Accumulated dose to the rectum, measured using dose–volume histograms and dose-surface maps, is different from planned dose in all patients treated with radiotherapy for prostate cancer

Abstract

Objective:We sought to calculate accumulated dose (DA) to the rectum in patients treated with radiotherapy for prostate cancer. We were particularly interested in whether dose–surface maps (DSMs) provide additional information to dose–volume histograms (DVHs).Methods:Manual rectal contours were obtained for kilovoltage and daily megavoltage CT scans for 10 participants from the VoxTox study (380 scans). Daily delivered dose recalculation was performed using a ray-tracing algorithm. Delivered DVHs were summated to create accumulated DVHs. The rectum was considered as a cylinder, cut and unfolded to produce daily delivered DSMs; these were summated to produce accumulated DSMs.Results:Accumulated dose-volumes were different from planned in all participants. For one participant, all DA levels were higher and all volumes were larger than planned. For four participants, all DA levels were lower and all volumes were smaller than planned. For each of these four participants, ≥1% of pixels on the accumulated DSM received ≥5 Gy more than had been planned.Conclusion:Differences between accumulated and planned dose-volumes were seen in all participants. DSMs were able to identify differences between DA and planned dose that could not be appreciated from the DVHs. Further work is needed to extract the dose data embedded in the DSMs. These will be correlated with toxicity as part of the VoxTox Programme.Advances in knowledge:DSMs are able to identify differences between DA and planned dose that cannot be appreciated from DVHs alone and should be incorporated into future studies investigating links between DA and toxicity.

Patterns in ano-rectal dose maps and the risk of late toxicity after prostate IMRT

“…Therefore, the current analysis was performed on the planned dose rather than an estimate of delivered dose. Scaife et al [39] showed that there can be large differences in DSM pixel values when using planned and delivered dose, respectively. As shown convincingly in [14], models based on planned dose have a lower predictive power due to the lower accuracy of the input data for model fitting.…”

Prostate external beam radiotherapy combined with high-dose-rate brachytherapy: dose-volume parameters from deformably-registered plans correlate with late gastrointestinal complications

“…A variety of methods have been used to estimate the impact of interfraction motion on rectum dose parameters and doseresponse modelling for prostate EBRT [8,52,[58][59][60][61]. To obtain appropriate mean estimates for the difference in EBRT rectum dose between the single CT based values and the motion-corrected values this study analysed the results of another study [52] that used the same registration software and registration algorithm.…”

“…It would also be useful to determine whether other aspects of the total registered dose distribution add predictive capability to dose-toxicity modelling e.g. including dose-shape toxicity modelling [60]. Exploring the association between toxicity and doses to other organs or regions may be useful for further explaining the incidence of toxicity (e.g.…”

Unwrapping 3D complex hollow organs for spatial dose surface analysis

“…This has been done previously on structures with simple geometries, such as the esophagus and rectum. 21,23,24 Munbodh et al 19 unwrap the rectum using a conformal mapping procedure 25 originally used for virtual colonography. Hoogeman et al 23 find the central axis of the rectum using the approximate minimum distance field approach and then create orthogonal cross-sections as described by Zhou et al 21 for the esophagus and the rectum.…”

“…Compared to previous methods applied to other organs, 21,23,24 which can only be used when the CT transaxial slices can be unwrapped individually, this approach allows for the unwrapping of any tubular organ and also provides a mechanism for checking and fixing overlapping planes. However, this thorough approach to a generalizable nonoverlapping tubular unwrapping technique also leads to an element of human interaction in the selection of start and end points.…”