Development of Dose Verification Method for In vivo Dosimetry in External Radiotherapy

Ui-Jung Hwang; Tae Seong Baek; Myonggeum Yoon

doi:10.14316/pmp.2014.25.1.23

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

Original Article

Progress in Medical Physics 2014;25(1):23-29.

Published online: 17 March 2014

DOI: https://doi.org/10.14316/pmp.2014.25.1.23

Development of Dose Verification Method for In vivo Dosimetry in External Radiotherapy

Ui-Jung Hwang^∗, Tae Seong Baek^†,^‡, Myonggeum Yoon^†,

^∗Department of Radiation Oncology, National Medical Center, Seoul, Korea

^†Department of Bio-convergence Engineering, Korea University, Seoul, Korea

^‡Department of Radiation Oncology, National Health Insurance Service Ilsan Hospital, Goyang, Korea

Correspondence: Myonggeum Yoon (radioyoon@korea.ac.kr) Tel: 82-2-940-2823, Fax: 82-2-940-2829

Received 28 February 2014 Accepted 13 March 2014

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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.

Keywords: Radiotherapy, Quality assurance, Electronic portal imaging device, Transit dose, In vivo dosimetry

REFERENCES

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Fig. 1.

Brief flowchart of patient dose calculation program.

Fig. 2.

Brief flowchart of dose distribution comparing program.

Fig. 3.

EPID signal according to MU from the LINAC.

Fig. 4.

Screen capture of developed software for calculating patient dose.

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.

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.

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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