TITLE:
The Effect of Treatment Position on Rectal and Bladder Dose-Volume Histograms for Prostate Radiotherapy Planned with 3-Dimensional Conformal Radiotherapy, Intensity-Modulated Radiotherapy and Volumetric Modulated Arc Therapy
AUTHORS:
Kotaro Terashima, Katsumasa Nakamura, Tomonari Sasaki, Saiji Ohga, Tadamasa Yoshitake, Kazushige Atsumi, Makoto Shinoto, Kaori Asai, Keiji Matsumoto, Hidenari Hirata, Yoshiyuki Shioyama, Akihiro Nishie, Hiroshi Honda
KEYWORDS:
Prostate Radiotherapy, Dosimetric Comparison, 3DCRT, IMRT, VMAT
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.3 No.2,
May
9,
2014
ABSTRACT: Purpose: To compare
target coverage and organ at risk (OAR) sparing in the supine and prone positions
with 3-dimensional conformal radiotherapy (3DCRT), intensity-modulated
radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) in low- and
high-risk prostate radiotherapy cases. Materials and Methods: Using magnetic
resonance images of five healthy volunteers, six treatment plans (supine 3DCRT,
prone 3DCRT, supine IMRT, prone IMRT, supine VMAT and prone VMAT) were
generated. Planning target volume 1 (PTV1) was defined as the prostate gland
plus the seminal vesicles with adequate margins in a high-risk setting, while
PTV2 was defined as prostate only with margins in a low-risk setting. The
mean dose for both PTV1 and PTV2 was set at 78 Gy. Plans generated by each of
the 3 techniques were compared between the supine and prone positions using
dose-volume histograms (DVHs). Results: For PTV1, prone 3DCRT provided a
significantly higher D98% than did supine 3DCRT, and its homogeneity index
(HI) was significantly better. IMRT and VMAT values did not differ
significantly between the prone and supine positions. For PTV2, no values
differed significantly between the supine and prone positions under any
treatment plan. With respect to OAR, the rectal D mean, D2%, V50, and V60
values of PTV1 were statistically higher in supine 3DCRT than in prone 3DCRT,
while there were no significant differences in rectal values between the
supine and prone positions with IMRT or VMAT. The rectal Dmean, V50, V60, V70,
and V75 values of prone 3DCRT were significantly higher than those of supine
IMRT or supine VMAT. There were no significant differences in any values for
the rectum and bladder for PTV2. Conclusion: Although prone 3DCRT was found to
be superior to supine 3DCRT in terms of rectal sparing in high-risk prostate
cancer, IMRT and VMAT techniques could possibly cover this disadvantage.