Dosimetric Effect Resulting From the Collimator Angle, the Isocenter Move, and the Gantry Angle Errors

Document Type : Original Paper


1 HASSAN II Oncology Center, University Hospital Mohammed VI & LPMR, Faculty of sciences, University Mohamed 1st, Oujda, Morocco

2 LPMR, Faculty of sciences, University Mohamed 1st, Oujda, Morocco

3 National School of Applied Sciences, University Mohamed 1st, Oujda, Morocco


Introduction: Dose distribution can be affected by diverse parameters, such as beam orientations, and collimator angles. These parameters should respect and maintain the international recommended levels during the realization of the quality assurance protocols of linear accelerators. This study aimed at evaluating the dosimetric effects on treatment quality considering the mechanical error fluctuations in the recommended range.
Material and Methods: This study included ten patients with head and neck cancer. All of them were treated using three-dimensional conformal radiotherapy with the simple 3-field classic technique. Initially, an optimized treatment plan was computed for each patient. Afterward, similar calculations were executed by varying isocenter position, gantry and collimator angles. Eventually, dosimetric evaluations based on dose-volume histograms were studied and analyzed by Wilcoxon signed rank test for each plan.
Results: The analysis of the dose-volume histograms of tumor volumes and organs at risk, as well as the dosimetry calculation, revealed that the small errors of 0.5° in gantry and collimator angles have minimal effects on dose distribution. However, the variation in isocenter coordinating up to 1 mm may influence the patients’ treatment quality, particularly in the spinal cord and the brainstem, in which Wilcoxon's test showed significant effects in all plans.
Conclusion: According to the results, the quality of the treatment plans is almost insensitive to the errors of the gantry and the collimator angles of the order 0.5° though it is relatively sensitive to isocenter errors (1 mm). These should be reduced in order to avoid overdose when applying the conventional 3-field technique.


