On the Use of Hyperpolarized Helium MRI for Conformal Avoidance Lung Radiotherapy

Department of Human Oncology, University of Wisconsin, Madison, 53792, USA.
Medical dosimetry: official journal of the American Association of Medical Dosimetrists (Impact Factor: 0.76). 10/2009; 35(4):297-303. DOI: 10.1016/j.meddos.2009.09.004
Source: PubMed


We wanted to illustrate the feasibility of using hyperpolarized helium magnetic resonance imaging (HPH-MRI) to obtain functional information that may assist in improving conformal avoidance of ventilating lung tissue during thoracic radiotherapy. HPH-MRI images were obtained from a volunteer patient and were first fused with a proton density-weighted (PD(w)) MRI to provide corresponding anatomic detail; they were then fused with the treatment planning computed tomography scan of a patient from our treatment planning database who possessed equivalent thoracic dimensions. An optimized treatment plan was then generated using the TomoTherapy treatment planning system, designating the HPH-enhancing regions as ventilation volume (VV). A dose-volume histogram compares the dosimetry of the lungs as a paired organ, the VV, and the lungs minus the VV. The clinical consequences of these changes was estimated using a bio-effect model, the parallel architecture model, or the local damage (f(dam)) model. Model parameters were chosen from published studies linking the incidence of grade 3+ pneumonitis, with the dose and volume irradiated. For two hypothetical treatment plans of 60 Gy in 30 fractions delivered to a right upper-lobe lung mass, one using and one ignoring the VV as an avoidance structure, the mean normalized total dose (NTD(mean)) values for the lung subvolumes were: lungs = 12.5 Gy₃ vs. 13.52 Gy₃, VV = 9.94 Gy₃ vs. 13.95 Gy₃, and lungs minus VV = 16.69 Gy₃ vs. 19.16 Gy₃. Using the f(dam) values generated from these plans, one would predict a reduction of the incidence of grade 3+ radiation pneumonitis from 12%-4% when compared with a conventionally optimized plan. The use of HPH-MRI to identify ventilated lung subvolumes is feasible and has the potential to be incorporated into conformal avoidance treatment planning paradigms. A prospective clinical study evaluating this imaging technique is being developed.

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Available from: Minesh P Mehta
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    • "Pulmonary functional imaging methods such as single photon emission computed tomography (SPECT) [5] [6], 4DCT [7] [8] and inhaled gas magnetic resonance imaging (MRI) [9] [10], have been previously incorporated in functional imaging lung avoidance schemes, but this approach is not currently the standard clinical practice. The feasibility of function-based intensity modulated radiation therapy (IMRT) treatment planning [5] [6] [9], has been demonstrated, in addition to measurements of lung function before and after radiation treatment [7] [11]. Importantly , when functional imaging was used to guide therapy in radiation planning studies, dose reductions to functioning lung were achievable [6] [10]. "
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    • "In order to rectify the bias, we are planning to improve the registration accuracy by adopting the deformable algorithm that can preserve radiation-induced changes while correcting for different breathing phases. Apart from expanding the dataset, we are also looking into applying this method to other imaging modalities such as single-photon emission computed tomography (SPECT) or hyperpolarized magnetic resonance imaging (MRI) (Hodge et al 2010) to complement the limitations of CT to anatomical representation with functional information. We have not tested the applicability of the model to SBRT-induced toxicity. "
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