論文の公開元へUrethral identification using three-dimensional magnetic resonance imaging and interfraction urethral motion evaluation for prostate stereotactic body radiotherapy
概要
Prostatic urethra identification is crucial in stereotactic body radiotherapy (SBRT) for prostate
cancer because urethral dose reduction can reduce the risk of urinary toxicity, such as frequency,
dysuria, and urethral stricture, without significantly increasing the risk of local recurrence.1,2
Because urethral visualization is difficult by computed tomography (CT), there are two strategies for achieving this goal: one is urinary catheter insertion, which is commonly employed1,3-5
and recommended by GEC/ESTRO.6 However, catheterization every time for multiple days of
irradiation is invasive and associated with a risk of infection, and is undesirable for patients. The
incidence of bacteriuria associated with indwelling catheterization is 3%–8% per day.7 Although
the risk of infection may be small,8 a previous study revealed that the Foley catheter-related
genitourinary trauma was as common as symptomatic urinary tract infection and concluded that
the elimination of unnecessary Foley catheterization could prevent symptomatic urinary tract
infection, unnecessary antimicrobial therapy for asymptomatic bacteriuria, and Foley catheterrelated trauma.9 Another is that catheter insertion during radiotherapy must be performed by
oncologists or radiology nurses who are unfamiliar with the procedure, which may increase
patient discomfort and infection risk. Furthermore, urethral catheter placement may displace the
urethral position,10,11 and removal of a catheter may cause prostate rotation,12 resulting in possible
planning inaccuracies. As another strategy without using a catheter, a previous study advocated
the concept of placing a “surrogate urethra” in the anatomic center of the prostate if the location
of the urethra cannot be visualized.13 However, another study demonstrated that the urethral dose
might be overestimated when using a surrogate urethra,14 and there were cases where the urethra
was not located in the anatomical center of the prostate.14,15 Therefore, clear urethral visualization
using a clinical image is desirable for accurate radiation treatment planning.
Magnetic resonance imaging (MRI) is increasingly used in radiation treatment planning
because of its superior soft tissue contrast16,17 and may be suitable for urethral identification
purposes.16 Several studies have investigated urethral identification using MRI; however, they
used only two-dimensional (2D) T2-weighted (T2W) turbo spin-echo (TSE) imaging.15,18-20 A
previous study proposed MRI while urinating; however, there were some problems regarding
the psychological burden on patients and the urine bag used to collect urine.19 To overcome
these drawbacks, Yoshimura et al demonstrated that it was possible to identify the prostatic
urethra using “posturination” MRI with good accuracy.20 However, there are disadvantages like
the bladder volume does not match that of CT imaging and the accuracy is inferior to that of
CT with catheter insertion. These limitations indicate that there is not yet a complete approach
for prostatic urethral identification noninvasively.
According to the prostate imaging reporting and data system (PI-RADS) guidelines,21 2D
T2W-TSE is a key sequence for diagnostic prostate MRI. However, recent advances have shown
that three-dimensional (3D) T2W-TSE sequences are more readily achievable with a clinically
acceptable acquisition time.22 Some studies have directly compared 2D- and 3D-T2W sequences,
focusing on image quality and tumor detection mainly for diagnostic purposes in prostate
MRI, and have shown the usefulness of 3D sequences.23,24 Additionally, some studies have
Nagoya J. Med. Sci. 85. ...
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