Main Subjects


    1. Thwaites DI, Mijnheer BJ, Mills JA. Quality assurance of external beam radiotherapy. Radiation oncology physics: a hand-book for teachers and students. 2005:470-50.
    2. Fuks Z, Leibel SA, Wallner KE, Begg CB, Fair WR, Anderson LL, et al. The effect of local control on metastatic dissemi-nation in carcinoma of the prostate: long-term results in patients treated with 1251 implantation. Int. J. Radiat. Oncol. Biol. Phys. 1991;21(3):537-47.
    3. Rubin P, Constine III LS, Nelson DF, Casarett GW. In: Rubin P, Saunders WB, editors. Clinical oncology: a multidiscipli-nary approach for physicians and students, 7th ed. New York: W.B. Saunders.1993.
    4. Xing L, Lin ZX, Donaldson SS, Le QT, Tate D, Goffinet DR, et al. Dosimetric effects of patient displacement and collimator and gantry angle misalignment on intensity modulated radiation therapy. Radiother Oncol. 2000;56(1):97-108.
    5. LoSasso T, Chui CS, Ling CC. Physical and dosimetric aspects of a multileaf collimation system used in the dynamic mode for implementing intensity modulated radiotherapy. Med. phys. 1998;25(10):1919-27.
    6. Abdel-Wahab M, Zubizarreta E, Polo A, Meghzifene A. Improving quality and access to radiation therapy—an IAEA per-spective. In Seminars in radiation oncology. 2017; 27(2): 109-17.
    7. Abdel-Wahab M, Bourque JM, Pynda Y, Iżewska J, Van der Merwe D, Zubizarreta E, et al. Status of radiotherapy resources in Africa: An International Atomic Energy Agency analysis. The lancet oncology. 2013;14(4):168-75.
    8. Quality Assurance Team for Radiation Oncology. Comprehensive audits of radiotherapy practices: a tool for quality im-provement. Vienna: International Atomic Energy Agency;2007.
    9. International Atomic Energy Agency. Setting up a radiotherapy programme: clinical, medical physics, radiation protection and safety aspects. Internat. Atomic Energy Agency; 2008.
    10. Aletti P, Bey P, Chauvel P, Chavaudra J, Costa A, Donnareix D,et al. Recommendations for a Quality Assurance Pro-gramme in External Radiotherapy, ESTRO.1995.
    11. Kutcher GJ, Coia L, Gillin M, Hanson WF, Leibel S, Morton RJ, et al. Comprehensive QA for radiation oncology: report of AAPM Radiation Therapy Committee Task Group 40. Med Phys. 1994; 21:581–618.
    12. Klein. QA of Medical Accelerators: report of AAPM Radiation Therapy Committee Task Group 142. Med Phys. 2009; 36:4197-210.
    13. Luxton G, Antony J, Loo BW, Carlson D, Maxim PG, Xing L. Dose Escalation Feasible Due to Gating in Lung Cancer Patients. Int. J. Radiat. Oncol. Biol. Phys. 2008;72(1):S625.
    14. Herrassi MY, Bentayeb F, Malisan MR. Comparative study of four advanced 3dconformal radiation therapy treatment planning techniques for head and neck cancer. J Med Phys. 2013; 38:98-105.
    15. Mesbahi A., Rasuli N., Nasiri B., mohammadzadeh M. Radiobiological Model. Based Comparison of Three Dimensional Conformal and Intensity Modulated Radiation Therapy Plans for Nasopharyngeal Carcinoma. Iran J Med Phys. 2017;14(4):190-6. DOI: 10.22038/ijmp.2017.22508.1213.
    16. Petrova D, Smickovska S, Lazarevska E. Conformity Index and Homogeneity Index of the Postoperative Whole Breast Radiotherapy. Open Access Maced J Med Sci. 2017;5(6):736.
    17. Feuvret L, Noël G, Mazeron JJ, Bey P. Conformity index: a review. Int. J. Radiat. Oncol. Biol. Phys. 2006;64(2):333-42.
    18. Stanley J, Breitman K, Dunscombe P, Spencer DP, Lau H. Evaluation of stereotactic radiosurgery conformity indices for 170 target volumes in patients with brain metastases. J APPL CLIN MED PHYS. 2011;12(2):245-53.
    19. Whitley E, Ball J. Statistics review 6: Nonparametric methods. Critical care. 2002; 6(6):509-13.
    20. Ricard D, De Greslan T, Soussain C, Bounolleau P, SallansonnetFroment M, Delmas J.M, et al. Neurological damage of brain tumor therapy. Rev Neurol (Paris). 2008; 164:575–87.
    21. DeSalvo MN. Radiation necrosis of the pons after radiotherapy for nasopharyngeal carcinoma: diagnosis and treatment. J Radiol Case Rep. 2012; 6:9–16.
    22. Zwicker F, Roeder F, Hauswald H, Thieke C, Timke C, Schlegel W,et al. Reirradiation with intensity modulated radiothera-py in recurrent head and neck cancer. Head Neck. 2011;33(12):1695-702. DOI: 10.1002/hed.21663.
    23. Hauptman JS, Barkhoudarian G, Safaee M, Gorgulho A, Tenn S, Agazaryan N, et al. Challenges in Linear Accelerator Radiotherapy for chordomas and chondrosarcomas of the skull base: focus on complications. Int. J. Radiat. Oncol. Biol. Phys. 2012; 83:542–551.
    24. Timmerman RD. An overview of hypofractionation and introduction to this issue of seminars in radiation oncology. Semin. Radiat. Oncol. 2008; 18:215–22.
    25. Guimas V, Thariat J, Graff-Cailleau P, Boisselier P, Pointreau Y, Pommier P, et al. Intensity modulated radiotherapy for head and neck cancer, dose constraint for normal tissue: Cochlea vestibular apparatus and brainstem. Cancer radiother. 2016;20(6-7):475-83.
    26. Mayo C, Yorke E, Merchant TE. Radiation Associated Brainstem Injury. Int J Radiat Oncol. 2010; 76:36–41.
    27. Yao CY, Zhou GR, Wang LJ, Xu JH, Ye JJ, Zhang LF, et al. A retrospective dosimetry study of intensity-modulated radio-therapy for nasopharyngeal carcinoma: radiation-induced brainstem injury and dose-volume analysis. Radiat Oncol. 2018;13(1):194. DOI: 10.1186/s13014-018-1105-z.
    28. Attalla E, Eldesoky I. The Dosimetric Effects of Different Multileaf Collimator Widths on Physical Dose Distributions. Iran J Med Phys. 2018;15(1):12-8.DOI: 10.22038/ijmp.2017.20058.1190.
    29. Bahreyni Toossi MT, Rajab Bolookat E, Salek R, Layegh M. Dose measurements of parotid glands and spinal cord in conventional treatment of nasopharyngeal carcinoma using rando phantom and thermoluminescent dosimeters. Iranian J Med Phys. 2015;12(2):78-84.DOI: 10.22038/ijmp.2015.4769.
    30. Adamus.Górka M, Mavroidis P, Lind BK, Brahme A. Comparison of Dose Response Models for Predicting Normal Tis-sue Complications from Cancer Radiotherapy: Application in Rat Spinal Cord. Cancers. 2011; 3(2): 2421-43. DOI:10.3390/cancers3022421.
    31. McKenzie A, van Herk M, Mijnheer B. Margins for geometric uncertainty around organs at risk in radiotherapy. Radio-therapy and Oncology. 2002;62(3):299-307.
    32. Majumder D, Patra NB, Chatterjee D, Mallick SK, Kabasi AK, Majumder A. Prescribed dose versus calculated dose of spinal cord in standard head and neck irradiation assessed by 3.D plan. South Asian J. Cancer. 2014; 3(1): 22-7. DOI:10.4103/2278.330X.126510.
    33. Boisselier P, Racadot S, Thariat J, Graff P, Pointreau Y.Intensity modulated radiotherapy of head and neck cancers. Dose constraint for spinal cord and brachial plexus. Cancer Radiother. 2016;20(6-7):459-66. DOI: 10.1016/j.canrad.2016.08.124.