OMPI Seminar: Eric Christiansen and Lesley Buckley

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Thursday, April 20, 2017

Time:3:30 - 5:00 pm, Refreshments start at 3:15 pm.

Location: Room RPB 205 (boardroom), Health Canada, 775 Brookfield Road, Ottawa. Please check in at the front desk.


1) "Implementation of VMAT in matRad, an open source treatment planning toolkit"

By Eric Christiansen, PhD student, Carleton University

Supervisor: Dr. Emily Heath

Abstract: Purpose: To implement and evaluate single-arc volumetric modulated arc therapy (VMAT) plan optimization within matRad, an open-source treatment planning system. Materials and Methods: The three-step approach to VMAT optimization was followed: fluence map optimization (FMO) followed by arc sequencing, then direct aperture optimization (DAO). FMO was performed at control points (CPs) spaced every 28°, with the optimal fluence maps sequenced in a sliding window fashion. Resulting apertures were spread to CPs neighbouring those initialized by FMO. These apertures were refined during the DAO step, with machine delivery constraints included in the optimization. Sequencing parameters were optimized using conformal index and delivery time as two preliminary benchmarks. Following this, three representative cases were planned: a C-shaped target surrounding a critical structure, a prostate target, and a head-and-neck target (both of the latter included lymph nodes). Dose volume metrics in the target and organs at risk (OARs) were calculated and compared to local clinical guidelines. Results: All clinical OAR constraints were met for the three investigated plans. Dose in each target exhibited varying degrees of homogeneity, with the C-shaped target, prostate, and head and neck having variations of 3.7%, 7.6%, and 9.2% between D95% and D5%. Delivery time ranged from 2.2-2.6 min; optimization time ranged from 9-12 min. Conclusions: matRad is now capable of optimizing high-quality VMAT plans that have reasonably short treatment times. VMAT optimization has been implemented as an extended module, which will be released in an upcoming update of matRad.

2)  "Imaging dose in radiation therapy: a sad tale of neglect"

By Lesley Buckley, PhD, The Ottawa Hospital Cancer Centre

Abstract: Increased use of imaging in radiation therapy has impacted many aspects of treatment: including targeting, patient positioning and dose fractionation. Many new treatment techniques rely heavily on the information provided by improved imaging at the time of both simulation and treatment. The radiation dose from imaging is small when compared to the therapeutic dose and is therefore seldom taken into account when computing the total patient dose. This talk will discuss the various sources of imaging dose for a patient undergoing radiation therapy and will quantify this dose for a variety of cases. Methods to reduce this dose will be discussed, including clinical protocols as well as software driven dose reduction techniques.