Fall 2005 | The Canadian Journal of Medical Radiation Technology | Automne 2005 •

ABSTRACTS OF CURRENT LITERATURE

De Crevoisier R, Tucker SL, Dong L, Mohan R, Cheung R, Cox JD, Kuban DA. International Journal of Radiation Oncology, Biology, Physic. July 2005;62(4):965-973.

PURPOSE: To retrospectively test the hypothesis that rectal distension on the planning computed tomography (CT) scan is associated with an increased risk of biochemical and local failure among patients irradiated for prostate carcinoma when a daily repositioning technique based on direct prostate–organ localization is not used.

METHODS AND MATERIALS: This study included 127 patients who received definitive three-dimensional conformal radiotherapy for prostate cancer to a total dose of 78 Gy at The University of Texas M. D. Anderson Cancer Center. Rectal distension was assessed by calculation of the average cross-sectional rectal area (CSA; defined as the rectal volume divided by length) and measuring three rectal diameters on the planning CT. The impact of rectal distension on biochemical control, 2-year prostate biopsy results, and incidence of Grade 2 or greater late rectal bleeding was assessed.

RESULTS: The incidence of biochemical failure was significantly higher among patients with distended rectums (CSA >11.2 cm2) on the planning CT scan (p = 0.0009, log–rank test). Multivariate analysis indicates that rectal distension and high-risk disease are independent risk factors for biochemical failure, with hazard ratios of 3.89 (95% C.I. 1.58 to 9.56, p = 0.003) and 2.45 (95% C.I. 1.18 to 5.08, p = 0.016), respectively. The probability of residual tumor without evidence of radiation treatment (as scored by the pathologist) increased significantly with rectal distension (p = 0.010, logistic analysis), and a lower incidence of Grade 2 or greater late rectal bleeding within 2 years was simultaneously observed with higher CSA values (p = 0.031, logistic analysis).

CONCLUSIONS: We found strong evidence that rectal distension on the treatment-planning CT scan decreased the probability of biochemical control, local control, and rectal toxicity in patients who were treated without daily image-guided prostate localization, presumably because of geographic misses. Therefore, an empty rectum is warranted at the time of simulation. These results also emphasize the need for image-guided radiotherapy to improve local control in irradiating prostate cancer. .

Macdonald G, Keyes M, Kruk K, Duncan G, Moravan V, Morris JW. International Journal of Radiation Oncology, Biology, Physics. March 17, 2005. Available to subscribers online at: http://www/sciencedirect.com/science/journal/03603016.

PURPOSE: To determine predictive factors for post-implant erectile dysfunction (ED) in a cohort of patients, according to prospectively collected data; specifically, to assess the impact of penile bulb volume and D50 and D95 (dose covering 50% and 95% of the penile bulb volume, respectively) on ED.

METHODS AND MATERIALS: Three hundred forty-two patients were identified who were potent before implant and who had at least 2 years ̓follow-up. Patient, tumor, treatment, and dosimetric data were collected on all patients. Post-implant ED was defined according to both physician-documented and patient-documented outcome data. Binary logistic regression analysis was used to create multivariable models of predictors for ED at 1, 2, and 3 years after implant.

RESULTS: Physician-documented rates of ED were 57%, 48%, and 38% at 1, 2, and 3 years after implant, respectively. Patient-documented rates of ED were 70% and 66% at 1 and 2 years, respectively. Multivariable analyses revealed age and degree of pre-implant erectile function to be consistently significant predictors of ED. Use of hormones was significant at the 1-year physician-documented ED endpoint but not thereafter, in keeping with the time course of testosterone recovery. Penile bulb volume, D50, and D95 were not found to be predictive for ED at any time point, in contrast to previous studies. In addition, planning ultrasound target volume, number of needles, and institutional case sequence number were significant predictors of ED at various time points, consistent with a traumatic etiology of ED.

CONCLUSIONS: We found no evidence to support penile bulb dosimetry as an independent predictive factor for ED after implant, using physician-documented or patient-documented outcomes. © 2005 Elsevier Inc.