Introduction
IGRT utilizes fractional image guidance to improve the agreement between the treatment plan and the dose delivered to the patient throughout the course of the treatment.1,2 Due to the steep dose fall-off, which is a characteristic feature of the IMRT and VMAT techniques aiming to spare the OARs, strict inverse treatment planning is required.3-10 Inter-fractional deviations in dose delivery are unavoidable in the current treatment process due to changes in bladder and rectal filling, changes to tumor size and internal organ deformation.1,2,11 DIR has been used to remap each day’s dose from the fractional CBCT, to the pCT, utilizing algorithms to warp doses to a reference geometry and allowing comparison of DVHs.1,2,7,12,13 In order for IGRT to be most accurate, the specific anatomy to which each fraction of treatment was administered has to be considered.
Typical implementation of DIR relies on a voxel intensity-based approach in order to register sets.14-17 However, recent studies suggest hybrid methods that rely on contour-based information while preserving the spatial relationship of information in intensity-based DIR methods provides improved performance over methods that rely solely on intensity- or contour- based methods.14-23 Evaluation of DIR methods used to assess dose accumulation in OARs that experience large changes in volume such as the bladder and rectum in the treatment of prostate cancer must consider image guidance modality and sources of variation that lead to uncertainty in the assessment of volumes related to high dose gradients.
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Geometric uncertainty in radiotherapy relates to inaccuracies in delivering dose
distribution to a specific 3D space.4 The IRCU defines two such sources inaccuracy: patient set- up variation, and organ motion and deformation.24 Patient set-up variation is largely mitigated through image-guided pretreatment patient realignment.16 The greatest challenge in reducing total geometric uncertainty in the future remains correction for organ deformation throughout treatment. Volumetric uncertainty relates to delineation challenges regarding patient anatomy and tumor volume.4 Both geometric and volumetric uncertainty must be overcome in order to accurately accumulate delivered dose based on specific anatomy.
This study aims at examining the impact of imaging modality used for IGRT and DIR algorithms (normalized intensity-based “intensity-based” and hybrid shadowed normalized intensity-based “contour-based” algorithms) in the accuracy of estimating the accumulated from all the fractions delivered dose distribution. Evaluation of dose delivery accumulation based on scaling a subset of fractions aims to estimate the benefit of partial automation in reducing
workload demand while maintaining the improved accuracy of dose accumulation that considers fractional anatomy. Determination of the variation of dose delivered to the OARs during
treatment of prostate cancer is a critical step in assessing the relationship of OAR delivered dose and patient outcome.
Section 4.1 Materials and Methods
Dataset Characterization
20 patients treated for prostate cancer using VMAT/IMRT were selected for this analysis. For the 10 IMRT patients, the CT-on-rails (CTOR) system was used for image guidance,
whereas the 10 VMAT patients were treated using the kV-CBCT modality of Elekta’s Versa HD linac. For each patient a number of image sets were collected. Those were comprised of the
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planning CT, fractional image guidance scans, planning contours, and planned dose distributions. The CTOR images consisted of 512 x 512 pixel slices with a field of view (FOV) depth of 50 to 100 pixels and voxel dimensions of 1 mm x 1 mm x 3 mm, while the CBCT images consisted of 512 x 512 pixel slices with a FOV depth of 50 to 100 pixels and voxel dimensions of 0.98 mm x 0.98 mm x 3 mm. A total of 453 fractions across those 20 patients were analyzed using bladder and rectum as the primary OARs.
Manual Fractional Contour Delineation
Image data was imported to MIM version 6.8 beta, a software suite developed by MIM Software, Inc. (Cleveland, OH). For 10 of the patients (5 of the CTOR and 5 of the CBCT groups), the contours of bladder and rectum were manually delineated on each fraction by a radiation oncologist. The remaining 10 patients had manually delineated contours on the first five fractions and weekly thereafter.
