To evaluate the effect of rectal distention on the planning computed tomogram on freedom
from biochemical failure (FFBF) of prostate cancer patients treated with image-guided
conformal arc radiotherapy.
The outcomes of 238 patients with T1-T3N0M0 tumors were analyzed, with a median follow-up
of 53 months (range, 24-93 months). In 213 patients, daily co-registration of X-rays
and digitally reconstructed radiographs was used for positioning, whereas in 25 patients
positioning was done using direct prostate visualization with implanted markers. The
rectal average cross-sectional area was determined on the planning computed tomogram.
The 5-year freedom from Grade 3 to 4 late gastrointestinal and urinary side effect,
according to the Radiation Therapy Oncology Group criteria, was 100% and 99.4% respectively.
The 5-year FFBF was 88.4%. On multivariate analysis the following variables were significantly
related to worse FFBF: risk group according to the National Comprehensive Cancer Network
(high- to very high risk vs. intermediate- to low-risk), dose (70 vs. 78 Gy), average
cross-sectional area (> or =16 vs. <16 cm(2)) and, unexpectedly, the use of implanted
markers as opposed to bony structures for patient positioning. In retrospect, the
margins around the clinical target volume appeared to be inadequate in the cases in
which markers were used.
Overall, the outcome of patients treated with image-guided conformal arc radiotherapy
is excellent. We were able to confirm the negative prognostic impact of a distended
rectum on the planning computed tomogram described by others. The study illustrates
the potential danger of image guidance techniques as to margin reduction around the
clinical target volume.