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Daily Fraction Dose Recalculation Based On Rigid Registration Using Cone Beam CT

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C Bosse

C Bosse*, R Tuohy , P Mavroidis , Z Shi , R Crownover , N Papanikolaou , S Stathakis , University of Texas Health Science Center, UTHSCSA, San Antonio, TX


SU-E-T-94 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:To calculate the daily fraction dose for a CBCT recalculation based on rigid registration and compare it to the planned CT dose.

Methods: For this study, 30 patients that were previously treated (10 SBRT lung, 10 prostate and 10 abdomen) were considered. The daily CBCT images were imported into the Pinnacle treatment planning system from Mosaic. The prescribing physician contoured the regions of interest (ROI) on each CBCT and then dose was computed on each CBCT. Each CBCT dose distribution was then compared against the plan. The evaluation was based on isodose line comparison and Dose Volume Histogram comparison.

Results:In the case of lung patients the dose differences between daily dose and plan dose were considered small. The PTV coverage was not compromised and the dose to the organs at risk had negligible differences. Larger differences were observed for prostate and abdomen patients. In these cases, although the PTV doses did not change on a daily basis, the doses to the organs at risk had significant differences. For a prostate patient, the bladder dose at 35% volume was 2714.444 cGy for the CT plan and 2844.747, 2801.556, 3552.37, and 2970.968 cGy for subsequent CBCTs. For the PTV on a SBRT patient, however, the CT plan had a dose at 35% volume of 6917.71 cGy and 6815.385, 6892.5, 6896.25, and 6922.9 cGy for the CBCTs.

Conclusion:Daily dose validation is feasible using CBCT and treatment planning system. It provides means to evaluate the course of treatment for the patient undergoing radiation therapy and can assist in the decision of the need of adaptation of the treatment plan.

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