An Inverse Dose Optimization Algorithm for Three-Dimensional Brachytherapy

Abstract

To report an implementation method and results of an inverse dose optimization algorithm (Gradient Based Planning Optimization, GBPO) in three-dimensional brachytherapy. The GBPO used a standard quadratic objective function, and a dwell time modulation item was added to the objective function to restrict the dwell time variance. We retrospectively selected 6 cervical cancer patients using different applicators and 15 cervical cancer patients using the Fletcher applicator. The plan quality of GBPO was assessed by isodose lines for the patients using different applicators. For the 15 patients used the same applicator, dose-volume histogram (DVH) parameters of CTV (D100%,V150%) and organs at risk (D0.1cc,D1cc , D2cc) were used to evaluate the difference between the GBPO plans and the IPSA (Inverse Planning Simulated Annealing) plans, the GBPO plans and the Graphic plans. For the patients using different applicators, the dose distributions are conformable. For the 15 patients using the Fletcher applicator, when the dwell time modulation factor (DTMF) is less than 20, the dwell time deviation reduces quickly, but the dwell time deviation has no remarkable change after the DTMF increased to 110. The difference of dosimetric parameters between the GBPO plans and the IPSA plans are not statistically significant (P<0.05). The GBPO plans has a higher D100% (3.57±0.36, 3.38±0.34; P = 0.00) and a lower V150% (55.73±4.06, 57.75±3.79; P = 0.00) than that of the Graphic plans. The differences of other DVH parameters are negligible between the GBPO plans and the Graphic plans. The GBPO plans have a comparable quality as the IPSA plans and the Graphic plans for cervical cancer cases. The GBPO algorithm could be integrated into a three-dimensional brachytherapy treatment planning system.Tabled 1Abstract 2689; Table; Comparison of DVH parameters between target and organs at risk for patients using the same type of applicator. The dose unit is Gy and the volume is relative volume (%).OrganParameterGBPOIPSAP valueGraphicP valueCTVD100%3.57±0.363.54±0.340.503.38±0.340.00V150%55.73±4.0656.43±4.210.0657.75±3.790.00BladderD0.1cc6.08±0.646.05±0.750.606.15±0.700.17D1cc5.12±0.535.11±0.570.915.14±0.560.18D2cc4.74±0.494.73±0.530.294.76±0.520.07RectumD0.1cc5.69±0.905.76±0.860.225.74±0.870.33D1cc4.63±0.604.68±0.600.214.70±0.640.15D2cc4.17±0.574.20±0.540.524.22±0.610.16IntestineD0.1cc2.77±1.412.80±1.340.512.69±1.320.20D1cc2.22±1.212.25±1.140.342.18±1.100.50D2cc2.00±1.122.02±1.040.511.96±1.000.39 Open table in a new tab