open access

Vol 23, No 2 (2018)
Original research articles
Published online: 2018-03-01
Submitted: 2017-04-15
Get Citation

Extended localization and adaptive dose calculation using HU corrected cone beam CT: Phantom study

K Mohamathu Rafic, S Amalan, B S Timothy Peace, B Paul Ravindran
DOI: 10.1016/j.rpor.2018.01.005
·
Rep Pract Oncol Radiother 2018;23(2):126-135.

open access

Vol 23, No 2 (2018)
Original research articles
Published online: 2018-03-01
Submitted: 2017-04-15

Abstract

Background and aim

The practicability of computing dose calculation on cone beam CT (CBCT) has been widely investigated. In most clinical scenarios, the craniocaudal scanning length of CBCT is found to be inadequate for localization. This study aims to explore extended tomographic localization and adaptive dose calculation strategies using Hounsfield unit (HU) corrected CBCT image sets.

Materials and methods

Planning CT (pCT) images of the Rando phantom (T12-to-midthigh) were acquired with pelvic-protocol using Biograph CT-scanner. Similarly, half-fan CBCT were acquired with fixed parameters using Clinac2100C/D linear accelerator integrated with an on-board imager with 2-longitudinal positions of the table. For extended localization and dose calculation, two stitching strategies viz., one with “penumbral-overlap” (S1) and the other with “no-overlap” (S2) and a local HU-correction technique were performed using custom-developed MATLAB scripts. Fluence modulated treatment plans computed on pCT were mapped with stitched CBCT and the dosimetric analyses such as dose-profile comparison, 3D-gamma (γ) evaluation and dose-volume histogram (DVH) comparison were performed.

Results

Localizing scanning length of CBCT was extended by up to 15[[ce:hsp sp="0.25"/]]cm and 16[[ce:hsp sp="0.25"/]]cm in S1 and S2 strategies, respectively. Treatment plan mapping resulted in minor variations in the volumes of delineated structures and the beam centre co-ordinates. While the former showed maximum variations of −1.4% and −1.6%, the latter showed maximum of 1.4[[ce:hsp sp="0.25"/]]mm and 2.7[[ce:hsp sp="0.25"/]]mm differences in anteroposterior direction in S1 and S2 protocols, respectively. Dosimetric evaluations viz., dose profile and DVH comparisons were found to be in agreement with one another. In addition, γ-evaluation results showed superior pass-rates (≥98.5%) for both 3%/3[[ce:hsp sp="0.25"/]]mm dose-difference (DD) and distance-to-agreement (DTA) and 2%/2[[ce:hsp sp="0.25"/]]mm DD/DTA criteria with desirable dosimetric accuracy.

Conclusion

Cone beam tomographic stitching and local HU-correction strategies developed to facilitate extended localization and dose calculation enables routine adaptive re-planning while circumventing the need for repeated pCT.

Abstract

Background and aim

The practicability of computing dose calculation on cone beam CT (CBCT) has been widely investigated. In most clinical scenarios, the craniocaudal scanning length of CBCT is found to be inadequate for localization. This study aims to explore extended tomographic localization and adaptive dose calculation strategies using Hounsfield unit (HU) corrected CBCT image sets.

Materials and methods

Planning CT (pCT) images of the Rando phantom (T12-to-midthigh) were acquired with pelvic-protocol using Biograph CT-scanner. Similarly, half-fan CBCT were acquired with fixed parameters using Clinac2100C/D linear accelerator integrated with an on-board imager with 2-longitudinal positions of the table. For extended localization and dose calculation, two stitching strategies viz., one with “penumbral-overlap” (S1) and the other with “no-overlap” (S2) and a local HU-correction technique were performed using custom-developed MATLAB scripts. Fluence modulated treatment plans computed on pCT were mapped with stitched CBCT and the dosimetric analyses such as dose-profile comparison, 3D-gamma (γ) evaluation and dose-volume histogram (DVH) comparison were performed.

Results

Localizing scanning length of CBCT was extended by up to 15[[ce:hsp sp="0.25"/]]cm and 16[[ce:hsp sp="0.25"/]]cm in S1 and S2 strategies, respectively. Treatment plan mapping resulted in minor variations in the volumes of delineated structures and the beam centre co-ordinates. While the former showed maximum variations of −1.4% and −1.6%, the latter showed maximum of 1.4[[ce:hsp sp="0.25"/]]mm and 2.7[[ce:hsp sp="0.25"/]]mm differences in anteroposterior direction in S1 and S2 protocols, respectively. Dosimetric evaluations viz., dose profile and DVH comparisons were found to be in agreement with one another. In addition, γ-evaluation results showed superior pass-rates (≥98.5%) for both 3%/3[[ce:hsp sp="0.25"/]]mm dose-difference (DD) and distance-to-agreement (DTA) and 2%/2[[ce:hsp sp="0.25"/]]mm DD/DTA criteria with desirable dosimetric accuracy.

Conclusion

Cone beam tomographic stitching and local HU-correction strategies developed to facilitate extended localization and dose calculation enables routine adaptive re-planning while circumventing the need for repeated pCT.

Get Citation

Keywords

Cone beam computed tomography; Hounsfied unit; Rigid; Registration; Dose calculation; Adaptive radiotherapy

About this article
Title

Extended localization and adaptive dose calculation using HU corrected cone beam CT: Phantom study

Journal

Reports of Practical Oncology and Radiotherapy

Issue

Vol 23, No 2 (2018)

Pages

126-135

Published online

2018-03-01

DOI

10.1016/j.rpor.2018.01.005

Bibliographic record

Rep Pract Oncol Radiother 2018;23(2):126-135.

Keywords

Cone beam computed tomography
Hounsfied unit
Rigid
Registration
Dose calculation
Adaptive radiotherapy

Authors

K Mohamathu Rafic
S Amalan
B S Timothy Peace
B Paul Ravindran

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