Dosimetric evaluation of the multi-shell simultaneous integrated boost volumetric modulated arc therapy for safe and effective dose escalation in lung cancer radiotherapy treatment

This study investigates the feasibility of multi-shell SIB-VMAT for escalating radiation doses in lung tumors while minimizing damage to healthy tissues, addressing challenges of tumor resistance and collateral damage in conventional treatment strategies. Twenty patients with locally advanced lung cancer, previously treated with radiotherapy to the primary tumor and involved lymph nodes, were retrospectively analyzed. An internal gross target volume (iGTV) was created with a 5–8 mm margin around the GTV, and the planning target volume (PTV) included additional margins for setup uncertainties and respiratory motion. Four concentric ring-shaped shells were added around the iGTV for dose escalation. Three VMAT plans were developed: VMAT60, VMAT66 and VMAT72. Plan quality was evaluated using dose–volume histograms, homogeneity index (HI), and conformity index (CI). HI comparisons showed significant differences between VMAT60-VMAT72 and VMAT66-VMAT72 (p ≤ 0.01), except VMAT66-VMAT72 (p = 0.055). CI decreased with dose escalation, significant between VMAT60-VMAT72 (p ≤ 0.01) and VMAT66-VMAT72 (p = 0.001), but not VMAT60-VMAT66 (p = 0.10). Lung dosimetry was similar, though VMAT66 increased V10 vs. VMAT60 (p = 0.030). VMAT66 increased mean heart dose (p = 0.021) but no differences in heart V25, V45, or VMAT72. VMAT66 slightly increased spinal cord dose; VMAT72 was lower, both nonsignificant. VMAT66 increased mean esophageal dose (p = 0.013); max dose and VMAT72 differences were nonsignificant. The multi-shell SIB-VMAT strategy appears feasible and promising for lung tumor treatment by escalating doses to specific tumor regions while sparing healthy tissues.