Intensity-Modulated Radiation Therapy Dose Prescription, Recording, and Delivery: Patterns of Variability Among Institutions and Treatment Planning Systems

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Abstract
Intensity-modulated radiation therapy (IMRT) is a widely accepted method for radiation treatment to provide a prescribed and uniform dose to the target volume and a minimum dose to normal tissues that is dependent on the IMRT software and the treatment machine. We examined the variation in IMRT dose prescription, treatment planning, dose recording, and dose delivery among cancer patients who were treated with different treatment planning systems at different medical institutions to assess variability in patient care. We conducted a retrospective analysis of 803 patients who were treated with IMRT between October 2004 and July 2006 for brain, head and neck, or prostate cancer at five medical institutions that used different treatment planning systems. The prescribed dose to the target volume, as recorded in the chart or as noted in the electronic data management system, was extracted for each patient. The planned dose that was delivered to the patient, as represented in the dose–volume histogram, was acquired from each treatment planning system. The actual minimum, maximum, median, and isocenter doses to the target volume were normalized to the prescribed dose and analyzed for each disease site and institution. Of the 803 patients, 12% were treated for brain cancer, 26% for head and neck cancer, and 62% for prostate cancer. The recorded dose variability from prescription was widespread for the minimum, maximum, and isocenter doses. A total of 46% of the patients received a maximum dose that was more than 10% higher than the prescribed dose, and 63% of the patients received a dose that was more than 10% lower than the prescribed dose. At all five institutions, the prostate cancer cases had the smallest dosimetric variation and the head and neck cancer cases had the largest variation. The median dose to the target varied from the prescribed dose by ±2% in 68% of the patients, by ±5% in 88% of the patients, and by ±10% in 96% of the patients. The recorded isocenter dose varied from prescription for all disease sites and treatment planning systems. Substantial variation in the prescribed and delivered doses exists among medical institutions, raising concerns about the validity of comparing clinical outcomes for IMRT. The isocenter dose in IMRT is simply a point dose and often does not reflect the prescription dose that is specified by a selected isodose line encompassing the target volume. This study suggests the need for national and/or international guidelines for dose prescription, planning, and reporting for a meaningful clinical trial in IMRT.