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Evaluation of 192Ir, 60Co and 169Yb Sources for High Dose Rate Prostate Brachytherapy Inverse Planning Using An Interior Point Constraint Generation Algorithm

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E Mok Tsze Chung

E Mok Tsze Chung1*, H Safigholi2 , A Nicolae2 , M Davidson2 , A Ravi2 , D Aleman1 , W Song2 , (1) University of Toronto, Toronto, Ontario, (2) Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, Ontario


SU-F-T-15 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: The effectiveness of using a combination of three sources, 60Co, 192Ir and 169Yb, is analyzed. Different combinations are compared against a single 192Ir source on prostate cancer cases. A novel inverse planning interior point algorithm is developed in-house to generate the treatment plans.

Methods: Thirteen prostate cancer patients are separated into two groups: Group A includes eight patients with the prostate as target volume, while group B consists of four patients with a boost nodule inside the prostate that is assigned 150% of the prescription dose. The mean target volume is 35.7±9.3cc and 30.6±8.5cc for groups A and B, respectively. All patients are treated with each source individually, then with paired sources, and finally with all three sources. To compare the results, boost volume V150 and D90, urethra Dmax and D10, and rectum Dmax and V80 are evaluated. For fair comparison, all plans are normalized to a uniform V100=100.

Results: Overall, double- and triple-source plans were better than single-source plans. The triple-source plans resulted in an average decrease of 21.7% and 1.5% in urethra Dmax and D10, respectively, and 8.0% and 0.8% in rectum Dmax and V80, respectively, for group A. For group B, boost volume V150 and D90 increased by 4.7% and 3.0%, respectively, while keeping similar dose delivered to the urethra and rectum. 60Co and 192Ir produced better plans than their counterparts in the double-source category, whereas 60Co produced more favorable results than the remaining individual sources.

Conclusion: This study demonstrates the potential advantage of using a combination of two or three sources, reflected in dose reduction to organs-at-risk and more conformal dose to the target. Our results show that 60Co, 192Ir and 169Yb produce the best plans when used simultaneously and can thus be an alternative to 192Ir-only in high-dose-rate prostate brachytherapy.

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