Is there an SIB boost regimen for a dominant prostate lesion for 60 Gy/20 fx to the whole prostate?

There are no phase III data providing guidance on the "isotoxic" boost dose for a 20-fraction, hypofractionated prostate treatment similar to the experimental arm in FLAME (Kerkmeijer et al., PMID 33471548), but there are two prospective studies of which I am aware, DELINEATE and ARO2020-01, which do report on such a treatment regimen.

The first, DELINEATE (Tree et al., PMID 36150450), had a cohort (cohort B) in which patients were treated with a 60 Gy/20# dose to the whole gland with a simultaneous boost up to 67 Gy/20# to the boost PTV (MRI-defined tumor + 2 mm intraprostatic margin excluding urethra). This trial had planned to sequentially initiate treatment on a cohort D which was to utilize a boost dose of 72 Gy/60#; however, owing to p...

Dr. @Dr. First Last has a good summary of the data. Outside of that, the NRG GU-010 trial allows for microboost and offers guidance for different dose/fractionation regimens based on BED conversions assuming an alpha/beta of 3. If using these non-validated regimens, I would encourage anyone to appropriately constrain the urethra, bladder, and anterior rectal wall.

NRG GU-010 Microboost Recommendations:

• 78 Gy/39 fractions -> Microboost of 97.5 Gy (2.5 Gy/fraction)
• 70 Gy/28 fractions -> Microboost of 88.2 Gy (3.15 Gy/fraction)
• 60 Gy/20 fractions -> Microboost of 78 Gy (3.9 Gy/fraction)
• 36.25 Gy/5 fractions -> Microboost of 45 Gy (9 Gy/fraction)

40 Gy/20 fractions is highly likely to eradicate subclinical carcinoma so 60/40 would be a good choice.