While the prevalence of central bronchial tumours is declining, that of peripheral lung tumours is increasing. Peripheral lung tumours present either as individual index lesion or as field cancerization, requiring for the former targeting of particular confined volumes of lung tissue versus a therapy for an entire lung or particular lobes thereof. Using FullMonte, a Monte Carlo code; the ability to achieve a tumour selective PDT by transbronchial light source placement was simulated for 525, 665 and 808 nm wavelength. Simulations were executed utilizing in silica models with up to 10 generations of the bronchial tree, tissue photosensitizer concentrations taken from literature or measure in preclinical model systems and tissue optical properties measured with alive ex vivo pig and human lungs perfused with either blood or a transparent low cellular (STEEN) fluid.
The measured effective attenuation coefficients [cm-1] at the three wavelengths for ventilated lungs with either blood 1.26±1.07, 1.93±0.534, 1.09±0.93 or STEEN fluid 1.01±0.873, 0.901±0.318, 0.641±0.31 used as perfusate. When modelling the PDT dose distribution in the lung’s the bronchial air ducts up to the eight generations perturb the fluence considerably.
In all simulations, a dose sufficient to cause necrosis in 98% of the target volume placement of 3 source fibres albeit with various extent of normal lung tumour damage. Full coverage of an entire lung lobe with only three source fibres placed does not provide for effective coverage of the diffuse disease unless a very high selective uptake of the photosensitizer in malignant tissues can be achieved.
The utility to perform treatment planning for transbronchial light delivery is investigated using Monte Carlo simulations. Optical properties of pig and human lungs were determined, and dose volume histograms determined. These dose volume histograms indicate for example the minimum photosensitizer specific uptake ratio required to achieve selective tumour destruction.
Background: The majority of de novo cancers are diagnosed in low and middle-income countries, which often lack the resources to provide adequate therapeutic options. None or minimally invasive therapies such as Photodynamic Therapy (PDT) or photothermal therapies could become part of the overall treatment options in these countries. However, widespread acceptance is hindered by the current empirical training of surgeons in these optical techniques and a lack of easily usable treatment optimizing tools. Methods: Based on image processing programs, ITK-SNAP, and the publicly available FullMonte light propagation software, a work plan is proposed that allows for personalized PDT treatment planning. Starting with, contoured clinical CT or MRI images, the generation of 3D tetrahedral models in silico, execution of the Monte Carlo simulation and presentation of the 3D fluence rate, Φ, [mWcm-2] distribution a treatment plan optimizing photon source placement is developed. Results: Permitting 1-2 days for the installation of the required programs, novices can generate their first fluence, H [Jcm-2] or Φ distribution in a matter of hours. This is reduced to 10th of minutes with some training. Executing the photon simulation calculations is rapid and not the performance limiting process. Largest sources of errors are uncertainties in the contouring and unknown tissue optical properties. Conclusions: The presented FullMonte simulation is the fastest tetrahedral based photon propagation program and provides the basis for PDT treatment planning processes, enabling a faster proliferation of low cost, minimal invasive personalized cancer therapies.
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