Proton-Based Stereotactic Ablative Radiotherapy in Early-Stage Non-Small-Cell Lung Cancer

Figure 2

Radiation treatment plan illustrating the dosimetric benefits of proton therapy in a patient with tumor near critical central structures. Prescribed tumor dose is 50 GyE in 4 fractions, with isodose line numbers displayed in units of cGyE. Significant radiation sparing of the aorta, esophagus, and lung is achieved due to the steep dose falloff of protons, while achieving appropriate target coverage for tumor cell kill. Beam angles are selected to traverse a minimal amount of lung tissue. Range differences based on the density heterogeneity of tissue traversed can be appreciated at the anterior aspect of the plan, where a peak of dose is deposited in normal lung. Careful attention must be paid to these dose variations and areas of range uncertainty such that dose tolerance of critical structures is not exceeded.