Hybrid Tri-Co-60 MRI radiotherapy for locally advanced rectal cancer: An in silico evaluation

Luca Boldrini; Elisa Placidi; Nicola Dinapoli; Luigi Azario; Francesco Cellini; Mariangela Massaccesi; Silvia Chiesa; Maria Antonietta Gambacorta; Gian Carlo Mattiucci; Danila Piccari; Stefania Teodoli; Marco De Spirito; Vincenzo Valentini

doi:10.1016/j.tipsro.2018.02.002

Hybrid Tri-Co-60 MRI radiotherapy for locally advanced rectal cancer: An in silico evaluation

Tech Innov Patient Support Radiat Oncol. 2018 Mar 31:6:5-10. doi: 10.1016/j.tipsro.2018.02.002. eCollection 2018 Jun.

Affiliations

¹ Polo Scienze Oncologiche ed Ematologiche, Istituto di Radiologia, Università Cattolica del Sacro Cuore, Fondazione Policlinico Universitario Agostino Gemelli, Largo Francesco Vito, 1 - 00168 Roma, Italy.
² Polo Scienze delle immagini, di laboratorio e infettivologiche, Università Cattolica del Sacro Cuore, Fondazione Policlinico Universitario Agostino Gemelli, Largo Francesco Vito, 1 - 00168 Roma, Italy.
³ Polo Scienze Oncologiche ed Ematologiche, Università Cattolica del Sacro Cuore, Fondazione Policlinico Universitario Agostino Gemelli, Largo Francesco Vito, 1 - 00168 Roma, Italy.
⁴ Polo Scienze delle immagini, di laboratorio e infettivologiche, Istituto di Fisica, Università Cattolica del Sacro Cuore, Fondazione Policlinico Universitario Agostino Gemelli, Largo Francesco Vito, 1 - 00168 Roma, Italy.

Abstract

Introduction: Aim of this paper is to investigate the plan quality of a tri-Co-60 MRI-Hybrid system for intensity-modulated radiation therapy (IMRT) in patients affected by locally advanced rectal cancer (LARC) undergoing neo-adjuvant radiotherapy.

Materials and methods: Ten consecutive LARC patients were selected. Tri-Co-60 step and shoot IMRT plans were generated simulating the presence of the magnetic field (B_on) or not (B_off) with the dedicated treatment planning system (TPS).The total planned dose was 45 Gy in 25 fractions to the mesorectum and the pelvic nodes (planning target volume 2, PTV2) and 55 Gy to the tumor and correspondent mesorectum (PTV1) through simultaneous integrated boost (SIB). Tri-Co-60 IMRT plans were compared with Volumetric Modulated Arc Therapy (VMAT) and IMRT plans for Linear Accelerator (Linac).

Results: B_on and B_off tri-Co-60 IMRT plans showed no relevant differences. Mean values of PTV1 and PTV2 receiving at least 95% of the D_p (V_95%) were higher than 95% in all treatment plans. All plans met the V_105% constraint for the PTV1. Mean values of V_105% for the PTV2 were 14.8, 5.0, and 7.3% respectively for tri-Co-60, VMAT and IMRT. Mean Wu's HI values were similar in all plans (7.4-7.8%). All plans met the V_45Gy constraint for small bowel, but mean V_45Gy value was higher with tri-Co-60.Bladder irradiation was comparable and always lower than the chosen D max 65 Gy constraint.Mean values of V_5Gy and V_20Gy to the body and median skin doses were higher with tri-Co-60 plans.

Discussion: Treatment plans with Tri-Co-60 step and shoot IMRT met the dose-volume objectives in patients with LARC. Nevertheless, a larger volume of normal tissue received low-moderate doses when compared with Linac based VMAT and IMRT.