The Dosimetric Impact of Shifts in Patient Positioning during Boron Neutron Capture Therapy for Brain Tumors

Jia-Cheng Lee; Yi-Wei Chen; Keh-Shih Chuang; Fang-Yuh Hsu; Fong-In Chou; Shih-Ming Hsu; Sang-Hue Yen; Yuan-Hung Wu

doi:10.1155/2018/5826174

The Dosimetric Impact of Shifts in Patient Positioning during Boron Neutron Capture Therapy for Brain Tumors

Biomed Res Int. 2018 Oct 1:2018:5826174. doi: 10.1155/2018/5826174. eCollection 2018.

Authors

Jia-Cheng Lee^{1

2}, Yi-Wei Chen^{1

3}, Keh-Shih Chuang², Fang-Yuh Hsu⁴, Fong-In Chou⁴, Shih-Ming Hsu⁵, Sang-Hue Yen¹, Yuan-Hung Wu^{1

3

5

6}

Affiliations

¹ Department of Oncology, Taipei Veterans General Hospital, Taipei, Taiwan.
² Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu, Taiwan.
³ School of Medicine, National Yang-Ming University, Taipei, Taiwan.
⁴ Nuclear Science and Technology Development Center, National Tsing Hua University, Hsinchu, Taiwan.
⁵ Department of Biomedical Imaging and Radiological Sciences, National Yang-Ming University, Taipei, Taiwan.
⁶ Institute of Public Health, National Yang-Ming University, Taipei, Taiwan.

Abstract

Unlike conventional photon radiotherapy, sophisticated patient positioning tools are not available for boron neutron capture therapy (BNCT). Thus, BNCT remains vulnerable to setup errors and intra-fractional patient motion. The aim of this study was to estimate the impact of deviations in positioning on the dose administered by BNCT for brain tumors at the Tsing Hua open-pool reactor (THOR). For these studies, a simulated head model was generated based on computed tomography (CT) images of a patient with a brain tumor. A cylindrical brain tumor 3 cm in diameter and 5 cm in length was modeled at distances of 6.5 cm and 2.5 cm from the posterior scalp of this head model (T_{6.5 cm} and T_{2.5 cm}, respectively). Radiation doses associated with positioning errors were evaluated for each distance, including left and right shifts, superior and inferior shifts, shifts from the central axis of the beam aperture, and outward shifts from the surface of the beam aperture. Rotational and tilting effects were also evaluated. The dose prescription was 20 Gray-equivalent (Gy-Eq) to 80 % of the tumor. The treatment planning system, NCTPlan, was used to perform dose calculations. The average decreases in mean tumor dose for T_{6.5 cm} for the 1 cm, 2 cm, and 3 cm lateral shifts composed by left, right, superior, and inferior sides, were approximately 1 %, 6 %, and 11 %, respectively, compared to the dose administered to the initial tumor position. The decreases in mean tumor dose for T_{6.5 cm} were approximately 5 %, 11 %, and 15 % for the 1 cm, 2 cm, and 3 cm outward shifts, respectively. For a superficial tumor at T_2.5cm, no significant decrease in average mean tumor dose was observed following lateral shifts of 1 cm. Rotational and tilting up to 15° did not result in significant difference to the tumor dose. Dose differences to the normal tissues as a result of the shifts in positioning were also minimal. Taken together, these data demonstrate that the mean dose administered to tumors at greater depths is potentially more vulnerable to deviations in positioning, and greater shift distances resulted in reduced mean tumor doses at the THOR. Moreover, these data provide an estimation of dose differences that are caused by setup error or intra-fractional motion during BNCT, and these may facilitate more accurate predictions of actual patient dose in future treatments.

MeSH terms

Boron Neutron Capture Therapy / methods*
Brain Neoplasms / radiotherapy*
Head / radiation effects
Humans
Monte Carlo Method
Patient Positioning / methods
Phantoms, Imaging
Radiometry / methods
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted / methods