Nicholas van As

Nicholas van As is Medical Director of The Royal Marsden and Professor in Precision Prostate Radiotherapy at the Institute of Cancer Research. He was chief investigator of PACE-B, which randomised 874 men with low or intermediate risk localised prostate cancer, none of them on androgen deprivation therapy, between 36.25 Gy in five fractions of stereotactic body radiotherapy and conventionally fractionated or moderately hypofractionated radiotherapy.

At a median 74 months, freedom from biochemical or clinical failure was 95.8 percent with the five-fraction schedule against 94.6 percent with the longer course, meeting the non-inferiority margin. The trial also reported what it cost: late genitourinary toxicity of grade 2 or worse at five years was 26.9 percent with stereotactic radiotherapy against 18.3 percent with the comparator, though the five-year patient-reported outcomes found no difference in pad use, leakage, sexual problems or bowel problems. NHS England's June 2026 commissioning policy for prostate stereotactic ablative radiotherapy is written on PACE-B's eligibility criteria and cites the trial by name.