Dosimetric benefits of robust treatment planning for intensity modulated proton therapy for base-of-skull cancers

Abstract

Purpose The clinical advantage of intensity modulated proton therapy (IMPT) may be diminished by range and patient setup uncertainties. We evaluated the effectiveness of robust optimization that incorporates uncertainties into the treatment planning optimization algorithm for treatment of base of skull cancers. Methods and materials We compared 2 IMPT planning methods for 10 patients with base of skull chordomas and chondrosarcomas: (1) conventional optimization, in which uncertainties are dealt with by creating a planning target volume (PTV); and (2) robust optimization, in which uncertainties are dealt with by optimizing individual spot weights without a PTV. We calculated root-mean-square deviation doses (RMSDs) for every voxel to generate RMSD volume histograms (RVHs). The area under the RVH curve was used for relative comparison of the 2 methods’ plan robustness. Potential benefits of robust planning, in terms of target dose coverage and homogeneity and sparing of organs at risk (OARs) were evaluated using established clinical metrics. Then the plan evaluation metrics were averaged and compared with 2-sided paired t tests. The impact of tumor volume on the effectiveness of robust optimization was also analyzed. Results Relative to conventionally optimized plans, robustly optimized plans were less sensitive for both targets and OARs. In the nominal scenario, robust and conventional optimization resulted in similar D95% doses (D95% clinical target volume [CTV]: 63.3 and 64.8 Gy relative biologic effectiveness [RBE]), P <.01]) and D5%-D95% (D5%-D95% CTV: 8.0 and 7.1 Gy[RBE], [P < .01); irradiation of OARs was less with robust optimization (brainstem V60: 0.076 vs 0.26 cm3 [P <.01], left temporal lobe V70: 0.22 vs 0.41 cm3, [P = .068], right temporal lobe V70: 0.016 vs 0.11 cm3, [P = .096], left cochlea Dmean: 28.1 vs 30.1 Gy[RBE], [P = .023], right cochlea Dmean: 23.7 vs 25.2 Gy [RBE], [P = .059]). Results in the worst-case scenario were analogous. Conclusions Robust optimization is effective for creating clinically feasible IMPT plans for tumors of the base of skull.

Technique for comprehensive head and neck irradiation using 3-dimensional conformal proton therapy

“…However, our technique of 3D conformal proton therapy with uniform scanning has some advantages when compared with multifield optimization, including being a well-established delivery system that is less susceptible to patient setup and range uncertainties or small misalignments in the proton beam, and has simpler quality assurance. 13,38 Conclusions A technique for cervical nodal irradiation using 3D conformal proton therapy with uniform scanning was developed and clinically implemented. Use of proton therapy for cervical nodal irradiation resulted in large volume of dose avoidance to the oral cavity and low dose exposure to midline structures of the larynx and the esophagus, with lower mean and integral dose to assessed OARs when compared with competing IMRT plans.…”

Redefine the role of range shifter in treating bilateral head and neck cancer in the era of Intensity Modulated Proton Therapy

“…Dosimetric quality of each plan was evaluated via organ‐at‐risks (OARs) dose volume histogram, target conformity (CI) and target volume homogeneity indexes (HI) based on the Radiation Therapy Oncology Group (RTOG) recommendations. The plan robustness was evaluated using the root‐mean‐square deviation doses (RMSDs) 12. In this study, RMSDs of the 21 scenarios (with ±3.5% range uncertainties, and setup uncertainties of ±3 mm for x,y,z directions) were calculated for every voxel.…”

“…In this study, RMSDs of the 21 scenarios (with ±3.5% range uncertainties, and setup uncertainties of ±3 mm for x,y,z directions) were calculated for every voxel. The area under the RMSD volume histograms (RVHs) curve (AUC) indicates the plan robustness 12. This concept is to quantitatively evaluate the plan robustness in the presence of setup and range uncertainties.…”

The role of image-guided intensity modulated proton therapy in glioma

“…Robustly optimized IMPT has been shown to make dose distributions not only more robust, but more homogeneous and conformal compared with the conventional IMPT optimization. 2,3,7 Reduction in uncertainties is also being achieved through the increasing use of volumetric imaging in treatment rooms that allows for more accurate image-guided setups, the use of dual-energy CT for characterizing tissues, and Monte Carlo techniques for calculation of proton dose distributions. Other areas of investigation to reduce uncertainties in proton therapy are PET and prompt gamma imaging (PGI) for the accurate determination of range of protons in vivo.…”