Conformal arc radiotherapy for prostate cancer: increased biochemical failure in patients with distended rectum on the planning computed tomogram despite image guidance by implanted markers.
OBJECTIVE
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Engels
Benedikt
B
Department of Radiotherapy, University Hospital Brussels, Belgium.
Soete
Guy
G
Verellen
D
D
Storme
Guy
G
D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D005270:Femur Head; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D020360:Neoadjuvant Therapy / Q000379:methods; D017430:Prostate-Specific Antigen / Q000097:blood; D011471:Prostatic Neoplasms / Q000097:blood / Q000000981:diagnostic imaging / Q000188:drug therapy / Q000532:radiotherapy*; D019736:Prostheses and Implants; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods*; D012007:Rectum / Q000000981:diagnostic imaging / Q000528:radiation effects; D014057:Tomography, X-Ray Computed; D001743:Urinary Bladder / Q000528:radiation effects
D017430:Prostate-Specific Antigen