Contour Propagation and Image Registration
An initial RIR algorithm was applied on the scans of each fraction using the pCT as reference. Subsequently, a DIR algorithm registered those scans with the pCT for each
accumulation interval (daily and weekly). One DIR algorithm employed a normalized intensity- based (NIB) DIR approach (“intensity-based”), while the second DIR algorithm used contour- based together with a NIB DIR approach that incorporated physician-defined volumetric feedback for each fraction (“contour-based”). The contour-based algorithm achieved contrast enhancement of the interior regions of the defined volumes through the addition of a scalar value to the HU values of the bladder voxels and application of a flat intensity mask technique applied to the rectum voxels. The deformation vector field for each registration algorithm was applied to propagate the contours of bladder and rectum from the pCT to each fractional image. A graphical
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representation of the data processing procedure is shown in Fig. 4.1. An evaluation of the accuracy of the three DIR algorithms was performed in a prior study. Fig. 4.2 provides an example of the contour propagation and manual delineation procedure. Fig. 4.3 illustrates the results of contour propagation using each of the DIR algorithms.
Fig. 4.1. Dose Accumulation Data Processing Procedure. Graphical representation of the data processing, which was applied to each patient. This flow-chart outlines the stages to accumulate the dose delivered to the OARs throughout treatment.
Dose Accumulation and Dosimetrics Calculation
The deformation vector fields derived from both DIR contour propagation models informed the dose translations between planning CT and image guidance. Fig. 4.4 shows a depiction of the dose translation and accumulation process for a single patient. The planning CT was used as a reference to accumulate dose based on the applied DIR algorithm in daily and weekly accumulation sets. The mean dose, D1cc (dose to the ‘hottest’ 1cc of the organ), and V50
(volume of the organ receiving at least 50Gy) dose metrics were calculated from the DVH of the accumulated doses.
The accumulated dose distributions were compared with the planned doses to the OARs via the mean dose, D1cc, and V50 dose metrics to assess the effects of internal organ deformation,
variable bladder and rectal filling states, and other volumetric uncertainties present throughout the course of the treatment. Delivered doses were accumulated on a daily or weekly basis. In the
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latter case, the weekly delivered doses were scaled to account for the rest fractions of the week. A comparison was performed between the daily and weekly accumulation procedures in order to realize whether there is a relation between the frequency of imaging guidance acquisition and accuracy in accumulated delivered dose estimation.
Fig. 4.2. Contour Propagation Model. Top) Illustration of the deformable registration between the pCT and a given CBCT and propagation of the planned contours to CBCT. Bottom) Illustration of the DIR propagated contours and comparison against the manually delineated contours.
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Fig. 4.3. Contour Propagation Comparison. Left: Original CBCT image data from three different fractions of a prostate cancer patient. The contours of the bladder and rectum shown in red are the contours that were manually delineated on the CBCT by a physician. The contours in yellow are the contours that were propagated from the planning CT using the NIB DIR. Right: The same CBCT image data are shown following contrast enhancement. The manually delineated contours (red) were used by the contour-based hybrid NIB DIR to guide the propagation of the planned contours (yellow).
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Fig. 4.4. Dose Accumulation Model. Graphical representation of the dose registration and accumulation procedure, which was applied on each OAR and DIR algorithm. Image guidance was generated with CBCT for the patients treated on Elekta Versa, and CT-on-rails for the patients treated on the Siemens.
Statistical Analysis
We analyzed difference in metrics (mean dose, D1cc, and V50) between different
algorithms (planned, intensity based, and contour based method) using linear mixed effect (LME) models. Given a metric (e.g., D1cc), modality (CT or CBCT), and location (Bladder or
Rectum), there were up to six values per subject, corresponding to different combinations of accumulation interval (daily or weekly) and algorithms. The observed metric values were
clustered within subjects (patients) and were thus correlated. We employ LME model to account for such correlated data. Specifically, in the LME model, the metric value (e.g., D1cc) was the
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based). There were two-layer of random effects, accumulation interval and subject, because metric values for different algorithms is clustered in accumulation interval (daily or weekly), and accumulation interval is then clustered in subjects. Difference between any two algorithms was claimed as significant if the corresponding estimated contrast was significantly different from 0 at 2-sided alpha level 0.05, using Tukey’s method to adjust for multiple pairwise comparisons. We use a similar procedure to examine the difference between daily and weekly metric values, except that we treat accumulation interval as a fixed effect, and algorithms (only intensity based or contour based) and subject as the two-layer random effects. LME model analysis was
conducted using SAS 9.4 (SAS Institute Cary, NC).
