On the use of hyperpolarized helium MRI for conformal avoidance lung radiotherapy.
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.
Hodge
C W
CW
Department of Human Oncology, University of Wisconsin, Madison, 53792, USA.
Tomé
Wolfgang A
WA
Fain
S B
SB
Bentzen
S M
SM
Mehta
M P
MP
D006371:Helium; D006801:Humans; D007554:Isotopes; D008168:Lung / Q000473:pathology*; D055370:Lung Injury / Q000209:etiology / Q000517:prevention & control*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D011659:Pulmonary Gas Exchange; D011832:Radiation Injuries / Q000209:etiology / Q000517:prevention & control*; D011835:Radiation Protection; D019275:Radiopharmaceuticals; D020266:Radiotherapy, Conformal / Q000009:adverse effects / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D007554:Isotopes; D019275:Radiopharmaceuticals; D006371:Helium