Evaluation of Dose Distribution and Normal Tissue Complication Probability of a Combined Dose of Cone-Beam Computed Tomography Imaging with Treatment in Prostate Intensity-Modulated Radiation Therapy

Tetsuya Tomita; Tomonori Isobe; Yoshinobu Furuyama; Hideyuki Takei; Daisuke Kobayashi; Yutaro Mori; Toshiyuki Terunuma; Eisuke Sato; Hiroshi Yokota; Takeji Sakae

doi:10.4103/jmp.JMP_4_20

Evaluation of Dose Distribution and Normal Tissue Complication Probability of a Combined Dose of Cone-Beam Computed Tomography Imaging with Treatment in Prostate Intensity-Modulated Radiation Therapy

J Med Phys. 2020 Apr-Jun;45(2):78-87. doi: 10.4103/jmp.JMP_4_20. Epub 2020 Jul 20.

Authors

Affiliations

¹ Graduate School of Comprehensive Human Sciences, University of Tsukuba, Ibaraki, Japan.
² Department of Radiology, University of Tsukuba Hospital, Ibaraki, Japan.
³ Faculty of Medicine, University of Tsukuba, Ibaraki, Japan.
⁴ Department of Radiology, Chiba University Hospital, Chiba, Japan.
⁵ Faculty of Health Sciences, Juntendo University, Tokyo, Japan.

Abstract

Purpose: The purpose of this study is to evaluate the effects of cone-beam computed tomography (CBCT) on dose distribution and normal tissue complication probability (NTCP) by constructing a comprehensive dose evaluation system for prostate intensity-modulated radiation therapy (IMRT).

Methods: A system that could combine CBCT and treatment doses with MATLAB was constructed. Twenty patients treated with prostate IMRT were studied. A mean dose of 78 Gy was prescribed to the prostate region, excluding the rectal volume from the target volume, with margins of 4 mm to the dorsal side of the prostate and 7 mm to the entire circumference. CBCT and treatment doses were combined, and the dose distribution and the NTCP of the rectum and bladder were evaluated.

Results: The radiation dose delivered to 2% and 98% of the target volume increased by 0.90 and 0.74 Gy on average, respectively, in the half-fan mode and on average 0.76 and 0.72 Gy, respectively, in the full-fan mode. The homogeneity index remained constant. The percent volume of the rectum and bladder irradiated at each dose increased slightly, with a maximum increase of <1%. The rectal NTCP increased by approximately 0.07% from 0.46% to 0.53% with the addition of a CBCT dose, while the maximum NTCP in the bladder was approximately 0.02%.

Conclusions: This study demonstrated a method to evaluate a combined dose of CBCT and a treatment dose using the constructed system. The combined dose distribution revealed increases of <1% volume in the rectal and bladder doses and approximately 0.07% in the rectal NTCP.

Keywords: Cone-beam computed tomography; image-guided radiation therapy; imaging dose; intensity-modulated radiation therapy; normal tissue complication probability.