DICOM-Based SSD Calculation Scripts (With & Without Couch Rotation)

This bundle includes two Python scripts for calculating Source-to-Skin Distance (SSD) directly from DICOM RT Plan and RT Structure Set files — no CT images required.

Both scripts use ray tracing to project the beam path from the source (isocenter + SAD) and compute SSD by finding the intersection with the external ROI contour in RTSTRUCT.

📦 Included Scripts:

1️⃣ CalcSSD_DICOM_v6_NoCouch.py

• Basic SSD calculation using gantry angle only
• Assumes couch angle = 0°
• Simple and fast — great for quick QA checks or educational use

2️⃣ CalcSSD_DICOM_v8_WithCouch.py

• Advanced SSD calculation with couch rotation correction
• Uses rotation matrix to adjust beam vector for true incidence angle
• Matches TPS SSD values within ~1 mm, even for rotated setups

✅ Highlights:

• ✔ No CT image stack needed
• ✔ Fully DICOM-based (only RTPLAN + RTSTRUCT required)
• ✔ Clean, dependency-light code (no rt-utils or external libraries)
• ✔ Ideal for QA checks, TPS validation, and training demos