4D dose calculation for pencil beam scanning proton therapy of pancreatic cancer using repeated 4DMRI datasets

Patrick Naumann,Kai Dolde,Ye Zhang,Regula Gnirs,Asja Pfaffenberger,Antony John Lomax,Damien Charles Weber,Christian Dávid,Marc Kachelrieß,Nami Saito

doi:10.1088/1361-6560/aad43f

Abstract

4D magnetic resonance imaging (4DMRI) has a high potential for pancreatic cancer treatments using proton therapy, by providing time-resolved volumetric images with a high soft-tissue contrast without exposing the patient to any additional imaging dose.In this study, we aim to show the feasibility of 4D treatment planning for pencil beam scanning (PBS) proton therapy of pancreatic cancer, based on five repeated 4DMRI datasets and 4D dose calculations (4DDC) for one pancreatic cancer patient. To investigate the dosimetric impacts of organ motion, deformation vector fields were extracted from 4DMRI, which were then used to warp a static CT of the patient, so as to generate synthetic 4DCT (4DCT-MRI).CTV motion amplitudes <15 mm were observed for this patient. The results from 4DDC show pronounced interplay effects in the CTV with dose homogeneity d5/d95 and dose coverage v95 being 1.14 and 91%, respectively, after a single fraction of the treatment. An averaging effect was further observed when increasing the number of fractions. Motion effects can become less dominant and dose homogeneity d5/d95 = 1.03 and dose coverage v95 = within the CTV can be achieved after 28 fractions. The observed inter-fractional organ and tumor motion variations underline the importance of 4D imaging before and during PBS proton therapy.

Highlights

Pancreatic cancer has a very poor prognosis, with a reported five-year survival rate of approximately 7% (Siegel et al 2015)
We aim to explore the feasibility of such a 4D dose calculations (4DDC) approach for pencil beam scanning (PBS) proton therapy of pancreatic cancer
We propose an approach for generating synthetic 4DCT based on repeated 4D magnetic resonance imaging (4DMRI), which is used in combination with 4DDC to quantify the dosimetric impacts of inter- and intra-fractional motion effects (Boye et al 2013, Bernatowicz et al 2013, Zhang et al 2016)

Summary

Introduction

Pancreatic cancer has a very poor prognosis, with a reported five-year survival rate of approximately 7% (Siegel et al 2015). After surgery and systemic chemotherapy, radiation therapy is an important option in the treatment armamentarium for unresectable, localized pancreatic cancer, often in combination with other modalities. The pancreas is affected by respiratory motion, which can induce range uncertainties and consequentially under- or overshooting of the target (Kumagai et al 2009, Durante et al 2010, Jayachandran et al 2010). In this scope, robust planning strategies of pancreatic cancer patients have been investigated based on repeated 3DCT images to investigate inter-fractional motion (Steitz et al 2016, Batista 2017). The suitability of 4DCT for planning purposes has been analyzed (Knecht et al 2017) and interfractional anatomical changes have been investigated by means of daily cone-beam CTs (Houweling et al 2016)

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