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Worth Attention prostate consensus-guidelines

Experts reached limited consensus on prostate GTV contouring and micro-boosting

Only 33% of statements reached consensus, but experts agreed on multimodality imaging, eligible lesions, and daily image guidance.

RadOncToday · ·1 min read

KEY POINTS

  • The study combined a contouring exercise with a two-round modified Delphi process. Fifteen of 20 invited international radiation oncologists completed the study; consensus and strong consensus required at least 75% and 90% agreement, respectively.
  • Experts contoured MRI- and PSMA-PET-defined GTVs in two cases. In the complex case, spatial agreement was only fair: Fleiss’ kappa was 0.35 for PSMA-PET and 0.36 for MRI, while MRI volumetric agreement was poor with an intraclass correlation coefficient of 0.45.
  • In the simpler case, agreement improved substantially. Intraclass correlation coefficients were 0.91 for PSMA-PET and 0.94 for MRI, with corresponding kappa values of 0.55 and 0.59.
  • PSMA-PET contours were consistently larger than MRI contours. Mean volumes were 6.5 versus 4.6 cm³ in the complex case and 3.1 versus 1.8 cm³ in the simpler case, demonstrating that imaging modality materially changes the boost target.
  • Only 43 of 131 statements (33%) reached consensus. For MRI-based delineation, experts agreed that T2-weighted and DWI/ADC sequences should both be available, with the GTV defined from the union rather than the intersection of abnormalities.
  • PI-RADS 4–5 lesions were considered appropriate for boosting, while PI-RADS 3 lesions could be included when anatomically correlated with clinically significant cancer of Gleason grade group 2 or higher. For PET, experts preferred ^68Ga- or ^18F-labelled PSMA tracers and rejected choline-based imaging.
  • Experts agreed that no CTV margin should be added when both MRI and PSMA-PET information are used, that rectum, bladder, and urethra should be contoured, and that organ-at-risk constraints should take precedence over GTV coverage. Daily CBCT or equivalent image guidance received 100% agreement.
  • No consensus was reached on SBRT micro-boosting outside trials, margins when only one imaging modality is available, or optimal dose. Nine of 15 experts favoured 74–80 Gy EQD2 to the uninvolved prostate, while eight of 15 selected 85–95 Gy EQD2 for the GTV; more than one quarter recommended a GTV dose above 110 Gy.

CLINICAL TAKEAWAY

The consensus provides a useful minimum framework for MRI- and PSMA-PET-guided focal boosting, particularly with conventional or moderately hypofractionated radiotherapy. It is not a complete treatment protocol: SBRT implementation, dose prescription, and target margins remain too variable for uniform practice without institutional guidance or clinical-trial support.

SOURCE

International Journal of Radiation Oncology, Biology, Physics