Daily Adaptive Radiotherapy After Prostate Surgery: Early Results from the DART-PHASER Study

A new clinical study is testing a smarter way to give radiation after prostate surgery. The approach, called daily adaptive radiotherapy, uses artificial intelligence to adjust the treatment plan every day based on how the patient’s anatomy looks at that moment. Early results from the first 42 patients in the DART-PHASER trial suggest the method improves how well the radiation hits the target while keeping dose to nearby organs, especially the rectum, lower than a standard “fixed” plan.

The study focuses on men who had their prostate removed for cancer but later showed signs that the cancer might be coming back, either as a rising PSA (biochemical relapse) or as visible spots on advanced PSMA PET scans (macroscopic relapse). Instead of waiting or giving long courses of radiation, these patients received a shorter, more intense schedule: 20 daily treatments over about four weeks. Those with only a PSA rise got 55 Gy in total; those with visible disease got 59 Gy. When needed, the pelvic lymph nodes were also treated with 45 Gy.

Each day, before treatment, a quick 3D scan (cone-beam CT) was taken on the treatment machine. An AI-powered system called Ethos used that scan to create two options: one that simply recalculated the dose on the day’s anatomy, and another that fully re-optimized the plan to match the day’s shape of the prostate bed, bladder, rectum, and bowel. The treating doctor then chose the better option for delivery. In practice, the re-optimized “adapted” plan was selected in 837 out of 840 treatment sessions.

When researchers compared the adapted plans to the non-adapted ones, they found clear advantages. The adapted plans covered the target area much more completely: on average, 98.5% of the prostate bed received the intended dose, compared to 92.1% with the non-adapted approach. Coverage of pelvic lymph nodes also improved. At the same time, dose to the rectum dropped in a meaningful way. The volume of rectum receiving a high dose (52.8 Gy) fell from about 17% to 13%, and the average rectum dose per session went from 1.54 Gy to 1.42 Gy. This is important because lower rectal dose is linked to fewer long-term bowel side effects. Bladder and bowel doses changed very little between the two approaches, largely because these organs move and fill differently each day, which even adaptation cannot fully control.

To check how closely the daily plans matched the original, carefully designed reference plan, the team used a statistical method called Bland–Altman analysis. For target coverage, the non-adapted plans consistently under-delivered dose compared to the reference (a systematic shortfall of about 7.5 percentage points), while the adapted plans stayed almost perfectly aligned with the reference. For the rectum, the non-adapted plans systematically over-exposed the organ by about 5 percentage points, whereas the adapted plans showed almost no bias. In short, daily adaptation kept the treatment much closer to what was originally intended.

Side effects in this early group were mild. These findings matter because giving higher doses per session (hypofractionation) after prostate surgery has been held back by concerns about long-term damage to nearby organs. This study suggests that daily adaptation can make hypofractionated salvage radiation safer and more precise, at least in the short term. The results are in line with other adaptive radiotherapy studies and meet the safety targets set by the trial designers.

There are important caveats. The follow-up so far is short (about 14 months on average), so the DART-PHASER study cannot yet speak to late side effects or how well the treatment controls the cancer over many years. So larger, longer studies are needed to confirm the benefits. Nonetheless, because no safety concerns emerged, the trial is continuing to enroll more patients.

Source.

Clinical trial.