Local dose analysis to predict acute and late urinary toxicities after prostate cancer radiotherapy: Assessment of cohort and method effects

Abstract

To perform bladder dose-surface map (DSM) analysis for (1) identifying symptomrelated sub-surfaces (Ssurf) and evaluating their prediction capability of urinary toxicity, (2) comparing DSM with dose-volume map (DVM) (method effect), and (3) assessing the reproducibility of DSM (cohort effect).Methods and materials: Urinary toxicities were prospectively analyzed for 254 prostate cancer patients treated with IMRT/IGRT at 78/80Gy. DSMs were generated by unfolding bladder surfaces in a 2D plane. Pixel-by-pixel analysis was performed to identify symptom-related Ssurf. Likewise, DVM analysis was performed to identify sub-volumes (Svol). The prediction capability of Ssurf and Svol DVHs was assessed by logistic/Cox regression using the area under the ROC curve (AUC). The Ssurf localization and prediction capability were compared to (1) the Svol obtained by DVM analysis in the same cohort and (2) the Ssurf obtained from other DSM studies.Results: Three Ssurf were identified in the bladder: posterior for acute retention (AUC =0.64), posterior-superior for late retention (AUC =0.68), and inferior-anterior-lateral for late dysuria (AUC=0.73). Five Svol were identified: one in the urethra for acute incontinence and four in the posterior bladder part for acute and late retention, late dysuria, and hematuria. The overlap between Ssurf and Svol was moderate for acute retention, good for late retention, and bad for late dysuria, and AUCs ranged from 0.62 to 0.81. The prediction capabilities of Ssurf and Svol models were not significantly different. Among five symptoms comparable between cohorts, common Ssurf was found only for late dysuria, with a good spatial agreement. Conclusion:Spatial agreement between methods is relatively good although DVM identified more sub-regions. Reproducibility of identified Ssurf between cohorts is low.

Technical note: rtdsm—An open‐source software for radiotherapy dose‐surface map generation and analysis

“…In addition to removing programming barriers, the accessibility of rtdsm has the potential to improve DSM reproducibility between groups, which is becoming an area of concern as the methodology gains in popularity. Mylona et al 35 recently reported poor reproducibility of toxicity-predictive subregions from bladder DSMs of prostate patients when comparing their results to three other studies. Despite similar DSM construction and analysis approaches, it appears variations in vertical mapping methods between groups (scaled mapping by Mylona, 1:1 mapping truncated at 25 or 45 mm by others 5,13 36 ) influenced the reproducibility of results.…”

“…In addition to removing programming barriers, the accessibility of rtdsm has the potential to improve DSM reproducibility between groups, which is becoming an area of concern as the methodology gains in popularity. Mylona et al 35 . recently reported poor reproducibility of toxicity‐predictive subregions from bladder DSMs of prostate patients when comparing their results to three other studies.…”

“…The references sections of relevant identified articles were also used to identify further relevant papers. Only papers that included a description of the DSM calculation process were included in the final list, which consisted of 30 publications 5,6,9–20,22–37 . The contents of each paper were read in detail to identify the methodology and parameters used for DSM calculation, and if the authors had made their code publicly available.…”

Predictors for late genitourinary toxicity in men receiving radiotherapy for high-risk prostate cancer using planned and accumulated dose

“…None of the DV metrics were selected during MVA. Moving forward, this study could be expanded to incorporate the use of dose surface maps (DSM) analysis with spatial information for the model-building to improve spatial dose–response correlations [51] . In addition, work is in progress to apply this model to determine the feasibility of performing dose escalation or hypofractionated regimens as well as incorporating advanced modalities, such as proton therapy to enhance the patient’s therapeutic ratio.…”

Planning With Patient-Specific Rectal Sub-Region Constraints Decreases Probability of Toxicity in Prostate Cancer Radiotherapy

“…Voxel-wise analysis by non-rigid registration has become a well-established methodology able to unveil the likely heterogeneous radiosensitivity across the organs, which may be helpful in the identification of sub-regions to be spared at the planning step. One of the major advantages of the voxel-wise analysis is its ability to explore the full 3D anatomy without prior assumptions regarding the location of regions correlating with toxicity (25). As compared with dose surface maps, which have also been used for this purpose, the voxel-based methods present the advantage of generating 3D volumes that can be transferred to the clinical practice in a straightforward way.…”