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

Abstract

Results 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. Conclusions 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. J Natl Cancer Inst 2008;100: 300 – 307 An improvement in radiation therapy outcomes could be achieved by periodic comparisons of clinical practices through outcome evaluations from clinical trials and studies. For a multicenter study, a meaningful comparison of clinical outcomes in response to radiation treatment requires a standardized process for dose specifi cation. Treatment outcome can be interpreted meaningfully only with accurate knowledge of the reference dose and the dose distribution. National guidelines for clinical reference dosimetry, such as those put forth by Task Groups 21 and 51 of the Radiation Therapy Committee of the American Association of Physicists in Medicine ( 1 , 2 ), recommend that the reference dose (machine output) should not vary by more than ±2% among centers. For patient treatment, the combined dosimetric uncertainty in the target volume (which includes differences in patient setup and