Effect of Low Magnetic Field on Dose Distribution in the Partial-Breast Irradiation

Jung-in Kim; So-Yeon Park; Yang Hoon Lee; Kyung Hwan Shin; Hong-Gyun Wu; Jong Min Park

doi:10.14316/pmp.2015.26.4.208

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Kim, Park, Lee, Shin, Wu, and Park: Effect of Low Magnetic Field on Dose Distribution in the Partial-Breast Irradiation

Original Article

Progress in Medical Physics 2015;26(4):208-214.

Published online: 20 January 2015

DOI: https://doi.org/10.14316/pmp.2015.26.4.208

Effect of Low Magnetic Field on Dose Distribution in the Partial-Breast Irradiation

Jung-in Kim^∗,^†,^‡,^§, So-Yeon Park^∗,^†,^‡,^║, Yang Hoon Lee^∗, Kyung Hwan Shin^∗,^†,^‡,^¶, Hong-Gyun Wu^∗,^†, Jong Min Park^∗,^†,^‡,^§

^∗Department of Radiation Oncology, Seoul National University Hospital, Seoul, Korea

^†Biomedical Research Institute, Seoul National University Hospital, Seoul, Korea

^‡Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, Korea

^§Center for Convergence Research on Robotics, Advanced Institutes of Convergence Technology, Suwon, Korea

^║Interdisciplinary Program in Radiation Applied Life Science, Seoul National University College of Medicine, Seoul, Korea

^¶Department of Radiation Oncology, Seoul National University College of Medicine, Seoul, Korea

Correspondence: Jong Min Park (leodavinci@naver.com) Tel: 82-2-2072-2527, Fax: 82-2-765-3317 cc This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Received 8 December 2015 Revised 17 December 2015 Accepted 18 December 2015

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 aim of this study is to investigate the effect of low magnetic field on dose distribution in the partial-breast irradiation (PBI). Eleven patients with an invasive early-stage breast carcinoma were treated prospectively with PBI using 38.5 Gy delivered in 10 fractions using the ViewRay^Ⓡ system. For each of the treatment plans, dose distribution was calculated with magnetic field and without magnetic field, and the difference between dose and volume for each organ were evaluated. For planning target volume (PTV), the analysis included the point minimum (D_min), maximum, mean dose (D_mean) and volume receiving at least 90% (V_90%), 95% (V_95%) and 107% (V_107%) of the prescribed dose, respectively. For organs at risk (OARs), the ipsilateral lung was analyzed with D_mean and the volume receiving 20 Gy (V₂₀ _Gy), and the contralateral lung was analyzed with only D_mean. The heart was analyzed with D_mean, D_max, and V₂₀ _Gy, and both inner and outer shells were analyzed with the point D_min, D_max and D_mean, respectively. For PTV, the effect of low magnetic field on dose distribution showed a difference of up to 2% for volume change and 4 Gy for dose. In OARs analysis, the significant effect of the magnetic field was not observed. Despite small deviation values, the average difference of mean dose values showed significant difference (p＜0.001), but there was no difference of point minimum dose values in both sehll structures. The largest deviation for the average difference of D_max in the outer shell structure was 5.0±10.5 Gy (p=0.148). The effect of low magnetic field of 0.35 T on dose deposition by a Co‐60 beam was not significantly observed within the body for PBI IMRT plans. The dose deposition was only appreciable outside the body, where a dose build‐up due to contaminated electrons generated in the treatment head and scattered electrons formed near the body surface.

Keywords: Low magnetic field, Dose distribution, Partial breast irradiation, MRI-guided radiation therapy system, IMRT

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Fig. 1.

The comparison of dose distribution for (a) with magnet field and (b) without magnet field in the case of PBI patient with a magnet field (B₀).

Fig. 2.

Dose and Volume difference values in PTV for each patients.

Fig. 3.

The dose distribution in saggital image between (a) with magent field (B₀) and (b) without magnet field.

Table 1.

The average dose volume analysis for PTV.

Analysis	With Magnet	Without Magnet	Difference value	p-value
D_mean (Gy)	40.7±0.4	40.6±0.4	0.1±0.1	0.003
D_min (Gy)	30.4±10.0	28.7±9.6	1.7±1.8	0.011
D_max (Gy)	44.0±0.5	43.9±0.4	1.0±0.3	0.351
V_90% (%)	99.9±0.1	99.5±0.5	0.4±0.4	0.025
V_95% (%)	98.9±0.6	98.1±1.2	0.8±0.8	0.01
V_107% (%)	39.7±10.7	39.0±10.9	0.7±0.8	0.013

Table 2.

The average dose volume analysis for organs at risk (OARs).

OAR	Analysis	With Magnet	Without Magnet	Difference value	p-value
Ipsilateral lung	D_mean (Gy)	7.7±1.8	7.7±1.8	0.0±0.04	1.000
	V₂₀ _Gy (%)	6.8±4.2	6.9±4.3	−0.1±0.2	0.116
Contralateral lung	D_mean (Gy)	2.1±1.0	2.2±1.0	−0.1±0.4	0.312
Heart	D_mean (Gy)	4.7±3.8	4.6±3.8	0.1±0.3	0.359
	D_max (Gy)	23.5±11.1	23.1±11.8	0.4±1.8	0.484
	V₂₀ _Gy (%)	2.1±3.7	2.1±3.7	0.0±0.01	0.221

Table 3.

The average dose analysis for shell structures.

Structure	Analysis	With magnet	Without magnet	Difference value	p-value
Inner shell	D_mean (Gy)	1.53±0.5	1.49±0.5	0.04±0.01	＜0.001
	D_min (Gy)	0.0±0.0	0.0±0.0	0.0±0.01	0.176
	D_max (Gy)	42.5±1.8	42.3±1.6	0.2±0.4	0.143
Outer shell	D_mean (Gy)	1.17±0.4	1.04±0.4	0.13±0.1	＜0.001
	D_min (Gy)	0.0±0.0	0.0±0.0	0.0±0.01	0.221
	D_max (Gy)	37.5±13.1	32.5±6.6	5.0±10.5	0.148

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