Assessing PTV Margins in Prostate Cancer Tomotherapy and Inter-Fractional Motion and Factors Impacting PTV and OAR Displacement

Treatment planning target volume (PTV) motion in prostate cancer tomotherapy is an important challenge in treatment planning. This study aimed to evaluate PTV margins for prostate cancer tomotherapy.

From 2021 to 2023, 20 patients with prostate cancer underwent tomotherapy. Before each treatment session, the MVCT image was taken from the patient, and the patient's settings were made using pelvic bone markers and tattoos. Before treatment, prostate volume was measured by ultrasound. Bladder volume was measured in MVCT images and compared with CTSim images. PTV displacements were measured and the required margin for 95% PTV dose was determined using the average prostate displacement. Correlation coefficients between bladder volume, prostate volume, and PTV displacement were calculated.

This study analyzed a total of 497 MVCT and 20 CT images. Anisotropic PTV margins, accounting for random uncertainties, were 14-6.9 mm for PTV1, 11.4-6.2 mm for PTV2, and 5.9-3.5 mm for PTV3 in the anterior-posterior direction, respectively.

This research reveals that a non-uniform PTV margin is needed to compensate for the random uncertainties caused by the movement of the prostate between tomotherapy sessions. Filling of the bladder and diet play a vital role in the displacement of the prostate.