The Rectal Dosimetric Effects of Perirectal Hydrogel Spacers in Men Undergoing Prostate Stereotactic Body Radiation Therapy (SBRT)

Long-Term Outcomes Following Fairly Brief Androgen Suppression and Stereotactic Radiation Therapy in High-Risk Prostate Cancer: Update From the FASTR/FASTR-2 Trials

PURPOSE

There is limited data on the long-term outcomes of ultrahypofractionated radiation therapy in high-risk prostate cancer. The FASTR and FASTR-2 trials were designed to assess the tolerability of stereotactic ablative radiation therapy (SABR) in this context. Herein, the long-term results are reported.

METHODS AND MATERIALS

Eligible patients had localized high-risk prostate cancer and were either ≥70 years old, had a score of ≥3 on the Vulnerable Elderly Scale, or declined standard therapy. Nineteen patients from a single institution were enrolled on FASTR between 2011 and 2015. They received 40 Gy to the prostate and 25 Gy to the pelvic lymph nodes in 5 weekly fractions, with 12 months of androgen deprivation therapy (ADT). Thirty patients from the same institution were enrolled on FASTR-2 between 2015 and 2017. They received 35 Gy to the prostate alone in 5 weekly fractions, with 18 months of ADT. Updated toxicity and outcomes were assessed retrospectively. Kaplan-Meier estimates were calculated for biochemical failure-free survival, freedom from distant metastases, prostate cancer-specific survival, and overall survival.

RESULTS

Forty-four patients were eligible for analysis, 16 from FASTR and 28 from FASTR-2. Thirty-four patients (77%) were >70 years old. High-risk features included Gleason score ≥8 (n = 20, 46%), T3-T4 disease (n = 12, 27%), and baseline prostate-specific antigen > 20 (n = 22, 50%). Median follow-up was 6.4 years. The 5-year cumulative incidence of late grade ≥3 genitourinary/gastrointestinal toxicity was 32% in FASTR and 11% in FASTR-2. At 5 years, the combined rates of biochemical failure-free survival, freedom from distant metastases, prostate cancer-specific survival, and overall survival were 72%, 90%, 92%, and 83%, respectively.

CONCLUSIONS

SABR can be safely delivered in high-risk prostate cancer by optimizing technical delivery, particularly with adherence to strict dose constraints for organs at risk. The clinical outcomes in FASTR and FASTR-2 were largely comparable to more standard fractionation schemes plus ADT, but further modifications may improve disease control. Larger randomized trials are necessary to better understand the efficacy and tolerability of this approach.

Dosimetric predictors of acute bowel toxicity after Stereotactic Body Radiotherapy (SBRT) in the definitive treatment of localized prostate cancer

INTRODUCTION

SBRT is an increasingly popular treatment for localized prostate cancer, though considerable variation in technical approach is common and optimal dose constraints are uncertain. In this study, we sought to identify dosimetric and patient-related predictors of acute rectal toxicity.

METHODS

Patients included in this study were treated with prostate SBRT on a prospective institutional protocol. Physician-graded toxicity and patient-reported outcomes were captured at one week, one month, and three months following SBRT. DVH data were extracted and converted into relative volume differential DVHs for NTCP modeling. Patient- and disease-related covariates along with NTCP model predictions were independently tested for significant association with physician-graded toxicity or a decline in bowel-related QoL. A multivariate model was constructed using forward selection, and significant parameter cutoff values were obtained with Fischer's exact test to group patients by risk of developing physician-graded toxicity or detriments in patient-reported QoL.

RESULTS

One hundred and three patients treated for localized prostate cancer with SBRT were included in our analysis. 52% of patients experienced a clinically significant decline in bowel-related QOL within 1 week of completion of treatment, while only 27.5% of patients developed grade 2+ physician-graded rectal toxicity. Sequential feature selection multivariate logistic regression identified rectal V22.5 Gy (p = 0.001) and D19% (p = 0.001) as independent predictors of clinically significant toxicity, while rectal V20Gy (p = 0.004) and D25.3% (p = 0.007) were independently correlated with physician-graded toxicity. Global multivariate step-wise logistic regression identified only D19% (p = 0.001) and V20Gy (p = 0.004) as independent predictors of acute bowel bother or physician-graded rectal toxicity respectively.

CONCLUSIONS

Moderate doses to large rectal volumes, D19% and V20Gy, were associated with an increased incidence of a clinically significant decrease in patient-reported bowel QOL and physician-scored grade 2+ rectal toxicity, respectively. These dosimetric parameters may help practitioners mitigate acute toxicity in patients treated with prostate SBRT.

Rationale for Utilization of Hydrogel Rectal Spacers in Dose Escalated SBRT for the Treatment of Unfavorable Risk Prostate Cancer

In this review we outline the current evidence for the use of hydrogel rectal spacers in the treatment paradigm for prostate cancer with external beam radiation therapy. We review their development, summarize clinical evidence, risk of adverse events, best practices for placement, treatment planning considerations and finally we outline a framework and rationale for the utilization of rectal spacers when treating unfavorable risk prostate cancer with dose escalated Stereotactic Body Radiation Therapy (SBRT).

Utilization of Iodinated SpaceOAR Vue™ During Robotic Prostate Stereotactic Body Radiation Therapy (SBRT) to Identify the Rectal-Prostate Interface and Spare the Rectum: A Case Report

We describe the utilization of SpaceOAR Vue™, a new iodinated rectal spacer, during Robotic Stereotactic Body Radiation Therapy (SBRT) for a Prostate Cancer Patient with a contraindication to Magnetic Resonance Imaging. A 69-year-old Caucasian male presented with unfavorable intermediate risk prostate cancer and elected to undergo SBRT. His medical history was significant for atrial fibrillation on Rivaroxaban with a pacemaker. He was felt to be at increased risk of radiation proctitis following SBRT due to the inability to accurately contour the anterior rectal wall at the prostate apex without a treatment planning MRI and an increased risk of late rectal bleeding due to prescribed anticoagulants. In this case report, we discuss the technical aspects of appropriate placement and treatment planning for utilizing SpaceOAR Vue™ with Robotic SBRT.