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Radiochromic Film-Based Validation of the Leksell GammaPlan Convolution Algorithm with Heterogeneity

J Rakowski1 , A Santiago2*, (1) Karmanos Cancer Institute, Detroit, MI, (2) Wayne State University, Detroit, MI


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

Room: Exhibit Hall

Purpose: To examine the performance of the Elekta Leksell GammaPlanâ„¢ version 10.1.1 convolution/superposition algorithm with heterogeneity.

Methods: An Alderson RANDO anthropomorphic head phantom was loaded with calibrated Gafchromicâ„¢ EBT-XD film, imaged by CT and irradiated with Gamma Knifeâ„¢. Single isocenter treatment plans were created in GammaPlanâ„¢ version 10.1.1 using CT tissue electron density. Treatment plans were generated using medium brain and sharp bone filter CT images for comparison. Target areas were Central, Left Inferior, Nasopharyngeal, Right Acoustic, and Cervical Spine, sampling a range of tissue/bone/air interfaces. Collimator sizes were 4mm, 8mm, and 18mm. Irradiated films were compared to the GammaPlanâ„¢ DICOM dose distributions. Absolute dose profiles and RITâ„¢ gamma analyses at 1%/1 mm, 2%/2mm, and 10% dose threshold were reviewed.

Results: Convolution/TMR-10 exposure time ratios ranged from 1.03 to 1.07. Unmodified horizontal and vertical dose profiles analyzed in Excel showed good agreement in peak regions and penumbras. 1%/1mm bone CT filter gamma analysis results were: Central 18 mm¬¬¬ 98.2%; Left Inferior 18 mm 93.4%; Nasopharyngeal 18 mm 98.5%; Nasopharyngeal 4 mm 100%; Right Acoustic 18 mm 86.3%; Cervical Spine 8 mm 99.9%. 1%/1mm soft tissue CT filter gamma analyses results were the following: Central 18 mm 100%; Left Inferior 18 mm 99.6%; Nasopharyngeal 18 mm 68.4%; Nasopharyngeal 4 mm 68.0%; Right Acoustic 18 mm 99.1%; Cervical Spine 8 mm 100%. 2%/2mm bone CT filter gamma analyses yielded: Central 18mm 100%; Left Inferior 18mm 99.6%; Nasopharyngeal 18mm 100%; Nasopharyngeal 4mm 100%; Right Acoustic 18mm 99.1%; Cervical Spine 8mm 100%. 2%/2mm soft tissue CT filter gamma analyses were: Central 18mm 100%; Left Inferior 18mm 99.6%; Nasopharyngeal 18mm 98.2%; Nasopharyngeal 4mm 99.7%; Right Acoustic 18mm 99.1%; Cervical Spine 8mm 100%.

Conclusion: Dose planning with tissue heterogeneity and CT bone filter using the GammaPlanâ„¢ convolution/superposition algorithm ensures dosimetric accuracy in Gamma Knifeâ„¢ radiosurgery.


Convolution/superposition, Gamma Knife, Dosimetry


TH- External beam- photons: gammaknife

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