Feasibility of MV CBCT-based treatment planning for urgent radiation therapy: dosimetric accuracy of MV CBCT-based dose calculations.

Mareike Held,Shannon E Fogh,Jean Pouliot,Olivier Morin,Penny K Sneed

doi:10.1120/jacmp.v16i6.5625

Mareike Held, Shannon E Fogh + Show 3 more

Open Access

https://doi.org/10.1120/jacmp.v16i6.5625

Copy DOI

Abstract

Unlike scheduled radiotherapy treatments, treatment planning time and resources are limited for emergency treatments. Consequently, plans are often simple 2D image‐based treatments that lag behind technical capabilities available for nonurgent radiotherapy. We have developed a novel integrated urgent workflow that uses onboard MV CBCT imaging for patient simulation to improve planning accuracy and reduce the total time for urgent treatments. This study evaluates both MV CBCT dose planning accuracy and novel urgent workflow feasibility for a variety of anatomic sites. We sought to limit local mean dose differences to less than 5% compared to conventional CT simulation. To improve dose calculation accuracy, we created separate Hounsfield unit–to–density calibration curves for regular and extended field‐of‐view (FOV) MV CBCTs. We evaluated dose calculation accuracy on phantoms and four clinical anatomical sites (brain, thorax/spine, pelvis, and extremities). Plans were created for each case and dose was calculated on both the CT and MV CBCT. All steps (simulation, planning, setup verification, QA, and dose delivery) were performed in one 30 min session using phantoms. The monitor units (MU) for each plan were compared and dose distribution agreement was evaluated using mean dose difference over the entire volume and gamma index on the central 2D axial plane. All whole‐brain dose distributions gave gamma passing rates higher than 95% for 2%/2 mm criteria, and pelvic sites ranged between 90% and 98% for 3%/3 mm criteria. However, thoracic spine treatments produced gamma passing rates as low as 47% for 3%/3 mm criteria. Our novel MV CBCT‐based dose planning and delivery approach was feasible and time‐efficient for the majority of cases. Limited MV CBCT FOV precluded workflow use for pelvic sites of larger patients and resulted in image clearance issues when tumor position was far off midline. The agreement of calculated MU on CT and MV CBCT was acceptable for all treatment sites.PACS numbers: 87.55.D‐, 87.57.Q‐

Highlights

459 Held et al.: MV CBCT-based dose calculation for urgent RT interest in using cone-beam CT images for other purposes, such as dose calculations and monitoring of patient anatomy, during the course of treatment
Dose calculations using MV CBCT images are feasible.[1,2] consistently converting CT numbers to electron density can be difficult.[3,4,5,6] Previous research studies reported a gamma index of 98% for 3% and 3 mm criteria that described dose calculation accuracy on MV CBCT for head-and-neck cases, using in-house developed image correction filters.[7] this was based on a limited patient population and dose calculations needed verification in more anatomical sites to be clinically relevant
The objective of this study was to investigate the feasibility of emergency radiotherapy treatment (ERT) dose planning on selected anatomical sites based on MV CBCT images acquired on a commercial treatment machine

Summary

Introduction

459 Held et al.: MV CBCT-based dose calculation for urgent RT interest in using cone-beam CT images for other purposes, such as dose calculations and monitoring of patient anatomy, during the course of treatment. Dose calculations using MV CBCT images are feasible.[1,2] consistently converting CT numbers to electron density can be difficult.[3,4,5,6] Previous research studies reported a gamma index of 98% for 3% and 3 mm criteria that described dose calculation accuracy on MV CBCT for head-and-neck cases, using in-house developed image correction filters.[7] this was based on a limited patient population and dose calculations needed verification in more anatomical sites to be clinically relevant. Other applications include emergency treatments using CBCT- and MV CT-based planning to reduce patient setup and waiting time.[9,10] Here, similar results to our initial experience with head-and-neck cases[7] have been verified for commercially available systems.

Objectives

Methods

Results

Discussion

Conclusion