A feasibility study of using conventional jaws to deliver complex IMRT plans for head and neck cancer

Abstract

Previous studies have demonstrated that simple intensity-modulated radiotherapy (IMRT) plans can be produced with a series of rectangular segments formed by conventional jaws. This study investigates whether complex IMRT plans for head and neck cancer can be delivered with the conventional jaws efficiently. Six nasopharyngeal cancer patients, previously treated with multi-leaf collimator (MLC)-IMRT plans, were re-planned using conventional jaw delivery options. All IMRT plans were subject to the plan acceptance criteria of the RTOG-0225 protocol. For a selected patient, the maximum number of segments varied from five to nine per beam, and was tested for both jaws-only IMRT (JO-IMRT) plans and MLC-IMRT plans. Subsequently, JO-IMRT plans and MLC-IMRT on the same treatment planning system were attempted for all patients with identical beams. The dose distribution, dose volume histograms (DVH), the conformal index (COIN), the uniformity index and delivery efficiency were compared between the MLC-IMRT and JO-IMRT plans. All JO-IMRT plans met the RTOG-0225 criteria for tumor coverage and sensitive structures sparing. The corresponding MLC-IMRT and JO-IMRT plans show comparable conformality and uniformity, with average COINs of the planning gross tumor volume(pGTV) 37.7% +/- 18.7% versus 37.9% +/- 18.1%, and the average uniformity index 82.8% +/- 2.5% versus 83.6% +/- 3.1%, respectively. The average monitor unit for JO-IMRT plans was about twice that of MLC-IMRT plans. In conclusion, conventional jaws can be used solely to deliver complex IMRT plans for patients with nasopharyngeal cancer yet still within a practical delivery time.

Evaluation and comparison of dose distributions for nasopharyngeal carcinoma patients treated by Jaws-Only IMRT technique and by 3D-CRT technique at Dong Nai General Hospital

“…Hiệu quả của IMRT chủ yếu là nhờ sử dụng các trường chiếu điều biến cường độ và sử dụng các thuật toán tối ưu trên máy tính; MLC chỉ đơn thuần là một công cụ góp phần cho cấp liều điều biến cường độ trở nên hiệu quả hơn. Xuất phát từ thực tế đó, từ năm 2002 đã có những công trình nghiên cứu khả năng thực hiện IMRT bằng các ngàm có sẵn trên máy gia tốc (Jaw-Only, viết tắt là JO) [7][8][9][10][11][12][13][14]. Từ năm 2006, kỹ thuật JO-IMRT được tích hợp trong phần mềm lập kế hoạch xạ trị Prowess panther, Prowess Inc, Mỹ và đã được áp dụng trong lâm sàng tại Mỹ, Ấn Độ, Trung Quốc, Iran.…”

Evaluation of jaws-only intensity modulated radiation therapy treatment plans using Octavius 4D system

“…Meanwhile, several oncology centers in developing countries are still using cobalt machines or linear accelerators (LINAC) without MLCs which are expensive acquisition costs, not yet available and some disadvantage. From the fact that, some investigators also intend to explore the use of independent jaws only instead of MLCs and compensators to deliver IMRT [7][8][9][10][11]. This IMRT was the socalled jaws-only IMRT technique (JO-IMRT).…”

A novel software and conceptual design of the hardware platform for intensity modulated radiation therapy

“…Due to considerations including the mechanical complexity, cost, accessibility and reliability of early MLCs, attempts have been made to use only the orthogonal jaws on conventional Linacs for IMRT. [6][7][8] Jawsonly IMRT requires the entire IMRT plan to be delivered using exclusively rectangular apertures. Different methods were reported to generate these apertures, including fluence stripping 9 and direct aperture optimization (DAO).…”

“…11 In a follow up study, Mu and Xia showed that even for more complex head and neck IMRT plans, the jaws-only approach can result in acceptable dosimetry, at a cost of longer delivery time. 6 With the maturation of MLC technology, the problems that plagued early MLC devices, such as reliability and cost, have been mitigated. However, there is still a need to miniaturize the dose modulator for purposes including small animal irradiator, robotic Linac, and high resolution dose modulation where reducing the leaf thickness for the application is no longer feasible, or the reduction requires significant compromise in field size, reliability, and interleaf leakage.…”