Biomedical Engineering Reference
In-Depth Information
of men are diagnosed to have early stage prostate cancer, compared to only 57%
between 1975 and 1979 [12,13].
When diagnosed at an early stage, the disease is curable; however, once the tu-
mour has extended beyond the prostate, the risk of metastases increases [5,14,15].
Nevertheless, treatment options vary depending on the extent of the cancer, and
the prognosis worsens when diagnosed at an advanced stage. Thus, the challenges
facing physicians managing patients with possible prostate cancer are to: (a) di-
agnose clinically relevant cancers at a stage when they are curable, (b) stage and
grade the disease accurately, (c) apply appropriate therapy accurately to optimize
destruction of cancer cells while preserving normal tissues [16,17], and (d) follow
patients to assess side effects and the effectiveness of the therapy.
While radical prostatectomy is a highly effective surgical method to treat
prostate cancer, over the past 10 years improvements in imaging technology,
computer-aided dosimetry, and new treatment options have stimulated investi-
gators to search for minimally invasive therapies for localized prostate cancer,
e.g., brachytherapy [17,18], cryosurgery [19-23], hyperthermia, interstitial laser
photocoagulation (ILP), and photodynamic therapy (PDT).
Effective delivery of therapy in all these techniques requires accurate dose
planning based on images of the prostate anatomy and its surrounding structures.
The most common method for acquisition of images for dose planning and guiding
the minimally invasive procedure is the use of 2D or 3D transrectal ultrasound
(TRUS). Typically, a biplane TRUS transducer is used, which contains a side-
firing linear transducer array and a curved array positioned near the tip, producing
an axial view perpendicular to the linear array. The probe is covered with a water-
filled condom to allow good contact with the rectal wall, inserted into the rectum,
and attached to the mechanical assembly used to guide and deliver the therapy.
Two imaging acquisition approaches are currently being used for dose and
therapy planning: 2D TRUS and 3D TRUS. For 2D TRUS, the US transducer is
typically withdrawn in 5-mm steps, while a 2D image is acquired at each step,
resulting in about 7 to 10 2D transverse images. For 3D TRUS, a motorized as-
sembly is attached to the transducer to rotate it around its long axis. While the
transducer rotates, 2D images are acquired at about 0.7
r
intervals at 30 Hz and
immediately reconstructed into a 3D image. While accurate and high-quality 2D
and 3D images of the prostate can be acquired rapidly, accurate and reproducible
segmentation of the prostate boundary is an important step in effective guidance
and delivery of treatment. Manual delineation of the margins of the prostate has
been shown to be time consuming and tedious, leading to increased variability and
an inability to use it effectively in intraoperative procedures [24]. Hence, many
investigators have been developing automatic and semiautomatic prostate bound-
ary segmentation techniques using 2D and 3D TRUS images [25-30]. Although
various image processing methods have been used for 2D and 3D prostate seg-
mentation, the Deformable Model approach has been most successful and is the
subject of this chapter.