Section 4.2 Results
Fig. 4.5 displays the delivered dose distributions and OAR contours (propagated via DIR or manually delineated) for two representative patients from each IGRT imaging modality (CT-on- rails and CBCT). Fig. 4.5 illustrates the effects that usually moderate changes in internal
anatomy may have on the dose delivered to organs at risk during treatment of prostate cancer with IMRT/VMAT. The information in this figure indicate that the ability or a DIR algorithm to properly segment a structure (e.g. OAR) directly affects the ability of automated methods to accurately determine the dose accumulated in this structure. Fig. 4.6 displays the planned and delivered DVHs of bladder and rectum for two representative patients, for each of the two applied DIR algorithms. The plots indicate that the deviation of the delivered from the planned DVHs was more pronounced for the intensity-based NIB DIR than for the contour-based NIB DIR. Greater deviation between the planned and delivered DVHs was observed in the CBCT than the CTOR case. Fig. 4.7 displays a comparison of the planned and delivered DVHs for two patients from each of the imaging modality groups. For the delivered doses, two sets of DVHs
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are plotted, which are based on daily and weekly dose accumulation using the contour-based NIB DIR. Fig. 4.8 displays the same information for the intensity-based NIB DIR.
Fig. 4.5. Isodose Overlay. Axial slices illustrating bladder, rectum and isodose lines from two representative patients with different IGRT imaging modalities CT-on-rails (left) and Cone Beam CT (right). In the upper panel, the planning CT is shown. In the lower panel, the IGRT images are shown with the shifted dose distributions overlaid. In the IGRT images there are three sets of contours for bladder and rectum, the manually drawn (yellow), the intensity-based DIR (light blue) and the contour-based DIR (orange).
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Fig. 4.6. Accumulated Dose Volume Histograms by Modality. DVHs of two representative patients with different IGRT imaging modalities: CT-on-rails (left) and Cone Beam CT (right). In each plot, the DVHs of bladder and rectum from the original plan, accumulated from all the fractions using the intensity-based deformable image registration (DIR) algorithm and accumulated from all the fractions using the contour-based deformable image registration (DIR) algorithm are shown. The solid lines refer to bladder and the dashed lines to rectum.
Fig. 4.7. Contour-based Dose Volume Histograms by Accumulation Interval. DVHs of two representative patients with different IGRT imaging modalities: CT-on-rails (left) and Cone Beam CT (right). In each plot, the DVHs of bladder and rectum from the original plan, accumulated from all the fractions using the contour-based deformable image registration (DIR) algorithm and accumulated from weekly fractions using the contour-based deformable image registration (DIR) algorithm are shown. The solid lines refer to bladder and the dashed lines to rectum.
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Fig. 4.8. Intensity-based Dose Volume Histograms by Accumulation Interval. DVHs of two representative patients with different IGRT imaging modalities: CT-on-rails (left) and Cone Beam CT (right). In each plot, the DVHs of bladder and rectum from the original plan, accumulated from all the fractions the using intensity-based deformable image registration (DIR) algorithm and the accumulated from weekly fractions using intensity-based deformable image registration (DIR) algorithm are shown. The solid lines refer to bladder and the dashed lines to rectum.
