Assessing PTV Margins in Prostate Cancer Tomotherapy and Inter-Fractional Motion and Factors Impacting PTV and OAR Displacement

Document Type : Original Article(s)

Authors

1 PhD Student, Department of Medical Physics, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran

2 Professor, Department of Medical Physics, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran

3 Associate Professor, Department of Radiotherapy and Oncology, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran

4 PhD, Department of Medical Physics, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran

5 MSc, Department of Medical Physics, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran

Abstract

Background: Treatment planning target volume (PTV) motion in prostate cancer tomotherapy is an important challenge in treatment planning. This study aimed to evaluate PTV margins for prostate cancer tomotherapy.
Methods: From 2021 to 2023, 20 patients with prostate cancer underwent tomotherapy. Before each treatment session, the MVCT image was taken from the patient, and the patient's settings were made using pelvic bone markers and tattoos. Before treatment, prostate volume was measured by ultrasound. Bladder volume was measured in MVCT images and compared with CTSim images. PTV displacements were measured and the required margin for 95% PTV dose was determined using the average prostate displacement. Correlation coefficients between bladder volume, prostate volume, and PTV displacement were calculated.
Findings: This study analyzed a total of 497 MVCT and 20 CT images. Anisotropic PTV margins, accounting for random uncertainties, were 14-6.9 mm for PTV1, 11.4-6.2 mm for PTV2, and 5.9-3.5 mm for PTV3 in the anterior-posterior direction, respectively.
Conclusion: This research reveals that a non-uniform PTV margin is needed to compensate for the random uncertainties caused by the movement of the prostate between tomotherapy sessions. Filling of the bladder and diet play a vital role in the displacement of the prostate.

Highlights

Ahmad Shanei: Google Scholar, PubMed

Mahnaz Roayaei: Google Scholar, PubMed

Keywords

Main Subjects


  1. Karampour- Najafabadi M, Jafari A, Najafizade N, Saeb M, Shanei A. Radiobiological evaluation and comparison of treatment plans in two methods of 3D adaptive radiation therapy and tomotherapy for left pendular breast cancer and the risk of pericarditis and pneumonia [in Persian]. J Isfahan Med School 2023; 41(726): 543-9.
  2. Ghilezan MJ, Jaffray DA, Siewerdsen JH, van Herk M, Shetty A, Sharpe MB, et al. Prostate gland motion was assessed with cine-magnetic resonance imaging (cine-MRI). Int J Radiat Oncol Biol Phys 2005; 62(2): 406-17.
  3. Gluck I, Vineberg KA, Ten Haken RK, Sandler HM. Evaluating the relationships between rectal normal tissue complication probability and the portion of seminal vesicles included in the clinical target volume in intensity-modulated radiotherapy for prostate cancer. Int J Radiat Oncol Biol Phys 2009;73(2): 334-40.
  4. Mak D, Gill S, Paul R, Stillie A, Haworth A, Kron T, et al. Seminal vesicle interfraction displacement and margins in image-guided radiotherapy for prostate cancer. Radiat Oncol 2012; 7: 139.
  5. Afkhami Ardekani M, Ghaffari H, Navaser M, Zoljalali Moghaddam SH, Refahi S. Effectiveness of rectal displacement devices in managing prostate motion: a systematic review. Strahlenther Onkol 2021; 197(2): 97-115.
  6. Dearnaley D, Syndikus I, Sumo G, Bidmead M, Bloomfield D, Clark C, et al. Conventional versus hypofractionated high-dose intensity-modulated radiotherapy for prostate cancer: preliminary safety results from the CHHiP randomized controlled trial. Lancet Oncol 2012; 13(1): 43-54.
  7. Polat B, Guenther I, Wilbert J, Goebel J, Sweeney RA, Flentje M, Guckenberger M. Intra-fractional uncertainties in image-guided intensity-modulated radiotherapy (IMRT) of prostate cancer. Strahlenther Onkol 2008; 184(12): 668-73.
  8. Tsai J-S, Micaily B, Miyamoto C. Optimization and quality assurance of an image-guided radiation therapy system for intensity-modulated radiation therapy radiotherapy. Med Dosim 2012; 37(3): 321-33.
  9. Nairz O, Merz F, Deutschmann H, Kopp P, Schöller H, Zehentmayr F, et al. A strategy for the use of image-guided radiotherapy (IGRT) on linear accelerators and its impact on treatment margins for prostate cancer patients. Strahlenther Onkol 2008; 184(12): 663-7.
  10. Remeijer P, Rasch C, Lebesque JV, van Herk M. A general methodology for three‚Äźdimensional analysis of variation in target volume delineation. Med Phys 1999; 26(6): 931-40.
  11. Oehler C, Lang S, Dimmerling P, Bolesch C, Kloeck S, Tini A, et al. PTV margin definition in hypofractionated IGRT of localized prostate cancer using cone beam CT and orthogonal image pairs with fiducial markers. Radiat Oncol 2014; 9: 229.
  12. Poli ME, Parker W, Patrocinio H, Souhami L, Shenouda G, Campos LL, et al. An assessment of PTV margin definitions for patients undergoing conformal 3D external beam radiation therapy for prostate cancer based on an analysis of 10,327 pretreatment daily ultrasound localizations. Int J Radiat Oncol Biol Phys 2007; 67(5): 1430-7.