ARCAND MAP-CHECKS )

The radiotherapy is a complex procedure and involves understanding of the principles of medical physics, radiobiology, radiation safety, dosimetry, radiation treatment planning, simulation and interaction of radiation with other treatment modalities. Each step in the integrated process of RT needs quality control and quality assurance to prevent errors and to give high confidence that patients will receive the prescribed treatment correctly. A patient-specific quality assurance program has been developed to facilitate the clinical implementation of the intensity-modulated radiotherapy delivered using a micro‐multileaf collimator. The methodology includes several dosimetric tasks that are performed prior to the treatment of each patient. Film dosimeter is performed for each individual field and the multifield composite plan. Individual field measurements are performed at a depth of 5 cm in a water equivalent slab phantom. The heterogeneity inserts of phantom are 2 cm×2 cm×22 cm with absorption characteristics of water, brain, muscle, lung, breast, adipose tissue, bone, and liver.


INTRODUCTION
The purpose of the research is related to the need to develop an analytical approach to planning and question anything different from the norm.This study was conducted to verify planar dose distributions acquired during the pretreatment step of the radiotherapy (RT), in particular, the patient-specific intensity-modulated-radiotherapy (IMRT) quality assurance (QA) delivered at LIV Hospital Radiation Medicine Centre (Tbilisi, Georgia).

EXPERIMENTALS
Our study took one year to provide the appropriate radiation database with clinical conditions: ELEKTA, type of treatment machine, and treatment planning systems (TPS); Treatment approaches: IMRT, S and S IMRT, SBRT, SRS, and volumetric-modulated-arc-therapy (VMAT); QAdevices: Subnuclear, Arc-Check, and Map-Check; Fraction dose: between 1.5-3.0Gy; and the number of patients: breast -87 and larynx -504.

RESULTS AND DISCUSSION
Five hundred ninety-one patient data were evaluated for a time ranging from 2017 to 2018.These data were gauged using several methods used in the QA process.Several patient plan QA in the latter years.
Patients were grouped according to several parameters including TPS, site of treatment, and type of treatment machine used in comparing the measured versus computed dose differences.
With the introduction of advanced RT techniques such as VMAT and IMRT, the three-dimensional (3D) dose distribution for radiation therapy has become both more conformal and complex.These features pose a great challenge for the QA of the dose distribution, which commonly consists of both point dose and two-dimensional (2D) plane dose measurements. 1And an urgent need for 3D dosimetry has also been stated. 2rious techniques have been developed to compare measured dose distributions with those generated by the treatment planning system.  The-index technique, 3,4 which is the standard method for planar dose verification in IMRT QA, 5,6 calculates the quantity c for each point of interest using preselected dose-difference (DD) and distance-to-agreement (DTA) criteria and then uses the c value to determine the outcome (pass-fail) of the IMRT QA.
QA measurements are conducted per year for each patient.Quality assurance is specifically defined as the systematic actions necessary to ensure that a product or process performs to specification.The accuracy of each step in the process has a direct impact on treatment outcome.
The following criteria are used for absolute dose and relative dose to determine if a point passes or fails: threshold (TH %), percent difference (Diff %), and distance (Dist, mm).TH % is the minimum dose percent value that must be met in either the device measured or planned dose data for the point to be included in the analysis.Global, so-called Van Dyk, Diff % is the percent difference between the doses at any measured point and the corresponding plan point normalized to a common point (a user-selected normalization point or the maximum dose pointdefault).
As for the Dist, it is a radius in mm around the measured point.This test refers to points, where the difference between measured and planned values of co-located points exceeds the selected percent difference.Using the distance to agreement criteria, measured point passes if, within a circle of DTA in mm, there exists at least one plan point that is greater than or equal to and at least one plan point that is less than or equal to the value of the measured point.The plot (Table 1) shows all the measurement points that are not in agreement.The points that record a higher value are shown in red (hot) while those that record a lower value are shown in blue (cold).If the Global % checkbox is selected in the analysis panel, the Van Dyk comparison is used during DTA and gamma analysis (Figures 1 and 2).
Global % difference for DTA analysis is defined as the following expression in the SNC patient software: where: PDEk,l is the percent dose difference between Mg,h and Pk,l, Mg,h is the measured value at the point (g, h), Pk,l is the planned value at the point (k, l), and Pnorm is the planned value at the normalization point.
Global % difference for gamma analysis is defined as the following expression in the SNC patient software: where: PDEk,l is the percent dose difference between Mg,h and Pk,l, Mg,h is the measured value at the point (g, h), Pk,l is the planned value at the point (k, l), and Mnorm is the measured value at the normalization point.

CONCLUSION
For dose distribution overlays or dose-difference determinations, the results were independent to within a sign of selection of the reference or evaluated distribution.However, for the DTA and γ tools, the results could be profoundly affected by the selection, especially when one or both of the dose distributions contained some noises.Typically, the reference and evaluated distributions would refer to measured and calculated distributions, respectively.But, the final selection should be based on which distribution is considered the standard by which the other is compared.
The γ tool provides a quantitative method for comparing two dose distributions.In this paper, we have shown the utility of the tool to compare two similar dose distributions and evaluated the sensitivity of the tool to pseudorandom noise.In all of these tests, the dose and distance criteria were fixed, preselected values.In practice, the values can be set as functions of space the location of the dose comparison or dose value.

Table 1 .
Quality assurance data of breast patients.

Table 2 .
Quality assurance data of larynx patients