Table 4.1 displays the dose metrics of mean dose, D1cc, and V50 for bladder and rectum
for all the CTOR patients, while Table 4.2 displays the values of the same metrics for all the CBCT patients. In general, those metrics indicate close agreement of each accumulation method with the planned dose delivery. However, in individual patients large deviations are also
observed.
The data from the selected patients demonstrated a greater deviation in the accumulated DVHs between the two IGRT imaging modalities and the two DIR algorithms rather than due to the dose accumulation frequency. Large inter-patient variability in the relation between the planned and accumulated doses (for each DIR algorithm and dose accumulation frequency) appeared to be related to the geometric inter-fraction variability of the specific anatomy and the proximity of the OARs to the target. Fig. 4.9 displays weekly accumulation series for two representative patients against the scaled planned dose for the bladder and rectum. Relatively uniform accumulation deviation growth was observed against the scaled planned dose delivery,
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indicating that variation of accumulated dose delivery compared to the planned dose delivery largely results from volumetric uncertainties in delineation of specific anatomy than with the geometric uncertainties of dose delivery or drastic changes to organ filling on a specific treatment fraction.
Fig. 4.9. Weekly Accumulated Dose Volume Histograms. Weekly Accumulated DVHs from all the fractions dose (solid) versus scaled planned DVH (dashed) for bladder (top) and rectum (bottom) for two representative patients of the CTOR (left) and CBCT (right) IGRT groups.
Table 4.1. CTOR Dosimetrics Summary. Summary of different dose metrics per organ (bladder, rectum), patient, and DIR algorithm (intensity-based, contour- based), for the CTOR cohort and weekly accumulation interval. The differences from the corresponding values from the original plan are listed as percent deviation.
CTOR1 Dif. from PlanCTOR2 Dif. from PlanCTOR3 Dif. from PlanCTOR4 Dif. from PlanCTOR5 Dif. from Plan CTOR6 Dif. from PlanCTOR7 Dif. from PlanCTOR8 Dif. from PlanCTOR9 Dif. from PlanCTOR10 Dif. from Plan Plan 66.60 0.00 65.68 0.00 39.73 0.00 51.53 0.00 48.81 0.00 Plan 53.04 0.00 51.44 0.00 38.21 0.00 42.97 0.00 57.62 0.00 Intensity-based 64.07 -3.80 64.63 -1.60 49.64 24.94 56.18 9.02 48.43 -0.78 Intensity-based 56.75 6.99 56.78 10.38 44.80 17.25 40.14 -6.59 57.01 -1.06 Contour-based 66.37 -0.35 65.81 0.20 50.89 28.09 54.46 5.69 43.94 -9.98 Contour-based 49.75 -6.20 57.19 11.18 40.16 5.10 43.11 0.33 57.34 -0.49 CTOR1 Dif. from PlanCTOR2 Dif. from PlanCTOR3 Dif. from PlanCTOR4 Dif. from PlanCTOR5 Dif. from Plan CTOR6 Dif. from PlanCTOR7 Dif. from PlanCTOR8 Dif. from PlanCTOR9 Dif. from PlanCTOR10 Dif. from Plan Plan 69.47 0.00 69.92 0.00 83.00 0.00 84.06 0.00 78.87 0.00 Plan 83.21 0.00 79.11 0.00 83.11 0.00 80.96 0.00 79.76 0.00 Intensity-based 69.35 -0.17 69.71 -0.30 83.03 0.04 84.09 0.04 78.86 -0.01 Intensity-based 83.67 