Parotid Gland Dose in Intensity-Modulated Radiotherapy for Head and Neck Cancer: Is What You Plan What You Get?

Deformable registration has migrated from a research topic to a widely used clinical tool that can improve radiotherapeutic treatment accuracy by tracking anatomical changes. Although various mathematical formulations have been reported in the literature and implemented in commercial software, we lack a straightforward method to verify a given solution in routine clinical use. We propose a metric using concepts derived from vector analysis that complements the standard evaluation tools to identify unrealistic wrappings in a displacement field. At the heart of the proposed procedure is identification of vortexes in the displacement field that do not correspond to underlying anatomical changes. Vortexes are detected and their intensity quantified using the CURL operator and presented as a vortex map overlaid on the original anatomy for rapid identification of problematic regions. We show application of the proposed metric on clinical scenarios of adaptive radiotherapy and treatment response assessment, where the CURL operator quantitatively detected errors in the displacement field and identified problematic regions that were invisible to classical voxel‐based evaluation methods. Unrealistic warping not visible to standard voxel‐based solution assessment can produce erroneous results when the deformable solution is applied on a secondary dataset, such as dose matrix in adaptive therapy or PET data for treatment response assessment. The proposed metric for evaluating deformable registration provides increased usability and accuracy of detecting unrealistic deformable registration solutions when compared to standard intensity‐based approaches. It is computationally efficient and provides a valuable platform for the clinical acceptance of image‐guided radiotherapy.PACS numbers: 87.57.nj; 87.55.Qr; 87.57.cp

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

A measure to evaluate deformable registration fields in clinical settings

Schreibmann

Pantalone

Waller

et al. 2012

“…This is reflected in the smaller systematic errors presented in this study of 1.3–1.4 mm as compared to other published works, where errors on the order of 2.0 mm were observed (range: 1–3 mm). ( 15 – 16 , 24 – 26 ) This is an important point, as offline correction strategies have been shown to significantly reduce systematic setup errors in head and neck patients. ( 25 – 26 ) In margin recipes, systematic errors are the dominant component of margin calculation.…”

Section: Discussionmentioning

confidence: 99%

“…Application of measured setup errors to HN‐IMRT dose distributions were reported previously in a few studies. For example, Lawson et al ( 11 ) measured setup errors for 12 patients using daily orthogonal kV X‐ray images, Hong et al ( 10 ) used a high precision optically guided localization system for 10 patients; and O'Daniel et al ( 16 ) used an integrated CT‐linac system for 11 patients. Comparatively, CBCT localization offers advantages over orthogonal image pair and optical guidance systems, such as an improved accuracy of measurement from 3D CT images, as well as a greater number of parameters (i.e.…”

Section: Introductionmentioning

confidence: 99%

“…( 17 – 18 ) Additionally, while O'Daniel et al did use CT imaging to measure patient setup errors, images were only taken twice per week throughout treatment and therefore the clinical setup error distribution used may not have been well represented. ( 16 ) In this study, we also investigated topics that have not been explored previously. These include analysis on the influence of dose distribution complexity to rigid setup errors, and investigation in the consistency of calculated dose delivered to the patient in the presence of setup errors, using two different computation methods – cumulative and average fractional summation.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Dosimetric assessment of rigid setup error by CBCT for HN‐IMRT

Worthy

2010

Dose distributions in HN‐IMRT are complex and may be sensitive to the treatment uncertainties. The goals of this study were to evaluate: 1) dose differences between plan and actual delivery and implications on margin requirement for HN‐IMRT with rigid setup errors; 2) dose distribution complexity on setup error sensitivity; and 3) agreement between average dose and cumulative dose in fractionated radiotherapy. Rigid setup errors for HN‐IMRT patients were measured using cone‐beam CT (CBCT) for 30 patients and 896 fractions. These were applied to plans for 12 HN patients who underwent simultaneous integrated boost (SIB) IMRT treatment. Dose distributions were recalculated at each fraction and summed into cumulative dose. Measured setup errors were scaled by factors of 2–4 to investigate margin adequacy. Two plans, direct machine parameter optimization (DMPO) and fluence only (FO), were available for each patient to represent plans of different complexity. Normalized dosimetric indices, conformity index (CI) and conformation number (CN) were used in the evaluation. It was found that current 5 mm margins are more than adequate to compensate for rigid setup errors, and that standard margin recipes overestimate margins for rigid setup error in SIB HN‐IMRT because of differences in acceptance criteria used in margin evaluation. The CTV‐to‐PTV margins can be effectively reduced to 1.9 mm and 1.5 mm for CTV1 and CTV2. Plans of higher complexity and sharper dose gradients are more sensitive to setup error and require larger margins. The CI and CN are not recommended for cumulative dose evaluation because of inconsistent definition of target volumes used. For fractionated radiotherapy in HN‐IMRT, the average fractional dose does not represent the true cumulative dose received by the patient through voxel‐by‐voxel summation, primarily due to the setup error characteristics, where the random component is larger than systematic and different target regions get underdosed at each fraction.PACS numbers: 87.53.Kn, 87.53.Tf.

Exploratory study of the association of volumetric modulated arc therapy (VMAT) plan robustness with local failure in head and neck cancer

Liu

Patel

Harrington

et al. 2017

This work is to show which is more relevant to cause local failures (LFs) due to patient setup uncertainty between the planning target volume (PTV) underdosage and the potential target underdosage subject to patient setup uncertainties in head and neck (H&N) cancer treated with volumetric‐modulated arc therapy (VMAT). Thirteen LFs in 10 H&N patients treated by VMAT were analyzed. Measures have been taken to minimize the chances of insufficient target delineation for these patients and the patients were clinically determined to have LF based on the PET/CT scan results by an experienced radiologist and then reviewed by a second experienced radiation oncologist. Two methods were used to identify the possible locations of LF due to underdosage: (a) examining the standard VMAT plan, in which the underdosed volume in the nominal dose distribution (UVN) was generated by subtracting the volumes receiving the prescription doses from PTVs, and (b) plan robustness analysis, in which in addition to the nominal dose distribution, six perturbed dose distributions were created by translating the CT iso‐center in three cardinal directions by the PTV margin. The coldest dose distribution was represented by the minimum of the seven doses in each voxel. The underdosed volume in the coldest dose distribution (UVC) was generated by subtracting the volumes receiving the prescription doses in the coldest dose distribution from the volumes receiving the prescription doses in the nominal dose distribution. UVN and UVC were subsequently examined for spatial association with the locations of LF. The association was tested using the binominal distribution and the Fisher's exact test of independence. We found that of 13 LFs, 11 were associated with UVCs (P = 0.011), while three were associated with UVNs (P = 0.99). We concluded that the possible target underdosage due to patient setup uncertainties appeared to be a more relevant factor associated with LF in VMAT for H&N cancer than the compromised PTV coverage at least for the patients included in this study.