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Biological Plan Evaluation for Linac-Based Stereotactic Radiosurgery: Comparison Between Single-Isocenter and Multiple-Isocenter Techniques

M Lee*, H Tsai, National Tsing Hua University, Hsinchu, TW H Wang, Houston Methodist Hospital, Houston, USA

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose:
To compare the impact of dose distribution between multiple-isocenter and single-isocenter treatment plans of linac-based cranial stereotactic radiosurgery (SRS). The considered impact includes the induced secondary cancer, tumor control rate, and the biological late effects. We established the biological evaluation program for SRS plans that combined secondary cancer risk assessment and biological models.

Methods:
Multiple-isocenter and single-isocenter stereotactic treatment plans were created and exported by Varian Eclipse (Varian Medical Systems, Palo Alto, CA) treatment planning system for each multiple brain metastasis case. For defined critical organs in medium and high-dose regions, Schneider’s organ equivalent dose (OED) model was used, and the parameters of life attributable risk (LAR) for cancer risk assessment were according to the BEIR VII report. The biological effect models include the tumor control probability (TCP) and the normal tissue complication probability (NTCP) with parameters that are applicable for SRS. An in-house MATLAB program imported DICOM and DICOM RT files from Eclipse planning system. The models were calculated by this program to establish a complete treatment plan evaluation system.

Results:
The secondary cancer risk of critical organs was higher for single-isocenter plans, and the comparison of NTCP was not significantly different between the two types of plans. However, some multiple-isocenter plans got worse TCP. Because those values were depending on lesion locations, we could use the uncomplicated and cancer-free control probability (UCFCP) model which proposed by the Sánchez-Nieto to score the plans.

Conclusion:
The shortened treatment time of single-isocenter plans improves efficiency and patient tolerance. However, there was a biological effect difference between these two techniques, even if they gave a similar physical dosimetric performance. This work gave the comprehensive system of biological evaluation for SRS plan.

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