On the use of hyperpolarized helium MRI for conformal avoidance lung radiotherapy

• Published in: Medical dosimetry : official journal of the American Association of Medical Dosimetrists Vol. 35; no. 4; p. 297
• Main Authors: Hodge, C W, Tomé, Wolfgang A, Fain, S B, Bentzen, S M, Mehta, M P
• Format: Journal Article
• Language: English
• Published: United States 2010
• Subjects: Helium; Humans; Isotopes; Lung - pathology; Lung Injury - etiology; Lung Injury - prevention & control; Magnetic Resonance Imaging - methods; Pulmonary Gas Exchange; Radiation Injuries - etiology; Radiation Injuries - prevention & control; Radiation Protection; Radiopharmaceuticals; Radiotherapy, Conformal - adverse effects; Radiotherapy, Conformal - methods; Reproducibility of Results; Sensitivity and Specificity
• ISSN: 1873-4022
• DOI: 10.1016/j.meddos.2009.09.004

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.