Premium
Sci‐AM2 Sat ‐ 06: IMRT prostate planning‐determination of the minimum MU/segment
Author(s) -
Grigorov G,
Chow J,
Barnett R
Publication year - 2005
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2031056
Subject(s) - monitor unit , nuclear medicine , dosimetry , pinnacle , radiation treatment planning , dose rate , medicine , prostate , percentage depth dose curve , ionization chamber , radiation therapy , physics , radiology , medical physics , cancer , ion , quantum mechanics , ionization
For step and shoot IMRT, the combination of high dose rate, multiple beam segments and low dose per segment can lead to significant differences between the planned and delivered dose to the patient. This problem, known as an “overshoot” effect, is the result of current dose servo limitations and is demonstrated by over‐ and under‐dose in the first and the last segment respectively. Segment dose inaccuracy in the range of 10 to 60% of the both segments for 1 monitor unit (MU) per segment irradiated with dose rate (DR) of 100 to 600 MU/min was measured. The object of this study was to find a method for segment dose correction when small MU and high DR are used, and specify the prostate IMRT planning limits for MU/segment and the DR. The reported results were obtained using Pinnacle 3 ‐V6 and Varian Clinac 2100 EX linear accelerator equipped with a 120‐leaf millennium MLC. The methodology for correcting dose employs small field segment dose ratio. The segment dose error after correction was measured to be less than 5 % for all dose rates. For prostate step and shoot IMRT a low limit of 1 MU per segment and DR with upper limit of 600 MU/min can be used. The results of this work relate to the agreement between planned and delivered doses of the prostate IMRT.