Wilkins CHHiP Dose Constraints

Background

Dosimetric planning study from the CHHiP trial and NRG GU-005, establishing organ-at-risk (OAR) dose constraints for conventionally fractionated (78 Gy/39 fx) and moderately hypofractionated (60 Gy/20 fx) prostate radiotherapy. Analyzed dosimetric data from 3,216 CHHiP patients to derive OAR constraints associated with acceptable late toxicity.

Interventions and follow up

Analysis: DVH thresholds for rectum/bladder from 3,216 CHHiP patients, validated against outcomes
Primary endpoint: DVH-based OAR constraints predictive of grade ≥2 late GI and GU toxicity
mFollow up: NR (planning study using CHHiP toxicity outcomes)

Results

Application: NRG GU-005 (28 fx) and CHHiP moderate hypofractionation (20 fx)
NRG GU-005 (28 fx, ~73.5 Gy): Rectum V70 <25%, V75 <15%; Bladder V65 <50%, V70 <35%, D0.03cc <73.5 Gy
CHHiP (20 fx, 60 Gy): Rectum V50 <50%, V60 <20%; Bladder V48 <50%, V60 <25%

Adverse events

Main adverse events: Planning study — no new toxicity data generated; constraints derived from CHHiP trial toxicity outcomes.

Conclusions

Dosimetric constraints derived from the CHHiP trial provide a validated framework for OAR sparing in moderately hypofractionated prostate RT, applicable to both 60 Gy/20 fx and 78 Gy/39 fx schedules, and incorporated into NRG GU-005 protocol guidelines.

Key Limitations

Constraints from one trial cohort (CHHiP); may not generalize to patients with pre-existing bowel/urological disease. Does not address ultra-hypofractionated SBRT constraints. Technique evolution (MRI-guided RT, daily adaptive planning) may permit further dose escalation.

Clinical Context

Directly applicable to prostate IMRT planning. CHHiP-derived constraints (60 Gy/20 fx) widely adopted in the UK and internationally. NRG GU-005 applies a modified 28-fraction schedule with constraints derived from this and related analyses. Prostate SBRT (PACE-B, HYPO-RT-PC) uses different constraint sets optimized for ultra-hypofractionated schedules.

References