Abstract
The time required to deliver intensity‐modulated radiation therapy (IMRT) treatments can be significantly longer than conventional treatments, especially for the segmented multileaf collimator (sMLC) delivery system with a large record and verification (R&V) overhead. In this work, we evaluate the impact of the number of intensity‐modulated beams (IMBs) and the number of intensity levels (ILs) on the quality and delivery efficiency of IMRT plans, generated by the Corvus planning system for sMLC delivery on a Siemens LINAC with the Lantis R&V system. Detailed studies were performed for three image data sets of previously treated oropharyngeal patients. Treatment plans for patient 1 were developed using 5, 7, 9, or 15 evenly spaced axial IMBs as well as one with 7 axial IMBs whose directions were user‐selected, each using ILs of 3, 5, 10, or 20. For patients 2 and 3, plans with 15 IMBs and 20 ILs were not attempted. A total of 42 plans were developed using three oropharyngeal cancer CT image data sets. Plan quality was evaluated by assessing compliance with the Radiation Therapy Oncology Group (RTOG) H‐0022 protocol criteria and the physician's clinical judgment. Plan efficiency was accessed by the number of segments of each plan. We found that for our treatment‐planning and delivery system, an IMRT plan that uses a moderate number of IMBs and ILs, such as 7 or 9 IMBs with 3 or 5 ILs, would appear to be the optimal approach when both quality of the plan and delivery efficiency are considered. Based on this study, we have routinely used 9 IMBs with 3 ILs or 7 IMBs with 5 ILs for head and neck patients. A retrospective comparison indicates that delivery efficiency is improved on the order of 30% compared to plans generated with 9 IMBs with 5 ILs.PACS number: 87.53.Tf
Highlights
In recent years, there has been great interest in implementing intensity-modulated radiation therapy (IMRT) in external beam radiation therapy
The purpose of this work is to evaluate the possibility of further reducing the number of intensity levels (ILs) and/or intensity-modulated beams (IMBs) to improve treatment delivery efficiency while maintaining compliance with the Radiation Therapy Oncology Group (RTOG) H-0022 dosimetric criteria for oropharyngeal IMRT treatment
The plans with 5 IMBs are clearly the worst in terms of dose-volume histogram (DVH) for planning target volumes (PTVs)-66. There is another dosimetric requirement for PTVs, namely, no more than 1% of any PTV will receive less than 93% of its prescribed dose
Summary
There has been great interest in implementing intensity-modulated radiation therapy (IMRT) in external beam radiation therapy. IMRT employs nonuniform beam intensity to deliver highly conformal radiation to the targets while minimizing doses to normal tissues and critical organs.[1,2] Head and neck cancer is one of the attractive sites for IMRT because of the complexity of the anatomy in this region, with many critical and radiation-sensitive tissues in close proximity to the targeted tumor.[3] Recently, the Radiation Therapy Oncology Group (RTOG) activated the first IMRT protocol for phase I/II study of oropharyngeal cancer, H-0022.(4) Conventional radiation therapy for advanced oropharyngeal tumors typically delivers high dose to the major salivary glands (parotid, submandibular, and sublingual) bilaterally In most cases, this a Present address: Department of Radiation Physics, Box 94, The University of Texas M. It has been demonstrated that, using conformal radiation techniques including IMRT, it is feasible to provide adequate irradiation of the targets while sparing major salivary glands.[4] To date, no uniform dose-volume criteria have been universally adopted for the delivery of IMRT for head and neck cancers Such criteria have been proposed and are currently being tested in the prospective head and neck IMRT trial, RTOG H-0022. These criteria include stringent requirements for dose coverage of the planning target volumes (PTVs) and for dose limits to critical structures
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