Haute Couture or Ready-to-Wear? Tailored Pelvic Radiotherapy for Prostate Cancer Based on Individualized Sentinel Lymph Node Detection.

Anne-Victoire Michaud,Vincent Fleury,Thierry Rousseau,Stephane Supiot,Mathilde Colombie,Gregory Delpon,Benoit Samain,Emmanuel Rio,Ludovic Ferrer,Maelle Le Thiec,Caroline Rousseau,Claire Dupuy,Melanie Dore,Valentine Guimas

doi:10.3390/cancers12040944

Abstract

Prostate cancer (PCa) pelvic radiotherapy fields are defined by guidelines that do not consider individual variations in lymphatic drainage. We examined the feasibility of personalized sentinel lymph node (SLN)-based pelvic irradiation in PCa. Among a SLN study of 202 patients, we retrospectively selected 57 patients with a high risk of lymph node involvement. Each single SLN clinical target volume (CTV) was individually segmented and pelvic CTVs were contoured according to Radiation Therapy Oncology Group (RTOG) guidelines. We simulated a radiotherapy plan delivering 46 Gy and calculated the dose received by each SLN. Among a total of 332 abdominal SLNs, 305 pelvic SLNs (beyond the aortic bifurcation) were contoured (mean 5.4/patient). Based on standard guidelines, CTV missed 67 SLNs (22%), mostly at the common iliac level (40 SLNs). The mean distance between iliac vessels and the SLN was 11mm, and despite a 15mm margin around the iliac vessels, 9% of SLNs were not encompassed by the CTV. Moreover, 42 SLNs (63%) did not receive 95% of the prescribed dose. Despite a consensus on contouring guidelines, a significant proportion of SLNs were not included in the pelvic CTV and did not receive the prescribed dose. A tailored approach based on individual SLN detection would avoid underdosing pelvic lymph nodes that potentially contain tumor cells.

Highlights

Prostate cancer (PCa) is a very lymphatic malignancy [1] and cancer spread to lymph nodes is a strong unfavourable prognostic factor [2]
We began by analyzing the anatomical distribution of sentinel lymph node (SLN) by lymphoscintigraphy (SPECT/CT)
Pelvic lymph nodes are anatomically defined as being located beyond the aortic bifurcation

Summary

Introduction

Prostate cancer (PCa) is a very lymphatic malignancy [1] and cancer spread to lymph nodes is a strong unfavourable prognostic factor [2]. Cancers 2020, 12, 944 radiotherapy to the prostate and the pelvic lymph nodes combined with long-term hormone therapy was shown to improve overall survival and is highly advocated [3]. All studies in high-risk PCa patients included irradiation of the lymph nodes [3]. Whereas the GETUG-01 study did not show any survival advantage in irradiating pelvic lymph nodes based on the Roach formula [4,5], the RTOG 9413 study showed a progression-free survival benefit [6]. More pelvic relapses were found following conformal radiotherapy compared to the four-field technique, suggesting that a too small clinical target volume (CTV) may miss micrometastatic lymph nodes [7]

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