Premium
SU‐FF‐T‐146: Pulsed Reduced Dose‐Rate Intensity Modulated Radiotherapy (IMRT) Delivery for Use in the High Dose Re‐Irradiation Setting
Author(s) -
Price R,
Lin T,
Kuritzky N,
Ma C
Publication year - 2009
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 - 10.1118/1.3181620
Subject(s) - nuclear medicine , dosimetry , radiation therapy , irradiation , medicine , dose rate , tomotherapy , radiation treatment planning , medical physics , radiology , physics , nuclear physics
Purpose: Pulsed reduced dose‐rate radiotherapy (PRDR) in the re‐irradiation setting has been reported in the literature. In an effort to reduce normal tissue toxicities a series of 0.2Gy pulses separated by 3 minute intervals are delivered for a time‐averaged dose rate of approximately 0.06Gy/min. We have combined PRDR with IMRT for increased conformality and normal tissue sparing. The purpose of this work was to explore the efficacy of this pairing. Method and Materials: The case presented represents a 31 year old patient with recurrent pancreatic cancer, previously treated with 3DCRT to 50.4Gy. Re‐irradiation of a 153cc PTV was planned to deliver 50Gy in 25 fractions via a 14 field, non‐coplanar IMRT plan on a Varian Trilogy, resulting in a total dose of 100.4Gy to parts of the target volume. The IMRT plan was delivered through 385 segments and 565 MU via the step‐and‐shoot method. MU linearity and a fluence map profile comparison were evaluated for both high and low dose rate settings. Due to the large number of low MU segments the treatment was delivered at 100MU/min to promote beam stabilization. A time‐averaged dose rate of approximately 0.06Gy/min was arrived at by inserting a 2 minute and 23 second time interval between the initiation of delivery for each beam. Results: The percentage of segments delivered using fractional MU between 1–2, 2–3, and 3–4 were 95.6%, 3.4% and 0.3%, respectively. Measured absolute dose and spatial distribution agreed to within 0.1% and within 3%/3mm DTA, respectively. Conclusions: A minimum of 10 beam directions are used to ensure relatively smooth intensity maps, adequate normal tissue sparing and that no aspect of the target volume is un‐irradiated for 2 consecutive pulses. With normal tissue sparing being the dominant endpoint for PRDR, IMRT is shown to provide an optimal and accurate delivery mechanism.