Feasibility Study of Patient Specific Quality Assurance Using Transit Dosimetry Based on Measurement with an Electronic Portal Imaging Device

Tae Seong Baek; Eun Ji Chung; Jaeman Son; Myonggeun Yoon

doi:10.14316/pmp.2017.28.2.54

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Baek, Chung, Son, and Yoon: Feasibility Study of Patient Specific Quality Assurance Using Transit Dosimetry Based on Measurement with an Electronic Portal Imaging Device

Original Article

Progress in Medical Physics 2017;28(2):54-60.

Published online: 17 June 2017

DOI: https://doi.org/10.14316/pmp.2017.28.2.54

Feasibility Study of Patient Specific Quality Assurance Using Transit Dosimetry Based on Measurement with an Electronic Portal Imaging Device

Tae Seong Baek^∗, Eun Ji Chung^∗, Jaeman Son^†, Myonggeun Yoon^†,

^∗Department of Radiation Oncology, National Health Insurance Co. Ilsan Hospital, Goyang, Korea

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

Corresponding author Myonggeun Yoon (radioyoon@korea.ac.kr) Tel: 82-2-3290-5651 Fax: 82-2-921-6434

Received 30 June 201710 June 2017 Accepted 10 June 2017

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

This study was designed to measure transit dose with an electronic portal imaging device (EPID) in eight patients treated with intensity modulated radiotherapy (IMRT), and to verify the accuracy of dose delivery to patients. The calculated dose map of the treatment planning system (TPS) was compared with the EPID based dose measured on the same plane with a gamma index method. The plan for each patient was verified prior to treatment with a diode array (MapCHECK) and portal dose image prediction (PDIP). To simulate possible patient positioning errors during treatment, outcomes were evaluated after an anthropomorphic phantom was displaced 5 and 10 mm in various directions. Based on 3%/3 mm criteria, the mean±SD passing rates of MapCHECK, PDIP (pre-treatment QA) for 47 IMRT were 99.8±0.1%, 99.0±0.7%, and, respectively. Besides, passing rates using transit dosimetry was 90.0±1.5% for the same condition. Setup errors of 5 and 10 mm reduced the mean passing rates by 1.3% and 3.0% (inferior to superior), 2.2% and 4.3% (superior to inferior), 5.9% and 10.9% (left to right), and 8.9% and 16.3% (right to left), respectively. These findings suggest that the transit dose-based IMRT verification method using EPID, in which the transit dose from patients is compared with the dose map calculated from the TPS, may be useful in verifying various errors including setup and/or patient positioning error, inhomogeneity and target motions.

Keywords: Linear accelerator, Transit dose, EPID, Gamma index

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Fig. 1.

EPID measurements of transit doses during treatment at the posterior surfaces of Patients (a) 1 (maxillary sinus) and (b) 3 (prostate).

Fig. 2.

Transit doses in field 3 from Patient 1 (a) calculated from TPS and (b) measured using EPID.

Fig. 3.

Dose maps calculated in field 3 of Patient 2 by (a) MapCHECK and (b) PDIP and measured by transit dosimetry at (c) 3%/3 mm and (d) 5%/3 mm.

Table 1.

Demographic and radiologic characteristics of the eight patients analyzed in this study.

Patient number	Treatment Site	Photon Energy	PTV (ml)	Number of fields	IMRT delivery technique
1	Maxillary sinus	6 MV	130.3	7	DMLC
2	Cervix	6 MV	171.4	5	DMLC
3	Prostate	6 MV	101.6	7	DMLC
4	Eye	6 MV	86.4	5	DMLC
5	Lung	6 MV	154.5	5	DMLC
6	Brain	6 MV	235.3	5	DMLC
7	Oropharynx	6 MV	228.8	7	DMLC
8	Brain	6 MV	122	6	DMLC

DMLC: Dynamic Multileaf collimator.

Table 2.

Pre-treatment passing rates (%) of results measured with MapCHECK (M) and PDIP (P) based on the gamma index for the eight included patients.

Patient No.	Field number
Patient No.	Dosimetric tool	1	2	3	4	5	6	7	Mean
1	M	100.0	99.8	100.0	100.0	99.7	97.7	100.0	99.6
	P	99.5	99.3	96.0	99.4	99.6	98.6	95.7	98.3
2	M	99.1	100.0	100.0	99.6	100.0			99.7
	P	99.9	96.9	99.7	99.9	99.9			99.3
3	M	100.0	99.8	100.0	98.9	100.0	99.8	100.0	99.8
	P	99.9	99.8	100.0	97.0	98.9	97.9	99.9	99.1
4	M	100.0	100.0	100.0	100.0	100.0			100.0
	P	99.9	98.7	100.0	98.4	99.9			99.4
5	M	99.8	100.0	99.1	100.0	100.0			99.8
	P	99.7	100.0	98.5	99.9	99.9			99.6
6	M	100.0	100.0	100.0	100.0	100.0			100.0
	P	99.9	99.9	100.0	99.9	99.9			99.9
7	M	98.9	100.0	99.8	100.0	99.4	100.0	99.8	99.7
	P	97.7	100.0	99.0	99.4	98.8	98.9	97.4	98.7
8	M	99.1	98.9	100.0	100.0	100.0	99.4		99.6
	P	96.4	95.8	95.2	99.8	98.8	98.7		97.5

Table 3.

Passing rates of results measured using transit dosimetry based on the gamma index values for the eight patients.

Patient	Field number
No.	t	1	2	3	4	5	6	7	Mean
1	3%/3 mm	90.0	83.1	90.5	92.4	93.3	88.0	89.6	89.6
2	3%/3 mm	95.1	86.7	94.9	86.5	85.4	-	-	89.7
3	3%/3 mm	96.5	96.4	86.8	79.4	84.9	91.6	95.3	90.1
4	3%/3 mm	94.9	95.3	92.4	95.9	87.3	-	-	93.2
5	3%/3 mm	89.2	87.9	82.7	94.0	86.5	-	-	88.1
6	3%/3 mm	94.9	93.4	81.4	92.9	94.1	-	-	91.3
7	3%/3 mm	89.6	92.9	90.0	91.8	87.2	87.6	86.4	89.4
8	3%/3 mm	96.2	88.0	89.7	86.4	86.9	82.5	-	88.3

Table 4.

Decreases in passing rates for phantom movement compared with the original passing rate without movement.

Patient number	IS		SI		LR		RL
Patient number	5 mm	10 mm	5 mm	10 mm	5 mm	10 mm	5 mm	10 mm
1	1.8	4.1	3.0	6.5	5.3	9.7	7.6	13.6
2	0.9	3.8	2.3	3.3	6.3	12.3	10.0	19.0
3	1.8	2.8	2.5	4.7	7.0	12.7	9.9	18.4
4	1.5	2.7	1.7	4.2	5.2	9.4	8.0	14.4
5	0.7	1.7	1.3	2.6	5.7	10.5	9.0	16.0
Mean	1.3	3.0	2.2	4.3	5.9	10.9	8.9	16.3
SD	0.5	0.9	0.6	1.3	0.7	1.3	1.0	2.1

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