Author: Bingqi Guo, Ping Xia 👨🔬
Affiliation: Cleveland Clinic 🌍
Purpose:
Spatially fractionated radiation therapy (SFRT) delivers a “GRID” or “lattice” of high and low doses to tumors to increase tumor control, minimize normal tissue damage, and preserve the immune function of the tumor microenvironment (TME). However, the arbitrary grid/lattice dose pattern does not agree with the tumor heterogeneity caused by hypoxia. This study proposes a partial tumor irradiation (PTI) strategy based on functional MRI and compares PTI with lattice SFRT for tumor hypoxia-corrected equivalent uniform dose (EUD), and effective dose to TME.
Methods:
Ten glioblastoma patients from the QIN-BRAIN-DSC-MRI dataset of the cancer imaging archive were selected. For each patient, the gross tumor volume (GTV), critical structures, and TME (5 mm rim of tissue surrounding GTV) were delineated, and cerebral blood perfusion (CBF) was derived from the dynamic susceptibility contrast MRI. A lattice plan was developed by inserting 2-5 spheres with 1.3cm diameter in the GTV and prescribing 18 Gy in 1 fraction to >=50% of each sphere. The PTI plan prescribed 10 Gy in 1 fraction to hypoxic GTV (sub volume of GTV with CBF < mean) while reducing the dose to TME with high CBF. Non-coplanar VMAT technique was used for all plans. For plan evaluation, hypoxia-corrected EUD was calculated using a modified linear-quadratic model incorporating oxygen enhancement ratio derived from CBF. TME effective dose was defined as the perfusion-weighted mean dose to TME.
Results:
Compared with lattice, PTI increased hypoxia-corrected EUD (4.51 +/- 0.54 Gy vs 3.98 +/- 0.50, p=0.003) and reduced TME effective dose (3.42 +/- 0.52 Gy vs 3.70 +/- 0.62 Gy, p=0.012). Maximal doses to critical structures and mean dose to the brain were comparable between PTI and lattice.
Conclusion: Functional MRI guided PTI improves EUD for hypoxic tumors and reduces the effective dose to tumor microenvironment.