Lower neck organs at risk sparing in nasopharyngeal carcinoma using hybrid volumetric-modulated arc therapy (hybrid-VMAT): a case report

Abstract

Introduction: Nasopharyngeal carcinoma (NPC) is a prevalent disease in Southern China. Radiation therapy remains the primary treatment modality for NPC due to its high radiation sensitivity. Conventional volumetric-modulated arc therapy (VMAT) can achieve excellent target volume coverage and superior conformal dose distributions while sparing organs at risk (OARs). However, VMAT may also produce substantial volume of low-dose region in the surrounding normal tissue. Our oncology centre has incorporated the concept of anterior cervical field with VMAT in clinical practice of NPC treatment planning. The purpose of this treatment-comparison case study is to demonstrate the lower neck OARs sparing ability of hybrid volumetric-modulated arc therapy (hybrid-VMAT) over conventional VMAT for NPC. Methods: Four patients diagnosed with NPC of different clinical lymph node staging (N staging) were enrolled for this treatment-comparison case study. Planning target volumes and OARs were delineated with reference to Radiation Therapy Oncology Group (RTOG) 0225/0615. Additional OARs from lower neck region, including thyroid, trachea, cervical spine and pharyngeal constrictor muscles (PCMs), were also delineated. Two treatment techniques, hybrid-VMAT and VMAT, were created for each patient’s dataset. Results and findings: Both treatment techniques produced adequate target coverage and reduced radiation dose to the OARs as suggested in RTOG 0225/0615. Hybrid-VMAT plans achieved superior dose reduction in larynx, oesophagus, middle PCM, inferior PCM, cervical spine and trachea comparing with VMAT plans. Hence, the clinical usability and functional outcome of hybrid-VMAT should be further investigated for NPC radiation therapy.

Volumetric modulated arc therapy versus tomotherapy for late T-stage nasopharyngeal carcinoma

“…Besides, the hybrid IMRT/VMAT, which combines IMRT and VMAT, has shown the potential benefit of improving the dose distribution by increasing the freedom to find the optimal combination of angular sampling and intensity modulation (8,9). Another hybrid VMAT technique, which combines open field and VMAT, has also been reported to result in superior dose distribution and OAR protections in certain circumstance (10,11). N o t e w o r t h y , c o m p a r e d wi t h t h e s e h y b r i d V MA T techniques, simple VMAT has advantages in lowering MUs and shortening delivery time.However, as most of these studies were based on regenerating a radiotherapy plan with either VMAT or tomotherapy in the same patient, comparisons of radiotherapy toxicities and clinical outcomes are not available.…”