Dosimetric Comparison of Three-Dimensional Conformal Radiotherapy in Salvage Radiotherapy for PSA Relapse after Radical Prostatectomy

The purpose of this study is to compare three-dimensional conformal radiotherapy (3D-CRT) plans in a setting of salvage radiotherapy after radical prostatectomy (RP) and to simulate whether dose escalation is possible with the most adequate 3D-CRT technique. This study included consecutive 10 patients underwent salvage radiotherapy (RT) for biochemical relapse of prostate cancer after RP. Normal structures included the rectum, bladder, and femoral head. For each patient, four different treatment plans including four fields RT (4F-RT), dynamic conformal arc radiotherapy (DCAT), six fields RT (6F-RT), and DCAT with rectum hollow-out technique (DCAT-HO), were created to entire the prostate bed. The parameters of the maximum and mean doses received by organs at risk (OAR), target coverage, dose homogeneity for the planning target volume (PTV) were compared. All plans were considered to be clinically tolerable for PTV coverage and dose homogeneity. The rectum sparing at the high dose area for DCAT-HO was considered to be the most superior to those for other three techniques by comparison of the dose delivered to a 1%, 5%, and 10% volume of the rectum. In the simulation of dose escalation to 70 Gy with DCAT-HO, OAR met a requirement of the dose-volume constraints. However, in the simulation of dose escalation to 72 Gy, the rectum that receives 60 to 65 Gy and bladder that receives 65 Gy exceeded the optimal dose-volume constraints. DCAT-HO was considered to be one of the most appropriate techniques in 3D-CRT if dose escalation to 70 Gy might be needed in a setting of salvage RT after RP in the future.