0.55 79.18 0.09 83.12 0.01 81.02 0.07 79.24 -0.65 Contour-based 69.41 -0.09 69.85 -0.10 82.98 -0.02 84.00 -0.07 78.90 0.04 Contour-based 83.18 -0.04 79.08 -0.04 83.22 0.13 81.01 0.06 80.22 0.58 CTOR1 Dif. from PlanCTOR2 Dif. from PlanCTOR3 Dif. from PlanCTOR4 Dif. from PlanCTOR5 Dif. from Plan CTOR6 Dif. from PlanCTOR7 Dif. from PlanCTOR8 Dif. from PlanCTOR9 Dif. from PlanCTOR10 Dif. from Plan Plan 97.26 0.00 93.61 0.00 25.40 0.00 45.52 0.00 48.05 0.00 Plan 49.36 0.00 47.50 0.00 32.29 0.00 31.44 0.00 67.07 0.00 Intensity-based 92.06 -5.35 92.34 -1.36 40.82 60.71 54.73 20.23 47.42 -1.31 Intensity-based 56.57 14.61 57.83 21.75 39.05 20.94 29.93 -4.80 65.83 -1.85 Contour-based 96.86 -0.41 94.16 0.59 45.43 78.86 51.45 13.03 41.65 -13.32 Contour-based 43.68 -11.51 59.32 24.88 34.95 8.24 32.05 1.94 66.18 -1.33
CTOR1 Dif. from PlanCTOR2 Dif. from PlanCTOR3 Dif. from PlanCTOR4 Dif. from PlanCTOR5 Dif. from Plan CTOR6 Dif. from PlanCTOR7 Dif. from PlanCTOR8 Dif. from PlanCTOR9 Dif. from PlanCTOR10 Dif. from Plan Plan 41.94 0.00 50.33 0.00 47.21 0.00 50.94 0.00 52.19 0.00 Plan 46.14 0.00 46.97 0.00 44.17 0.00 30.78 0.00 52.77 0.00 Intensity-based 38.69 -7.75 47.00 -6.62 47.75 1.14 48.50 -4.79 52.82 1.21 Intensity-based 44.12 -4.38 45.46 -3.21 38.81 -12.13 28.62 -7.02 51.73 -1.97 Contour-based 41.54 -0.95 49.03 -2.58 46.54 -1.42 48.44 -4.91 52.95 1.46 Contour-based 46.12 -0.04 41.07 -12.56 40.96 -7.27 28.39 -7.76 52.23 -1.02 CTOR1 Dif. from PlanCTOR2 Dif. from PlanCTOR3 Dif. from PlanCTOR4 Dif. from PlanCTOR5 Dif. from Plan CTOR6 Dif. from PlanCTOR7 Dif. from PlanCTOR8 Dif. from PlanCTOR9 Dif. from PlanCTOR10 Dif. from Plan Plan 67.68 0.00 69.11 0.00 78.31 0.00 79.05 0.00 75.53 0.00 Plan 80.36 0.00 77.01 0.00 79.37 0.00 78.79 0.00 75.81 0.00 Intensity-based 66.22 -2.16 69.00 -0.16 77.79 -0.66 75.62 -4.34 77.53 2.65 Intensity-based 79.16 -1.49 76.08 -1.21 71.04 -10.50 77.07 -2.18 75.07 -0.98 Contour-based 67.54 -0.21 68.98 -0.19 76.39 -2.45 74.81 -5.36 77.25 2.28 Contour-based 80.04 -0.40 67.89 -11.84 77.05 -2.92 76.49 -2.92 75.04 -1.02 CTOR1 Dif. from PlanCTOR2 Dif. from PlanCTOR3 Dif. from PlanCTOR4 Dif. from PlanCTOR5 Dif. from Plan CTOR6 Dif. from PlanCTOR7 Dif. from PlanCTOR8 Dif. from PlanCTOR9 Dif. from PlanCTOR10 Dif. from Plan Plan 43.64 0.00 61.62 0.00 41.56 0.00 47.15 0.00 60.23 0.00 Plan 36.17 0.00 39.72 0.00 37.60 0.00 21.96 0.00 56.24 0.00 Intensity-based 33.57 -23.08 53.66 -12.92 42.50 2.26 42.30 -10.29 59.16 -1.78 Intensity-based 34.25 -5.31 37.03 -6.77 25.02 -33.46 17.77 -19.08 52.17 -7.24 Contour-based 42.75 -2.04 58.66 -4.80 40.60 -2.31 41.40 -12.20 63.38 5.23 Contour-based 38.00 5.06 21.35 -46.25 30.50 -18.88 17.56 -20.04 54.41 -3.25 D1cc (Gy) V50 (%) Bladder
Mean Dose (Gy)
D1cc (Gy)
V50 (%)
Rectum
Mean Dose (Gy)
Table 4.2. CBCT Dosimetrics Summary. Summary of different dose metrics per organ (bladder, rectum), patient, and DIR algorithm (intensity-based, contour- based), for the CBCT cohort and weekly accumulation interval. The differences from the corresponding values from the original plan are listed as percent deviation.
