Influence of image slice thickness on rectal dose–response relationships following radiotherapy of prostate cancer

Abstract

When pooling retrospective data from different cohorts, slice thicknesses of acquired computed tomography (CT) images used for treatment planning may vary between cohorts. It is, however, not known if varying slice thickness influences derived dose-response relationships. We investigated this for rectal bleeding using dose-volume histograms (DVHs) of the rectum and rectal wall for dose distributions superimposed on images with varying CT slice thicknesses. We used dose and endpoint data from two prostate cancer cohorts treated with 3D-CRT to either 74 Gy (N=159) or 78 Gy (N=159) @ 2 Gy per fraction. The rectum was defined as the whole organ with content, and the morbidity cut-off was Grade ≥2 late rectal bleeding. Rectal walls were defined as 3-mm inner margins added to the rectum. DVHs for simulated slice thicknesses from 3 to 13 mm were compared to DVHs for the originally acquired slice thicknesses at 3 and 5 mm. Volumes, mean, and maximum doses were assessed from the DVHs, and gEUD values were calculated. For each organ and each of the simulated slice thicknesses, we performed predictive modeling of late rectal bleeding using the Lyman-Kutcher-Burman (LKB) model. For the most coarse slice thickness, rectal volumes increased (≤18%), whereas maximum and mean doses decreased (≤0.8 Gy and ≤4.2 Gy, respectively). For all a values, the gEUD for the simulated DVHs were ≤1.9 Gy different than the gEUD for the original DVHs. The best-fitting LKB model parameter values with 95% CIs were consistent between all DVHs. In conclusion, we found that the investigated slice thickness variations had minimal impact on rectal dose-response estimations. From the perspective of predictive modeling, our results suggest that variations within 10 mm in slice thickness between cohorts are unlikely to be a limiting factor when pooling multi-institutional rectal dose data that include slice thickness variations within this range.

Impact of CT slice thickness on volume and dose evaluation during thoracic cancer radiotherapy

“…A study by Caivano et al study recommended 1 or 2 mm slice thicknesses for small targets in stereotactic body radiotherapy, and 4–6 mm for other volumes in three-dimensional conformal radiation therapy or IMRT. 13 A similar study was also found on rectal cancer, 14 however, a study evaluating slice thicknesses in thoracic cancer was not found.…”

A simple method of evaluating margin-growing accuracy in image-guided radiation therapy

“…Olsson et al 9 investigated this for rectal bleeding using dose-volume histograms of the rectum and rectal wall with varying CT slice thicknesses from two prostate cancer cohorts treated with 3D conformal radiotherapy and found that the investigated SS variations had minimal impact on rectal doseresponse estimations. 9 New delivery techniques, such as intensitymodulated radiotherapy and volumetric-modulated arc therapy, enable complex dose distributions with sharp dose gradients to be delivered and achieve superior target conformity than conventional 3D conformal radiotherapy. It is not known if similar results can be found for these advanced techniques due to the influence of SS on target volume (Figure 3).…”

Parameters of the Lyman Model for Calculation of Normal-Tissue Complication Probability: A Systematic Literature Review

“…Radiation techniques used included CRT and IMRT with CF, 2.5 Gy/fraction and 3.0 Gy/fraction. It should be noted that an identical patient cohort was used for fitting of parameters in the 2010 Liu 26 and 2014 Olsson 27 publications and some of the authors were also involved in both publications.…”