728 S. Hayashi et al. PSA level, and pathologic findings from the surgical speci- men, such as the Gleason score, the status of the surgical margins, seminal vesicle invasion, lymphovascular invasion (LVI) and perineural invasion, have all been suggested as predictive factors [3, 5, 7, 8–13]. A minimum total radi- ation dose of 64 Gy has been recommended [5, 6]. In this study, we evaluated the outcome of salvage RT following RP and identified predictive factors, focusing on the detailed pathological findings, radiation dose and size of the radiation field. MATERIALS AND METHODS Between May 2000 and October 2006, 41 patients were treated with external beam radiotherapy as salvage RT because of increasing PSA levels following an RP at our institution. Informed consent for treatment was obtained from all the patients. This study was approved by the uni- versity’s research ethics committee. The median age at the time of surgery was 64 years (range, 50–72 years). All the patients underwent a bone scintigraphy or computed tomography (CT) examination before the RP and were diagnosed as being free from me- tastasis. Sixteen patients (39%) received hormonal therapy prior to surgery. Pelvic lymph node dissection was per- formed in 36 patients (88%), and 11 patients (27%) had preserved neurovascular bundles. At our institute, most prostatectomy surgeries are performed using a minimum in- cision endoscopic surgical technique, in which the surgeons operate via a single incision just large enough to permit the extraction of the specimen; the surgery is performed using an endoscope without gas insufflations, any trocar ports or injury to the peritoneum [14]. Table 1 shows the clinical and pathological features of the enrolled patients. The pathologic features of the prosta- tectomy specimen were confirmed by at least two patholo- gists using light microscopy. Pathologic evaluation of specimen was based on Hematoxylin–Eosin staining and Elastica–Van-Gieson staining. In the cases where it was dif- ficult to distinguish lymphatic vessel invasion (LI) from vascular invasion (VI), D2-40 immunostaining was supple- mentarily used to detect lymphatic vessel invasion. The pathological staging of the specimens according to the seventh Union for International Cancer Control – Tumor, Node, Metastasis classification was as follows: T2a, 3 patients; T2b, 6 patients; T2c, 9 patients; T3a, 16 patients; T3b, 6 patients; N0, 34 patients; N1, 2 patients; and NX, 5 patients. The Gleason scores of the excised specimens were as follows: 3 + 3, 7 patients; 3 + 4, 12 patients; 4 + 4, 6 patients; 4 + 4, 2 patients; 4 + 5, 3 patients; 5 + 4, 3 patients; and 5 + 5, 1 patient. One patient had no microscopic residual cancer cells because of preoperative hormonal therapy. The surgical margin was positive in 19 patients (46%) and negative in 22 patients (54%). Pathological tumor invasion was observed as follows: seminar vesicle invasion in 6 patients (15%); extracapsular invasion in 21 patients (51%); LI in 17 patients (41%); VI in 16 patients (39%); perineural invasions in 23 patients (56%), and urethral mucosa invasion in 1 patient (2%). Many previous reports have combined LI and VI as LVI, but we dis- tinguished between LI and VI to enable a more detailed analysis. None of the patients had bladder or rectal wall invasion. Urologists were primarily responsible for monitoring a patient’s condition after the RP and for making the decision to refer the patient to undergo salvage RT or to receive hormonal therapy. The follow-up evaluations after the RP consisted of a medical history, physical examination and PSA level measurement. Before April 2002, the con- ventional limit for PSA measurements was 0.2 ng/ml using a radioimmunoassay (RIA). After April 2002, high- sensitivity PSA measurements became possible using a chemiluminescent-enzyme immunoassay (CLEIA). The de- tection limits of the PSA measurements were 0.02 ng/ml (2002.4–2003.2), 0.004 ng/ml (2003.2–2006.3) and 0.008 ng/ml (2006.4–2006.7). After July 2006, the conventional PSA level was measured using a fluorescence-enzyme im- munoassay (FEIA), and the detection limit was 0.01 ng/ml. The median interval between the RP and postoperative bio- chemical failure was 370 days (range, 81–2363 days). The median interval between postoperative biochemical failure and salvage RT was 27 days (range, 0–173 days). As a result, the median interval between the RP and the salvage RT was 438 days (range, 84–2342 days). The preradiother- apy PSA level ranged from 0.02 to 4.26 ng/ml (median, 0.43 ng/ml). The PSA doubling time (PSA-DT) was calcu- lated using the log-linear regression method as previously described: PSA-DT = log(2) × T(log [ final PSA] – log [initial PSA]) [15]. T is the interval between the initial and the final PSA level. Final PSA is the PSA level noted at the time of postoperative biochemical failure, and initial PSA is that noted at the time of the nadir for the PSA level. The median PSA-DT was 4.08 months (range, 0.94– 21.3 months). RT was performed using dynamic arc conformal radio- therapy using 10-MV X-ray photons. The clinical target volume (CTV) was the prostate bed, and an arc with an angle of 180° of rotation (from 270 to 180°) was used with dynamic conformal fitting of the multileaf collimator (MLC) to the CTV with a 1-cm margin. Additional bilat- eral ports with manually adjusted MLC were made to prevent the irradiation of the posterior rectal wall in three patients. The prescribed radiation dose ranged from 60 to 70 Gy (median, 66 Gy) in 26–35 fractions. Thirty-three patients were treated with five fractions of 2 Gy per week, and eight patients were treated with four fractions of 2.5 Gy per week. The size of the arc radiation field at gantry 0° ranged from 16.00 cm2 (transverse, 4.0 cm;