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. 2020 Mar-Apr;25(2):282-292.
doi: 10.1016/j.rpor.2019.11.003. Epub 2019 Dec 10.

A new strategy for craniospinal axis localization and adaptive dosimetric evaluation using cone beam CT

Kather Hussain Mohamathu Rafic  1 , Christopher Sujith  1 , Balakrishnan Rajesh  1 , Ebenezer Suman Babu S  1 , Peace Balasingh Timothy  1 , B Selvamani  1 , Paul B Ravindran  1
Affiliations

A new strategy for craniospinal axis localization and adaptive dosimetric evaluation using cone beam CT

Kather Hussain Mohamathu Rafic et al. Rep Pract Oncol Radiother. 2020 Mar-Apr.

Abstract

Background and aim: Computational complexities encountered in craniospinal irradiation (CSI) have been widely investigated with different planning strategies. However, localization of the entire craniospinal axis (CSA) and evaluation of adaptive treatment plans have traditionally been ignored in CSI treatment. In this study, a new strategy for CSI with comprehensive CSA localization and adaptive plan evaluation has been demonstrated using cone beam CT with extended longitudinal field-of-view (CBCTeLFOV).

Materials and methods: Multi-scan CBCT images were acquired with fixed longitudinal table translations (with 1 cm cone-beam overlap) and then fused into a single DICOM-set using the custom software coded in MatLab™. A novel approach for validation of CBCTeLFOV was demonstrated by combined geometry of Catphan-504 and Catphan-604 phantoms. To simulate actual treatment scenarios, at first, the end-to-end workflow of CSI with VMAT was investigated using an anthropomorphic phantom and then applied for two patients (based on random selection).

Results: The fused CBCTeLFOV images were in excellent agreement with planning CT (pCT). The custom developed software effectively manages spatial misalignments arising out of the uncertainties in treatment/setup geometry. Although the structures mapped from pCT to CBCTeLFOV showed minimal variations, a maximum spatial displacement of up to 1.2 cm (and the mean of 0.8 ± 0.3 cm) was recorded in phantom study. Adaptive plan evaluation of patient paradigms showed the likelihood of under-dosing the craniospinal target.

Conclusion: Our protocol serves as a guide for precise localization of entire CSA and to ensure adequate dose to the large and complex targets. It can also be adapted for other complex treatment techniques such as total-marrow-irradiation and total-lymphoid-irradiation.

Keywords: Adaptive radiotherapy; Cone beam CT; Craniospinal irradiation; Volumetric modulated arc therapy.

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Figures

Fig. 1
Fig. 1
Reconstructed blank slices in the multi-scanned CBCT image sets (7 half-fan cone beam volumetric scans) of an anthropomorphic phantom with a 1 cm penumbral overlap using the XI system.
Fig. 2
Fig. 2
The acquisition geometry of proposed QA approach using combined Catphan 504 and Catphan 604 phantoms for validation of fused CBCTeLFOV images.
Fig. 3
Fig. 3
The custom developed software interface with fused CBCTeLFOV image of an anthropomorphic phantom (fusion of 5 cone beam scans).
Fig. 4
Fig. 4
(a) The fused central slices of the overlapping regions occurred at slice geometry test modules of Catphan-504 (Top) and Catphan-604 (bottom), respectively, with and without MMA (arrow marks indicate the ramp alignment). (b) The pCT and multi-scan CBCTeLFOV image sets (with and without MMA) of combined Catphan phantoms (arrow marks indicate minor mismatch in the CBCTeLFOV in the absence of MMA).
Fig. 5
Fig. 5
Illustration of minor rotational shift in treatment setup during online localization with anthropomorphic phantom (arrow marks show the spatial displacements).
Fig. 6
Fig. 6
The deviation from original dose distribution at the spinal PTV regions across the field boundaries of the anthropomorphic phantom. (a) pCT and (b) CBCTeLFOV.
Fig. 7
Fig. 7
The difference in rigid registration between pCT and CBCTeLFOV (acquired on-table treatment position) of one patient with irreproducible hand position.
See this image and copyright information in PMC

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