Modeling the pelvic anatomy of prostate cancer patients. A patient without an ER imaging coil [(a)–(c)]; a patient with an ER imaging coil [(d)–(f)]. The prostate (P), rectum (R), pelvic bone (PB) and urethra (U) are manually segmented from a series of axial T2w MR images [(a) and (d)]. The location of the NVBs is determined based on the prostate shape (Ref. 35). The segmented structures are used to create 3D patient-specific anatomical models, which are incorporated in the computer simulations of transurethral ultrasound prostate therapy. (b) and (e) show a cross-sectional view of the 3D anatomical models, illustrating the dimensions of the cortical (CB) and trabecular (TB) components of the pelvic bone, as well as the rectal wall (RW) and virtual ECD. (c) and (f) show the complete 3D view of the anatomical models.
The spatial characteristics of the prostate and surrounding anatomy for patient models with a small and large ECD. (a) Schematic illustrating the different spatial measurements. (b) The distribution of prostate radius values, (c) distance from prostate to pelvic bone, and (d) distance from the NVB to the ECD. The large ECD distorts the shape of the prostate and decreases the distance between the prostate and the pelvic bone as well as the distance between the NVB and the ECD.
Heating of the rectum: (a) Patients with a small ECD and (b) patients with a small ECD. The figures show a log-plot of the thermal dose absorbed in of rectal tissue as a function of distance to the boundary of thermal coagulation ( isotherm) for three ECD cooling temperatures (body temperature, room temperature, and ). The region of reversible thermal damage and 240 EM43 are shown for reference. The points to the left of the dotted line (negative distances) represent rectum voxels whose peak temperatures during therapy were greater than . With a body temperature ECD, portions of the rectum are heated to the level of irreversible damage. As the ECD temperature decreases, the region of thermal coagulation does not extend into the rectum. There is a greater spread in the data points in (a) due to the larger rectal wall thickness. Each figure contains more than 13 000 data points.
Visualizing the thermal impact of transurethral ultrasound prostate therapy on the rectum. For each case, a 3D view of the heating on the outer rectal wall is shown (anterior rectum, portion neighboring the prostate) along with a cross-sectional view showing the maximum extent of heating within the rectal wall. (a) Worst-case heating of the rectum for three ECD cooling temperatures (body temperature, room temperature and ) and (b) typical case. The dotted lines represent the region of the rectum which neighbors the prostate. The extent of the heating is limited to the superficial 1 mm layer of the rectum only for an ECD below . While room temperature ECD cooling typically limits the heating of the rectum (b), a small portion of patients requires a colder ECD to provide the same protective effect (a).
Heating of the pelvic bone for patients with small and large ECDs, and two values of cortical bone thermal conductivity (low of and high of ). The figures show a log-plot of the thermal dose absorbed in of pelvic bone as a function of distance from the prostate. Each plot shows the data for two frequency control strategies: TTFC where the ultrasound frequency is changed solely based on the dimensions of the prostate, and SAFC where the ultrasound frequency is set to 9.7 MHz whenever the pelvic bone is located less than 10 mm away from the prostate boundary. The reversible damage region, irreversible damage threshold, and 240 EM43 are shown for reference. A low increases the thermal dose in the pelvic bone. The patients with a large ECD have shorter distances between the pelvic bone and the prostate increasing the thermal dose. In all cases, the heating of the pelvic bone can be limited by using SAFC. Each figure contains over 26 000 data points.
Visualizing the thermal impact of transurethral ultrasound prostate therapy on the pelvic bone for the worst-case patients ([(a) and (c)] with a small ECD and [(b) and (d)] with a large ECD) assuming a cortical bone thermal conductivity of . (a) and (b) show the heating for TTFC, and (c) and (d) show the heating for SAFC with 9.7 MHz. The dotted lines show the region of the pelvic bone which neighbors the prostate. While the patients with a small ECD have limited heating even with the TTFC, the SAFC approach can reduce the thermal dose to within safety limits for all patients.
Visualizing the thermal impact of transurethral ultrasound prostate therapy on the NVB for a patient with a small ECD. (a) The thermal dose absorbed along the right NVB with the prostate treatment accuracy achieved using no treatment margins. (b) By defining a 2 mm treatment margin, the thermal dose in the NVB is greatly reduced with only a small section reaching 120 EM43. (c) A 4 mm treatment margin completely spares the NVB from thermal damage, with greater loss in treatment accuracy.
Heating lateral to the ultrasound transducer during transurethral ultrasound prostate therapy. Each data point represents one patient and there is no distinction between those with a small or large ECD. The regions of reversible and irreversible damage as well as 240 EM43 are shown for reference. The results of using two urethral cooling temperatures are shown with offset points. (a) The maximum thermal dose reached outside the prostate base as a function of the distance from the last ultrasound transducer. (b) A similar graph for tissues outside the prostate apex. The extent of thermal damage is 1 mm greater at the prostate base, near the internal urinary sphincter. Reducing the urethral cooling temperature from 37 to reduces the extent of thermal damage by 1 mm.
(a) Patients without ER coil (small ECD) and (b) Patients with ER coil (large ECD).
Physical parameters used in acoustic calculations and biothermal simulations.
Tissue thermal tolerances.
Effect of ECD temperature on the heating of the rectum and posterior prostate treatment accuracy, using SAFC with 9.7 MHz. Values shown represent the population average (, each group). An undertreated prostate volume of represents approximately 2% of the prostate volume neighboring the rectum.
Percentage of patients whose NVB is spared from thermal damage ( EM43 along the entire NVB).
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