TITLE:
Dosimetric Comparison between Bone and Target Matching Considering Interfractional Prostate Motion in Volumetric Modulated Arc Therapy
AUTHORS:
Ryuta Nakahara, Kentaro Ishii, Nobuhide Wakai, Ryu Kawamorita, Wataru Okada, Shun Kishimoto, Kazuki Kubo, Toshifumi Nakajima, Masatoshi Hasegawa
KEYWORDS:
Radiotherapy, Image-Guided, Radiation Dosage, Prostate
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.7 No.1,
February
13,
2018
ABSTRACT: Adequate matching
methods are critical for accurate volumetric-modulated arc therapy (VMAT). We
investigated the dosimetric differences in the target and organs at risk (OARs)
between bone matching and target matching in patients with prostate cancer
treated with VMAT. The relationship between the dosimetric differences and
interfractional motion of the prostate was also evaluated. Forty patients with
prostate cancer classified as intermediate risk were enrolled in a study to
assess the differences in dosimetry between two matching methods. These patients were treated with VMAT and
prescribed dose was 78 Gy. The dose distribution was calculated using cone-beam computed
tomography (CBCT) for this study. We selected clinical target volume (CTV) as
the target, and the rectum and bladder as the OARs. The Dmean, D98, D95, and D2
to the target and V10-V70 to the OARs were calculated as different dose from target matching
value minus bone matching value. Multiple regression analysis was used to
evaluate the effect of interfractional motion of the prostate on the
differences in dose. The CTV D95 values differed by -0.22 ± 1.01 Gy
(mean ± standard deviation). Rectum and bladder V70 values differed by 4.6% ± 7.2% and -2.6% ± 7.2%, respectively. There was a correlation between interfractional
motion of the prostate and the dose differences to OARs (R2 = 0.73 - 0.94). The dose
differences to OARs also varied depending on the direction of the prostate’s
motion. We found that bone matching resulted in an increased rectal dose and
high risk of decreasing dose to the CTV.