Journal List > Prog Med Phys > v.25(1) > 1098447

Hwang, Baek, and Yoon: Development of Dose Verification Method for In vivo Dosimetry in External Radiotherapy

Abstract

The purpose of this study is to evaluate the developed dose verification program for in vivo dosimetry based on transit dose in radiotherapy. Five intensity modulated radiotherapy (IMRT) plans of lung cancer patients were used in the irradiation of a homogeneous solid water phantom and anthropomorphic phantom. Transit dose distribution was measured using electronic portal imaging device (EPID) and used for the calculation of in vivo dose in patient. The average passing rate compared with treatment planning system based on a gamma index with a 3% dose and a 3 mm distance-to-dose agreement tolerance limit was 95% for the in vivo dose with the homogeneous phantom, but was reduced to 81.8% for the in vivo dose with the anthropomorphic phantom. This feasibility study suggested that transit dose-based in vivo dosimetry can provide information about the actual dose delivery to patients in the treatment room.

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Fig. 1.
Brief flowchart of patient dose calculation program.
pmp-25-23f1.tif
Fig. 2.
Brief flowchart of dose distribution comparing program.
pmp-25-23f2.tif
Fig. 3.
EPID signal according to MU from the LINAC.
pmp-25-23f3.tif
Fig. 4.
Screen capture of developed software for calculating patient dose.
pmp-25-23f4.tif
Fig. 5.
Gamma distribution evaluated between dose distributions calculated from the EPID and given from the treatment planning system. (a) homogeneous solid phantom, (b) inhomogeneous humanoid phantom.
pmp-25-23f5.tif
Fig. 6.
Box plot of gamma passing rates represented in Table 2. Average passing rate was 95% for solid phantom and 81.8% for humanoid phantom.
pmp-25-23f6.tif
Table 1.
Patient characteristics, prescribed radiation dose and fraction size.
Patient Treatment Site Age (years) PTV (ml) Number of Fields Number of Fractions Prescribed Dose (cGy)
1 Lung 77 34 6 33 6600
2 Lung 78 19 6 32 6400
3 Lung 82 31 6 27 5400
4 Lung 71 57 6 33 6600
5 Lung 77 23 6 34 6800
Table 2.
Comparison of gamma passing rates evaluated by commercial software and home-made software respectively.
RIT Home-made
96.02 95.72
94.33 93.76
93.45 94.25
94.76 96.29
94.48 91.23
92.64 94.14
92.72 92.92
91.34 91.18
92.66 95.45
91.94 92.82
96.62 93.79
95.45 96.13
95.74 92.63
95.26 93.48
97.44 93.11
92.01 90.64
93.55 94.62
93.06 96.21
Table 3.
Gamma passing rates for patient dose distribution in solid phantom and humanoid phantom respectively.
Solid Phantom Field1 Field2 Field3 Field4 Field5 Field6 Avg SD
Case 1 95.0 96.0 95.7 93.5 89.6 94.7 94.1 2.35
Case 2 98.1 97.3 88.0 98.2 98.6 97.7 96.3 4.08
Case 3 94.9 97.6 95.8 94.0 90.2 95.1 94.6 2.46
Case 4 94.6 95.4 98.8 94.7 98.2 92.9 95.8 2.28
Case 5 94.1 95.3 96.7 88.5 94.1 97.7 94.4 3.21
Lung Phantom Field1 Field2 Field3 Field4 Field5 Field6 Avg SD
Case 1 79.9 77.8 83.1 82.1 80.6 81.4 80.8 1.84
Case 2 80.5 90.9 79.3 82.2 70.6 72.5 79.3 7.31
Case 3 82.9 84.6 80.6 79.1 89.8 79.7 82.8 3.99
Case 4 81.3 81.9 79.5 89.5 94.3 75.2 83.6 7.00
Case 5 82.1 85.0 79.2 76.3 87.2 85.4 82.5 4.14
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