Prostate gland motion and deformation caused by needle placement during brachytherapy.

PURPOSE: To determine the extent of edge and gland position changes caused by needle insertion in patients undergoing prostate brachytherapy. METHODS AND MATERIALS: Nineteen patients with T1-T3 prostate cancer were implanted with the real-time method by using a two-phase peripheral loading technique. Serial contours of the prostate at 5-mm intervals were acquired by the dose-planning system. All of the peripheral needles were then placed and spaced 5-10 mm apart by using the largest transverse ultrasound image as the reference plane. The position of the probe was relocated at the zero plane, and the difference between the preneedle and postneedle zero plane was recorded as the difference in the z axis. Axial ultrasound images were again acquired. The second set of captured images, which matched in number the first set, was contoured over the previously contoured preneedle images. Prostate gland deformation and displacement were determined by comparing the preneedle contoured image with the images captured after needle placement. Deformation was determined by calculating the differences between the edges of the gland as measured at the major axis of the gland (x and y planes). Displacement was determined by measuring the differences between the center positions of the two contoured structures. Deformation and displacement were determined on each acquired 5-mm image. Differences were compared by student's t test. RESULTS: The mean preneedle prostate volume was 47 ml (range, 21.5-68.7 ml), compared with 48.1 ml (range, 19.4-80.3 ml; p = 0.228) after peripheral needle placement. A median of 16 (range, 12-19) peripheral needles were placed. The median change in the base position of the prostate was 1.5 cm (range of 0 to 3.0 cm; p = 0.0034). The mean x and y deformation was 6.8 mm (median, 7.9 mm; range, 4.3-8.1 mm) and 3.6 mm (median, 3.3 mm; range, 1.0-5.5 mm), respectively. The greatest deformation for any individual slice for x was 21.6 mm and for y was 15.3 mm. The mean number of slices that were found with a >2-, 5-, and 10-mm deformation in the x axis was 7 (range, 3-10), 4 (range, 1-3), and 1 (range, 0-4), respectively. Similar deformation in the y axis was found in 6 (range, 3-10), 2.5 (range, 0-6), and 0.3 (range, 0-2) slices. The mean x and y displacement was 1.9 mm (median, 1.8 mm; range, 0.3-6.6 mm) and 2.8 mm (median, 1.9 mm; range, 2-5.8 mm). The greatest displacement for any individual slice for x was 7 mm and for y was 10 mm. The mean number of slices with a displacement >2, 5, and 10 mm in the x axis was 5 (range, 1-10), 0.8 (range, 0-5), and 0, respectively. Similar displacement in the y axis was found in 5 (range, 0-9), 1.7 (range, 0-7), and 0 slices, respectively. CONCLUSIONS: Placing most needles in the periphery results in a minimal prostate volume increase, suggesting little need to overplan the implant when this method is used. However, significant edge and gland position changes caused by the needle insertion did occur. These changes may explain some of the difficulty in reproducing the preplan and should be taken into consideration for all types of prostate brachytherapy planning.

Comparison of intraoperative dosimetric implant representation with postimplant dosimetry in patients receiving prostate brachytherapy.

PURPOSE: To compare the results of intraoperative dosimetry with those of CT-based postimplant dosimetry in patients undergoing prostate seed implantation. METHODS AND MATERIALS: Seventy-seven patients with T1-T3 prostate cancer received an ultrasound-guided permanent seed implant (36 received (125)I, 7 (103)Pd, and 34 a partial (103)Pd implant plus external beam radiation therapy). The implantation was augmented with an intraoperative dosimetric planning system. After the peripheral needles were placed, 5-mm axial images were acquired into the treatment planning system. Soft tissue structures (prostate, urethra, and rectum) were contoured, and exact needle positions were registered. Seeds were placed with an applicator, and their positions were entered into the planning system. The dose distributions for the implant were calculated after interior needle and seed placement. Postimplant dosimetry was performed 1 month later on the basis of CT imaging. Prostate and urethral doses were compared, by using paired t tests, for the real-time dosimetry in the operating room (OR) and the postimplant dosimetry. RESULTS: The mean preimplant prostate volume was 39.8 cm(3), the postneedle planning volume was 41.5 cm(3) (p<0.001), and the 1-month CT volume was 43.6 cm(3) (p<0.001). The mean difference between the OR dose received by 90% of the prostate (D(90)) and the CT D(90) was 3.4% (95% confidence interval, 2.5-6.6%; p=0.034). The mean dose to 30% of the urethra was 120% of prescription in the OR and 138% on CT. The mean difference was 18% (95% confidence interval, 13-24%; p<0.001). CONCLUSIONS: Although small differences exist between the OR and CT dosimetry results, these data suggest that this intraoperative implant dosimetric representation system provides a close match to the actual delivered doses. These data support the use of this system to modify the implant during surgery to achieve more consistent dosimetry results.