12 Background: To compare toxicity profiles and biochemical tumor control outcomes between patients treated with high-dose image-guided radiotherapy (IGRT) and high-dose intensity-modulated radiotherapy (IMRT) for clinically localized prostate cancer. Methods: 186 patients with prostate cancer were treated with IGRT to a dose of 86.4 Gy with daily correction of the target position based upon kilovoltage imaging of implanted prostatic fiducial markers. This group of patients was retrospectively compared with a similar cohort of 190 patients who were treated with IMRT to the same prescription dose without, implanted fiducial markers in place (non-IGRT). In both groups the margins used for the prostate were the same. The median follow-up time was 2.8 years (range, 2-4 years). Results: A significant reduction in late urinary toxicity was observed for IGRT patients compared with the non-IGRT patients. The 3-year likelihood of urinary toxicity for the IGRT and non-IGRT cohorts were 10.4% and 20.0%, respectively (p=0.02).Multivariate analysis identifying predictors for late urinary toxicity demonstrated that, in addition to the baseline IPSS, IGRT was associated with significantly less late urinary toxicity compared with non-IGRT. The incidence of late rectal toxicity was low for both treatment groups (1.0% and 1.6%, respectively; p = 0.81). No differences in prostate-specific antigen relapse–free survival outcomes were observed for low- and intermediate-risk patients when treated with IGRT and non-IGRT. For high-risk patients a significant improvement was observed at 3-years for patients treated with IGRT compared with non-IGRT. Conclusions: IGRT is associated with a reduction in late urinary toxicity and improvement in biochemical tumor control after definitive high-dose external beam radiotherapy compared with high-dose IMRT. These data suggest that, for definitive radiotherapy, the placement of fiducial markers and daily tracking of target positioning should be the preferred mode of external beam radiotherapy delivery for the treatment of prostate cancer.
MRI visibility of gold fiducial markers for image-guided radiotherapy of rectal cancer
