A radiobiology-based inverse treatment planning method for optimisation of permanent l-125 prostate implants in focal brachytherapy

Abstract

Treatment plans for ten patients, initially treated with a conventional approach to low dose-rate brachytherapy (LDR, 145 Gy to entire prostate), were compared with plans for the same patients created with an inverse-optimisation planning process utilising a biologically-based objective. The 'biological optimisation' considered a non-uniform distribution of tumour cell density through the prostate based on known and expected locations of the tumour. Using dose planning-objectives derived from our previous biological-model validation study, the volume of the urethra receiving 125% of the conventional prescription (145 Gy) was reduced from a median value of 64% to less than 8% whilst maintaining high values of TCP. On average, the number of planned seeds was reduced from 85 to less than 75. The robustness of plans to random seed displacements needs to be carefully considered when using contemporary seed placement techniques. We conclude that an inverse planning approach to LDR treatments, based on a biological objective, has the potential to maintain high rates of tumour control whilst minimising dose to healthy tissue. In future, the radiobiological model will be informed using multi-parametric MRI to provide a personalised medicine approach.

Progress towards Patient-Specific, Spatially-Continuous Radiobiological Dose Prescription and Planning in Prostate Cancer IMRT: An Overview

“…More sophisticated intra-tumour biology was modeled for Betts et al and Haworth et al [55][56][57], where they used location-dependent cell density distributions to drive biological optimisation of prostate low-dose-rate brachytherapy. The prostate was divided into the apex, mid, and base segments where each was further divided into four quadrants.…”

“…One such approach proposed by Haworth et al is called the biofocused radiotherapy (BiRT) [57,75]. The BiRT approach utilises machine learning methods to generate voxel maps of tumour biology information from imaging data, which is then used in the calculation of a parameterised voxel-level TCP objective for plan optimisation.…”

Hybrid optimization based on non-coplanar needles for brachytherapy dose planning

“…To better evaluate the proposed method in this research, we compared the result of malignant tumor of spine case with existing algorithms [14,34,35,36,37]. Most of the current inverse optimization algorithms were developed for prostate cancer.…”

“…D'Souza et al used a mixed-integer linear programming and a branch-andbound algorithm to generate treatment plans [14]. An inverse optimization planning process utilizing a biologically-based objective was proposed [34]. The IPSA inverse planning algorithm was modified to include multiple dose matrices for the calculation of dose from different sources, and a selection algorithm was implemented to allow for the swapping of source type at any given source position [35].…”

Determining optimal eluter design by modeling physical dose enhancement in brachytherapy

“…26,27 Additional models that are related to the EUD or to biological outcome such as tumor control probability and normal tissue complication probabilities are in use. 28,29 The different models try to quantify the expected outcome of the treatment but on different levels of complexity and are interchangeable. In general, the effect is linked to the enhanced dose distribution delivered to the various anatomic structures.…”