TITLE:
Dosimetric Impact of Tumor Position and Lung Density Variations in Lung Stereotactic Body Radiotherapy
AUTHORS:
Hideharu Miura, Norihisa Masai, Ryoong-Jin Oh, Hiroya Shiomi, Kouichi Yamada, Muhammad Nauman Usmani, Toshihiko Inoue
KEYWORDS:
Lung Cancer; Stereotactic Body Radiotherapy; Tumor Position Error; Lung Density; Monte Carlo
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.3 No.1,
January
29,
2014
ABSTRACT: Purpose of this
study was to evaluate the variation of the dose to gross tumor volume (GTV)
related to tumor position and lung density for lung stereotactic body
radiotherapy (SBRT) using a virtual phantom. The density of the equivalent lung
surrounding the GTV (10 mm diameter) was defined as 0.10, 0.15, 0.25, 0.35, and
0.45 g/cm3. A planning target volume (PTV) was generated by adding a
uniform 8 mm margin to the internal target volume (ITV). We defined that the
99% of the GTV should be covered by 100% of the prescribed dose using Monte
Carlo (MC) calculation. The GTV structure was replicated from ITV to the PTV
periphery at 1 mm intervals. Planned dose to the GTV was defined as the
predicted dose in the replicated GTV structure. Simulated dose to the GTV was
defined as the calculated dose in the replicated GTV structure taking into
account the tumor position error. D99 of the planned dose to the GTV at the 8
mm shift position was 78.1%, 81.6%, 87.3%, 91.4% and 94.4% at equivalent lung densities of 0.10,
0.15, 0.25, 0.35, and 0.45 g/cm3, respectively. D99 of the simulated
dose to the GTV at the 8 mm shift
position was 96.9%, 95.3%,
94.2%, 95.1 % and 96.3% at equivalent lung densities of 0.10, 0.15, 0.25, 0.35,
and 0.45 g/cm3, respectively. Planned dose to GTV is strongly
dependent on lung density and tumor position errors, while simulated dose to GTV
does not show any significant dependence.