Dose Distribution Analysis in Stereotactic Body Radiotherapy Using Dynamic Conformal Multiple Arc Therapy

Purpose We have used dynamic conformal multiple arc therapy (DCMAT) for stereotactic body radiotherapy (SBRT) since 2001. We investigated the consistency of DCMAT for SBRT using dose–volume histogram analysis. Methods and Materials A total of 50 patients with peripheral lung tumors underwent SBRT. The median tumor diameter was 2.4 cm (range, 0.9–5.9). Treatment planning was performed using a superposition algorithm. The prescribed 50 Gy dose was divided into five fractions. The prescribed dose was defined as 80% of the maximal dose in the planning target volume (PTV), and the leaf margins were modified to ensure the PTV was included in the 80% isodose surface. The dose–volume histogram analysis was used to assess the PTV and normal lung volume. Results The median dose covering 95% of the PTV was 50.27 Gy (range, 46.14–52.67), essentially consistent with the prescribed dose. The median homogeneity and conformity index was 1.41 (range, 1.31–1.53) and 1.73 (range, 1.41–2.21), respectively. The median volume of lung receiving ≥20 Gy (V20 ) was 4.2% (range, 1.4–10.2%). A linear correlation was found between the tumor diameter and V20 , and an even stronger correlation was found between the PTV/(normal lung volume) and V20 . The estimated V20 was 7.1% (range, 3.9–10.4%) for a 5-cm-diameter tumor, assumed to be the maximal size limitation for SBRT. Conclusion SBRT with DCMAT achieved high conformity and delivered adequate doses within the PTV. The median dose covering 95% of the PTV was consistent with the prescribed dose. V20 can be estimated using the tumor diameter and normal lung volume. DCMAT was thus both a feasible and a reproducible method of SBRT delivery.