Potential Applications of Image-Guided Radiotherapy for Radiation Dose Escalation in Patients with Early Stage High-Risk Prostate Cancer

To report the long-term results of a randomized radiotherapy dose escalation trial for prostate cancer. From 1993 to 1998, a total of 301 patients with stage T1b to T3 prostate cancer were accrued to a randomized external beam dose escalation trial using 70 Gy versus 78 Gy. The median follow-up is now 8.7 years. Kaplan-Meier analysis was used to compute rates of prostate-specific antigen (PSA) failure (nadir + 2), clinical failure, distant metastasis, disease-specific, and overall survival as well as complication rates at 8 years post-treatment. For all patients, freedom from biochemical or clinical failure (FFF) was superior for the 78-Gy arm, 78%, as compared with 59% for the 70-Gy arm (p = 0.004, and an even greater benefit was seen in patients with initial PSA >10 ng/ml (78% vs. 39%, p = 0.001). The clinical failure rate was significantly reduced in the 78-Gy arm as well (7% vs. 15%, p = 0.014). Twice as many patients either died of prostate cancer or are currently alive with cancer in the 70-Gy arm. Gastrointestinal toxicity of grade 2 or greater occurred twice as often in the high dose patients (26% vs. 13%), although genitourinary toxicity of grade 2 or greater was less (13% vs. 8%) and not statistically significantly different. Dose-volume histogram analysis showed that the complication rate could be significantly decreased by reducing the amount of treated rectum. Modest escalation in radiotherapy dose improved freedom from biochemical and clinical progression with the largest benefit in prostate cancer patients with PSA >10 ng/ml.

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. Between 2008 and 2009, 186 patients with prostate cancer were treated with IGRT to a dose of 86.4 Gy with daily correction of the target position based on kilovoltage imaging of implanted prostatic fiducial markers. This group of patients was retrospectively compared with a similar cohort of 190 patients who were treated between 2006 and 2007 with IMRT to the same prescription dose without, however, implanted fiducial markers in place (non-IGRT). The median follow-up time was 2.8 years (range, 2-6 years). A significant reduction in late urinary toxicity was observed for IGRT patients compared with the non-IGRT patients. The 3-year likelihood of grade 2 and higher urinary toxicity for the IGRT and non-IGRT cohorts were 10.4% and 20.0%, respectively (p = 0.02). Multivariate analysis identifying predictors for grade 2 or higher late urinary toxicity demonstrated that, in addition to the baseline Internatinoal Prostate Symptom Score, IGRT was associated with significantly less late urinary toxicity compared with non-IGRT. The incidence of grade 2 and higher 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. IGRT is associated with an improvement in biochemical tumor control among high-risk patients and a lower rate of late urinary toxicity compared with high-dose IMRT. These data suggest that, for definitive radiotherapy, the placement of fiducial markers and daily tracking of target positioning may represent the preferred mode of external-beam radiotherapy delivery for the treatment of prostate cancer. Copyright © 2012 Elsevier Inc. All rights reserved.

Hypofractionated radiotherapy has an intrinsically different normal tissue and tumor radiobiology. The results of a prospective trial of stereotactic body radiotherapy (SBRT) for prostate cancer with long-term patient-reported toxicity and tumor control rates are presented. From 2003 through 2009, 67 patients with clinically localized low-risk prostate cancer were enrolled. Treatment consisted of 36.25 Gy in 5 fractions using SBRT with the CyberKnife as the delivery technology. No patient received hormone therapy. Patient self-reported bladder and rectal toxicities were graded on the Radiation Therapy Oncology Group scale (RTOG). Median follow-up was 2.7 years. There were no grade 4 toxicities. Radiation Therapy Oncology Group Grade 3, 2, and 1 bladder toxicities were seen in 3% (2 patients), 5% (3 patients), and 23% (13 patients) respectively. Dysuria exacerbated by urologic instrumentation accounted for both patients with Grade 3 toxicity. Urinary incontinence, complete obstruction, or persistent hematuria was not observed. Rectal Grade 3, 2, and 1 toxicities were seen in 0, 2% (1 patient), and 12.5% (7 patients), respectively. Persistent rectal bleeding was not observed. Low-grade toxicities were substantially less frequent with QOD vs. QD dose regimen (p = 0.001 for gastrointestinal and p = 0.007 for genitourinary). There were two prostate-specific antigen (PSA), biopsy-proven failures with negative metastatic workup. Median PSA at follow-up was 0.5 ± 0.72 ng/mL. The 4-year Kaplan-Meier PSA relapse-free survival was 94% (95% confidence interval, 85%-102%). Significant late bladder and rectal toxicities from SBRT for prostate cancer are infrequent. PSA relapse-free survival compares favorably with other definitive treatments. The current evidence supports consideration of stereotactic body radiotherapy among the therapeutic options for localized prostate cancer. Copyright © 2012 Elsevier Inc. All rights reserved.