Local failure is a dominant mode of recurrence in locally advanced and clinical node positive prostate cancer patients treated with combined pelvic IMRT and androgen deprivation therapy

Ablative Radiotherapy in Prostate Cancer: Stereotactic Body Radiotherapy and High Dose Rate Brachytherapy

Simple Summary

Radiation therapy is a standard of care treatment option for men with localized prostate cancer. Over the years, various radiation delivery modalities have contributed to the increased precision of radiation, employing radiobiological insights to shorten the overall treatment time with hypofractionation, while improving oncological control without increasing toxicities. Here, we discuss and compare two ablative radiation modalities, stereotactic body radiation therapy (SBRT) and high-dose-rate brachytherapy (HDRBT), in terms of oncological control, dose/fractionation and toxicities in men with localized prostate cancer. This review will highlight the levels of evidence available to support either modality as a monotherapy, will summarize safety and efficacy, help clinicians gain a deeper understanding of the safety and efficacy profiles of these two modalities, and highlight ongoing research efforts to address many unanswered questions regarding ablative prostate radiation.

Abstract

Prostate cancer (PCa) is the most common noncutaneous solid organ malignancy among men worldwide. Radiation therapy is a standard of care treatment option that has historically been delivered in the form of small daily doses of radiation over the span of multiple weeks. PCa appears to have a unique sensitivity to higher doses of radiation per fraction, rendering it susceptible to abbreviated forms of treatment. Stereotactic body radiation therapy (SBRT) and high-dose-rate brachytherapy (HDRBT) are both modern radiation modalities that allow the precise delivery of ablative doses of radiation to the prostate while maximally sparing sensitive surrounding normal structures. In this review, we highlight the evidence regarding the radiobiology, oncological outcomes, toxicity and dose/fractionation schemes of SBRT and HDRBT monotherapy in men with low-and intermediate-risk PCa.

Overall survival comparison between androgen deprivation therapy (ADT) plus external beam radiation therapy (EBRT) vs ADT plus EBRT with brachytherapy boost in clinically node-positive prostate cancer

PURPOSE

Optimal therapy for clinically node-positive, nonmetastatic (cN1) prostate cancer (PC) patients remains controversial, ranging from aggressive local therapy to palliative systematic therapy alone. Despite guideline support, it is unclear if a brachytherapy (BT) boost should be considered for cN1 patients as these patients were excluded from randomized trials establishing its benefit. Herein, we compare definitive radiation therapy (RT) with or without a BT boost in cN1 PC.

METHODS AND MATERIALS

The National Cancer Database was used to identify men with cN1 PC treated with definitive RT and concomitant androgen deprivation therapy between 2004 and 2013. Overall survival (OS) was compared between those who received external beam RT (EBRT) or combination EBRT plus BT boost (EBRT + BT) using Kaplan-Meier with propensity score matching and Cox proportional hazards.

RESULTS

With a median followup of 48.5 months, 1,650 patients were eligible for this analysis, 103 (6.2%) of whom received EBRT + BT. Younger age, no medical comorbidities, and Gleason score of six were associated with higher likelihood of receiving EBRT + BT over EBRT alone. The mean (median) OS for EBRT and EBRT + BT was 99.0 (110.6) months vs 109.2 (not reached) months, respectively (p = 0.048). However, no significance difference in OS was observed between the groups after propensity score matching. On multivariable analysis, EBRT + BT was not significantly associated with improved OS (adjusted HR 0.67, 95% CI, 0.41-1.07, p = 0.098).

CONCLUSIONS

In this retrospective, observational study of patients with cN1 PC treated with definitive RT and concomitant androgen deprivation therapy, EBRT + BT had an unadjusted improvement in OS compared with EBRT alone that lost statistical significance after multivariable adjustment and propensity score matching.

Simultaneous Metabolic and Perfusion Imaging Using Hyperpolarized 13C MRI Can Evaluate Early and Dose-Dependent Response to Radiation Therapy in a Prostate Cancer Mouse Model

PURPOSE

To investigate use of a novel imaging approach, hyperpolarized (HP) ¹³C magnetic resonance imaging (MRI) for simultaneous metabolism and perfusion assessment, to evaluate early and dose-dependent response to radiation therapy (RT) in a prostate cancer mouse model.

METHODS AND MATERIALS

Transgenic Adenocarcinoma of Mouse Prostate (TRAMP) mice (n = 18) underwent single-fraction RT (4-14 Gy steep dose across the tumor) and were imaged serially at pre-RT baseline and 1, 4, and 7 days after RT using HP ¹³C MRI with combined [1-¹³C]pyruvate (metabolic active agent) and [¹³C]urea (perfusion agent), coupled with conventional multiparametric ¹H MRI including T2-weighted, dynamic contrast-enhanced, and diffusion-weighted imaging. Tumor tissues were collected 4 and 7 days after RT for biological correlative studies.

RESULTS

We found a significant decrease in HP pyruvate-to-lactate conversion in tumors responding to RT, with concomitant significant increases in HP pyruvate-to-alanine conversion and HP urea signal; the opposite changes were observed in tumors resistant to RT. Moreover, HP lactate change was dependent on radiation dose; tumor regions treated with higher radiation doses (10-14 Gy) exhibited a greater decrease in HP lactate signal than low-dose regions (4-7 Gy) as early as 1 day post-RT, consistent with lactate dehydrogenase enzyme activity and expression data. We also found that HP [¹³C]urea MRI provided assessments of tumor perfusion similar to those provided by ¹H dynamic contrast-enhanced MRI in this animal model. However, apparent diffusion coefficien , a conventional ¹H MRI functional biomarker, did not exhibit statistically significant changes within 7 days after RT.

CONCLUSION

These results demonstrate the ability of HP ¹³C MRI to monitor radiation-induced physiologic changes in a timely and dose-dependent manner, providing the basic science premise for further clinical investigation and translation.