# Institutional DVH Constraints — Prostate IMRT 78 Gy / 39 fx

## Prescription
- Total dose: 78 Gy / 39 fx / 2.0 Gy per fraction / 6 MV photons
- Target: PTV_7800 (derived from CTV_Prostate+SV)

## Target constraints (PTV_7800)
- V95% >= 95% (V_{74.1 Gy} at minimum 95 percent of PTV volume)
- V107% <= 2% (V_{83.5 Gy} at most 2 percent of PTV volume)
- Dmax <= 83 Gy (maximum point dose)

## Organ-at-risk (OAR) constraints
| Structure | Metric | Limit |
|---|---|---|
| Rectum | V70Gy | <= 20% |
| Rectum | V50Gy | <= 50% |
| Bladder | V70Gy | <= 25% |
| Bladder | V50Gy | <= 65% |
| Femoral head L/R | V50Gy | <= 5% |
| Bowel bag | Dmax | <= 50 Gy |
| Penile bulb | Mean dose | <= 52.5 Gy |

## PTV margin recipe (for deriving PTV_7800 from CTV)
- CTV to PTV: +7 mm uniform margin EXCEPT
- Posterior: +5 mm margin (rectum-sparing reduction)
- Rasterize onto the CT grid (3 mm) before writing to RTSTRUCT.
