Assessment of Dosimetric Accuracy and Plan Quality in Prostate SBRT Using RapidArc with Analysis of Varian MLC Parameters

Document Type : Original Paper

Authors

1 Department of Radiotherapy, Meherbai Tata Memorial Hospital, Jamshedpur

2 Department of Radiotherapy,Tata MainHospital, Jamshedpur

10.22038/ijmp.2025.88593.2564

Abstract

Introduction: Prostate cancer is a highly prevalent malignancy worldwide. Advances in radiotherapy, particularly SBRT, have enabled ultra-hypofractionated treatments that improve tumor control while reducing treatment time. This study evaluates the dosimetric accuracy and plan quality of prostate SBRT delivered using RapidArc technology on a Varian Millennium Multi Leaf Collimator (MLC) system.
Material and Methods: Twenty-four patients with localized prostate adenocarcinoma received SBRT with a prescribed dose of 36.25 Gy in five fractions. Treatment planning was performed using Eclipse v15.6 with the Acuros XB algorithm, employing three 6 MV Flattening Filter Free (FFF) arcs. Planning Target Volume (PTV) coverage, Organs At Risk (OAR) doses, Paddick Conformity Index (PCI), Gradient Index (GI), and Monitor Units (MU) were analyzed. MLC performance was assessed using trajectory log files to evaluate leaf speed and positional accuracy. Pre-treatment Quality Assurance (QA) was conducted using Electronic Portal Imaging Device (EPID)-based gamma analysis.
Results: The mean PTV D95 was 35.80 ± 0.46 Gy, with Dmax and Dmean of 39.80 ± 1.05 Gy and 37.10 ± 0.40 Gy, respectively. V95% averaged 99.13 ± 1.14%, confirming adequate coverage. The bladder and rectum Dmax slightly exceeded constraints, while all other OAR objectives were met. Gamma pass rates exceeded 99.6% for the 2%/2mm criterion. MLC leaf speed remained below 2.5 cm/s, ensuring delivery accuracy.
Conclusion: RapidArc-based prostate SBRT demonstrated high conformity, efficient delivery, and acceptable OAR sparing. Intra-fraction CBCT improved setup accuracy, and MLC log-file analysis confirmed mechanical precision, supporting the feasibility of this approach for localized prostate cancer.
 

Keywords

Main Subjects

References

  1. Dearnaley D, Syndikus I, Mossop H, Khoo V, Birtle A, Bloomfield D, et al. Conventional versus hypofractionated high-dose intensity-modulated radiotherapy for prostate cancer: 5-year outcomes of the randomised, non-inferiority, phase 3 CHHiP trial. Lancet Oncol. 2016;17(8):1047-60.
  2. Freeman DE, King CR. Stereotactic body radiotherapy for low-risk prostate cancer: five-year outcomes. Radiat Oncol. 201;6:3.
  3. Wieslander E, Jóhannesson V, Nilsson P, Kjellén E, Gunnlaugsson A. Ultrahypofractionated Radiation Therapy for Prostate Cancer Including Seminal Vesicles in the Target Volume: A Treatment-planning Study Based on the HYPO-RT-PC Fractionation Schedule. Adv Radiat Oncol. 2024;9(7):101531.
  4. van As N, Griffin C, Tree A, Patel J, Ostler P, van der Voet H, Loblaw A, et al. Phase 3 Trial of Stereotactic Body Radiotherapy in Localized Prostate Cancer. N Engl J Med. 2024;391(15):1413-25.
  5. McDermott LN, Wendling M, van Asselen B, Stroom J, Sonke JJ, van Herk M, et al. Clinical experience with EPID dosimetry for prostate IMRT pre-treatment dose verification. Med Phys. 2006;33(10):3921-30.
  6. Kjaer-Kristoffersen F, Ohlhues L, Medin J, Korreman S. RapidArc volumetric modulated therapy planning for prostate cancer patients. Acta Oncol. 2009;48(2):227-32.
  7. Yoo S, Wu QJ, Lee WR, Yin FF. Radiotherapy treatment plans with RapidArc for prostate cancer involving seminal vesicles and lymph nodes. Int J Radiat Oncol Biol Phys. 2010;76(3):935-42.
  8. Rana S, Rogers K, Lee T, Reed D, Biggs C. Dosimetric impact of Acuros XB dose calculation algorithm in prostate cancer treatment using RapidArc. J Cancer Res Ther. 2013;9(3):430-5.
  9. Rana S, Rogers K, Pokharel S, Cheng C. Evaluation of Acuros XB algorithm based on RTOG 0813 dosimetric criteria for SBRT lung treatment with RapidArc. J Appl Clin Med Phys. 2014;15(1):4474.
  10. Huang K, Palma DA, Scott D, McGregor D, Gaede S, Yartsev S, et al. Inter- and intrafraction uncertainty in prostate bed image-guided radiotherapy. Int J Radiat Oncol Biol Phys. 2012;84(2):402-7.
  11. Jolly D, Alahakone D, Meyer J. A RapidArc planning strategy for prostate with simultaneous integrated boost. J Appl Clin Med Phys. 2010;12(1):3320.
  12. Paddick I. A simple scoring ratio to index the conformity of radiosurgical treatment plans. Technical note. J Neurosurg. 2000;93 Suppl 3:219-22.
  13. Wilke L, Andratschke N, Blanck O, Brunner TB, Combs SE, Grosu AL, et al. ICRU report 91 on prescribing, recording, and reporting of stereotactic treatments with small photon beams : Statement from the DEGRO/DGMP working group stereotactic radiotherapy and radiosurgery. Strahlenther Onkol. 2019;195(3):193-98.
  14. Chen J, Cui W, Fu Q, Zhang H, Huang X, Han F, et al. Influence of maximum MLC leaf speed on the quality of volumetric modulated arc therapy plans. J Appl Clin Med Phys. 2020;21(11):37-47.
  15. Lin X, Sun T, Liu X, Zhang G, Yin Y. Comparison of MLC positioning deviations using log files and establishment of specific assessment parameters for different accelerators with IMRT and VMAT. Radiat Oncol. 2022;17(1):123.
Iranian Journal of Medical Physics
Volume 22, Issue 5 - Serial Number 5
September and October 2025
Pages 290-297

Files

History

  • Receive Date: 29 May 2025
  • Revise Date: 23 July 2025
  • Accept Date: 12 November 2025

Share

How to cite

Statistics