Couch Absolute Coordinates ESAPI Script

This VARIAN ESAPI script computes the treatment couch absolute coordinates for a VARIAN TrueBeam radiotherapy plan prepared in Eclipse.

This is a game-changer for anyone accustomed to manually computing couch coordinates or applying manual shifts from the tattooed isocenter. It significantly improves workflow efficiency, speed, and safety on the first treatment day.

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Using the Script

Three fixed reference points are defined on our ORFIT carbon board:

• Head
• Thorax
• Abdomen

In Eclipse, scroll to one of the three points and simply enter the displayed Z-coordinate.

The script then displays the couch absolute coordinates, which can be manually entered into Treatment Preparation.

Unfortunately, there is currently no way for VARIAN ESAPI to directly write these values back into the plan.

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Features

• Supports Head-First and Feet-First patient positions
• Independent of the User Origin position in the planning image
• Independent of the Isocenter position within the patient

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Adapting the Script to Your Local Practice

⚠️ CAUTION
This script is designed specifically for our ORFIT immobilization system and will require adaptation for other manufacturers.

If you plan to adapt the code to another carbon board, please consider the following guidelines:

• Always index the carbon board at the CT scanner, i.e. place it at the same position on the CT couch
• Always index the carbon board at the LINAC
• Choose three visible reference points on the carbon board
  (we selected points at the level of the patient’s head, shoulders, and abdomen)
• Replace the coordinates of VVector Point1, Point2, and Point3 (LAT, VRT, LONG, in mm) at the beginning of the code
  • The easiest approach is to place Point1 on the central axis
• Determine the LONG coordinate for Point1
  • A simple method is to use our value, run the script on a dummy plan with the isocenter placed exactly at your Point1, and compare the script output with the value obtained when centering the same Point1 on your carbon board at the LINAC isocenter
• Derive the LONG (and LAT, if applicable) coordinates for Point2 and Point3 by measuring their relative distances to Point1

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Disclaimer and Clinical Use

⚠️ Important Notice

This script is provided as a workflow assistance tool only. Before any clinical use, it must be thoroughly validated within your local environment.

Users are strongly encouraged to perform extensive retrospective testing, comparing the couch absolute coordinates computed by the script against actual values used for real patients. Validation should cover all relevant treatment sites, patient orientations (Head-First / Feet-First), image orientations, and any other clinical configurations used in routine practice.

This script is not intended as a full replacement for established IGRT (Image-Guided Radiotherapy) or SGRT (Surface-Guided Radiotherapy) procedures. All standard imaging, verification, and safety checks required by local clinical protocols must continue to be applied.

The responsibility for validation, commissioning, and clinical use of this script remains entirely with the end user and their institution.