With an estimated 180,890 new cases and 26,120 deaths related to the disease in 2016, prostate cancer has the highest incidence rate (21%) and the second-highest mortality rate (8%) among all types of cancer in the male population of the United States [1]. Treatment outcomes – survival rate and post-treatment quality of life – depend on risk categorization at the time of diagnosis, as well as preexisting contraindications and the selected course of treatment.
Primary Prostate Cancer Treatment Selection: Failure-Free and Overall Survival
As Sooriakumaran and colleagues discovered, cancer-specific survival after radical prostatectomy (RP) is higher compared to external beam radiation therapy (EBRT), with a traditional covariate-adjusted subdistribution hazard ratio (sHR) of cancer-related deaths for non-metastatic risk groups (1-3) at 1.77 in favor of surgery. In a cohort of patients with metastatic prostate cancer (group 4), no significant difference was observed between mortality rates, but sHR value of 0.65 indicates that radiotherapy may be the more beneficial treatment modality [2].
The efficiency of EBRT can, however, be improved by dose escalation. A comparative study of treatment outcomes in 664 patients that received either 78 Gy or 68 Gy three-dimensional conformal radiotherapy revealed that freedom from failure (definition by American Society of Therapeutic Radiation Oncology) was 64% and 54% respectively while no significant difference was observed in terms of overall survivability (OS). In terms of quality of life treatment outcomes, the incidence of late gastrointestinal toxicity of grade 2 or more was slightly increased [3]. In patients with preexisting dysfunctions that receive contraindicated or »mismatched« treatment, adverse effects are even more pronounced. EBRT, for example, led to worsened bowel symptoms while nerve-saving RP did not improve outcomes after baseline sexual dysfunction and brachytherapy worsened urinary symptoms [4].
Implications of Prostate Immobilization Using a Rectal Balloon
With a clear dose-response relationship of external beam radiation therapy modalities, dose escalation and/or mitigation of surrounding tissue toxicity have a significant impact on primary treatment selection as well as resulting outcomes. Prostate immobilization using a rectal balloon not only reduces the prostate motion between and during radiation sessions, allowing for smaller planning target volume margins (PTV) and consequent safe dose escalation, but also reduces acute and late GI toxicity by anterior rectal wall sparing and rectal wall distension.
The results of a study of escalated-dose hypofractionated intensity-modulated radiotherapy (Hypo-IMRT) with the use of a customized rectal balloon on 30 prostate cancer patients revealed that EBRT could still be a safe and efficient alternative to RP, even for low- and intermediate-risk patients (groups 1 and 2). 5-year biochemical failure-free survival in the study was 92.9% (100% for groups 1 and 2, 88.5% for group 3), with no cancer-specific deaths in any of the risk groups [5]. Other implications of prostate immobilization using a rectal balloon include the mitigation of adverse effects in patients with preexisting bowel symptoms that could not typically undergo ERBT and reduced treatment toxicity in patients for which ERBT is the primary treatment choice.
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