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On the accuracy of bulk synthetic CT for MR-guided online adaptive radiotherapy

  • Magnetic Resonance Imaging
  • Published:
La radiologia medica Aims and scope Submit manuscript

Abstract

Purpose

MR-guided radiotherapy (MRgRT) relies on the daily assignment of a relative electron density (RED) map to allow the fraction specific dose calculation. One approach to assign the RED map consists of segmenting the daily magnetic resonance image into five different density levels and assigning a RED bulk value to each level to generate a synthetic CT (sCT). The aim of this study is to evaluate the dose calculation accuracy of this approach for applications in MRgRT.

Methods

A planning CT (pCT) was acquired for 26 patients with abdominal and pelvic lesions and segmented in five levels similar to an online approach: air, lung, fat, soft tissue and bone. For each patient, the median RED value was calculated for fat, soft tissue and bone. Two sCTs were generated assigning different bulk values to the segmented levels on pCT: The sCTICRU uses the RED values recommended by ICRU46, and the sCTtailor uses the median patient-specific RED values. The same treatment plan was calculated on two the sCTs and the pCT. The dose calculation accuracy was investigated in terms of gamma analysis and dose volume histogram parameters.

Results

Good agreement was found between dose calculated on sCTs and pCT (gamma passing rate 1%/1 mm equal to 91.2% ± 6.9% for sCTICRU and 93.7% ± 5.3% b or sCTtailor). The mean difference in estimating V95 (PTV) was equal to 0.2% using sCTtailor and 1.2% using sCTICRU, respect to pCT values

Conclusions

The bulk sCT guarantees a high level of dose calculation accuracy also in presence of magnetic field, making this approach suitable to MRgRT. This accuracy can be improved by using patient-specific RED values.

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Abbreviations

ART:

Adaptive radiotherapy

BMI:

Body mass index

CT:

Computed tomography

DVH:

Dose volume histogram

GPU:

Graphical processing unit

HU:

Hounsfield unit

IMRT:

Intensity modulated radiation therapy

MRI:

Magnetic resonance imaging

MR:

Magnetic resonance

MRgRT:

MR-guided radiotherapy

OARs:

Organs at risk

sCTtailor:

pCT uses the median patient-specific RED values

sCTICRU:

pCT uses the RED values recommended by ICRU46

pCT:

Planning CT

PTV:

Planning target volume

RT:

Radiation treatment

RED:

Relative electron density

sCT:

Synthetic CT

WMW:

Wilcoxon–Mann–Whitney

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Funding

This study was not funded by any company.

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Authors and Affiliations

  1. Fondazione Policlinico Universitario A. Gemelli, IRCCS, Largo Agostino Gemelli 8, 00168, Rome, Italy

    Davide Cusumano, Lorenzo Placidi, Stefania Teodoli, Luca Boldrini, Francesca Greco, Silvia Longo, Francesco Cellini, Nicola Dinapoli, Vincenzo Valentini, Marco De Spirito & Luigi Azario

Authors
  1. Davide Cusumano
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  2. Lorenzo Placidi
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  3. Stefania Teodoli
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  4. Luca Boldrini
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  5. Francesca Greco
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  6. Silvia Longo
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  7. Francesco Cellini
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Corresponding author

Correspondence to Lorenzo Placidi.

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Conflict of interest

Dr. L. Boldrini, Dr. D. Cusumano, Dr. F. Cellini and Dr. N. Dinapoli have received speaker honorarium ViewRay Technologies, Inc. The other authors do not have no conflicts of interest to disclose.

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Cusumano, D., Placidi, L., Teodoli, S. et al. On the accuracy of bulk synthetic CT for MR-guided online adaptive radiotherapy. Radiol med 125, 157–164 (2020). https://doi.org/10.1007/s11547-019-01090-0

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