Clinical Investigations Radiobiologically based treatment plan evaluation for prostate seed implants

Abstract

PurposeAccurate prostate low dose-rate brachytherapy treatment plan evaluation is important for future care decisions. Presently, an evaluation is based on dosimetric quantifiers for the tumor and organs at risk. However, these do not account for effects of varying dose-rate, tumor repopulation and other biological effects. In this work, incorporation of the biological response is used to obtain more clinically relevant treatment plan evaluation.Material and methodsEleven patients were evaluated. Each patient received a 145 Gy implant. Iodine-125 seeds were used and the treatment plans were created on the Prowess system. Based on CT images the post-implant plan was created. In the post-plan, the tumor, urethra, bladder and rectum were contoured. The biologically effective dose was used to determine the tumor control probability and the normal tissue complication probabilities for the urethra, bladder, rectum and surrounding tissue.ResultsThe average tumor control probability and complication probabilities for the urethra, bladder, rectum and surrounding tissue were 99%, 29%, 0%, 12% and 6%, respectively. These measures provide a simpler means for evaluation and since they include radiobiological factors, they provide more reliable estimation of the treatment outcome. ConclusionsThe goal of this work was to create more clinically relevant prostate seed-implant evaluation by incorporating radiobiological measures. This resulted in a simpler descriptor of treatment plan quality and was consistent with patient outcomes.

AAPM Task Group Report 267: A joint AAPM GEC‐ESTRO report on biophysical models and tools for the planning and evaluation of brachytherapy

“…Radiobiological topics investigated in the literature for LDR prostate brachytherapy include, but are not limited to, basic feature elucidation 29,31 ; impact of tumor shrinkage 102 ; effects of dose heterogeneity 103,104 ; RBE of different radionuclides 105 ; prescription dose for newer sources 106,108 ; optimal decay half -lives 109 ; effects of mixing sources with different decay halflives 110 ; effects of prostate edema [111][112][113][114] ; dose escalation considerations 115 ; effects of combining prostate brachytherapy with EBRT 116 ; comparison of the RE of LDR and HDR 117 ; modeling of dose-gradient effects in brachytherapy 118 ; use of BED as an implant quality index for a 125 I implant dose response study 119 ; tumor control consequences of seed loss and migration 132 ; probabilities of tumor control 232 and long-term normal tissue complications 219,233 ; optimization of LDR brachytherapy considering a nonuniform distribution of tumor cell density through the prostate tissue 234 ; inverse planning 234 ; treatment plan evaluation 235 ; search for radiobiological and dosimetric predictors of biochemical control 236 ; influence of tumor cell repopulation 179 ; investigation of optimal brachytherapy protraction schemes 180 ; investigation of the role of tumor radiosensitivity, clonogenic repopulation, tumor shrinkage, and radionuclide RBE in LDR prostate brachytherapy 231 ; evaluation of NTCP of the rectum, bladder, urethra, and femoral heads 39 ; and estimation of the α/β value. 180 Readers can consult the original articles for details on the applications of biophysical models to specific ...…”