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20 patients with biopsy proven intermediate to high grade prostatic malignancies were included in the study.
All patients underwent multiparametric MRI with T2,
diffusion,
dynamic contrast enhancement (DCE) and spectroscopy sequences as part of diagnostic work up and for delineation of organ confirmed malignancy.
We performed multi parametric prostate imaging in a 1.5T Philips Achieva MR System,
using a 16 Channel Sense Torso XL phased array coil.
T2-weighted MR imaging is the mainstay of prostate MR imaging and can clearly differentiate intermediate to high signal intensity peripheral zone from low-signal intensity central and transitional zones.
Axial,
coronal and sagittal thin section,
high spatial-resolution T2 weighted fast spin-echo (FSE) images through the prostate and seminal vesicles are obtained using the following parameters: TR/TE - 4,336/120 milliseconds; field of view (FOV) – 18 x 18 cm; slice thickness - 3 mm; inter-slice gap – 1 mm. On T2-weighted images,
prostate cancer appears as low signal intensity within high signal intensity of normal peripheral zone.
Diffusion weighted imaging reflects tissue cellularity and membrane integrity and is quantified by the Apparent Diffusion Coefficient (ADC).Axial DWI covering the entire prostate and seminal vesicles is performed using a single-shot echo-planar imaging with background signal suppression technique using the following parameters: TR/TE of 5,772/71 milliseconds; FOV – 51 x 51 cm,
slice thickness - 5 mm; inter-slice gap - 1 mm; EPI factor – 63 and b values 0,
600 and 1,200 s/mm2.
In addition,
a larger FOV was used for DWI sequences than for T1- and T2-weighted imaging to optimize signal-to-noise ratio of DWI images.
Malignant lesions destroy normal glandular structure resulting in high signal on diffusion images.
On ADC maps,
prostate cancer often shows lower ADCs in comparison to surrounding healthy peripheral zone prostate tissue.
MR spectroscopy evaluates biochemical changes within prostatic tissue and provides information about relative concentrations of metabolites such as citrate,
creatine and choline.
Normal peripheral zone depicts high levels of citrate with low choline levels.
Tumour focus shows high levels of choline with low citrate levels.
DCE-MRI uses 3D T1-weighted fast spoiled gradient echo sequence to repeatedly image a volume of interest after the intravenous bolus administration of contrast agent. DCE-MRI reflects microvessel density and permeability.
DCE-MRI can be analyzed by qualitative,
semi-quantitative or quantitative approach.
Semi-quantitative approach is most widely used,
which generates three types of curve after initial uptake: type 1 - persistent increase; type 2 - plateau; type 3 - decline after initial upslope.
Type 3 curve is most suspicious for malignancy.
This pattern of enhancement is thought to be due to tumor angiogenesis resulting in increased number of vessels within the tumor tissue with leaky membranes.
The entire data was transferred to the CyberKnife treatment planning system.
The CTV and GTV were contoured by a team of Radiologists and Radiation Oncologists.
Gold fiducials are placed in the prostate prior to the treatment for the real time tracking of the target.The gross tumor volume (GTV) was based on tumor extent on all sequences and spectroscopy data.
The Clinical Target Volume (CTV) was based on high resolution T2 weighted imaging which provided a clear demarcation of capsule thus avoiding significant dose to the rectum and muscles of the pelvic floor.
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