Optimization of brachytherapy for cervical cancer using inverse planning algorithms

Sammanfattning: Carcinoma of the cervix is a global problem. Brachytherapy (BT) is one of the mainradiation therapy components used in the management of cervical cancer. With theadvent of scientific and technological developments in treatment planning, inverse optimizationin BT has been imposed; however, to harness the full potential of inverseplanning in brachytherapy, its thorough comparison with manual optimization methodsis warranted.Although inverse optimization algorithms are based on different mathematical approaches,their goals are similar. The underlying principles of these algorithms willallow them to be applied with the aim of respecting normal structures absorbed doselimits while delivering high enough tumouricidal dose.In this work, the physical parameters minimum dose received by 98% and 90% ofthe target volume represented by D98 and D90, respectively, were used to evaluate thetreatment plans with respect to the target while the minimum dose received by 2cm3volume, D2cm3 , was used to investigate complications in organs at risk (OARs). Theconformity index (COIN), was used to describe the coverage of the target by the prescribeddose (PD) and the fraction of each OAR volume that receives a critical dose,which may cause complication. The treatment plan evaluation was also performedin terms of the complication-free tumour control probability, P+. The physical andradiobiological evaluation corresponding to plans obtained by the inverse planningsimulated annealing algorithm (IPSA) and the hybrid inverse planning optimization(HIPO) have been compared with corresponding ones for plans obtained using a manualgraphical optimization method.The main observations of this work are that well tuned class solutions of inverseoptimization methods are able to produce similar dose volume histograms to thoseproduced with manual graphical optimization and inverse methods have the potentialto spare organs at risk while delivering acceptable dose to the target. In addition, radiobiologicalindexes such as the P+ can be useful complements to physical parametersin treatment plan evaluation.