Feasibility of CBCT‐based dose with a patient‐specific stepwise HU‐to‐density curve to determine time of replanning

Abstract

Purpose(a) To investigate the accuracy of cone‐beam computed tomography (CBCT)–derived dose distributions relative to fanbeam–based simulation CT‐derived dose distributions; and (b) to study the feasibility of CBCT dosimetry for guiding the appropriateness of replanning.Methods and materialsImage data corresponding to 40 patients (10 head and neck [HN], 10 lung, 10 pancreas, 10 pelvis) who underwent radiation therapy were randomly selected. Each patient had both intensity‐modulated radiation therapy and volumetric‐modulated arc therapy plans; these 80 plans were subsequently recomputed on the CBCT images using a patient‐specific stepwise curve (Hounsfield units‐to‐density). Planning target volumes (PTVs; D98%, D95%, D2%), mean dose, and V95% were compared between simulation‐CT–derived treatment plans and CBCT‐based plans. Gamma analyses were performed using criterion of 3%/3 mm for three dose zones (>90%, 70%~90%, and 30%~70% of maximum dose). CBCT‐derived doses were then used to evaluate the appropriateness of replanning decisions in 12 additional HN patients whose plans were previously revised during radiation therapy because of anatomic changes; replanning in these cases was guided by the conventional observed source‐to‐skin‐distance change‐derived approach.ResultsFor all disease sites, the difference in PTV mean dose was 0.1% ± 1.1%, D2% was 0.7% ± 0.1%, D95% was 0.2% ± 1.1%, D98% was 0.2% ± 1.0%, and V95% was 0.3% ± 0.8%; For 3D dose comparison, 99.0% ± 1.9%, 97.6% ± 4.4%, and 95.3% ± 6.0% of points passed the 3%/3 mm criterion of gamma analysis in high‐, medium‐, and low‐dose zones, respectively. The CBCT images achieved comparable dose distributions. In the 12 previously replanned 12 HN patients, CBCT‐based dose predicted well changes in PTV D2% (Pearson linear correlation coefficient = 0.93; P < 0.001). If 3% of change is used as the replanning criteria, 7/12 patients could avoid replanning.Conclusions CBCT‐based dose calculations produced accuracy comparable to that of simulation CT. CBCT‐based dosimetry can guide the decision to replan during the course of treatment.

An evaluation of techniques for dose calculation on cone beam computed tomography

“…17 More intensive techniques have attempted to overcome the CBCT image quality issues by employing density override techniques. 11,16,18 Many techniques are based on exploiting the accurate HU information contained within pCT images to correct the CBCT images. Marchant et al developed a software to correct CBCT images by comparing corresponding pCT and CBCT axial slices.…”

Enhancement of Hounsfield unit distribution in cone-beam CT images for adaptive radiation therapy: Evaluation of a hybrid correction approach

“…In this study the accuracy of a hybrid method combining two pCTbased approaches to correct HU distribution in CBCT images was evaluated. In contrast to other works where these two approaches were applied singularly for correcting CBCT images for dose calculation [19,[23][24][25][26][27][28], our proposed method consisted of applying first a HM process, followed by MLT on CBCT images.…”

“…These strategies include: the integration of physical instruments as anti-scatter grids to reduce the impact of scatter on the CBCT reconstruction quality [5][6][7], scatter measurement and correction based on the imaging system simulation [8][9][10][11], calibration of CBCT system using phantoms [12][13][14][15][16][17][18][19] and finally the use of pCT-based approaches. The latter approaches aim to map hounsfield units (HU) from pCT to CBCT images [20,21], match the peaks of their histograms [22,23] or assign to the CBCT images exact HU values extracted from the pCT [19,[23][24][25][26][27][28].…”

Development of a Collaboration Model between Two Cancer Centres to Maintain Patient Access to Radiation Therapy during the Replacement of a Sole CT Simulator at a Regional Cancer Centre

“…It would permit a local solution for onsite simulations of defined treatment sites using homogeneous dose calculation. The image quality was not sufficient for complex planning, as the CT numbers needed an alternative mapping methodology for dose calculation, which was not available in the current treatment planning system [5,6]. Specifically, this approach was considered for patients requiring urgent or emergent radiation treatments.…”