Objective: To define the planning target volume (PTV) margins in intensity-modulated radiotherapy (IMRT) for prostate cancer without imaging guidance using B-mode acquisition and targeting (BAT) ultrasound-based prostate localization.
Methods: Ten patients with prostate cancer underwent BAT ultrasound alignment before each IMRT session. The set-up deviations, each consisting of isocenter displacements in 3 directions (anterior-posterior, right-left lateral, and superior-inferior), were recorded for a total of 225 times and analyzed with Kolmogorov-Smimov (K-S) method.
Results: The isocenter shift in each direction, which represented an average from all the patients, was 3.56∓2.71 mm, 4.08∓3.99 mm, and 3.20∓2.92 mm in the lateral (RL), anteroposterior (AP), and superior-inferior (SI) dimensions, respectively, and the deviations in each direction conformed to a normal distribution (P=0.806, P=0.061, and P=0.106, respectively). In the absence of imaging guidance for IMRT for prostate cancer, the PTV margin should expand by 8.97 mm in the right, 1.87 mm in the left, 12.05 mm in the anterior, 3.91 mm in the posterior, 9.06 mm in the superior and 2.66 mm in the inferior to allow 95% isodose curve to cover 90% of the clinical target volume.
Conclusion: The ultrasound imagining guided localization, with simple operation, nonirradiation and small systemic error, can be real-time corrected.