Dosimetric comparison for Volumetric Modulated Arc Therapy and Intensity-Modulated Radiotherapy on the Left-sided Chest Wall and Internal Mammary Nodes Irradiation in Treating Post-mastectomy Breast Cancer

Abstract

Background: Toevaluate the dosimetric benefit of applyingvolumetric modulated arc therapy (VMAT) on the post-mastectomy left-sidedbreast cancer patients, with the involvement of internal mammarynodes. Methods: The prescription dose was 50 Gy delivered in 25fractions, and the clinical target volume included the left chest wall (CW) andIMN. VMAT plans were created and compared with IMRT plans on Pinnacle treatmentplanning system. Comparative endpoints were dose homogeneity within planningtarget volume (PTV), target dose coverage, doses to the critical structures including heart, lungs and thecontralateral breast, number of monitor units and treatment delivery time.Results: VMATand IMRT plans showed similar PTV dose homogeneity, BUT VMAT provided a better dosecoverage for IMN than IMRT(p=0.017). The mean dose (Gy), V30 (%) and V10 (%) for the heart were 13.5±5.0 Gy,9.9%±5.9% and 50.2%±29.0% byVMAT, and 14.0±5.4 Gy, 10.6%±5.8% and 55.7%±29.6% by IMRT, respectively. The left lung mean dose (Gy), V20(%), V10 (%) and the right lung V5 (%) were significantlyreduced from 14.1±2.3 Gy, 24.2%±5.9%, 42.4%±11.9% and 41.2%±12.3% with IMRT to12.8±1.9 Gy, 21.0%±3.8%, 37.1%±8.4% and 32.1%±18.2% with VMAT. The mean dose tothe contralateral breast was 1.7±1.2 Gy with VMAT and 2.3±1.6 Gy with IMRT. Finally,VMAT reduced the number of monitor units by 24% and the treatment timeby 53%, as compared to IMRT.Conclusions: Compared to 5-beamstep-and-shot IMRT, VMATachieves similar or superior target coverage and a better normal tissuesparing, with fewer monitor units and shorter delivery time.