Journal of Radiation Safety and Measurement

Journal of Radiation Safety and Measurement

Impact of Pelvic Lymph Node Contouring Variability on PTV Coverage and OAR Dose in Prostate IMRT: DVH-based Statistical Analysis

Document Type : Original Article

Authors
Maryam Yaftian 1
Elham Saeedzadeh 1
Hossein Arabi 2
Farshid Babapour -Mofrad 1
1 Department of Radiation Medical Engineering, SR.C., Islamic Azad University, Tehran, Iran
2 Division of Nuclear Medicine and Molecular Imaging, Geneva University Hospital, Geneva, Switzerland
10.22052/rsm.2026.259497.1174
Abstract
Elective pelvic nodal irradiation using intensity-modulated radiation therapy (IMRT) is widely utilized in selected prostate cancer patients. Interobserver variability in pelvic lymph node contouring may affect target dose coverage and organs at risk (OARs) sparing. This study systematically evaluated the dosimetric consequences of interobserver contouring variability among three independent radiation oncologists. In this retrospective treatment planning study, three radiation oncologists independently delineated the clinical target volume (CTV) for pelvic lymph nodes in 60 prostate cancer patients. For each observer-specific contour set, dose–volume histogram (DVH) parameters were generated for the planning target volume (PTV) and selected OARs (bladder, rectum, small bowel, and femoral heads). Primary endpoints included pelvic nodal volume, PTV V95%, PTV D_mean, as well as OAR D_mean and D_max. Interobserver differences were evaluated using repeated-measures ANOVA, and agreement was quantified using the intraclass correlation coefficient (ICC). Bland–Altman analysis and boxplots were employed to characterize interobserver variability. Mean pelvic lymph node contour volumes were 259.18 ± 11.65 cm³ for Observer 1, 263.70 ± 11.41 cm³ for Observer 2, and 267.16 ± 11.40 cm³ for Observer 3 respectively. Target coverage remained highly robust across observers, with no statistically significant difference in PTV V95% (p=0.178). Regarding OARs, bladder and rectum D_mean remained stable across observers, whereas bladder and rectum D_max differed significantly (both p<0.001). The small bowel exhibited the greatest dosimetric sensitivity, demonstrating significant differences in both D_mean and D_max (both p<0.001). Femoral head D_mean also varied significantly p<0.001), whereas femoral head D_max remained stable (p=0.851). Interobserver contouring variability had minimal impact on PTV coverage, but significantly influenced PTV D_mean and several OAR dosimetric parameters, particularly small bowel exposure and peak doses to the bladder and rectum. These findings emphasize the necessity of implementing standardized contouring guidelines and structured peer-review processes to mitigate clinically relevant dosimetric variation.
Keywords
Prostate cancer
Intensity-modulated radiation therapy (IMRT)
Pelvic lymph node delineation
Dose&‌‌‌ndash
volume histogram (DVH)
1. O. De Hertogh, G. Le Bihan, T. Zilli, S. Palumbo, M. Jolicoeur, G. Crehange, T. Derashodian, G. Roubaud, C. Salembier, S. Supiot, O. Chapet, V. Achard, P. Sargos, Consensus Delineation Guidelines for Pelvic Lymph Node Radiation Therapy of Prostate Cancer: On Behalf of the Francophone Group of Urological Radiation Therapy (GFRU). Int. J. Radiat. Oncol. Biol. Phys. 118 (2024) 29-40.
2. W. A. Hall, E. Paulson, B. J. Davis, D. E. Spratt, T. M. Morgan, D. Dearnaley, A. C. Tree, J. A. Efstathiou, M. Harisinghani, A. B. Jani, M. K. Buyyounouski, T. M. Pisansky, P. T. Tran, R. J. Karnes, R. C. Chen, F. L. Cury, J. M. Michalski, S. A. Rosenthal, B. F. Koontz, A. C. Wong, P. L. Nguyen, T. A. Hope, F. Feng, H. M. Sandler, C. A. F. Lawton, NRG Oncology Updated International Consensus Atlas on Pelvic Lymph Node Volumes for Intact and Postoperative Prostate Cancer. Int. J. Radiat. Oncol. Biol. Phys. 109 (2021) 174-185.
3. A. Dal Pra, P. Dirix, V. Khoo, C. Carrie, C. Cozzarini, V. Fonteyne, P. Ghadjar, A. Gomez-Iturriaga, V. Panebianco, A. Zapatero, A. Bossi, T. Wiegel. ESTRO ACROP guideline on prostate bed delineation for postoperative radiotherapy in prostate cancer. Clin. Transl. Radiat. Oncol. 41 (2023) 100638.
4. G. Ortner, X. Hoderlein, F. Barbato, D. Beyersdorff, L. Budäus, I. A. Burger, M. Eiber, M. Graefen, B. Hadaschik, A. Haese, K. Herrmann, L. Maack, I. Maric, A. Mattei, I. Rauscher, G. Salomon, M. Sauer, L. Schimmöller, A. Schlaefer, H.-P. Schlemmer, S. K. B. Spohn, L. Umutlu, J. Walz, C. Würnschimmel, D. Koehler, T. Maurer, The Pelvic Rosetta Classification Project: An Interdisciplinary Proposal for a Lymph Node Map of the Pelvis in Prostate Cancer. J. Nucl. Med. 67 (2026) 154-159.
