Monte Carlo (MC)-based volumetric modulated arc therapy (VMAT) in locally advanced esophageal cancer with potential for dose escalation.

Abstract

77 Background: Previous attempts at dose escalation in esophagus radiotherapy (RT), mostly based on older planning techniques, have not shown improved outcomes. We aimed to investigate the importance of newer, sophisticated dose algorithms and treatment techniques in escalating target dose and reducing dose to organs at risk (OAR). Methods: Treatment plans for 10 patients were retrospectively evaluated using 3D conformal radiotherapy (3DCRT), MC based intensity modulated radiotherapy (IMRT), and VMAT. Prescription dose was 45 Gy to the planning target volume (PTV) in 25 fractions followed by a 5.4 Gy boost in 3 fractions. PTV (mean±s.d. = 681±236 cc) were planned with BrainLab iPlan 4.1 software as IMRT and VMAT. Dose distributions were calculated with both pencil beam (PB) and MC algorithms. Each PTV was normalized to receive at least 95% of 50.4 Gy or 60 Gy dose. OARs were evaluated as per RTOG1010 dose guidelines. Paired t-tests were used for statistical analysis. Results: IMRT vs. 3DCRT PTV 50.4 Gy: IMRT plans decreased heart and lung average Dmean by 4.7 Gy (p = 0.053) and 1.9 Gy (p = 0.001) respectively when compared to 3DCRT. In addition, average values of lung V5, V10, and V30 also reduced by 7.1%, 5.5%, and 3.6% respectively (p < 0.05). There was a 12.1% decrease in heart V40 (p=0.053) and 3.7% reduction in liver V30 (p=0.08). PTV 60Gy: IMRT plans at 60 Gy led to lower OAR doses compared to 3DCRT at 50.4 Gy. MC based IMRT results did not significantly differ from PB, with the exception of lung V5 which was 4.4% higher (p <0.001). VMAT vs. IMRT PTV 50.4 Gy: VMAT based planning, compared to IMRT, lowered V20 (3.4%, p=0.029), V30 (1.6%, p = 0.013), and spinal cord Dmax (5.4 Gy, p = 0.001). However, lung Dmean, V5, and V10 increased by 1.2 Gy, 11.7%, 16.7% respectively (p < 0.001). PTV 60 Gy: With VMAT planning, all OAR dose parameters were within the RTOG 1010 limits, although lung V5 and V10 exceeded acceptable limits by 1.6% and 2.6% respectively. Conclusions: Compared to 3DCRT, target dose escalation with IMRT and VMAT is possible with improved OAR dose sparing, as evaluated with MC algorithms. Increased dose values for V5 and V10 as seen in MC based VMAT plans call for reassessment of RTOG 1010 guidelines.