Session Item

Tuesday
May 10
08:30 - 09:10
Auditorium 15
Toxicity vs tumour control: What makes a good pelvic radiotherapy plan?
Peter Hoskin, United Kingdom
4000
Teaching lecture
Interdisciplinary
16:10 - 16:20
Outcomes in focal vs. dose-painted salvage HDR brachytherapy for locally recurrent prostate cancer
OC-0038

Abstract

Outcomes in focal vs. dose-painted salvage HDR brachytherapy for locally recurrent prostate cancer
Authors:

INMACULADA NAVARRO1, Lisa Joseph2, Zhihui (Amy) Liu3, Daniel Taussky4, Guila Delouya4, Maroie Barkati4, Marie-Claude Beauchemin4, Tamim Niazi5, Alejandro Berlin2, Joelle Helou2, Srinivas Raman2, Dominic Beliveau-Nadeau4, Samuel Kadoury6, Alexandra Rink2, Peter Chung2, Cynthia Ménard7

1Princess Margaret Cancer Centre, University of Toronto, Radiaiton Oncology, Toronto, Canada; 2Princess Margaret Cancer Centre, University of Toronto, Radiation Oncology, Toronto, Canada; 3Princess Margaret Cancer Centre, University of Toronto, Principal Biostatistician and Clinician Investigator, Toronto, Canada; 4Centre Hospitalier de l’Université de Montréal (CHUM), Radiation Oncology, Montreal, Canada; 5Jewish General Hospital, McGill University, Radiation Oncology, Montreal, Canada; 6Polytechnique Montreal, Radiation Oncology, Montreal, Canada; 7Centre Hospitalier de l’Université de Montréal (CHUM), Radiation Oncology, Toronto, Canada

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Purpose or Objective

To report toxicity and cancer control outcomes in a combined cohort of patients with locally recurrent prostate cancer treated with MRI-guided focal or dose-painted salvage high dose rate (HDR) brachytherapy (BT).

Material and Methods

Between 2009-2020, 79 patients with pathologically confirmed and MRI visible local recurrence after previous EBRT and/or BT received salvage brachytherapy at 1 of 2 academic cancer centres. BT was delivered in 2 fractions over a median 7 days (range, 5-14), differentiated into two cohorts: dose-painted whole gland (dpBT) to a dose of 16-22 Gy with tumour boost of 22-26 Gy (n=15), and focal BT (fBT) to a dose of 26Gy (n=64). Failure free survival (FFS) was defined as the time from salvage brachytherapy to biochemical failure, local or regional recurrence, distant metastasis, or death from any cause. Fisher’s exact test was used to compare toxicity, and Kaplan-Meier method was used for FFS.

Results

The median age at salvage treatment was 71 years (56-85). At initial diagnosis, 22% presented with low, 66% intermediate, and 13% high risk localized disease (NCCN). The median time between initial and salvage treatment was 7 years (3-17).  Median PSA prior to salvage PSA BT was 4.6 (1.2-24), with median PSA doubling time of 15 months (5-51). Gleason grade group at initial failure was 4 or 5 in 34%, and short course adjuvant ADT was used in 33%.

At a median follow up of 38 months (6-134), the 3 and 5 year FFS (95% CI) rates were 67.8% (56.7-80.9) and 49.1% (35.8 – 67.4) respectively, with a median time to progression of 59.3 months (42.4-not reached). The 3 and 5 year cumulative incidence of local failure (LF) was 13.9% (95% CI, 4.1-23.7) and 30.1% (14.6-45.7), respectively. LF occurred earlier in the fBT cohort (Figure 1), but no statistically significant difference was found (fBT vs. dpBT, 19% vs. 0% p=0.32 at 3 years, and 27.8% vs. 23.3% at 5 years).  The 3 and 5-year cumulative incidence of DM was 2.9% (0-6.9) and 12.6% (1.2-24), respectively.

 There were no G3 toxicity events attributable to salvage brachytherapy. Overall, grade 2 genitourinary (GU) and gastrointestinal (GI) toxicity events were reported in 24% and 4% of patients, respectively. The fBT approach resulted in substantially fewer grade 2 GU and GI toxicity events compared with the dpBT approach (p<0.001, Table1).


Figure1. Local failure in dpBT and fBT cohorts.

Table1. Toxicity by Type of Therapy


Conclusion

Focal and dose-painted salvage HDR brachytherapy is associated with minimal toxicity, particularly in those treated with fBT. However, suboptimal local control with local failures occurring earlier in the fBT approach remain an issue. Dose escalation may be feasible and justified in order to improve local control outcomes. Further analysis will seek to identify those patients destined for early failure after fBT.