Treatment Planning Methods in High Dose Rate Interstitial Brachytherapy of Carcinoma Cervix: A Dosimetric and Radiobiological Analysis

Abstract

Treatment planning is a trial and error process that determines optimal dwell times, dose distribution, and loading pattern for high dose rate brachytherapy. Planning systems offer a number of dose calculation methods to either normalize or optimize the radiation dose. Each method has its own characteristics for achieving therapeutic dose to mitigate cancer growth without harming contiguous normal tissues. Our aim is to propose the best suited method for planning interstitial brachytherapy. 40 cervical cancer patients were randomly selected and 5 planning methods were iterated. Graphical optimization was compared with implant geometry and dose point normalization/optimization techniques using dosimetrical and radiobiological plan quality indices retrospectively. Mean tumor control probability was similar in all the methods with no statistical significance. Mean normal tissue complication probability for bladder and rectum is 0.3252 and 0.3126 (P = 0.0001), respectively, in graphical optimized plans compared to other methods. There was no significant correlation found between Conformity Index and tumor control probability when the plans were ranked according to Pearson product moment method (r = −0.120). Graphical optimization can result in maximum sparing of normal tissues.

Dosimetric and radiobiological evaluation of treatment plan for cervical cancer high-dose-rate intracavitary brachytherapy

“…In this study, it was assumed that the time interval between the fractions was sufficient to allow the full repair of sub-lethal damage, therefore G was considered as 1. The values of ρ and α were assumed to be constant throughout the target volume (ρ = 10 7 cells/cc, and α = 0.35 Gy -1 ) in the present study, which was also assumed in previous studies in the literature [ 13 , 20 ]. The assumption of constant ρ throughout HR-CTV could not be expressed due to lack of MRI-based planning.…”

Robustness of IPSA optimized high-dose-rate prostate brachytherapy treatment plans to catheter displacements

“…where V T,1.5ref is the volume of the PTV receiving a dose greater than or equal to the 150% isodose, and V T,ref is as described above. Finally, the ODI parameter [ 17 ] indicates the amount of high dose (greater than 200%) within the PTV: …”

Dosimetric comparison of volume-based and inverse planning simulated annealing–based dose optimizations for high–dose rate brachytherapy

“…ODI 11 is the ratio of the target volume that receives a dose equal to or more than twice the reference dose. [11][12][13][14] is defined as the ratio of high-dose volume relative to the reference volume. DNR is used to evaluate the quality of the plan.…”