Variation of dose distribution of stereotactic radiotherapy for small-volume lung tumors under different respiratory conditions

Kunieda, E.; Deloar, H.M.; Kishitani, N.; Fujisaki, T.; Kawase, T.; Seki, S.; Oku, Y.; Kubo, A.

doi:10.1016/j.ejmp.2008.02.002

« Previous Next »Physica Medica: European Journal of Medical Physics
Volume 24, Issue 4 , Pages 204-211, December 2008

Variation of dose distribution of stereotactic radiotherapy for small-volume lung tumors under different respiratory conditions

E. Kunieda
- Department of Radiation Oncology, Keio University, Tokyo, Japan
- Corresponding author. Department of Radiation Oncology, Keio University, 35 Shinanomachi, Shinjuku, Tokyo 160-8582, Japan. Tel.: +81 3 3353 1211x62531; fax: +81 3 3359 7425.
H.M. Deloar
- Department of Medical Physics and Bioengineering, Christchurch Hospital, Christchurch, New Zealand
N. Kishitani
- Department of Radiological Sciences, Ibaraki Prefectural University of Health Sciences, Ibaraki, Japan
T. Fujisaki
- Department of Radiological Sciences, Ibaraki Prefectural University of Health Sciences, Ibaraki, Japan
T. Kawase
- Department of Radiation Oncology, Keio University, Tokyo, Japan
S. Seki
- Department of Radiation Oncology, Keio University, Tokyo, Japan
Y. Oku
- Department of Radiation Oncology, Keio University, Tokyo, Japan
A. Kubo
- Department of Radiation Oncology, Keio University, Tokyo, Japan

Received 4 July 2007; received in revised form 6 February 2008; accepted 8 February 2008. published online 07 April 2008.

Abstract

Purpose

To clarify the effects of respiratory condition on dose calculation for stereotactic radiotherapy of small lung tumors.

Methods and materials

Computed tomography (CT) data were obtained for nine tumors (diameter, 2.1–3.6cm; mean, 2.7cm) during the stable state, deep expiration, and deep inspiration breath-hold states. Rotational Irradiation with 3 non-coplanar arcs (Rotational Irradiation) and static irradiation with 18 non-coplanar ports (Static Irradiation) using 6-MV photons were evaluated using Fast Fourier Transform (FFT) convolution and Multigrid (MG) superposition algorithms. Dose-volume histograms (DVHs), mean path-length (PL) and mean effective path-length (EPL) were calculated.

Results

Although the PL was larger for the inspiration state than for the stable state and the expiration state, the EPL was 0.4–0.5cm smaller in the inspiration state than in the expiration state (p=0.01 for Rotational Irradiation; p=0.03 for Static Irradiation). The isocenter dose obtained by the FFT convolution algorithm was 7–12% higher than that obtained with the MG superposition algorithm. A leftward shift of the DVH obtained by MG superposition was noted for the inspiration state compared with the expiration state.

Conclusions

The choice of the proper algorithm is important to accounting for changes in respiration state. Differences in isocenter dose were not large among the respiratory states analyzed. EPL was a little shorter for inspiration than for expiration, although there were larger and reverse trends in path length. A leftward shift of the DVH obtained for the inspiration state when MG superposition was used.

Keywords: Stereotactic radiotherapy, Lung tumor, Path-length, Electron density