Monte Carlo simulation of respiratory motion induced penumbral broadening in dose distribution using PENELOPE

Vanessa Panettieri, Craig Lancaster, Chuan Dong Wen, Trevor Ackerly

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Background: Image guided respiratory gating for lung and liver cancers was commissioned at William Buckland Radiotherapy Centre. Treatments are delivered on a Novalis Classic accelerator with Brainlab ExacTracTM robotic couch capable of tracking implanted fiducial markers. Objective: Commissioning was performed to understand the characteristics of gated beams. The effect of the dosedistribution penumbral broadening caused by respiration was analysed as function of the motion amplitude in free-breathing. The effect of gating was evaluated as function of the duty-cycle. Method: The PENELOPE Monte Carlo (MC) code validated against Gafchromic film was used. The film was placed on the MotionSimXY/4DTM moving bed and was irradiated with a 6MV 5x5 cm2 field size. The device was programmed with sinusoidal patterns to reproduce breathing movements in the superior-inferior direction with amplitudes ranging from 3 to 45 mm. MC calculations were performed with similar set-up and breathing motion was simulated by combining discrete movements according to their weights. The broadening width was estimated in the 90-10% and 80-20% half-width-nominalmaximum penumbral regions with free-breathing and gating with 33% and 50% duty-cycles. Results: In the non-gated case, in the 90-10% region films and MC are in agreement for all motions within MC statistical uncertainties. In the 80-20% region MC results are in agreement up to 18 mm motion amplitude. Similar results can be found for the gated case both for 33% and 50% windows, and absolute differences between the two levels are within 1 mm. Conclusions: Monte Carlo models were validated with film measurements and were used to study treatment delivered in free-breathing or with gated beams. The results showed that for patients breathing regularly and SI motion amplitudes up to 20 mm it may be worth using a wide duty-cycle of 50% in order to improve efficiency of treatments and preserve dosimetric characteristics of the beam.

Original languageEnglish
Title of host publicationWorld Congress on Medical Physics and Biomedical Engineering
Subtitle of host publicationMay 26-31, 2012, Beijing, China
EditorsMian Long
Place of PublicationBerlin
Number of pages4
ISBN (Electronic)9783642293054
ISBN (Print)9783642293047
Publication statusPublished - 2013
Externally publishedYes
EventWorld Congress on Medical Physics and Biomedical Engineering 2012 - Beijing, China
Duration: 27 May 201231 May 2012

Publication series

NameIFMBE Proceedings
Volume39 IFMBE
ISSN (Print)1680-0737
ISSN (Electronic)1433-9277


ConferenceWorld Congress on Medical Physics and Biomedical Engineering 2012
Abbreviated titleWC 2012


  • commissioning
  • ExacTrac
  • iPlan
  • Monte Carlo
  • respiratory gating

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