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An Efficient Dose Correction Algorithm Accounting for Tissue Heterogeneities in LDR Brachytherapy

S Mashouf

S Mashouf¹*, P Lai² , A Karotki³ , B Keller⁴ , D Beachey⁵ , J Pignol⁶ , (1),(2) University of Toronto, Medical Biophysics Dept., Toronto, ON, (3),(4),(5),(6) Sunnybrook Health Sciences Centre, Toronto, ON,

Presentations

SU-E-T-477 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Seed brachytherapy is currently used for adjuvant radiotherapy of early stage prostate and breast cancer patients. The current standard for calculation of dose surrounding the brachytherapy seeds is based on American Association of Physicist in Medicine Task Group No. 43 (TG-43 formalism) which generates the dose in homogeneous water medium. Recently, AAPM Task Group No. 186 emphasized the importance of accounting for tissue heterogeneities. This can be done using Monte Carlo (MC) methods, but it requires knowing the source structure and tissue atomic composition accurately. In this work we describe an efficient analytical dose inhomogeneity correction algorithm implemented using MIM Symphony treatment planning platform to calculate dose distributions in heterogeneous media.

Methods: An Inhomogeneity Correction Factor (ICF) is introduced as the ratio of absorbed dose in tissue to that in water medium. ICF is a function of tissue properties and independent of source structure. The ICF is extracted using CT images and the absorbed dose in tissue can then be calculated by multiplying the dose as calculated by the TG-43 formalism times ICF. To evaluate the methodology, we compared our results with Monte Carlo simulations as well as experiments in phantoms with known density and atomic compositions.

Results: The dose distributions obtained through applying ICF to TG-43 protocol agreed very well with those of Monte Carlo simulations as well as experiments in all phantoms. In all cases, the mean relative error was reduced by at least 50% when ICF correction factor was applied to the TG-43 protocol.

Conclusion: We have developed a new analytical dose calculation method which enables personalized dose calculations in heterogeneous media. The advantages over stochastic methods are computational efficiency and the ease of integration into clinical setting as detailed source structure and tissue segmentation are not needed.


Funding Support, Disclosures, and Conflict of Interest: University of Toronto, Natural Sciences and Engineering Research Council of Canada


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