RESUMO
OBJECTIVE: The aim of this study was to assess the feasibility of flattening filter-free (FFF) photon beams in hybrid intensity-modulated radiation therapy (H-IMRT) and hybrid volumetric modulated arc therapy (H-VMAT) for left-sided whole-breast radiation therapy with a boost volume (RT) using a hypofractionated dose regimen. PATIENTS AND METHODS: RT plans of 25 patients with left-sided early-stage breast cancer were created with HIMRT and HVMAT techniques under breath-hold conditions using 6MV FFF beams. In hybrid techniques, three-dimensional conformal radiotherapy (3DCRT) plans were kept as base-dose plans for the VMAT and IMRT plans. In addition, HIMRT in step-and-shoot mode was also calculated to assess its achievability with FFF beams. RESULTS: All hybrid plans achieved the expected target coverage. HVMAT showed better coverage and homogeneity index results for the boost target (pâ¯< 0.002), while HIMRT presented better results for the whole-breast target (pâ¯< 0.001). Mean doses to normal tissues were comparable between both plans, while HIMRT reduced the low-dose levels to heart and ipsilateral lung (pâ¯< 0.05). HVMAT revealed significantly better results with regard to monitor units (MU) and treatment time (pâ¯< 0.001). CONCLUSION: The 6MV FFF beam technique is feasible for large-field 3DCRT-based hybrid planning in whole-breast and boost planning target volume irradiation. For breath-hold patients, the HVMAT plan is superior to HIMRT for hypofractionated dose regimens, with reduced MU and treatment delivery time.
Assuntos
Neoplasias da Mama/radioterapia , Hipofracionamento da Dose de Radiação , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia Conformacional/métodos , Radioterapia de Intensidade Modulada/métodos , Neoplasias da Mama/patologia , Terapia Combinada , Estudos de Viabilidade , Feminino , Humanos , Mastectomia Segmentar , Estadiamento de Neoplasias , Fótons/uso terapêutico , Radiometria , Carga TumoralRESUMO
PURPOSE: To find an optimal arc design for hybrid volumetric modulated arc therapy (H-VMAT), a combination of conventional 3DCRT and VMAT plans for left-sided whole breast radiation therapy. METHODS AND MATERIALS: A total of 26 left-sided early-stage breast cancer patients were selected for this study. To find the superior plan, H-VMAT with three different arc designs including, two partial arcs (2A), four partial arcs (4A) and four tangential arcs (TA) were created for each study case by combining 3DCRT and VMAT with 75% 3DCRT/25% VMAT dose proportion of prescription dose. RESULTS: All H-VMAT plans achieved the expected target coverage. A higher conformity index and homogeneity index were achieved for 2A and 4A H-VMAT plans and significantly differ from TA H-VMAT (p < 0.003). The heart and ipsilateral lung dose parameters were comparable among all plans except heart V40Gy which was significantly less in 4A H-VMAT plan (p < 0.05). The contralateral lung, contralateral breast, spinal cord, normal tissue doses and MU were significantly less in TA H-VMAT (p < 0.03). The beam-on time was significantly less in 2A H-VMAT (p < 0.0001). CONCLUSION: 2A and 4A H-VMAT techniques are effective in improving the PTV dosimetric parameters as well as reducing the OAR doses. Further, 2A H-VMAT delivers less MU and beam-on time compared to 4A H-VMAT.