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TCP-Driven Biological Planning for High-Dose Rate Brachytherapy

E Lee

E Lee1*, F Yuan2, A Templeton3, R Yao4, K Kiel5, J Chu6, (1) Georgia Institute of Technology, Atlanta, GA, (2) Georgia Institute of Technology, Atlanta, GA, (3) Rush University, Chicago, Illinois, (4) Rush University Medical Center, Chicago, IL, (5) Rush University Medical Center, Chicago, IL, (6) Rush University Medical Center, Oak Brook, IL

SU-D-500-1 Sunday 2:05PM - 3:00PM Room: 500 Ballroom

Purpose: Tumor control probability(TCP) measures the probability that no malignant cells are left in the affected organ. It is an important clinical metric for measuring treatment success. Zaider and Minerbo provide a complex yet important TCP formalism which links the treatment duration, dose deposit, radiobiology of tumor cells and cell life characteristics. We perform feasibility tests on TCP-driven biological planning for high-dose-rate brachytherapy(HDR) where the objective maximizes TCP of the treatment plans. Plan robustness is tested, and plan quality and potential outcome significance are evaluated.

Methods:CT and 18F-fluorodeoxyglucose based-PET images are obtained for 15 cervical cancer patients. All received prior external-beam radiation. The CTV prescribed dose is 5Gy for 4 fractionations, with the PET-identified pockets prescribed an escalated-dose ranging from 7.5-9.0Gy per fraction. The treatment model determines the dwell time and seed location that maximizes TCP while constraining PTV coverage, the lower/upper dose, and dose-volume shape for organs-at-risk and PTV. We contrast the standard HDR plan and PET-pocket escalated plan.

Results:TCP ranges from 48-63% for standard plans versus 82-99% for PET-guided escalated plans. The increase is most significant with the smallest PET-identified pockets. Uniformly, urethra and rectum receive 5-8% reduced dose. There is marginal difference in PTV dose between standard and escalated plans. All resulting TCP-driven plans are clinically acceptable.

Conclusion:TCP can be a very important objective for treatment plan optimization. With advances in biological/functional imaging, there is an urgent need to incorporate radiobiological parameters and TCP within planning. This study marks the first use of TCP as the driving objective for treatment planning. The optimization problem is very difficult to solve and requires computational breakthroughs. The resulting plans improve significantly the overall local tumor control, and reduce organs-at-risk dose. Rush University began clinical studies in 2011. A long term outcome study must be carried out to gauge the overall impact.

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