Cost- and time-sparing simplified conformal therapy for prostate cancer: is it feasible?

It was hypothesized that using a simplified technique of volumes profiles determination (STVPD) based on CT data sets (correlate and projection) would increase the target dose without increasing the bladder and rectal dose obtained by conventional simulation techniques. To test this hypothesis, patients referred for radical radiation treatment for prostate carcinoma were prospectively evaluated by performing treatment planning using standard simulation, with (SSB) and without corner blocks (SSWB), STVPD, and 3D beam's eye view.

Twenty-one patients with prostate carcinoma (stage B: 7; stage C: 14) underwent four treatment planning procedures where the field arrangement was defined by standard simulation (SSB and SSWB), STVPD, and 3D beam's eye view (BEV) with a four field (10 MV photons) box technique. Dose-volume histograms (DVHs) for the planning target volume (PTV), bladder, and rectum (relatives to the four techniques) were generated for all patients and compared; average percentage dose to the bladder and rectum were also calculated.

STVPD and 3D BEV treated an increased percentage of PTV at 95% isodose level, in comparison to standard simulation (with and without blocks). No statistically significant differences were found between the two techniques. A significant reduction of irradiated bladder volume was found between 3D BEV and STVPD versus simulation with and without blocks (mean percentage dose: 77.3%, 81.8%, 93.5%, and 92.6% respectively). No marked differences were recorded in rectal irradiation (mean percentage dose: 53.1%, 53.7%, 51.9%, and 50.2% respectively). Time required for treatment planning (excluding CT scan and definitive simulation) was less than 15 minutes for STVPD and more than 120 minutes for 3D BEV.

Our results confirm the inadequacy of standard simulation. It is possible, with conformal therapy, to increase the dose to the PTV, decreasing the irradiated volume of the bladder. The absence of sparing effect in the rectum is discussed. Using a box technique, STVPD can be used routinely to define the PTV in patients with prostate cancer, reducing the time required for treatment planning, with dosimetric results similar to those of 3D BEV.