The image distortions (“shadows”) produced by the posterior (dorsal) catheters can obscure the view of more anterior (ventral) catheters during treatment planning, and the catheters themselves can obscure the prostate contour especially near the apex. Schmid et al. (29) compared needle reconstruction accuracy with ultrasound to CT using a phantom. The two main problems were spurious echoes on TRUS and difficulty with craniocaudal

needle tip identification (up to 6 mm). In addition, definition of contours of the rectum and to a lesser extent the bladder may be less accurately rendered with real time TRUS planning than with CT-based planning. Newer 3D ultrasound probes will likely reduce some of these technical difficulties ( Fig. 2). Monitoring and adjustment of catheters is not unique to CT dosimetry or TRUS, but rather p38 MAPK apoptosis it is a key element of multifraction HDR brachytherapy. Most of the catheter displacement studies are based on the CT dosimetry process, which involves moving the patient between simulation and treatment delivery. Kovalchuk et al. (30) at the Mayo Clinic did a

dosimetry study of catheter displacement by comparing initial dosimetry with doses that would be delivered with displaced catheters. They noted a mean needle displacement of 3.5 mm between fractions. The D90 ≥ 95% was 100% vs. 82% (initial vs. displaced), V100 ≥ 95% was 87% vs. 53%, and urethra V115 ≤ 10% was 78% vs. 69%. Replanning improved the dosimetry. Huang et al. (31) at Henry Ford Hospital performed CT scans before every HDR fraction Panobinostat in vivo in 13 patients and made catheter adjustments when there was >3 mm catheter displacement. Adjustments were made on 30% catheters by an average of 5.8 mm. Without adjustments, the D90 would have been 10–32% less than the originally planned and after making adjustments, the D90 was within 10% of the original plan. Holly et al. (32) from Ontario Canada performed cone-beam CT to assess catheter displacement between planning

and the first treatment in 20 consecutive patients and evaluated the ability to improve dosimetry dipyridamole by catheter readjustment. A mean catheter displacement of 11 mm was noted, and it would have resulted in a decrease in mean V100 from 98% to 77% (p < 0.001), mean D90 from 111% to 73% (p < 0.001), and an increase in urethra D10 from 118% to 125% (p = 0.0094) had it not been corrected. Catheter readjustments were helpful (V100 90%, D90 97%, and urethra D10 126%) but did not completely restore the original dosimetry. These and other studies demonstrate that catheter displacement can be a source of discrepancy between the calculated and delivered dose [33], [34] and [35]. The clinical significance of small (e.g., <3 mm) changes in catheter position has not been demonstrated. There are two TRUS treatment planning interfraction motion studies. Seppenwoolde et al.