The gamma evaluation method as a routine QA procedure of IMRT

This study evaluated the feasibility of utilizing a 3D-printed anthropomorphic patient-specific head phantom for patient-specific quality assurance (QA) in intensity-modulated radiotherapy (IMRT). Contoured left and right head phantoms were converted from DICOM to STL format. Fused deposition modeling (FDM) was used to construct an anthropomorphic patient-specific head phantom with a 3D printer. An established QA technique and the patient-specific head phantom were used to compare the calculated and measured doses. When the established technique was used to compare the calculated and measured doses, the gamma passing rate for γ ≤ 1 was 97.28%, while the gamma failure rate for γ > 1 was 2.72%. When the 3D-printed patient-specific head phantom was used, the gamma passing rate for γ ≤ 1 was 95.97%, and the gamma failure rate for γ > 1 was 4.03%. The 3D printed patient-specific head phantom was concluded to be highly feasible for patient-specific QA prior to complicated radiotherapy procedures such as IMRT.

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“…In recent years, the gamma index has been widely used to compare calculated and measured doses [6,7,14]. …”

Section: Methodsmentioning

confidence: 99%

Feasibility of a 3D-printed anthropomorphic patient-specific head phantom for patient-specific quality assurance of intensity-modulated radiotherapy

et al. 2017

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“…The gamma index directly compares the predicted and the delivered doses, accounting for the distance accuracy. For each measured position

{\overset{false\to}{r}}_{m}

, it is defined as:

γ false({\overset{false\to}{r}}_{m} false) = min \sqrt{\frac{false| {\overset{r}{true}}_{c}, {\overset{r}{true}}_{m} |^{2}}{D T A^{2}} + \frac{false| D false({\overset{false\to}{r}}_{m} false) - D false({\overset{false\to}{r}}_{c} false) |^{2}}{Δ D^{2}}}

where

{\overset{false\to}{r}}_{c}

represents the reference position,

false| {\overset{r}{true}}_{c}, {\overset{r}{true}}_{m} false|

the distance between the analyzed points,

false| D false({\overset{false\to}{r}}_{m} false) - D false({\overset{false\to}{r}}_{c} false) false|

the dose difference, and DTA (Distance‐To‐Agreement) and Δ D are the required accuracies for the distance and dose, respectively. In our study, DTA was chosen to be 0.1 mm, corresponding to the targeting accuracy recommended in Verhaegen et al .…”

Section: Methodsmentioning

confidence: 99%

“…The gamma index directly compares the predicted and the delivered doses, accounting for the distance accuracy. For each measured position r m , it is defined as: 31,34 cðr m Þ ¼ min…”

Section: D Evaluation Of the Treatment Planningmentioning

confidence: 99%

Analytical dose modeling for preclinical proton irradiation of millimetric targets

et al. 2017

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Purpose: Due to the considerable development of proton radiotherapy, several proton platforms have emerged to irradiate small animals in order to study the biological effectiveness of proton radiation. A dedicated analytical treatment planning tool was developed in this study to accurately calculate the delivered dose given the specific constraints imposed by the small dimensions of the irradiated areas. Methods: The treatment planning system (TPS) developed in this study is based on an analytical formulation of the Bragg peak and uses experimental range values of protons. The method was validated after comparison with experimental data from the literature and then compared to Monte Carlo simulations conducted using GEANT4. Three examples of treatment planning, performed with phantoms made of water targets and bone-slab insert, were generated with the analytical formulation and GEANT4. Each treatment planning was evaluated using dose-volume histograms and gamma index maps. Results: We demonstrate the value of the analytical function for mouse irradiation, which requires a targeting accuracy of 0.1 mm. Using the appropriate database, the analytical modeling limits the errors caused by misestimating the stopping power. For example, 99% of a 1-mm tumor irradiated with a 24-MeV beam receives the prescribed dose. The analytical dose deviations from the prescribed dose remain within the dose tolerances stated by report 62 of the International Commission on Radiation Units and Measurements for all tested configurations. In addition, the gamma index maps show that the highly constrained targeting accuracy of 0.1 mm for mouse irradiation leads to a significant disagreement between GEANT4 and the reference. This simulated treatment planning is nevertheless compatible with a targeting accuracy exceeding 0.2 mm, corresponding to rat and rabbit irradiations. Conclusion: Good dose accuracy for millimetric tumors is achieved with the analytical calculation used in this work. These volume sizes are typical in mouse models for radiation studies. Our results demonstrate that the choice of analytical rather than simulated treatment planning depends on the animal model under consideration.

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“…The comparison of the dose plane measured on the treatment unit with the expected dose distribution is performed on the self-made GammaEval software based on a gamma algorithm. 7 Distance-to-agreement (DTA) and acceptable dose deviation (D max ) are set at 3 mm and 3.3% of the local dose. As a result of the comparison, a 2-D matrix of -values is obtained for each field, which is typically to a colouredimage transformed and then the histograms, which combine the -index value with area of corresponding part of field, are created.…”

Section: Methodsmentioning

confidence: 99%

“…A quantitative estimation of dose delivery is possible owing to -histograms which combine the information about a -index value with that of the area of corresponding part of the field. 5,6 In our previous paper, 7 we discussed the difference between the global gamma conception and its variety, local gamma, when the acceptable dose deviation (D max ) was proportional to the expected dose value D( r c ) for each element of the calculated dose matrix r c . The advantages and disadvantages of both approaches have been presented.…”

Section: Introductionmentioning

confidence: 99%