Fig. 2

Examples of dose conversions for two patients treated with re-RT. a Example of physical dose to BED₃ conversion for a 61-year-old patient treated with 50 Gy in 4 fractions to a right lower lobe T1N0 NSCLC lesion in 2007. The patient did well for three years but then experienced isolated local recurrence in the same lobe. He was treated to this nearby area using 50 Gy in 4 fractions. The figure depicts how the nominal doses in Gy for each of this patient’s individual plans were separately converted to their corresponding BED₃ values. In this conversion, the patient’s two plans each had 2.5 mm³ voxels converted to corresponding BED₃ values. This voxel-by-voxel conversion enabled an accurate anatomic and volumetric depiction of BED dose throughout the plans and organs at risk. The two plans were then summed to generate a BED composite, shown here. The patient developed symptomatic right rib fracture, correlated with BED₃ of 100 Gy but less than 50 Gy by simple summation of the physical dose. The patient also developed shortness of breath requiring supplemental oxygen that may have been precipitated by RLL collapse, correlated with BED₃ > 100 Gy in the right bronchial tree. b Example of physical dose to BED₃ conversion for a patient who underwent SABR followed by IMRT. This 77-year-old patient received 50 Gy in 4 fractions for left upper lobe Stage I NSCLC, and 6 months later developed left hilar and mediastinal nodal recurrence which was treated with concurrent chemoradiotherapy to 60 Gy in 30 fractions with simultaneous integrated boost of gross disease to 66 Gy. The patient developed partial collapse of the left lower lobe and episodes of pneumonia, requiring supplemental oxygen. The damage to the left lower lobe tertiary bronchial tree is correlated with a BED₃ dose sum of 200 Gy, but less than 70 Gy by simple summation of the nominal doses