Techniques in DosimetricReviewAnd immediate clinical applications with Velocity

Megan A. Hyun, PhD, DABR2020 Midwest Radiation Oncology Symposium

Introduction and COI

• I am a board-certified therapeutic medical physicist, Assistant Professor at UNMC in Radiation Oncology

• No relevant conflicts of interest to disclose

• Any references to products throughout the talk are for information purposes only, not endorsement

Megan A. Hyun, PhD, DABR

Outline

Dosimetric review in Radiation Oncology

Tools needed for dosimetric review

Available software

Demonstration with Velocity/Eclipse

Discussion of challenges encountered with Velocity

What is dosimetric review?

Standard-of-care:• Simulation• Treatment planning• Imaging before, during, and/or after treatment• Treatment delivery• Review of treatment images

(and what it isn’t)

SimulationTreatment planning

Imaging

Treatment delivery

Image review

What is dosimetric review?

Dosimetric review:• Simulation• Treatment planning• Imaging before, during, and/or after treatment• Treatment delivery• Review of changing dose distribution• Possible adaptive therapy

(and what it isn’t)

SimulationTreatment planning

Imaging

Treatment delivery

Dosimetricreview

Why dosimetric review?

Images are part of a study reviewed and approved by the UNMC IRB (Protocol #842-18-EP)

Treatment Plan Treatment Plan

Weekly CBCT

Original bladder volume: 343 ccWorst-case bladder volume: 90 cc (26% of planned volume)

Why dosimetric review?

1. Chen et al., “Dosimetric impact of…” Rad Onc 11(103) 20162. Velec et al., “Accumulated dose in…” Int J Rad Onc Biol Phys 83(4) 2012

Bladder dose affected by bladder fill variation over the course of prostate treatment1

Liver tumor dose affected by geometric errors over the course of treatment2

Changes in patient anatomy or positioning may adversely affect tumor coverage and the sparing of organs-at-risk

Dosimetric review allows ARTWhat is ART?• Adapting a patient’s treatment plan based on

changing metrics that are either expected or observed (including anatomical changes seen on daily imaging)

• Online ART is done at the machine, but is only achievable with dedicated machines

• Offline ART requires regular monitoring of daily images, with adaptation between treatments• Assessment and adaptation can be done at a single

timepoint, at timed intervals, or triggered by observed changes

Why ART?• Dose differences from patients’ changing anatomy can cause

large dose differences compared to planning (>20%), affecting tumor and healthy tissue1-3

1. M Velec et al (2012)2. K Lim et al (2009)3. Z Chen et al (2016)

Tools needed for dosimetric reviewSmooth and efficient image

import/export/storage

Rigid and deformable image registration algorithms

Contouring tools

Dose calculation algorithm

Dose display and comparison

Options for dosimetric review

Basic TPS with deformable image

registration

TPS + Ancillary Software

Advanced TPS

TPS = Treatment Planning System

TPS Examples: Eclipse, Pinnacle

Examples of ancillary software: MIM, Velocity

Example: Raystation

Comparison of DIR algorithms

Algorithms vary in accuracy when tested using digital phantoms

Pukala et al., “Benchmarking of five commercial…” JACMP 17(3) 2016

Comparison of DIR algorithms

Kadoya et al., “Multi-institutional study…” Int J Rad Onc Biol Phys 96(2) 2016

Algorithms vary in accuracy when tested using digital phantoms

Comparison of DIR algorithms

Intensity-based DIR (MIM, Velocity) is often inferior to hybrid DIR (RayStation)

Takayama et al., “Evaluation of the performance…” J Rad Res 58(4) 2017

DemonstrationBasic TPS with

deformable image registration

TPS (Eclipse) + Ancillary Software

(Velocity)

Advanced TPS

Sample resultsDosimetric review of H&N patients

Planning CT Adapted CT

Sample resultsDosimetric review of H&N patients

pCT CBCT DIR

Challenges of dosimetric review

Velocity’s DIR algorithm has demonstrated limitations for our prostate patient cohort, likely due to:

A. Contrast enhancement on the planning CT, not on CBCTB. Poor delineation of bladder edge on CBCTC. Large (>50%) changes in bladder fillingD. Limited extent of CBCT

Structure-guided deformation offers some improvement, but many CBCTs still cannot be adapted and analyzed

Using Eclipse + Velocity

Challenges of dosimetric reviewUsing Eclipse + Velocity

CBCT Fusion of CBCT and Planning CT

Adapted CT, un-guided deformable image registration

Adapted CT, structure-based deformable image registration

Challenges of dosimetric reviewUsing Eclipse + Velocity

Challenges of dosimetric review

We aim to address these challenges through improving bladder fill consistency

Possible interventions:1. Managing bladder fill at the time of

sim2. Always using a non-contrast sim

image for DIR with CBCT3. Threshold or “no-go” contours4. Patient consultations with

physicists1-2

Using Eclipse + Velocity

1. T Atwood et al., Int J Rad Onc Biol Phys 102 (3), 20182. M Hyun and A Hyun, Ethics and Error in Medicine, Routledge, 2019

Outline

Dosimetric review in Radiation Oncology

Tools needed for dosimetric review

Available software

Demonstration with Velocity/Eclipse

Discussion of challenges encountered with Velocity

AcknowledgementsStudent and resident researchers• April Smith• Purvi Patel• Wei Nie• Sarah Wisnoskie

UNMC Department of Radiation Oncology faculty and clinical team• Dandan Zheng• Brett Thomas