Coolens, C., Evans, P. M., Seco, J., Webb, S., Blackall, J. M., Rietzel, E., Chen, G. T. Y. (2006) The susceptibility of IMRT dose distributions to intrafraction organ motion: An investigation into smoothing filters derived from four dimensional computed tomography data. MEDICAL PHYSICS, 33 (8). pp. 2809-2818. ISSN 0094-2405

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Abstract

The susceptibility of IMRT dose distributions to intrafraction organ motion: An investigation into smoothing filters derived from four dimensional computed tomography data This study investigated the sensitivity of static planning of intensity-modulated beams (IMBs) to intrafraction deformable organ motion and assessed whether smoothing of the IMBs at the treatment-planning stage can reduce this sensitivity. The study was performed with a 4D computed tomography (CT) data set for an IMRT treatment of a patient with liver cancer. Fluence profiles obtained from inverse-planning calculations on a standard reference CT scan were redelivered on a CT scan from the 4D data set at a different part of the breathing cycle. The use of a nonrigid registration model on the 4D data set additionally enabled detailed analysis of the overall intrafraction motion effects on the IMRT delivery during free breathing. Smoothing filters were then applied to the beam profiles within the optimization process to investigate whether this could reduce the sensitivity of IMBs to intrafraction organ motion. In addition, optimal fluence profiles from calculations on each individual phase of the breathing cycle were averaged to mimic the convolution of a static dose distribution with a motion probability kernel and assess its usefulness. Results from nonrigid registrations of the CT scan data showed a maximum liver motion of 7 mm in superior-inferior direction for this patient. Dose-volume histogram (DVH) comparison indicated a systematic shift when planning treatment on a motion-frozen, standard CT scan but delivering over a full breathing cycle. The ratio of the dose to 50% of the normal liver to 50% of the planning target volume (PTV) changed up to 28% between different phases. Smoothing beam profiles with a median-window filter did not overcome the substantial shift in dose due to a difference in breathing phase between planning and delivery of treatment. Averaging of optimal beam profiles at different phases of the breathing cycle mainly resulted in an increase in dose to the organs at risk (OAR) and did not seem beneficial to compensate for organ motion compared with using a large margin. Additionally, the results emphasized the need for 4D CT scans when aiming to reduce the internal margin (IM). Using only a single planning scan introduces a systematic shift in the dose distribution during delivery. Smoothing beam profiles either based on a single scan or over the different breathing phases was not beneficial for reducing this shift. (C) 2006 American Association of Physicists in Medicine.

Item Type:	Article
Authors (ICR Faculty only):	Evans, Phil and Webb, Steve
All Authors:	Coolens, C., Evans, P. M., Seco, J., Webb, S., Blackall, J. M., Rietzel, E., Chen, G. T. Y.
Uncontrolled Keywords:	IMRT; organ motion; deformable image registration; treatment uncertainty Intensity-modulated beams; induced liver-disease; respiratory motion; hepatocellular-carcinoma; conformal radiotherapy; images; ct; constraints; ultrasound; delivery
Research teams:	ICR divisions > Radiotherapy and Imaging > Radiotherapy Physics Modelling Closed research groups > Radiotherapy Physics Imaging
Depositing User:	EPrints Services
Date Deposited:	10 Aug 2007 20:54
Last Modified:	16 Nov 2015 09:51
URI:	http://publications.icr.ac.uk/id/eprint/2634

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