Is a 3-mm intrafractional margin sufficient for daily image-guided intensity-modulated radiation therapy of prostate cancer?

PURPOSE: To determine whether a 3-mm isotropic target margin adequately covers the prostate and seminal vesicles (SVs) during administration of an intensity-modulated radiation therapy (IMRT) treatment fraction, assuming that daily image-guided setup is performed just before each fraction. MATERIALS AND METHODS: In-room computed tomographic (CT) scans were acquired immediately before and after a daily treatment fraction in 46 patients with prostate cancer. An eight-field IMRT plan was designed using the pre-fraction CT with a 3-mm margin and subsequently recalculated on the post-fraction CT. For convenience of comparison, dose plans were scaled to full course of treatment (75.6 Gy). Dose coverage was assessed on the post-treatment CT image set. RESULTS: During one treatment fraction (21.4+/-5.5 min), there were reductions in the volumes of the prostate and SVs receiving the prescribed dose (median reduction 0.1% and 1.0%, respectively, p<0.001) and in the minimum dose to 0.1 cm(3) of their volumes (median reduction 0.5 and 1.5 Gy, p<0.001). Of the 46 patients, three patients' prostates and eight patients' SVs did not maintain dose coverage above 70 Gy. Rectal filling correlated with decreased percentage-volume of SV receiving 75.6, 70, and 60 Gy (p<0.02). CONCLUSIONS: The 3-mm intrafractional margin was adequate for prostate dose coverage. However, a significant subset of patients lost SV dose coverage. The rectal volume change significantly affected SV dose coverage. For advanced-stage prostate cancers, we recommend to use larger margins or improve organ immobilization (such as with a rectal balloon) to ensure SV coverage.

Changes in the pelvic anatomy after an IMRT treatment fraction of prostate cancer.

PURPOSE: To quantify the three-dimensional variations of pelvic anatomy after a single treatment fraction. METHODS AND MATERIALS: Forty-six prostate cancer patients underwent computed tomography (CT) scanning with an in-room CT-on-rail system, before and immediately after one intensity-modulated radiotherapy (IMRT) session. To study the soft-tissue anatomy changes, the pre- and post-treatment CT images were registered using the bony structure with an in-house image registration software system. The center of volume for both the prostate and seminal vesicles was used to assess the relative displacement of the same structure after the treatment fraction. RESULTS: During one treatment fraction (21 +/- 4 min), both the prostate and seminal vesicles showed statistically significant systematic trends in the superior and anterior directions of the patient's anatomy. The net increase in bladder volume was huge (127 +/- 79 cm(3)), yet this change did not translate into large target displacements. Although the population mean displacements in either direction were 1.3 +/- 2.9 mm for the prostate and 1.2 +/- 4.1 mm for the seminal vesicles in the anterior direction, a few patients had displacements as large as 8.4 mm and 15.6 mm, respectively. These large displacements correlated strongly (p < 0.001) with large rectal volume increases caused by gaseous build-up in the rectum. CONCLUSION: The observed intrafraction variations in anatomy during prostate IMRT sessions suggest that, for any given fraction, the organ motion and volume changes can potentially lead to compromised target coverage in about 15% of patients in whom the prostate position shifted >4 mm.

Symptomatic local recurrence of prostate carcinoma after radiation therapy.

BACKGROUND: Symptomatic local recurrence of prostate carcinoma (SLRPC) after radiation therapy (RT) is associated with morbidity and debilitating symptoms that have a substantial impact on the patient's quality of life. Most reports on the results of RT for localized prostate carcinoma (PC) do not address this endpoint. The objective of this study was to determine the incidence of SLRPC and to identify the risk factors for this endpoint. METHODS: The medical charts of 1006 patients who received RT for localized PC at the University of Texas M. D. Anderson Cancer Center between 1987 and 1997 were reviewed. Local symptoms were defined as hematuria, voiding symptoms, urinary obstruction, and pelvic pain. Progressive symptoms accompanied by either confirmatory histology or cystoscopic findings were attributed to PC. Univariate and multivariate analyses using Cox proportional hazards models were applied to identify risk predictors. RESULTS: Among 964 patients for whom follow-up data were available, 277 patients had prostate-specific antigen (PSA) progression, and 45 patients died of PC during a median follow-up of 9.4 years. In total, 33 patients (3.4%) developed SLRPC. In patients who experienced biochemical progression, the actuarial 5-year incidence of SLRPC was 8.3%. Among the patients who had developed SLRPC, 23 patients (69.7%) died of PC at a median of 25.3 months from the onset of local symptoms. Adverse histologic tumor subtypes (ductal, small cell, and sarcomatoid) were associated significantly with SLRPC (hazard ratio, 8.4; 95% confidence interval, 2.99-23.63). Clinical T classification at diagnosis, Gleason score, and initial PSA level showed a trend toward an increased hazard ratio. CONCLUSIONS: SLRPC after radiotherapy therapy was an uncommon but clinically significant event. Aggressive histologic subtypes were predictive of this endpoint. Clinical T classification, Gleason score, and initial prostate-specific antigen levels also may have predictive value.

Racial influence on biochemical disease-free survival in men treated with external-beam radiotherapy for localized prostate cancer.

BACKGROUND: We retrospectively analyzed the clinical characteristics and outcomes of various racial and ethnic groups who underwent radiotherapy alone for localized or locally advanced prostate cancer. METHODS: From April 1987 to January 1998, 964 patients underwent full-dose, external-beam radiotherapy alone for localized or locally advanced prostate cancer and were included in the study. The patients' medical records were reviewed for pertinent information. RESULTS: Of the 964 patients, 810 were non-Hispanic white, 86 were African-American, 54 were Hispanic, and 14 were Asian. The most significant difference between groups was in the proportion of patients who presented with initial PSA levels > 20 ng/ml. More than 20% of men in all minority groups presented with a serum PSA > 20 ng/ml, compared to only 11% of whites (p = 0.0012). Similarly, 14% of minorities presented with Gleason scores > or = 8 compared to only 11% of whites (p = 0.0265). Hispanic and Asian patients exhibited a higher incidence of Gleason score > or = 8 prostate cancer. When comparing the time intervals of 1995-1998 vs. 1987-1994, the number of men presenting for EBRT with PSA levels < 10 ng/ml increased to 74% from 57% for Caucasians (p < 0,001), 71% from 40% for African Americans (p = 0.012), 67% from 49% for Hispanics (p = 0.1 18), and no change (50%) for Asians. CONCLUSIONS: The number of African-American patients presenting with favorable characteristics (PSA < 10 ng/ml) is increasing. These findings suggest that the message of screening and early detection may be reaching the African-American community. Continued diligence in screening and early detection may improve prostate cancer outcome for other minority populations.