The comparison of radiotherapy techniques for treatment of the prostate cancer: the three-field vs. the four-field.

Our purpose was to compare the three-field and the four-field planning techniques in patients with localized prostate cancer. Twenty patients with localized prostate cancer stage (T1-T2N0M0) were chosen for the analysis of treatment plans. Simulation and CT planning were performed in all cases in the supine position with a "comfortably" full bladder. The planning treatment volume (PTV) was defined as the prostate gland with a 10 mm margins around the clinical target volume (CTV), except for the posterior margin (prostate gland - the anterior part of rectum wall), where a 5 mm margin was applied. The clinical target volume (CTV) was defined as prostate gland. For each patient the following organs at risk (OAR) were outlined: rectum, bladder, and right femoral head. The following three-field and four-field plans were made: 3 field techniques with beam angles orientations 0 degree, 120 degrees, 240 degrees and 0 degree, 90 degrees, 270 degrees, and 4 field technique (0 degree, 90 degrees, 180 degrees, 270 degrees). Two versions of treatment plans were also made including different range of applied energy of photons (6 MV or 20 MV) for the therapeutic machine - Clinac 2300 CD. Beam portals were conformal by shaped by a multileaf collimator (MLC). The daily fractionation dose 1.8 Gy and the total dose 73.8 Gy were applied in each case. One hundred and twenty treatment plans were made and compared according to the following parameters: the mean total dose (MTD) in the target, the tumor control probability (TCP), the mean total dose (MTD) in the OAR (rectum, bladder, and right femoral head), the normal tissue complication probabilities (NTCP), and the volume of OARs which received arbitrary chosen fraction (%) of the total prescribed dose (73.8 Gy=100%). ANOVA statistical methods to verify the significance of differences between the treatment plans were used. There were no significant differences in the distribution of MTD and TCP in the PTV for the evaluated treatment plans. There were no significant differences in the MTD, NTCP, V80, and V90 distribution in bladder. The distribution of MTD, NTCP, and V80 for rectum indicated that lower parameters were achieved in the case of the three-field technique with the orientation of beams 0 degree, 90 degrees, 270 degrees. The distribution of MTD, NTCP, and V70 in right femoral head for each treatment plan was below the tolerance dose. The study has shown that the three-field technique (an anterior and two opposing lateral fields with the portals orientation 0 degree, 90 degrees, 270 degrees) and applied energy photons 20 MV, provides the best rectal protection. All evaluated plans according to the dose distribution in the target (PTV) have not indicated any significant differences. None of the techniques has shown any significant advantages in sparing bladder. The risk of morbidity in the femoral heads for all the applied techniques, in a dose up to 73.8 Gy was not a therapeutic problem. However, the three-field technique with beams orientation 0 degree, 120 degrees, 240 degrees gave the best sparing effect for femoral heads.