Achievable Dosimetric Constraints in Stereotactic Reirradiation for Recurrent Prostate Cancer

Manon Baty; David Pasquier; Khemara Gnep; Joel Castelli; Nolwenn Delaby; Thomas Lacornerie; Renaud de Crevoisier

doi:10.1016/j.prro.2023.05.007

Achievable Dosimetric Constraints in Stereotactic Reirradiation for Recurrent Prostate Cancer

Pract Radiat Oncol. 2023 Nov-Dec;13(6):e515-e529. doi: 10.1016/j.prro.2023.05.007. Epub 2023 Jun 8.

Authors

Manon Baty¹, David Pasquier², Khemara Gnep³, Joel Castelli⁴, Nolwenn Delaby⁵, Thomas Lacornerie⁶, Renaud de Crevoisier⁷

Affiliations

¹ Department of Radiotherapy, Center Eugène Marquis, Rennes, France. Electronic address: manon.baty2@gmail.com.
² Department of Radiation Oncology, Center Oscar Lambret, Lille University, France.
³ Department of Radiotherapy, Center Eugène Marquis, Rennes, France.
⁴ Department of Radiotherapy, Center Eugène Marquis, Rennes, France; Laboratoire Traitement du Signal et de l'Image, Rennes, France.
⁵ Department of Medical Physics, Center Eugène Marquis, Rennes, France.
⁶ Department of Radiation Oncology, Center Oscar Lambret, Lille, France.
⁷ Department of Radiotherapy, Center Eugène Marquis, Rennes, France; Laboratoire Traitement du Signal et de l'Image, Rennes, France; Laboratoire Traitement du Signal et de l'Image, University of Rennes, Rennes, France.

PMID: 37295723
DOI: 10.1016/j.prro.2023.05.007

Abstract

Purpose: Stereotactic body radiation therapy has been proposed as a salvage treatment for recurrent prostate cancer after irradiation. One crucial issue is choosing appropriate dose-volume constraints (DVCs) during planning. The objectives of this study were to (1) quantify the proportion of patients respecting the DVCs according to the Urogenital Tumor Study Group GETUG-31 trial, testing 36 Gy in six fractions, (2) explain geometrically why the DVCs could not be respected, and (3) propose the most suitable DVCs.

Methods and materials: This retrospective dosimetric analysis included 141 patients treated for recurrent prostate cancer with Cyberknife (Accuray), according to GETUG-31 DVCs: V_95% ≥ 95% for the planning target volume (PTV), V_12Gy < 20% and V_27Gy < 2 cc for the rectum, and V_12Gy < 15% and V_27Gy < 5 cc for the bladder. The percentage of patients not respecting the DVCs was quantified. Correlations between the DVCs and anatomic structures were examined. New DVCs were proposed.

Results: Only 19% of patients respected all DVCs, with a mean PTV of 18.5 cc (range, 3-48 cc), although the mean PTV was 40.5 cc (range, 3-174 cc) in the whole series. A total of 98% of the patients with a clinical target volume (CTV)/prostate ratio >0.5 could not respect the DVCs in the organs at risk. The target coverage and organ-at-risk sparing decreased significantly with increase in the values of PTV, CTV, CTV/prostate ratio, the overlapping volume between the PTV and bladder wall and between the PTV and rectal wall. Threshold values of PTV, >20 cc and 40 cc, allowed for the PTV and bladder DVCs, respectively. To improve DVC respect in case of large target volume, we proposed the following new DVCs: V_12Gy < 25% and 25% and V_27Gy < 2 cc and 5 cc for the rectum and bladder, respectively.

Conclusions: GETUG-31 DVCs are achievable only for small target volumes (CTV more than half of the prostate). For a larger target volume, new DVCs have been proposed.

MeSH terms

Humans
Male
Prostatic Neoplasms* / pathology
Prostatic Neoplasms* / radiotherapy
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted / methods
Radiotherapy, Conformal* / methods
Radiotherapy, Intensity-Modulated* / methods
Re-Irradiation*
Rectum / radiation effects
Retrospective Studies