RAYSTATION

Description of Event or Problem

AN ISSUE WAS FOUND WITH THE HANDLING OF THE DENSITY UNCERTAINTY IN THE ROBUST OPTIMIZATION AND THE PLAN EVALUATION OF RAYSTATION 4-2024B, INCLUDING SOME SERVICE PACKS. NO PATIENT HAS BEEN IMPACTED OR INVOLVED. TO THE BEST OF OUR KNOWLEDGE, THE ISSUE HAS NOT CAUSED ANY PATIENT MISTREATMENT OR OTHER INCIDENTS. A TREATMENT PLANNING SYSTEM, TPS, SUCH AS RAYSTATION CALCULATES ESTIMATED RADIATION DOSE IN A PATIENT MODEL BASED ON PATIENT CT IMAGES ACQUIRED PRIOR TO TREATMENT. THE ACCURACY OF THIS ESTIMATE DEPENDS ON HOW WELL THE PATIENT MODEL CORRESPONDS TO THE PATIENT AT THE TIME OF TREATMENT. IF, E.G., THE PATIENT ANATOMY AT THE TIME OF TREATMENT DIFFERS FROM THE IMAGES, THE DELIVERED DOSE WILL DIFFER FROM THE NOMINAL DOSE ESTIMATED BY THE TPS. TOOLS FOR EVALUATING PLAN ROBUSTNESS ARE USED TO INVESTIGATE HOW THE DOSE DISTRIBUTION MAY DIFFER FROM THE NOMINAL DOSE DUE TO INACCURACIES IN THE PATIENT MODEL. IN RAYSTATION, ROBUST EVALUATION CAN BE USED TO INVESTIGATE THE EFFECTS OF UNCERTAINTIES IN PATIENT SETUP, DENSITY INTERPRETATION FROM THE CT, AND ORGAN MOTION. ROBUST OPTIMIZATION CAN BE USED TO CREATE PLANS THAT ARE MORE ROBUST AGAINST WITH RESPECT TO SUCH VARIATIONS. DOSE CANNOT BE CALCULATED DIRECTLY ON CT IMAGE DATA. CALIBRATION CURVES ARE USED FOR CONVERTING THE IMAGE DATA TO VALUES APPROPRIATE FOR DOSE CALCULATION. FOR ION DOSE COMPUTATION, CT IMAGE VALUES CAN BE CONVERTED EITHER TO MASS DENSITIES, MD IMAGES, OR TO STOPPING POWER RATIOS, SPR IMAGES. DURING INTERNAL TESTING, AN INCONSISTENCY IN THE USE OF DENSITY UNCERTAINTY WAS FOUND. IN ROBUST OPTIMIZATION AND WHEN USING ROBUST EVALUATION FOR SPR IMAGES, THE SELECTED DENSITY UNCERTAINTY RESULTS IN THE SAME UNCERTAINTY IN DOSE RANGE. THIS IS THE EXPECTED BEHAVIOR. HOWEVER, IN ROBUST EVALUATION FOR MD IMAGES, THE RESULTING UNCERTAINTY IN DOSE RANGE WILL TYPICALLY BE LOWER THAN EXPECTED. THE ROBUST EVALUATION IMPLEMENTATION FOR MD IMAGES ISN'T INCORRECT, BUT IT IS NOT WHAT A USER EXPECTS, AND IT IS NOT CONSISTENT WITH THE OTHER USE CASES. RANGE UNCERTAINTY EVALUATION IS ONLY RELEVANT FOR ION PLANNING. OTHER TREATMENT MODALITIES ARE NOT AFFECTED.