ASTRO 2021: Local Control in Tumor-Targeted Dose Escalation for Localized Prostate Cancer

(UroToday.com) In a GU session at the American Society for Radiation Oncology (ASTRO) Annual Congress, Dr. Padayachee presented on the role of tumor-targeted dose escalation for local control in localized prostate cancer.

In this study, Dr. Padayachee and colleagues sought to assess rates of local control for patients with prostate cancer who received tumor-directed dose escalation, using a 3-year post-radiotherapy MRI or MRI-guided targeted biopsy. Secondarily, they sought to assess spatial patterns of local relapse, biochemical failure-free survival, and rates of late toxicity.

To do so, they undertook a non-randomized, phase II trial which was accrued between 2012 and 2016. Patients were including if they had localized prostate cancer which intra-prostatic tumor identified on mpMRI which comprised <33% of the overall prostate volume. Patients, once enrolled, received whole gland prostate EBRT with 76 Gy in 38 fractions as well as a VMAT/HDR tumor boost and androgen deprivation therapy for up to 6 months at the discretion of the treating physician.

The choice of boost technique depended on the patient and physician decision and included in arm 1 an integrated boost with VMAT, up to 95 Gy in 38 fractions. In arm 2, patients received an HDR focal boost with 10 Gy in 1 fraction.

In total, the authors treated 80 patients on trial of whom 40 received each of the integrated VMAT boost and the HDR boost. Most patients had clinical T2a disease, ISUP grade group 2 or 3, and were classified as intermediate risk. ADT was used in only 4% of included patients.

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Among the 80 enrolled patients, the primary outcome could be assessed for 66, notably with the majority of these assessed by MRI without biopsy. 61 of these patients had local control with 31 of 32 patients treated with IB-VMAT showing a complete response and 1 having persistent disease. Among the 34 patients treated with HDR-VMAT, 30 had a complete response and 4 had an indeterminate response.

With longer follow-up, an addition 4 patients (3 of whom received HDR-VMAT) had intraprostatic failure, outside the boost volume. The relapse sites were typically closely adjacent to the initial treated lesion.

At a median follow-up of 55 months, the five year biochemical recurrence free survival is 92% (95% CI 85-99%). Further, late GI and GU toxicities were comparable between the two treatment approaches with grade 2 or 3 GU toxicity seen in 25% of patients treated with IB-VMAT and 27.5% of patients treated with HDR-VMAT and grade 2 or 3 GI toxicity seen in 7.5% of patients treated with IB-VMAT and 5% of patients treated with HDR-VMAT.

The authors therefore concluded that tumor targeted dose-escalation offers high rates of local control with the majority of local relapses occurring outcomes the dose escalated volume.

Presented by: Jerusha Padayachee, UHN Princess Margaret Cancer Centre, Division of Radiation Oncology, University of Toronto

Written by: Christopher J.D. Wallis, University of Toronto, Twitter: @WallisCJD during the 2021 American Society for Radiation Oncology (ASTRO) Hybrid Annual Meeting, Sat, Oct 23 – Wed, Oct 27, 2021.

 

 

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