Original articleImaging for Prostate Cancer
Introduction
The increased detection of prostate cancer has generated new challenges for diagnostic imaging and radiotherapy. Improvements in radiotherapy technique, and the desire to optimise the treatment for individual patients, have demanded more precise delineation of the location and extent of prostate cancer. Appropriate patient selection needs high quality and clinically relevant imaging that is best managed through multidisciplinary working, in which diagnostic radiologists can understand the clinical issues raised and radiotherapists can appreciate the indications and limitations of the imaging available to them.
Prostate imaging began with the introduction of transrectal ultrasound in the early 1970s [1], and has developed into a multimodality approach that has benefited considerably from technological developments in the past few decades. Our increased awareness of prostate cancer as a major cause of male cancer mortality has challenged the power of imaging to detect aggressive prostate cancers while still confined to the prostate gland. Traditional morphologically based prostate imaging is now being complemented by functional and molecular imaging techniques that yield information about the biology of prostate cancer. The ultimate goal is to identify the most appropriate treatment strategy for each patient while minimising treatment-associated morbidity.
The introduction of serum prostate-specific antigen (PSA) has improved the earlier diagnosis and facilitated treatment monitoring of prostate cancer; however, the clinical dilemmas of how to institute active treatment for this disease remain. Clinical factors are paramount to the choice of treatment used, but imaging can contribute to this clinical decision by helping to identify more aggressive and potentially life-threatening cancers that might benefit from early intervention. PSA-based prostate cancer detection has led to a gradual downward stage migration at initial diagnosis, and nowadays most newly diagnosed cases have intermediate-grade, organ-confined prostate cancer [2]. The effect on diagnostic imaging has been significant, with increased emphasis on early diagnosis in response to elevation in the serum PSA. Clinicians can use nomograms, such as Partin's Tables [3], to counsel individual patients and make clinical decisions about management; however, currently, we have no reliable imaging method to distinguish prostate cancers that are biologically aggressive from those that may have a more indolent clinical course in life. This need to stratify prostate cancers by their life-threatening potential and tailor individual treatments accordingly is driving the development of molecular-based prostate cancer imaging, in particular. Our future understanding and delineation of the genetic factors underlying the pathogenesis of prostate cancer will become an integral part of the management of the patient and facilitate the integration of radiotherapy into the treatment plan.
Imaging-guided delivery of radiation therapy to the prostate is now a sophisticated process that uses three-dimensional reconstruction and targeting of tumour target volumes. Optimal integration of imaging data into the planning and delivery of radiation requires anatomical knowledge of the tumour target as well as technical expertise in volume-based treatment-planning techniques. The use of additional information from functional imaging and, ultimately, molecular imaging will require careful collaboration between radiologists and oncologists, closely supported by medical physics.
The purpose of this paper is to review the current status of diagnostic imaging in the diagnosis of prostate cancer, and the role of imaging in the treatment of prostate cancer.
Section snippets
Transrectal Ultrasound
Transrectal ultrasound is widely used as the initial investigation for prostate cancer, and has benefited from major technical advances since its introduction over 3 decades ago. In the early days of prostate ultrasound, before the advent of serum PSA testing, many cancers presented at a relatively advanced stage, and were typically visible as hypoechoic areas in the peripheral gland. Nowadays, with the earlier PSA-based detection of a larger proportion of T1c tumours, many cancers are not
Magnetic Resonance Imaging and Magnetic Resonance Spectroscopy
Magnetic resonance imaging (MRI) of the prostate provides the most accurate information to date about the anatomy and location of tumour within the prostate gland. A field strength of 1.5 Tesla is recommended for adequate imaging, and the best results are obtained using a combination of endorectal and pelvic phased-array coils [18]. MRS is carried out in combination with conventional MRI, and requires the use of an endorectal coil. The exact imaging parameters used will depend on the
Radiotherapy Planning
As radiotherapy techniques improve and become more conformal, the need for more precise localisation of the tumour target becomes increasingly important. It is strange to reflect that, despite the array of diagnostic imaging techniques we now have, the technique that is currently in widespread clinical use for planning radiation treatment to the prostate is computed tomography (CT) scanning. CT is the one imaging technique that does not show tumour within the gland, cannot define margins with
Conclusion
Prostate imaging now incorporates sophisticated and highly accurate anatomical imaging, together with physiological and biological imaging that yield an expanding volume of data about the location and potential lethality of the tumour. The challenge that faces all involved in the management of prostate cancer is to use the information available from modern diagnostic imaging in to the radiation planning and treatment delivery to the prostate target. Biological targeting of the most active
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