Abstract: 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°, 120°, 240° and 0°,
90°, 270°, and 4 field technique (0°, 90°, 180°, 270°). 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°, 90°, 270°. 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°, 90°, 270°) 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°, 120°, 240° gave
the best sparing effect for femoral heads.
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