CBCT1 Dif. from PlanCBCT2 Dif. from PlanCBCT3 Dif. from PlanCBCT4 Dif. from PlanCBCT5 Dif. from Plan CBCT6 Dif. from PlanCBCT7 Dif. from PlanCBCT8 Dif. from PlanCBCT9 Dif. from PlanCBCT10 Dif. from Plan Plan 37.87 0.00 43.77 0.00 18.60 0.00 50.64 0.00 21.41 0.00 Plan 46.28 0.00 37.02 0.00 43.85 0.00 36.22 0.00 13.87 0.00 Intensity-based 37.12 -1.98 49.65 13.43 23.24 24.95 53.89 6.42 30.05 40.35 Intensity-based 57.34 23.90 39.04 5.46 50.65 15.51 37.97 4.83 11.12 -19.83 Contour-based 37.30 -1.51 39.15 -10.56 21.81 17.26 43.99 -13.13 27.19 27.00 Contour-based 60.28 30.25 36.17 -2.30 45.81 4.47 33.44 -7.68 15.86 14.35 CBCT1 Dif. from PlanCBCT2 Dif. from PlanCBCT3 Dif. from PlanCBCT4 Dif. from PlanCBCT5 Dif. from Plan CBCT6 Dif. from PlanCBCT7 Dif. from PlanCBCT8 Dif. from PlanCBCT9 Dif. from PlanCBCT10 Dif. from Plan Plan 55.27 0.00 69.99 0.00 68.84 0.00 68.68 0.00 46.48 0.00 Plan 80.58 0.00 46.80 0.00 68.66 0.00 53.83 0.00 46.56 0.00 Intensity-based 53.90 -2.48 68.24 -2.50 68.13 -1.03 69.01 0.48 46.04 -0.95 Intensity-based 80.49 -0.11 46.31 -1.05 68.07 -0.86 54.33 0.93 46.32 -0.52 Contour-based 51.84 -6.21 68.26 -2.47 67.96 -1.28 68.43 -0.36 46.03 -0.97 Contour-based 80.57 -0.01 46.01 -1.69 67.98 -0.99 50.66 -5.89 46.44 -0.26 CBCT1 Dif. from PlanCBCT2 Dif. from PlanCBCT3 Dif. from PlanCBCT4 Dif. from PlanCBCT5 Dif. from Plan CBCT6 Dif. from PlanCBCT7 Dif. from PlanCBCT8 Dif. from PlanCBCT9 Dif. from PlanCBCT10 Dif. from Plan Plan 5.21 0.00 54.28 0.00 15.47 0.00 61.06 0.00 0.00 0.00 Plan 41.62 0.00 0.00 0.00 46.66 0.00 3.59 0.00 0.00 0.00 Intensity-based 2.76 -47.02 64.90 19.57 17.72 14.54 65.60 7.44 0.00 0.00 Intensity-based 62.71 50.67 0.00 0.00 59.47 27.45 4.44 23.68 0.00 0.00 Contour-based 0.77 -85.22 43.75 -19.40 15.52 0.32 48.83 -20.03 0.00 0.00 Contour-based 69.82 67.76 0.00 0.00 48.15 3.19 0.59 -83.57 0.00 0.00
CBCT1 Dif. from PlanCBCT2 Dif. from PlanCBCT3 Dif. from PlanCBCT4 Dif. from PlanCBCT5 Dif. from Plan CBCT6 Dif. from PlanCBCT7 Dif. from PlanCBCT8 Dif. from PlanCBCT9 Dif. from PlanCBCT10 Dif. from Plan Plan 24.42 0.00 33.19 0.00 34.77 0.00 34.86 0.00 14.52 0.00 Plan 53.72 0.00 30.32 0.00 36.62 0.00 28.95 0.00 11.42 0.00 Intensity-based 22.82 -6.55 29.75 -10.36 38.45 10.58 31.08 -10.84 20.01 37.81 Intensity-based 55.85 3.97 33.88 