Ano-rectal wall dose-surface maps localize the dosimetric benefit of hydrogel rectum spacers in prostate cancer radiotherapy. (January 2019)

• Record Type: Journal Article
• Authors: Vanneste, Ben G.L.; Buettner, Florian; Pinkawa, Michael; Lambin, Philippe; Hoffmann, Aswin L.
• Is Part Of: Clinical and translational radiation oncology. Volume 14(2019)
• Page Start: 17
• Page End: 24
• Publication Date: 2019-01
• Subjects: Prostate cancer -- Radiotherapy -- Rectum spacer -- Dose-surface maps -- Toxicity reduction; Cancer -- Radiotherapy -- Periodicals; Oncology -- Periodicals; Cancer -- Radiotherapy; Oncology; Radiation Oncology; Neoplasms -- radiotherapy; Translational Medical Research; Periodicals; Electronic journals; Periodicals; 616.9940642
• DOI: 10.1016/j.ctro.2018.10.006
• Languages: English
• ISSNs: 2405-6308

Abstract

Highlights: Implantable rectum spacers (IRS) separate the ano-rectal wall (ARW) from the prostate. Dose-surface maps (DSMs) are a tool to take spatio-dosimetric info into account. Spatio-dosimetric differences in ARW DSMs exist comparing IMRT with and without IRS. IRS reduces the lateral and longitudinal extent of areas >50 Gy. IRS reduces these high-dose areas in anterior and superior-inferior directions. Abstract: Background and purpose: To evaluate spatial differences in dose distributions of the ano-rectal wall (ARW) using dose-surface maps (DSMs) between prostate cancer patients receiving intensity-modulated radiation therapy with and without implantable rectum spacer (IMRT+IRS; IMRT−IRS, respectively), and to correlate this with late gastro-intestinal (GI) toxicities using validated spatial and non-spatial normal-tissue complication probability (NTCP) models. Materials and methods: For 26 patients DSMs of the ARW were generated. From the DSMs various shape-based dose measures were calculated at different dose levels: lateral extent, longitudinal extent, and eccentricity. The contiguity of the ARW dose distribution was assessed by the contiguous-DSH (cDSH). Predicted complication rates between IMRT+IRS and IMRT−IRS plans were assessed using a spatial NTCP model and compared against a non-spatial NTCP model. Results: Dose surface maps are generated for prostate radiotherapy using an IRS. Lateral extent, longitudinal extent and cDSH were significantly lower in IMRT+IRS than for IMRT−IRS at high-dose levels. Largest significant differences were observed for cDSH at dose levels >50 Gy, followed by lateral extent at doses >57 Gy, and longitudinal extent in anterior and superior-inferior directions. Significant decreases ( p = 0.01) in median rectal and anal NTCPs (respectively, Gr 2 late rectal bleeding and subjective sphincter control) were predicted when using an IRS. Conclusions: Local-dose effects are predicted to be significantly reduced by an IRS. The spatial NTCP model predicts a significant decrease in Gr 2 late rectal bleeding and subjective sphincter control. Dose constraints can be improved for current clinical treatment planning.