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Dosimetry Effects of Small Field Sizes Between Treatment Plans Computed with Finite Size Pencil Beam Algorithm (FSPB) and Monte Carlo Algorithm (MC) Using InCiseâ„¢ Multileaf Collimators Equipped CyberKnife System (CK-MLC)

K Galpayage Dona1*, C Shang2 , Z Christ3 , A Shramm4 , B Erika5 , J Cole6 , B Rashmi7 , M Kasper8 , (1) Florida Atlantic University, Boca Raton, Florida (FL), (2) Boca Raton Regional Hospital, Boca Raton, AA, (3) Florida Atlantic University, Boca Raton, FLORIDA, (4) Boca Raton RegionalHospital, Boca Raton, Florida, (5) Boca Raton RegionalHospital, Boca Raton, Florida, (6) Boca Raton Regional Hospital, Boca Raton, FL, (7) Boca Raton RegionalHospital, Boca Raton, Florida, (8) Boca Raton RegionalHospital, Boca Raton, Florida


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: Since the release of CK-MLC, it has been a constant concern on the realistic dose differences computed with its early-available FSPB from those by industry well-accepted algorithms. This study was designed to quantify these dose disparities between FSPB and Accuray recently released MC for the CK-MLC plans for selected anatomic sites.

Methods: A total of thirty CK-MLC hypofractionate plans computed with FSPB were retrospectively reviewed and compared with MC results, including plans for detached lung cancer where the tumor is fully encompassed by meaningful amount of lung tissues, non-detached lung cancer, and intracranial lesions. All the selected plans were recomputed respectively using both algorithms on a Precision™ planning system with planned fields (PF) and with only small MLC fields (SF, ≤2x2cm2). Dose deviation (Dev, = (MC-FSPB)/FSPB) for PTV are used for quantitative analysis.

Results: MC PF-plans show significantly reduced (P value < 0.001) lung PTV_D95 and Dmean by 16.18%-17.85% and 13.04%-13.88% respectively, while larger differences are seen in the detected tumors and tumors with lower densities. Due to lack of lateral electron equilibrium, SF-plans indicate less deviation. Also, significant Dev values (0-13.3%) are displayed for nearby organs.

Conclusion: Compared with MC, this investigation further suggests that FSPB computed CK-MLC plans overestimate lung PTV-D95 by about 16-18%, especially for tumors with or surrounded by low densities. Less dose difference is indicated in plans with small MLC segments. No meaningful dose differences are seen intracranial plans. These results contribute initial baselines in evaluating CK-MLC plans.


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