EURURO Vol. 71 No. 4

E123 692

Letter to the Editor
Reply to Filippo Alongi, Rosario Mazzola, Dario Aiello
and Matteo Salgarello’s Letter to the Editor re: Re:
Daniel E. Spratt, Hebert A. Vargas, Zachary S. Zumsteg, et
al. Patterns of Lymph Node Failure after Dose-escalated
Radiotherapy: Implications for Extended Pelvic Lymph
Node Coverage. Eur Urol 2017;71:37–43. A Step Forward
in the Era of Functional Imaging?
Functional Imaging and Micrometastatic Disease:
Implications for Radiotherapy Field Design
We thank Dr. Alongi and colleagues for their interest in our
article . As they correctly noted, our study did not utilize
functional molecular imaging, such as prostate-specific
membrane antigen positron emission tomography (PSMA-
PET), and relied on standard-of-care computed tomogra-
phy. PSMA-PET continues to demonstrate impressive
sensitivity and specificity for detecting metastatic pros-
tate cancer, especially in patients with moderately
elevated PSA (>2 ng/ml) after treatment . Unfortunate-
ly, the ability to detect micrometastatic disease in patients
with biochemical recurrence of prostate cancer with low
PSA (<0.5 ng/ml) has been markedly less successful ( 50%
sensitivity) . Thus, at present the utilization of PSMA-
PET as a staging tool before treatment to evaluate for the
presence of micrometastatic disease in lymph nodes has
uncertain value. We would agree that if a functional
imaging tool were developed that could effectively
identify micrometastatic deposits within lymph nodes,
this information would be extraordinarily helpful in the
design of lymph node radiation portals. However, at
present we do not believe that PSMA imaging can reliably
serve as a predictive biomarker to guide pelvic lymph node
contouring for radiation treatments. Furthermore, there is
no evidence yet from any prospective randomized trials to
date to demonstrate that treating PSMA-PET–positive
lesions alters a patient’s disease course and improves
long-term outcomes (ie, rates of distant metastasis or
survival).
The goal of our study was to elucidate patterns of
lymph node metastasis utilizing traditional anatomic
imaging, and we demonstrated that nodal dissemination
falls outside the confines of traditional radiation lymph
node portals. We agree that it is quite possible that if
PSMA-PET were routinely used at the time of metastatic
disease for our patient cohort, the information obtained
could have provided further details about patterns of
spread. However, we believe that from the information
obtained in our patient cohort with anatomic imaging we
can already appreciate the fact that predominant nodal
spread is observed outside of classic radiation portals,
corroborating the notions suggested by other investiga-
tors. Future biomarkers and imaging that can more
reliably identify the location of micrometastatic disease
would be ideal to allow personalization of radiotherapy
field design. Overly relying on functional imaging such as
PSMA-PET at the present time in the absence of well-
designed prospective studies may be a clinically impru-
dent approach.
Although we share the enthusiasm of Alongi and
colleagues for the potential benefits of molecular imaging
in prostate cancer, we anxiously await the results of ongoing
and future clinical trials that will hopefully demonstrate
meaningful benefits to patients and gain approval of
PSMA-PET for routine use.
Conflicts of interest: The authors have nothing to disclose.
References
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ava ilable at
journal homepage:
DOIs of original articles: , .
0302-2838/# 2016 European Association of Urology. Published by Elsevier B.V. All rights reserved.