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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

Pictures of the experimental setup and axial views of IMRT calculations maps. (a) a homogeneous plastic phantom, (b) an anthropomorphic phantom, (c) a homogeneous plastic phantom and (d) an anthropomorphic phantom.
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Fig1: Pictures of the experimental setup and axial views of IMRT calculations maps. (a) a homogeneous plastic phantom, (b) an anthropomorphic phantom, (c) a homogeneous plastic phantom and (d) an anthropomorphic phantom.

Mentions: We evaluated 24 IMRT fields used in the radiotherapy of 4 randomly selected lung cancer patients (see Table 1). All IMRT QA was carried out with the sliding window technique, after modifying the gantry angles of all treatment fields to 0 degrees. The patient-specific planned dose distributions were calculated using the Eclipse treatment planning system Version 8.0.3 (Varian Medical Systems, Salt Lake City, UT, USA) with AAA algorithm. Figure 1(a) and (b) show pictures of the experimental setup with a homogeneous solid water phantom (Plastic Water, New York, USA) and an inhomogeneous anthropomorphic phantom (Rando, NY, USA), respectively. Using the CT (LightSpeed RT16 CT-Simulator, GE Healthcare, Milwaukee, WI, USA) scanned phantom, an IMRT QA plan used for transit dosimetry was made in the TPS for selected fields. Figure 1(c) and (d) show examples of the axial view of the transit dose passing through a homogeneous plastic water phantom and anthropomorphic phantom, respectively, as calculated by the TPS.Table 1


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)

Pictures of the experimental setup and axial views of IMRT calculations maps. (a) a homogeneous plastic phantom, (b) an anthropomorphic phantom, (c) a homogeneous plastic phantom and (d) an anthropomorphic phantom.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig1: Pictures of the experimental setup and axial views of IMRT calculations maps. (a) a homogeneous plastic phantom, (b) an anthropomorphic phantom, (c) a homogeneous plastic phantom and (d) an anthropomorphic phantom.
Mentions: We evaluated 24 IMRT fields used in the radiotherapy of 4 randomly selected lung cancer patients (see Table 1). All IMRT QA was carried out with the sliding window technique, after modifying the gantry angles of all treatment fields to 0 degrees. The patient-specific planned dose distributions were calculated using the Eclipse treatment planning system Version 8.0.3 (Varian Medical Systems, Salt Lake City, UT, USA) with AAA algorithm. Figure 1(a) and (b) show pictures of the experimental setup with a homogeneous solid water phantom (Plastic Water, New York, USA) and an inhomogeneous anthropomorphic phantom (Rando, NY, USA), respectively. Using the CT (LightSpeed RT16 CT-Simulator, GE Healthcare, Milwaukee, WI, USA) scanned phantom, an IMRT QA plan used for transit dosimetry was made in the TPS for selected fields. Figure 1(c) and (d) show examples of the axial view of the transit dose passing through a homogeneous plastic water phantom and anthropomorphic phantom, respectively, as calculated by the TPS.Table 1

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