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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

Transit dose comparisons for fields 1 and 5 of patient 2. (a) field 1 with a homogeneous phantom, (b) field 5 with a homogeneous phantom, (c) field 1 with an anthropomorphic phantom and (d) field 5 with an anthropomorphic phantom.
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Fig3: Transit dose comparisons for fields 1 and 5 of patient 2. (a) field 1 with a homogeneous phantom, (b) field 5 with a homogeneous phantom, (c) field 1 with an anthropomorphic phantom and (d) field 5 with an anthropomorphic phantom.

Mentions: The effectiveness of the proposed method was first evaluated using a 20 cm-thick homogeneous plastic phantom. Figure 3(a) and (b) show the GI maps of transit doses passing through a homogeneous solid water phantom for fields 1 and 5 of patient 2 in Table 1, respectively. The passing rates were 96.6% and 95.4%, respectively, indicating that the transit dose map measured with the EPID is well matched with the dose distribution calculated by the TPS. This finding suggested that the gamma index-based comparison of measured and TPS calculated transit dose can be used to prevent accidents in radiotherapy since the passing rate will decrease significantly if errors occur during treatment. That is, the proposed method can effectively assess the errors of the treatment plan at the final stage (i.e., in the treatment room). Table 2 shows the detailed passing rate for the 24 IMRT fields, revealing an average normal beam delivery of 94.2%.Figure 3


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)

Transit dose comparisons for fields 1 and 5 of patient 2. (a) field 1 with a homogeneous phantom, (b) field 5 with a homogeneous phantom, (c) field 1 with an anthropomorphic phantom and (d) field 5 with an anthropomorphic phantom.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig3: Transit dose comparisons for fields 1 and 5 of patient 2. (a) field 1 with a homogeneous phantom, (b) field 5 with a homogeneous phantom, (c) field 1 with an anthropomorphic phantom and (d) field 5 with an anthropomorphic phantom.
Mentions: The effectiveness of the proposed method was first evaluated using a 20 cm-thick homogeneous plastic phantom. Figure 3(a) and (b) show the GI maps of transit doses passing through a homogeneous solid water phantom for fields 1 and 5 of patient 2 in Table 1, respectively. The passing rates were 96.6% and 95.4%, respectively, indicating that the transit dose map measured with the EPID is well matched with the dose distribution calculated by the TPS. This finding suggested that the gamma index-based comparison of measured and TPS calculated transit dose can be used to prevent accidents in radiotherapy since the passing rate will decrease significantly if errors occur during treatment. That is, the proposed method can effectively assess the errors of the treatment plan at the final stage (i.e., in the treatment room). Table 2 shows the detailed passing rate for the 24 IMRT fields, revealing an average normal beam delivery of 94.2%.Figure 3

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