A preliminary study of template library-based auto-planning of volume modulated arc therapy

Abstract

Objective To explore the feasibility of the volume modulated arc therapy (VMAT) auto-planning based on template library (TL). Methods VMAT plans of 68 patients diagnosed with postoperative rectal cancer in Eclipse system were retrospectively selected. The prescription dose was 50 Gy/25F. In 19 patients, the feature values of target and organs at risk were extracted as the vectors. The final optimized restricted conditions were saved as the TL. Then, the plans of 15 rectal cancer patients (10 cases from TL and 5 outside TL) were automatically optimized. According to the multi-dimensional vector similarity principle, the similarity parameter αwas defined. The designed program automatically selected the optimal-object template in an in-house software developed with Matlab. The dosimetric parameters of the auto-optimized plans with the optimal-object template (ATP) and the clinical plan (CP) were compared by the paired t-test. The changes in the dosimetric parameters and similarity parameter α were statistically compared by Pearson′s correlation analysis. The linear fitting of the dosimetric parameters with α was used by least squares method to explore the tendency of the ATP dosimetric parameters relative to CP. Results The dosimetric parameters of ATP for 13 cases were slightly worse than those of CP. The conformal index (P=0.004), heterogeneous index (P=0.015), V40(P=0.003) and mean dose (P=0.022) of the intestine significantly differed. The α values of these 13 cases were 2.67, 2.60, 2.60, 2.49, 2.67, 2.74, 2.72, 2.48, 2.53, 2.86, 2.68, 2.56 and 2.63. The α value was significantly correlated with the V40 or mean dose of the bladder (r=0.649 and 0.603, P=0.016 and 0.029). Along with the increase of α value, V40 and mean dose of the intestine for ATP were gradually deteriorated than those of CP. The remaining dosimetric para-meters of ATP were close to or superior to those of CP. Conclusions The results of ATP are slightly worse than those of CP, whereas can satisfy the clinical requirements. The TL, the quality of TL and ATP remain to be further optimized. Key words: Radiotherapy; Template library; Auto-optimize; Volume modulated arc therapy plan