ASTRO 2022: Superior Post-Treatment Biopsy Outcomes with High Dose SBRT Compared to High-Dose Conventionally Fractionated IMRT for Clinically Localized Prostate Cancer

(UroToday.com) The 2022 American Society for Radiation Oncology (ASTRO) Annual Meeting held in San Antonio, TX between October 23rd and 26th, 2022 was host to a State of the Art session for the selection and treatment of localized prostate cancer. Dr. Michael Zelefsky presented results of a study evaluating post-treatment biopsy outcomes with high dose stereotactic body radiation therapy (SBRT) compared to high-dose conventionally fractionated intensity-modulation radiation therapy (IMRT) for clinically localized prostate cancer.

 

Dr. Zelefsky began his talk by defining the overall study purpose: To retrospectively compare post-treatment biopsy outcomes of prostate cancer patients treated with high-dose conventionally fractionated IMRT versus high dose SBRT. He emphasized the prognostic significance of a negative post-treatment biopsy result after high dose IMRT, highlighting his team’s prior work demonstrating that patients with a negative post-IMRT biopsy had significantly improved PSA failure, distant metastasis, and cancer specific mortality rates.1

ASTRO 2022 _Michael J. Zelefsky_0 

This study included 416 patients with low and intermediate risk prostate cancer who underwent a post-treatment biopsy (following high-dose EBRT). 186 patients were treated with conventional fractionation IMRT with a median dose of 81 Gy (range: 75.6 – 81 Gy), and 230 patients received SBRT to a median dose of 40 Gy in 5 fractions (range: 37.5 – 40 Gy). Biopsies were performed two to three years after radiation therapy (median 12 – 15 cores).

 

Looking at baseline patient characteristics, about 80% of patients in this cohort were NCCN intermediate risk. Use of short-term ADT (6 months) was more common in patients in the SBRT arm (84% versus 56%), and, as expected, radiation dose was higher in the IMRT group (81 Gy versus 40 Gy).

 

ASTRO 2022 _Michael J. Zelefsky_1 

The proportion of patients with a positive post-treatment biopsy was significantly lower in the SBRT arm (11% versus 38% in the IMRT arm, p<0.001). It bears note that these were not patients that necessarily ha a PSA relapse, but those who underwent an a priori scheduled biopsy.

 

ASTRO 2022 _Michael J. Zelefsky_2 

 

Incidence of a post-treatment positive biopsy was significantly higher in patients who did not receive ADT (28%) compared to those who received ADT 13%, p=0.002).

 

ASTRO 2022 _Michael J. Zelefsky_3 

Next, restricting analysis to patients with unfavorable intermediate risk disease and looking at ADT use among the IMRT versus SBRT cohorts, the authors determined that use of ADT in these patients was associated with a decreased incidence of a positive prostate biopsy, irrespective of radiation regimen as demonstrated below:

 

ASTRO 2022 _Michael J. Zelefsky_4 

 

Multivariable logistic regression analysis evaluating predictors of a positive post-treatment biopsy demonstrated increased odds in the following subcohorts:

  • IMRT conventional fractionation (OR: 2.7, 95% CI: 0.21 – 0.62, p<0.001)
  • No use of concurrent ADT (OR 2.2, 95% CI: 0.19 – 0.99, p=0.05)
  • Unfavorable intermediate versus low/favorable intermediate disease (OR: 1.43, 95% CI: 0.81 – 2.49, p=0.21)

There was no sufficient evidence to suggest that the effect of hormone therapy on biopsy outcomes differed either between the two radiation types or between the different risk groups.

 

Dr. Zelefsky concluded his presentation as follows:

  • Among patients (mostly intermediate risk) who underwent post-treatment biopsies following high-dose radiotherapy, the most significant variable associated with an improved biopsy outcome was SBRT compared to IMRT
  • There was a trend for a significant reduction in positive biopsy outcomes for patients treated with short course ADT (p=0.05).
  • Improved local eradication of prostatic disease appears to be more frequently achieved with high-dose SBRT, likely in combination with short-term ADT.

 

Presented by: Dr. Michael J. Zelefsky, MD, Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY

 

Written by: Rashid Sayyid, MD, MSc – Society of Urologic Oncology (SUO) Clinical Fellow at The University of Toronto, @rksayyid on Twitter during the 2022 American Society of Radiation Oncology (ASTRO) Annual Hybrid Meeting, San Antonio, TX, Sat, Oct 22 – Wed, Oct 26, 2022.

References:

  1. Zelefsky MJ, et al. Long-Term Implications of a Positive Posttreatment Biopsy in Patients Treated with External Beam Radiotherapy for Clinically Localized Prostate Cancer. J Urol. 2019;201(6):1127-33.
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