A study on a method for restricting dwell time variation in brachytherapy plan optimization / 中华放射医学与防护杂志

ABSTRACT

Objective:To report an implementation method and result of an inverse dose optimization algorithm (GBPO) that can control the dwell time variation in three-dimensional brachytherapy.Methods:The GBPO used a quadratic objective function. A dwell time modulation item was added to the objective function to restrict the dwell time variation, and a DTMF (dwell time modulation factor) was used to adjust the dwell time variation. A retrospective study was made of 15 cervical cancer patients treated using the Fletcher applicator. The relationship between the DTMF and dwell time deviation was analyzed. Dose-volume histogram (DVH) parameters of HR-CTV ( D100%, V150%) and organs at risk (OARs) ( D0.1 cm 3, D1 cm 3, D2 cm 3) were used to evaluate the difference between the GBPO plans and the commercial treatment plan system (using the IPSA algorithm) plans. Results:When the DTMF was less than 20, the dwell time deviation decreased quickly. However, after the DTMF increased to 100, and the dwell time deviation had no remarkable change. The D100% of GBPO plan was higher than that of IPSA plan (3.63±0.36 vs. 3.53±0.34, t=2.45, P<0.05), and the difference in other dosimetric parameters between the GBPO plans and the IPSA plans was not statistically significant ( P>0.05). Conclusions:The method reported in this study to control the dwell time variation was feasible. The GBPO plans have a comparable quality as the IPSA plans for the studied cervical cancer cases. The GBPO algorithm could be integrated into a three-dimensional brachytherapy treatment planning system.