Evaluating intra-fraction motion and its dosimetric impact in ethos online adaptive radiotherapy for prostate cancer

Abstract

Purpose: This study evaluated the geometric and dosimetric uncertainties during online adaptive radiotherapy (ART) for prostate cancer.

Methods: Sequential cone beam computed tomography (CBCT) scans from 52 sessions involving 13 patients were analyzed. An ART plan was generated using CBCT1, followed by a verification scan (CBCT2) acquired 13.1 ± 3.0 minutes before treatment delivery. New contours (prostate, seminal vesicles, bladder, rectum, and bowel) were delineated on CBCT2 and transferred to CBCT1 for dose distribution analysis. Three dimensional contour variations were quantified, new planning target volume (PTV) margins were calculated, and their dosimetric benefits were assessed.

Results: No significant differences were observed in the high-dose volumes (V60 Gy and V57 Gy) of the bladder and rectum (P > 0.05). PTV margins were 2.6 mm, 2.4 mm, and 2.6 mm in the lateral, vertical, and longitudinal directions for the prostate, and 3.9 mm, 3.8 mm, and 4.3 mm for the seminal vesicles, respectively. These margin reductions led to a 37% reduction in the dose to the surrounding critical organs, while maintaining consistent target coverage.

Conclusion: This study supports symmetric PTV margins of 3 mm for the prostate and 4.5 mm for the seminal vesicles in online ART, thereby contributing to the development of optimized treatment strategies for prostate cancer.

Keywords

Ethos treatment planning system / planning target volume / prostate cancer

References

[1] Barker JL,, Garden AS, Ang KK, et al. Quantification of volumetric and geometric changes occurring during fractionated radiotherapy for head-and-neck cancer using an integrated CT/linear accelerator system. Int J Radiat Oncol Biol Phys. 2004; 59(4): 960-970.

[2] Hirotaki K, Moriya S, Tachibana H, Sakae T. Detection of anatomical changes using two-dimensional x-ray images for head and neck adaptive radiotherapy. Med Phys. 2022; 49(5): 3288-3297.

[3] Lavrova E, Garrett MD, Wang YF, et al. Adaptive Radiation Therapy: A Review of CT-based Techniques. Radiol Imaging Cancer. 2023; 5(4): e230011.

[4] Benitez CM, Chuong MD, Kunzel LA, Thorwarth D. MRI-Guided Adaptive Radiation Therapy. Semin Radiat Oncol. 2024; 34(1): 84-91.

[5] Sonke JJ, Aznar M, Rasch C. Adaptive Radiotherapy for Anatomical Changes. Semin Radiat Oncol. 2019; 29(3): 245-257.

[6] Buschmann M, Majercakova K, Sturdza A, et al. Image guided adaptive external beam radiation therapy for cervix cancer: Evaluation of a clinically implemented plan-of-the-day technique. Z Med Phys. 2018; 28(3): 184-195.

[7] Zhang P, Simon A, Rigaud B, et al. Optimal adaptive IMRT strategy to spare the parotid glands in oropharyngeal cancer. Radiother Oncol. 2016; 120(1): 41-47.

[8] Ahunbay E, Parchur AK, Paulson E, Chen X, Omari E, Li XA. Development and implementation of an automatic air delineation technique for MRI-guided adaptive radiation therapy. Phys Med Biol. 2022; 67(14).

[9] Bohoudi O, Bruynzeel AME, Tetar S, Slotman BJ, Palacios MA, Lagerwaard FJ. Dose accumulation for personalized stereotactic MR-guided adaptive radiation therapy in prostate cancer. Radiother Oncol. 2021; 157: 197-202.

[10] van Timmeren JE, Chamberlain M, Bogowicz M, et al. MR-Guided Adaptive Radiotherapy for Head and Neck Cancer: Prospective Evaluation of Migration and Anatomical Changes of the Major Salivary Glands. Cancers (Basel). 2021; 13(21): 5404.

[11] Weisz Ejlsmark M, Bahij R, Schytte T, et al. Adaptive MRI-guided stereotactic body radiation therapy for locally advanced pancreatic cancer - A phase II study. Radiother Oncol. 2024; 197(1): 110347.

[12] Xiong Y, Rabe M, Rippke C, et al. Impact of daily plan adaptation on accumulated doses in ultra-hypofractionated magnetic resonance-guided radiation therapy of prostate cancer. Phys Imaging Radiat Oncol. 2024; 29: 100562.

[13] Calvo-Ortega JF, Moragues-Femenia S, Laosa-Bello C, Torices-Caballero J, Hermida-Lopez M, Casals-Farran J. Clinical Experience in Prostate Ultrahypofractionated Radiation Therapy With an Online Adaptive Method. Pract Radiat Oncol. 2022; 12(2): e144-e152.

[14] Archambault Y, Boylan C, Bullock D, et al. Making on-line adaptive radiotherapy possible using artificial intelligence and machine learning for efficient daily re-planning. Med Phys Int J. 2020; 8(2): 77-86.

[15] Yoganathan SA, Riyas M, Sukumaran R, Hammoud R, Al-Hammadi N. Ultra-Hypofractionated Prostate Radiotherapy With Online Adaptive Technique: A Case Report. Cureus. 2024; 16(7): e64101.

[16] Byrne M, Archibald-Heeren B, Hu Y, et al. Varian ethos online adaptive radiotherapy for prostate cancer: Early results of contouring accuracy, treatment plan quality, and treatment time. J Appl Clin Med Phys. 2022; 23(1): e13479.

[17] de Muinck Keizer DM, Kerkmeijer LGW, Willigenburg T, et al. Prostate intrafraction motion during the preparation and delivery of MR-guided radiotherapy sessions on a 1.5T MR-Linac. Radiother Oncol. 2020; 151: 88-94.

[18] Morgan HE, Wang K, Yan Y, et al. Preliminary Evaluation of PTV Margins for Online Adaptive Radiation Therapy of the Prostatic Fossa. Pract Radiat Oncol. 2023; 13(4): e345-3e53.

[19] Byrne M, Teh AYM, Archibald-Heeren B, et al. Intrafraction Motion and Margin Assessment for Ethos Online Adaptive Radiotherapy Treatments of the Prostate and Seminal Vesicles. Adv Radiat Oncol. 2024; 9(3): 101405.

[20] van Herk M, Remeijer P, Rasch C, Lebesque JV. The probability of correct target dosage: dose-population histograms for deriving treatment margins in radiotherapy. Int J Radiat Oncol Biol Phys. 2000; 47(4): 1121-1135.

[21] The Royal College of Radiologists SaCoR, Institute of Physics and Engineering in Medicine, National Patient Safety Agency, British Institute of Radiology. On target: ensuring geometric accuracy in radiotherapy. 2008.

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2025 The Author(s). Precision Radiation Oncology published by John Wiley & Sons Australia, Ltd on behalf of Shandong Cancer Hospital & Institute.