Image guidance protocols: balancing imaging parameters against scan time

Bates, A.; Scaife, J.E.; Tudor, G.; Jena, R.; Romanchikova, Marina; Dean, J.C.; Hoole, A.; Simmons, M P D; Burnet, N.G.

doi:10.1259/bjr.20130385

Cited by 5 publications

(4 citation statements)

References 25 publications

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“…We chose patients who were treated with radiotherapy to pelvic lymph nodes as well as the prostate, as our previous work had demonstrated that the image guidance scans for this group were longer in the SI direction than for patients having their prostate alone treated. 20 The rectum was analysed in thirds, which is the traditional anatomical approach for this organ. 21 , 22 …”

Section: Discussionmentioning

confidence: 99%

Random variation in rectal position during radiotherapy for prostate cancer is two to three times greater than that predicted from prostate motion

Scaife

Harrison²,

Romanchikova³

et al. 2014

BJR

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Objective:Radiotherapy for prostate cancer does not explicitly take into account daily variation in the position of the rectum. It is important to accurately assess accumulated dose (DA) to the rectum in order to understand the relationship between dose and toxicity. The primary objective of this work was to quantify systematic (Σ) and random (σ) variation in the position of the rectum during a course of prostate radiotherapy.Methods:The rectum was manually outlined on the kilo-voltage planning scan and 37 daily mega-voltage image guidance scans for 10 participants recruited to the VoxTox study. The femoral heads were used to produce a fixed point to which all rectal contours were referenced.Results:Σ [standard deviation (SD) of means] between planning and treatment was 4.2 mm in the anteroposterior (AP) direction and 1.3 mm left–right (LR). σ (root mean square of SDs) was 5.2 mm AP and 2.7 mm LR. Superior–inferior variation was less than one slice above and below the planning position.Conclusion:Our results for Σ are in line with published data for prostate motion. σ, however, was approximately twice as great as that seen for prostate motion. This suggests that DA may differ from planned dose in some patients treated with radiotherapy for prostate cancer.Advances in knowledge:This work is the first to use daily imaging to quantify Σ and σ of the rectum in prostate cancer. σ was found to be greater than published data, providing strong rationale for further investigation of individual DA.

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Section: Discussionmentioning

confidence: 99%

Random variation in rectal position during radiotherapy for prostate cancer is two to three times greater than that predicted from prostate motion

Scaife

Harrison²,

Romanchikova³

et al. 2014

BJR

Self Cite

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“…Researchers argued that normal MVCT scans are superior to coarse scan for the registration of shifts in the superior–inferior directions, with an improvement in residual error of about 0·4 mm evaluated from a head phantom 15 . The spatial resolution in the longitudinal direction may be slightly compromised, but the axial resolution of coarse scan does not degrade significantly 16 …”

Section: Discussionmentioning

confidence: 99%

“…15 The spatial resolution in the longitudinal direction may be slightly compromised, but the axial resolution of coarse scan does not degrade significantly. 16 To date, Ho et al and Woodford et al agreed that images acquired in coarse scans under its corresponding reconstruction slice thickness showed no significant image quality degradation and low residual error in contrast to normal and fine mode in 4 slices/gantry rotation reconstruction. 17,18 These non-significant differences have pronounced the possibility of selecting the coarse mode for MVCT verification in routine practice so as to keep the radiation dose as minimal as possible.…”

Section: Optimisation On Imaging Modementioning

confidence: 93%

Imaging dose of megavoltage computed tomography (MVCT) for treatment verification in the tomotherapy of breast cancer

et al. 2017

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AimThe purpose of this study was to investigate whether significant difference exists on radiation dose delivered to organs at risks in megavoltage computed tomography (MVCT) verification using three predefined scanning modes, namely fine (2 mm), normal (4 mm) and coarse (6 mm). This will provide information for the imaging protocol of tomotherapy for the left breast.Materials and methodsOrgan doses were measured using thermoluminescent dosimeters (TLD-100) placed within a female Rando phantom for MVCT imaging. Kruskal–Wallis test was conducted with p<0·05 to evaluate the significant difference between the three MVCT scanning modes.ResultsStatistically significant difference existed in organ absorbed dose between different scan mode selections (p<0·001). Relative to the normal scan selection (4 mm), the absorbed dose to the organs of interests can be scaled down by 0·7 and scaled up by 2·1 for coarse (6 mm) and fine scans (2 mm) respectively.ConclusionsOptimisation of imaging protocols is of paramount importance to keep the radiation exposure ‘as low as reasonably achievable’. The recommendation of undergoing daily coarse mode for MVCT verification in breast tomotherapy not only mitigates the radiation exposure to normal tissues, but also trims the scan-acquisition time.

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“…MVCT specifications were: 512 × 512 pixels per slice, pixel size 0.754 mm, slice thickness 6 mm. The field of view for MVCT imaging was limited to typically 8–12 slices according to local protocols to minimise additional dose and time for prostate IGRT (Bates et al 2013), so only a proportion of the rectum was imaged.…”

Section: Methodsmentioning

confidence: 99%

Autosegmentation of the rectum on megavoltage image guidance scans

Shelley

Sutcliffe

Harrison

et al. 2019

Biomed. Phys. Eng. Express

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Autosegmentation of image guidance (IG) scans is crucial for streamlining and optimising delivered dose calculation in radiotherapy. By accounting for interfraction motion, daily delivered dose can be accumulated and incorporated into automated systems for adaptive radiotherapy. Autosegmentation of IG scans is challenging due to poorer image quality than typical planning kilovoltage computed tomography (kVCT) systems, and the resulting reduction of soft tissue contrast in regions such as the pelvis makes organ boundaries less distinguishable. Current autosegmentation solutions generally involve propagation of planning contours to the IG scan by deformable image registration (DIR). Here, we present a novel approach for primary autosegmentation of the rectum on megavoltage IG scans acquired during prostate radiotherapy, based on the Chan-Vese algorithm. Pre-processing steps such as Hounsfield unit/intensity scaling, identifying search regions, dealing with air, and handling the prostate, are detailed. Post-processing features include identification of implausible contours (nominally those affected by muscle or air), 3D self-checking, smoothing, and interpolation. In cases where the algorithm struggles, the best estimate on a given slice may revert to the propagated kVCT rectal contour. Algorithm parameters were optimised systematically for a training cohort of 26 scans, and tested on a validation cohort of 30 scans, from 10 patients. Manual intervention was not required. Comparing Chan-Vese autocontours with contours manually segmented by an experienced clinical oncologist achieved a mean Dice Similarity Coefficient of 0.78 (SE < 0.011). This was comparable with DIR methods for kVCT and CBCT published in the literature. The autosegmentation system was developed within the VoxTox Research Programme for accumulation of delivered dose to the rectum in prostate radiotherapy, but may have applicability to further anatomical sites and imaging modalities.

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Image guidance protocols: balancing imaging parameters against scan time

Cited by 5 publications

References 25 publications

Random variation in rectal position during radiotherapy for prostate cancer is two to three times greater than that predicted from prostate motion

Random variation in rectal position during radiotherapy for prostate cancer is two to three times greater than that predicted from prostate motion

Imaging dose of megavoltage computed tomography (MVCT) for treatment verification in the tomotherapy of breast cancer

Autosegmentation of the rectum on megavoltage image guidance scans

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