RT of lung cancer Helical tomotherapy for SIB and hypo-fractionated treatments in lung carcinomas: A 4D Monte Carlo treatment planning study Edmond Sterpin ⇑,1 , Guillaume Janssens 1 , Jonathan Orban de Xivry, Samuel Goossens, Marie Wanet, John A. Lee, Antoine Delor, Vanesa Bol, Stefaan Vynckier, Vincent Gregoire, Xavier Geets Université Catholique de Louvain, Brussels, Belgium article info Article history: Received 27 September 2011 Received in revised form 29 May 2012 Accepted 17 June 2012 Available online 28 July 2012 Keywords: Monte Carlo 4D IMRT Tomotherapy Intrafraction motion Non-deformable registration abstract Purpose: To evaluate the impact of intra-fraction motion induced by regular breathing on treatment qual- ity for helical tomotherapy treatments. Material and methods: Four patients treated by simultaneous-integrated boost (SIB) and three by hypo- fractionated stereotactic treatments (hypo-fractionated, 18 Gy/fraction) were included. All patients were coached to ensure regular breathing. For the SIB group, the tumor volume was delineated using CT infor- mation only (CTV CT ) and the boost region was based on PET information (GTV PET , no CTV extension). In the hypo-fractionated group, a GTV based on CT information was contoured. In both groups, ITVs were defined according to 4D data. The PTV included the ITV plus a setup error margin. The treatment was planned using the tomotherapy TPS on 3D CT images. In order to verify the impact of intra-fraction motion and interplay effects, dose calculations were performed using a previously validated Monte Carlo model of tomotherapy (TomoPen): first on the planning 3D CT (‘‘planned dose’’) and second, on the 10 phases of the 4D scan. For the latter, two dose distributions, termed ‘‘interplay simulated’’ or ‘‘no interplay’’ were computed with and without beamlet-phase correlation over the 10 phases and combined using deformable dose registration. Results: In all cases, DVHs of ‘‘interplay simulated’’ dose distributions complied within 1% of the original clinical objectives used for planning, defined according to ICRU (report 83) and RTOG (trials 0236 and 0618) recommendations, for SIB and hypo-fractionated groups, respectively. For one patient in the hypo-fractionated group, D mean to the CTV CT was 2.6% and 2.5% higher than ‘‘planned’’ for ‘‘interplay sim- ulated’’ and ‘‘no interplay’’, respectively. Conclusion: For the patients included in this study, assuming regular breathing, the results showed that interplay of breathing and tomotherapy delivery motions did not affect significantly plan delivery accu- racy. Hence, accounting for intra-fraction motion through the definition of an ITV volume was sufficient to ensure tumor coverage. Ó 2012 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 104 (2012) 173–180 For radiotherapy treatments involving dynamic intensity mod- ulation, the effects of intra-fraction motion due to breathing have been a matter of study for more than a decade [1,2]. The main con- cern has been the impact of intra-fraction and leaf motion inter- play which may result in differences in hot and cold spots by a factor of more than four from planned to delivered fluences, as evaluated in an analytical study by Yu et al. [3]. For non-rotational IMRT strategies, there is an overall consensus [4–6] that the effect of motion interplay tends to average out when multiple fractions are considered but that caution is required for single- to few-frac- tion treatments. Helical tomotherapy has a unique design that includes a binary multileaf collimator (MLC) and continuous gantry and couch mo- tion [7]. Therefore, a new issue to be considered compared to more conventional dynamic IMRT treatments is the intra-fraction and couch motions interplay. Kissick et al. [8] studied the problem for- mally and drew similar conclusions as for fixed-beam IMRT, that is, differences are averaged when dose is delivered over multiple frac- tions. Slow treatment couch speeds (<0.1 cm/s) lead to more acceptable deliveries as well [9]. However, differences may be sig- nificant for hypo-fractionated treatments. Finally, regular breath- ing, achieved through patient coaching, is definitely preferred to non-regular breathing [10]. Many strategies exist to control motion like breath holding [11,12], tumor gating [12–15] or tracking [16,17]. However, the unique design of tomotherapy treatment, for instance inability to quickly start and stop the beam, requires dedicated motion 0167-8140/$ - see front matter Ó 2012 Elsevier Ireland Ltd. All rights reserved. http://dx.doi.org/10.1016/j.radonc.2012.06.005 ⇑ Corresponding author. Address: Université Catholique de Louvain, Center for Molecular Imaging, Radiotherapy and Oncology, 54 av. Hippocrate, 1200 Brussels, Belgium. E-mail address: esterpin@yahoo.fr (E. Sterpin). 1 The two first authors contributed equally to the study. Radiotherapy and Oncology 104 (2012) 173–180 Contents lists available at SciVerse ScienceDirect Radiotherapy and Oncology journal homepage: www.thegreenjournal.com