THE INFLUENCE OF AIR CAVITY ON DOSIMETRIC PROPERTIES

THE INFLUENCE OF AIR CAVITY ON DOSIMETRIC PROPERTIES OF THE NEW BRACHYTHERAPY APPLICATOR SAVITM G. Yegin, B. Camgoz*, M. N. Kumru* Celal Bayar University, Physics Department, Manisa *Ege University, Institute of Nuclear Science. Izmir, Turkey The Fifth Eurasian Conferance on Nuclear Science and its Application 14 -17 October 2008 Ankara-TURKEY

The SAVITM Applicator SAVI device (Cianna Medical, Aliso Viejo, CA) has been developed to make a better partial breast irradiation in brachytherapy treatment of breast cancer.

The SAVITM Applicator SAVI has 6, 8 or 10 catheters that surround a central catheter. These surrounding catheters allow geometric optimization of the dwell positions for the brachytherapy source SAVI 6 ----- 6 periperal 1 central catheter SAVI 8 ----- 8 periperal 1 central catheter SAVI 10 ----- 10 periperal 1 central catheter The device was cleared for patient treatments in July 2006.

A 3 D Model of The SAVITM Applicator

Air cavity problem The SAVI device is not filled with water which leaves the lumpectomy cavity full of air or partially filled with seroma. In current practice, dose distribution around brachytherapy sources is calculated based on a formalism described in AAPM Task Group 43 report. This formalism does not take into account of the heterogeneity due to the air cavity at the center of the applicator.

TG-43 dosimetry formalism Dose is calculated in an infinite, homogeneous water phantom.

A CT slice showing SAVI in the breast of a patient

What is the influence of air cavity on dose values? In this work, we calculated the influence of the central air cavity on predicted dose values around the aplicator volume. In our calculations, we used the Brachy. Dose Monte Carlo code to perform dose calculations in water medium

Brachy. Dose A Monte-Carlo dose calculation engine for brachy-therapy sources Brachy. Dose is developed in a joint project between Carleton University in Canada and Celal Bayar University in Turkey The code can model brachytherapy seeds in a voxel geometry. Code is based on the Multi-Geometry package and EGSnrc Code is very fast!

Examples of 192 -Ir source models modeled in Brachy. Dose project

The geometry used in Monte Carlo calculations

Isodose pictures of two cases

Dose difference due to the air cavity (xy-cros section)

Dose difference due to the air cavity (yz-cros section)

Second Geometry Model

Third Geometry Model

Isodose pictures of three calculations

Dose difference due to the air cavity (yz-cros section)

Dose difference due to the air cavity (only points having dose difference greater than 5% are shown )

Dose difference due to the air cavity (yz-cros section)

Dose difference due to the air cavity (only points having dose difference greater than 5% are shown )

Models Different seeds Amersham Model 6711 Theragenics Model 200 Prosta. Seed Echo. Seed Model 6733

Acknowledgments We would like to thank to Dr. Salih Gurdalli from and Brain Briscoll from for providing us the applicator’s specifications and their useful comments

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