Volumetric modulated arc therapy versus conformal radiation therapy for conditioning of allogenic bone marrow transplantation (ABMT) in acute lymphoblastic leukemia.

Abstract

e18532 Background: Total body irradiation is performed as part of the conditioning regimen for patients eligible for ABMT. New techniques have been investigated to target more selectively of total medular irradiation. Purpose:In this study a preclinical investigation was undertaken to explore a treatment technique for total marrow irradiation using a volumetric modulated arc technique (VMAT) versus conformal radiation therapy. Methods: Ten patients conditioning for ABMT between the periods of April to October 2016 were evaluated. A comparative dosimetric analysis between conformal and VMAT radiation therapy techniques was performed. Treatment plan was performed by using ten arcs with three isocenters with a collimator angle between 10°-100°, optimized for energy of 6MV. The prescribed dose was 12 Gy. In order to cover the bone marrow the PTV was defined as the bones from the cranium vertex to the middle third of the femur. The organs at risk constraints had a median restriction of ≤ 10Gy. Radiation therapy integral dose, conformity, homogeneity and coverage index were evaluated. Results: The average volume of body irradiated was 52,433cc (37,221-73,968cc), the average volume of the PTV was 10,379cc (8,449-13,325cc). The average dose for the planning target volume (PTV) using conformal radiation technique and with VMAT was 15.3Gy and 13.1 Gy (p < 0.0001), respectively. The median dose for the organs at risk with the conformal technique was 17.5Gy and 10.4Gy for the VMAT (p = 0.0013). The median of index of conformity using the conformal technique was 5.21 and 1.99 with VMAT (p = 0.0003). The homogeneity index was 1.87 and 1.37(p < 0.0001) respectively. The quality of coverage was 0.82 and 0.81 (p = 0.951), respectively. The integral dose was 7,699.73 and 6,615.8 kg/Gy (p < 0.0001) respectively. Conclusions: For patients conditioning for ABMT requiring bone marrow irradiation the intensity modulated VMAT radiation therapy technique offers a better conformity and homogeneity index and also offers a reduction in the integral dose, suggesting the possibility of incorporating this technique in the treatment options for patients.