On-line adaptive MR guided radiotherapy for locally advanced pancreatic cancer: Clinical and dosimetric considerations

Lorenzo Placidi; Angela Romano; Giuditta Chiloiro; Davide Cusumano; Luca Boldrini; Francesco Cellini; Gian Carlo Mattiucci; Vincenzo Valentini

doi:10.1016/j.tipsro.2020.06.001

On-line adaptive MR guided radiotherapy for locally advanced pancreatic cancer: Clinical and dosimetric considerations

Tech Innov Patient Support Radiat Oncol. 2020 Jul 2:15:15-21. doi: 10.1016/j.tipsro.2020.06.001. eCollection 2020 Sep.

Authors

Lorenzo Placidi^{1

2}, Angela Romano², Giuditta Chiloiro², Davide Cusumano², Luca Boldrini^{1

2}, Francesco Cellini², Gian Carlo Mattiucci^{1

2}, Vincenzo Valentini^{1

2}

Affiliations

¹ Università Cattolica del Sacro Cuore, Largo Agostino Gemelli 8, 00168 Rome, Italy.
² Fondazione Policlinico Universitario Agostino Gemelli IRCCS , Largo Francesco Vito 1, 00168 Rome, Italy.

Abstract

Introduction: Magnetic Resonance-guided Radiation Therapy (MRgRT) allows online adaptations (OA) of the treatment plan to optimize daily dose distribution based on patient's anatomy, just before fraction delivery. The aim of this study is to evaluate feasibility and the dosimetric improvement of the OA workflow implemented in our institution for locally advanced pancreatic cancer (LAPC) patients, in terms of target coverage and organs at risk (OARs) sparing.

Methods: We retrospectively analysed 8 LAPC patients treated with MRgRT in combination with the OA approach, using video-assisted inspiratory breath-hold for a total of 38 fractions with a dose ranging from 30 Gy to 40 Gy in 5 fractions.Dose distribution of the baseline plan was first calculated based on daily anatomy, obtaining a "predicted" plan to assess the dosimetric improvement. If the dose distribution did not meet the constraints set in the planning phase, PTV, GTV and OARs were re-contoured within a distance of 3 cm from the PTV external edge and a new online "adaptive" plan was generated. Other clinical and planning parameters were also evaluated to assess the feasibility and the dosimetic benefit of the online adaptive workflow.

Results: Out of 38 total fractions, 26 (68.4%) were adapted online and 12 (31.6%) were delivered using the baseline plan. The use of the adaptive workflow resulted to be feasible in our clinical practice and advantageous in all the patients: mean PTV V95% increased by 10.8% (5.7-20.8) while mean CTV V98% of 12.6% (7.3-17.7). Also OARs V33 and V25 showed a positive trend avoiding unnecessary irradiation.

Conclusion: OA workflow improves the dosimetric benefit of MRgRT, preventing the occurrence of high-doses to OARs and increasing the safety of stereotactic treatment for LAPC, without any drawback for our daily clinical practice routine.

Keywords: Locally advanced pancreatic cancer; Magnetic resonance guided radiation therapy; Online adaptive radiotherapy.