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Feasibility study on the verification of actual beam delivery in a treatment room using EPID transit dosimetry.

Baek TS, Chung EJ, Son J, Yoon M - Radiat Oncol (2014)

Bottom Line: The proposed method was evaluated by comparing the calculated dose map from TPS and EPID measurement on the same plane using a gamma index method with a 3% dose and 3 mm distance-to-dose agreement tolerance limit.The passing rate of the transit dose for 24 IMRT fields was lower with the anthropomorphic phantom, averaging 86.8% ± 3.8%, a reduction partially due to the inaccuracy of TPS calculations for inhomogeneity.The simulation study indicated that the passing rate of the gamma index was significantly reduced, to less than 40%, when a wrong field was erroneously irradiated to patient in the treatment room.

View Article: PubMed Central - PubMed

Affiliation: Department of Bio-convergence Engineering, Korea University, Jeongneungro 161, Seongbuk-gu, Seoul, 136-703, Korea. taesb@nhimc.or.kr.

ABSTRACT

Purpose: The aim of this study is to evaluate the ability of transit dosimetry using commercial treatment planning system (TPS) and an electronic portal imaging device (EPID) with simple calibration method to verify the beam delivery based on detection of large errors in treatment room.

Methods and materials: Twenty four fields of intensity modulated radiotherapy (IMRT) plans were selected from four lung cancer patients and used in the irradiation of an anthropomorphic phantom. The proposed method was evaluated by comparing the calculated dose map from TPS and EPID measurement on the same plane using a gamma index method with a 3% dose and 3 mm distance-to-dose agreement tolerance limit.

Results: In a simulation using a homogeneous plastic water phantom, performed to verify the effectiveness of the proposed method, the average passing rate of the transit dose based on gamma index was high enough, averaging 94.2% when there was no error during beam delivery. The passing rate of the transit dose for 24 IMRT fields was lower with the anthropomorphic phantom, averaging 86.8% ± 3.8%, a reduction partially due to the inaccuracy of TPS calculations for inhomogeneity. Compared with the TPS, the absolute value of the transit dose at the beam center differed by -0.38% ± 2.1%. The simulation study indicated that the passing rate of the gamma index was significantly reduced, to less than 40%, when a wrong field was erroneously irradiated to patient in the treatment room.

Conclusions: This feasibility study suggested that transit dosimetry based on the calculation with commercial TPS and EPID measurement with simple calibration can provide information about large errors for treatment beam delivery.

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Related in: MedlinePlus

Flow chart for the verification of radiotherapy beam in the treatment room using comparisons of transit doses.
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Fig5: Flow chart for the verification of radiotherapy beam in the treatment room using comparisons of transit doses.

Mentions: Figure 5 shows an example of flow chart for the treatment beam monitoring using comparisons of the transit dose. The first step is to obtain calculated and measured dose maps from TPS and EPID, respectively. This is followed by defining a common rectangular region of interest (ROI) for later comparison of dose correlations. In the next step, doses are compared based on gamma index (GI) analysis. If these comparisons pass the predefined tolerance value, the treatment proceeds to the next field; if not, the treatment should be stopped and the reason for the mismatch should be verified. Although the proposed method is simple, it needs further refinement as a future study since the EPID signal should be converted to absorbed dose using actual treatment field size and patient thickness.Figure 5


Feasibility study on the verification of actual beam delivery in a treatment room using EPID transit dosimetry.

Baek TS, Chung EJ, Son J, Yoon M - Radiat Oncol (2014)

Flow chart for the verification of radiotherapy beam in the treatment room using comparisons of transit doses.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4262986&req=5

Fig5: Flow chart for the verification of radiotherapy beam in the treatment room using comparisons of transit doses.
Mentions: Figure 5 shows an example of flow chart for the treatment beam monitoring using comparisons of the transit dose. The first step is to obtain calculated and measured dose maps from TPS and EPID, respectively. This is followed by defining a common rectangular region of interest (ROI) for later comparison of dose correlations. In the next step, doses are compared based on gamma index (GI) analysis. If these comparisons pass the predefined tolerance value, the treatment proceeds to the next field; if not, the treatment should be stopped and the reason for the mismatch should be verified. Although the proposed method is simple, it needs further refinement as a future study since the EPID signal should be converted to absorbed dose using actual treatment field size and patient thickness.Figure 5

Bottom Line: The proposed method was evaluated by comparing the calculated dose map from TPS and EPID measurement on the same plane using a gamma index method with a 3% dose and 3 mm distance-to-dose agreement tolerance limit.The passing rate of the transit dose for 24 IMRT fields was lower with the anthropomorphic phantom, averaging 86.8% ± 3.8%, a reduction partially due to the inaccuracy of TPS calculations for inhomogeneity.The simulation study indicated that the passing rate of the gamma index was significantly reduced, to less than 40%, when a wrong field was erroneously irradiated to patient in the treatment room.

View Article: PubMed Central - PubMed

Affiliation: Department of Bio-convergence Engineering, Korea University, Jeongneungro 161, Seongbuk-gu, Seoul, 136-703, Korea. taesb@nhimc.or.kr.

ABSTRACT

Purpose: The aim of this study is to evaluate the ability of transit dosimetry using commercial treatment planning system (TPS) and an electronic portal imaging device (EPID) with simple calibration method to verify the beam delivery based on detection of large errors in treatment room.

Methods and materials: Twenty four fields of intensity modulated radiotherapy (IMRT) plans were selected from four lung cancer patients and used in the irradiation of an anthropomorphic phantom. The proposed method was evaluated by comparing the calculated dose map from TPS and EPID measurement on the same plane using a gamma index method with a 3% dose and 3 mm distance-to-dose agreement tolerance limit.

Results: In a simulation using a homogeneous plastic water phantom, performed to verify the effectiveness of the proposed method, the average passing rate of the transit dose based on gamma index was high enough, averaging 94.2% when there was no error during beam delivery. The passing rate of the transit dose for 24 IMRT fields was lower with the anthropomorphic phantom, averaging 86.8% ± 3.8%, a reduction partially due to the inaccuracy of TPS calculations for inhomogeneity. Compared with the TPS, the absolute value of the transit dose at the beam center differed by -0.38% ± 2.1%. The simulation study indicated that the passing rate of the gamma index was significantly reduced, to less than 40%, when a wrong field was erroneously irradiated to patient in the treatment room.

Conclusions: This feasibility study suggested that transit dosimetry based on the calculation with commercial TPS and EPID measurement with simple calibration can provide information about large errors for treatment beam delivery.

Show MeSH
Related in: MedlinePlus