5. P. Darby, E. Kilgour, C. K. Then, A. Bromiley, J. McLellan, A. E. Kiltie, Inter-observer variability in radiotherapy contouring with the use of autocontouring software: A systematic review. Clin. Transl. Radiat. Oncol. 58 (2026) 101144.
6. W. Zheng, X. Yang, Z. Cheng, J. Lian, E. Li, S. Mo, Y. Liu, S. Huang, Interobserver and sequence variability in the delineation of pelvic organs at risk on magnetic resonance images. Radiol. Oncol. 59 (2025) 139-146.
7. B. Hentschel, W. Oehler, D. Strauss, A. Ulrich, A. Malich, Definition of the CTV prostate in CT and MRI by using CT-MRI image fusion in IMRT planning for prostate cancer. Strahlenther. Onkol. 187 (2011) 183-190. doi: 10.1007/s00066-010-2179-1.
8. M. P. Jones, J. Martin, K. Foo, P. Estoesta, L. Holloway, M. Jameson, The impact of contour variation on tumour control probability in anal cancer. Radiat. Oncol. 13 (2018) 97. doi: 10.1186/s13014-018-1033-y.
9. A. Barghi, C. Johnson, A. Warner, G. Bauman, J. Battista, G. Rodrigues, Impact of Contouring Variability on Dose-Volume Metrics used in Treatment Plan Optimization of Prostate IMRT. Cureus 5 (2013) e144.
10. D. Giavarina, Understanding Bland Altman analysis. Biochem. Med. (Zagreb) 25 (2015) 141-151. doi: 10.11613/BM.2015.015.
11. R. Zaki, A. Bulgiba, R. Ismail, N. A. Ismail, Statistical Methods Used to Test for Agreement of Medical Instruments Measuring Continuous Variables in Method Comparison Studies: A Systematic Review. PLoS One 7 (2012) e37908. doi: 10.1371/journal.pone.0037908.
12. K. Han, L. Ryu, Statistical Methods for the Analysis of Inter-Reader Agreement Among Three or More Readers. Korean J. Radiol. 25 (2024) 325-327. doi: 10.3348/kjr.2023.0965.
13. C. Chamunyonga, K. Mengersen, C. Hargrave, Inter-observer variation in radiation oncology contouring: A scoping review of contour comparison methods, and reporting of impact on the organ at risk plan dose variations. Radiography (Lond.) 32 (2026) 103295.
14. L. Gómez, C. Andrés, A. Ruiz, Dosimetric impact in the dose–volume histograms of rectal and vesical wall contouring in prostate cancer IMRT treatments. Rep. Pract. Oncol. Radiother. 22 (2017) 223-230.
15. Y. Li, P. Li, W. Hsi, Z. Hong, S. Fu, Q. Zhang, Normal tissue complication probability (NTCP) models of acute urinary toxicity (AUT) following carbon ion radiotherapy (CIRT) for prostate cancer. Radiother. Oncol. 156 (2021) 69-79.
16. O. Yariv, K. Camphausen, A. V. Krauze, Small Bowel Dose Constraints in Radiation Therapy—Where Omics-Driven Biomarkers and Bioinformatics Can Take Us in the Future. BioMedInformatics 4 (2024) 158-172.
17. A. Augurio, G. Macchia, L. Caravatta, M. Lucarelli, F. Di Gugliemo, A. Vinciguerra, B. Seccia, V. De Sanctis, R. Autorino, C. Delle Curti, S. Meregalli, E. Perrucci, D. Raspanti, A. Cerrotta, Contouring of emerging organs-at-risk (OARS) of the female pelvis and interobserver variability: A study by the Italian association of radiotherapy and clinical oncology (AIRO). Clin. Transl. Radiat. Oncol. 43 (2023) 100688.
18. A. N. Viswanathan, E. D. Yorke, L. B. Marks, P. J. Eifel, W. U. Shipley, Radiation Dose–Volume Effects of the Urinary Bladder. Int. J. Radiat. Oncol. Biol. Phys. 76 (2010) S116-S122.
19. S. K. Vinod, M. Min, M. G. Jameson, L. C. Holloway, A review of interventions to reduce inter-observer variability in volume delineation in radiation oncology. J. Med. Imaging Radiat. Oncol. 60 (2016) 393-406.
20. S. H. Choi, J. W. Park, Y. Cho, G. Yang, H. I. Yoon, Automated Organ Segmentation for Radiation Therapy: A Comparative Analysis of AI-Based Tools Versus Manual Contouring in Korean Cancer Patients. Cancers (Basel) 16 (2024) 3670.
21. P. Lambin, R. T. H. Leijenaar, T. M. Deist, J. Peerlings, E. E. C. de Jong, J. van Timmeren, S. Sanduleanu, R. T. H. M. Larue, A. J. G. Even, A. Jochems, Y. van Wijk, H. Woodruff, J. van Soest, T. Lustberg, E. Roelofs, W. van Elmpt, A. Dekker, F. M. Mottaghy, J. E. Wildberger, S. Walsh, Radiomics: the bridge between medical imaging and personalized medicine. Nat. Rev. Clin. Oncol. 14 (2017) 749-762.
22. J. Cacicedo, A. Navarro-Martin, S. Gonzalez-Larragan, B. De Bari, A. Salem, M. Dahele, Systematic review of educational interventions to improve contouring in radiotherapy. Radiother. Oncol. 144 (2020) 86-92.