Qualitative Evaluation of 2D Dosimetry System for Helical Tomotherapy

Sun Young Ma; Tae Sig Jeung; Jang Bo Shim; Sangwook Lim

doi:10.14316/pmp.2014.25.4.193

Journal List > Prog Med Phys > v.25(4) > 1098441

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Ma, Jeung, Shim, and Lim: Qualitative Evaluation of 2D Dosimetry System for Helical Tomotherapy

Original Article

Progress in Medical Physics 2014;25(4):193-198.

Published online: 20 January 2014

DOI: https://doi.org/10.14316/pmp.2014.25.4.193

Qualitative Evaluation of 2D Dosimetry System for Helical Tomotherapy

Sun Young Ma^∗, Tae Sig Jeung^∗, Jang Bo Shim^†, Sangwook Lim^∗

^∗Department of Radiation Oncology, Kosin University College of Medicine, Busan, Korea

^†Department of Radiation Oncology, Guro Hospital, College of Medicine, Korea University, Seoul, Korea

Correspondence:Sangwook Lim(medicalphysics@hotmail.com) Tel:82-51-990-6393, Fax:82-2-6280-6247

Received 20 October 2014 Revised 29 October 2014 Accepted 24 November 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 see the feasibility of the newly developed 2D dosimetry system using phosphor screen for helical tomotherapy. The cylindrical water phantom was fabricated with phosphor screen to emit the visible light during irradiation. There are three types of virtual target, one is one spot target, another is C-shaped target, and the other is multiple targets. Each target was planned to be treated at 10 Gy by treatment planning system (TPS) of tomotherapy. The cylindrical phantom was placed on the tomotherapy table and irradiated as calculations of the TPS. Every frame which acquired by CCD camera was integrated and the doses were calculated in pixel by pixel. The dose distributions from the fluorescent images were compared with the calculated dose distribution from the TPS. The discrepancies were evaluated as gamma index for each treatment. The curve for dose rate versus pixel value was not saturated until 900 MU/min. The 2D dosimetry using the phosphor screen and the CCD camera is respected to be useful to verify the dose distribution of the tomotherapy if the linearity correction of the phosphor screen improved.

Keywords: Tomotherapy, Phosphor screen, Dose distribution, Blur kernel, Gamma index

References

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Fig. 1.

Custom made cylindrical water phantom for tomotherapy: The phosphor screen placed axially in the phantom and the CCD camera captures the visible light from the phosphor screen during the irradiation. The LCD monitor is used to check the focus and the setup of the phantom and the CCD camera.

Fig. 2.

Dose distributions from treatment planning for three types of virtual targets in the cylindrical water phantom; there are single (a), C-shaped (b), and multiple targets (c). 10 Gy was to be delivered to each target with dose rate of 900 MU/min.

Fig. 3.

Every frame were calibrated and cumulated. Right picture shows example of reconstructed dose map for C-shaped virtual target.

Fig. 4.

Profile of point dose from phosphor screen: (a) shows the point radiation on the phosphor screen. Blurring kernel (k) was obtained from the profile (b).

Fig. 5.

Dose rate dependency; the relative pixel values were measured versus dose rates from 100 MU/min to 900 MU/min. The solid line and the dotted line are the measurements and the fitting, respectively.

Fig. 6.

The dose distributions for three cases of virtual targets were analyzed. (a), (b), and (c) are cumulated gray scale images for single target, C-shpaed target, and multiple targets, respectively. (d), (e), and (f) are the gamma evaluation map between calculated and measured doses for three types of target. (d), (e), and (f) are the gamma evaluation map between calculated and measured dose distributions for three types of target. The pass rates are 84.46%, 80.38%, and 83.28%, respectively.

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