11.74 32.05 -12.48 27.21 -6.01 9.78 -14.36 Contour-based 23.63 -3.24 31.02 -6.54 36.06 3.71 30.58 -12.28 20.20 39.12 Contour-based 57.57 7.17 32.28 6.46 35.00 -4.42 29.14 0.66 12.04 5.43 CBCT1 Dif. from PlanCBCT2 Dif. from PlanCBCT3 Dif. from PlanCBCT4 Dif. from PlanCBCT5 Dif. from Plan CBCT6 Dif. from PlanCBCT7 Dif. from PlanCBCT8 Dif. from PlanCBCT9 Dif. from PlanCBCT10 Dif. from Plan Plan 45.09 0.00 66.88 0.00 67.84 0.00 69.15 0.00 46.06 0.00 Plan 79.53 0.00 45.36 0.00 68.05 0.00 46.69 0.00 45.75 0.00 Intensity-based 42.99 -4.66 60.76 -9.15 67.20 -0.94 67.88 -1.84 46.00 -0.13 Intensity-based 79.75 0.28 45.88 1.15 66.55 -2.20 45.86 -1.78 39.11 -14.51 Contour-based 44.15 -2.08 67.55 1.00 67.40 -0.65 67.67 -2.14 46.02 -0.09 Contour-based 80.24 0.89 45.43 0.15 67.12 -1.37 46.43 -0.56 44.01 -3.80 CBCT1 Dif. from PlanCBCT2 Dif. from PlanCBCT3 Dif. from PlanCBCT4 Dif. from PlanCBCT5 Dif. from Plan CBCT6 Dif. from PlanCBCT7 Dif. from PlanCBCT8 Dif. from PlanCBCT9 Dif. from PlanCBCT10 Dif. from Plan Plan 0.00 0.00 19.36 0.00 26.92 0.00 25.79 0.00 0.00 0.00 Plan 52.72 0.00 0.00 0.00 27.74 0.00 0.19 0.00 0.00 0.00 Intensity-based 0.00 0.00 13.65 -29.49 34.36 27.64 14.84 -42.46 0.00 0.00 Intensity-based 60.35 14.47 0.00 0.00 17.21 -37.96 0.00 -100.00 0.00 0.00 Contour-based 0.00 0.00 19.30 -0.31 29.63 10.07 15.87 -38.46 0.00 0.00 Contour-based 61.97 17.55 0.00 0.00 20.70 -25.38 0.00 -100.00 0.00 0.00
V50 (%)
Bladder
Mean Dose (Gy)
D1cc (Gy)
V50 (%)
Rectum
Mean Dose (Gy)
D1cc (Gy)
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Fig. 4.10 displays the average values and 95% confidence intervals for CT-on-rails for the examined dose metrics for each DIR algorithm and the plan, while Fig. 4.11 displays the same results for the case of CBCT. The same type of analysis was performed regarding the dose accumulation frequency (daily and weekly) and the results are shown in Figs. 4.12 and 4.13. Table 4.3 displays p-values assessing the similarity of different dose metrics between each DIR algorithm against each other and against the plan.
Fig. 4.10. Accumulation Algorithm CT Dosimetrics 95% Confidence Intervals. Comparison of the average values and 95% confidence intervals of the delivered and planned doses for each algorithm for the CT modality for the