Three-dimensional Conformal Radiation Planning Study for Limited-stage Small-cell Lung Cancer

To carry out a preliminary study to evaluate the dose distribution variation between the analytical anisotropic algorithm (AAA) and the Boltzmann transport equation, and between point and volume prescriptions in three-dimensional conformal radiation for limited-stage small-cell lung cancer.

We retrospectively selected patients with limited-stage small-cell lung cancer who received radiotherapy alone or chemoradiotherapy. Gross tumor volume (GTV), clinical target volume (CTV), and planning target volume (PTV) were evaluated. Dose evaluation was performed for PTV, with AAA as point prescription, AAA as 50% prescription of PTV, Boltzmann transport equation as point prescription, and Boltzmann transport equation as 50% prescription of PTV.

A total of 22 patients (15 males, 7 females; mean age=63.4 years) were included. The mean radiation doses for AAA/point AAA/D50, Boltzmann transport/point, and Boltzmann transport/D50 methods were 99.97±1.5%, 102.1±1.2%, 100.8±1.2%, and 101.3±1.3% to the GTV; 98.4±2.1%, 100.4±0.5%, 99.6±1.9%, 100.1±1.0% to the CTV; and 96.7±2.5%, 97.4±4.6%, 97.6±2.3%, 98.3±0.8% to the PTV, respectively. For AAA/point, AAA/D50, Boltzmann transport/point, and Boltzmann transport/D50 prescription methods, the correlation between the GTV (102.5±107.8 ml) and mean dose to the GTV was 0.23 (p=0.4), -0.476 (p=0.04), 0.00 (p=0.97), -0.79 (p<0.01); between CTV (342.7±242.6 ml) and mean dose to the CTV were 0.52 (p<0.01), -0.68 (p<0.01), 0.35 (p=015), -0.50 (p=0.03); between PTV (514.7±306.0 ml) and mean dose to the PTV were 0.59 (p<0.01) 0.75 (p<0.01),0.82 (p<0.01) and 0.78 (p<0.01), respectively.

The AAA point-prescription approach can systematically underestimate target dose in 3D conformal radiotherapy for limited-stage small-cell lung cancer and shows less robust dose-volume behavior across GTV, CTV, and PTV compared with volume-based prescription and Boltzmann transport calculations. Therefore, AAA with point prescription should be avoided for dose calculation in this setting.