Characterization of Wedge Factors and Dose Distributions in Radiotherapy with Symmetric and Asymmetric Physical Wedged Beams of 6 MV Photon Beam

Document Type : Original Paper


1 Medical Physicist, Department of Medical Physics and Department of Clinical Oncology, School of Medicine, Ahvaz Jundishapur University of Medical Sciences, Golestan Blvd., Ahvaz 61357-33118, Iran

2 Department of Medical Physics, School of Medicine, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran.

3 Department of Clinical Oncology, School of Medicine, Ahvaz Jundishapur University of Medical Sciences, Golestan Blvd., Ahvaz 61357-33118, Iran

4 Medical Physicist, Department of Medical Physics, School of Medicine, Ahvaz Jundishapur University of Medical Sciences, Golestan Blvd., Ahvaz 61357-33118, Iran


Introduction: Physical wedge by modify photon beam shape and intensity has been utilized in radiotherapy to obtain uniformly dose distribution in tumor site with reduced hot spots. Calculation of dosimetric parameters for both symmetric and asymmetric wedged fields is proved necessary during linear accelerator (Linac) commissioning. The present study aimed to achieve output factors and dose profiles for symmetric and asymmetric wedged fields of 6 MV beams.
Material and Methods: The Siemens PRIMUS Linac head for 6 MV beam was simulated by BEAMnrc and all dose calculations were performed by DOSXYZnrc code. Percentage depth dose (PDD) and profiles for open and wedged (15° and 45°) fields were compared with corresponding measurements. Wedge factors for 10 x 10 cm2 field were obtained as a function of lateral distance as well for half beam wedged fields.
Results: Based on the results of the present study, the calculated doses were in agreement with the measured data. The output factors on the central axis of symmetric wedged beams decreased to 0.693 and 0.307 for 15˚, and 45˚ wedges. The total photon fluence of 15˚ and 45˚ physical wedged fields reduced to 71.6% and 27.7% of open field, respectively.
Conclusion: The output factor for asymmetric wedged fields was found to be lower than corresponding symmetric open and wedged fields, particularly at field edges. Lack of scattering photons near the half beam edges resulted in dose fall-off in these regions possible to be overestimated by treatment planning system and consequently caused cold spots at target volume.


Main Subjects


    1. ICRU. Report 50: Prescribing, recording and reporting photon beam therapy. Bethesda, MD: International Commission on Radiation Units and Measurements, 1993.
    2. Muren LP, Hafslund R, Gustafsson A, Smaaland R, Dahl O. Partially wedged beams improve radiotherapy treatment of urinary bladder cancer. Radiother Oncol. 2001; 59(1):21-30.
    3. Prabhakar R, Julka PK, Rath GK. Can field-in-field technique replace wedge filter in radiotherapy treatment planning: a comparative analysis in various treatment sites. Australas Phys Eng Sci Med. 2008; 31(4):317-24.
    4. Vinagre FL, Simoes PC, Rachinhas PJ. Omni-wedge technique for increased dose homogeneity in head and neck radiotherapy. Physica medica. 2009; 25(3):154-9.
    5. Pasquino M, Casanova Borca V, Tofani S, Ozzello F. Verification of Varian Enhanced Dynamic Wedge implementation in masterplan treatment planning system. J Appl Clin Med Phys. 2009; 10(2):2867.
    6. Kowalik A, Litoborski M. Multienergetic verification of dynamic wedge angles in medical accelerators using multichannel linear array. Rep Pract Oncol Radiother. 2013; 18(4):220-34.
    7. Ansari S, Satpathy S, Paul S.Dose Distribution Analysis of Rapid Arc and Intensity Modulated Radiotherapy Plan in Head and Neck Cancer. IJMP. 2019; 16(2):139-44.
    8. Farhood B, Bahreyni Toossi MT, Soleymanifar S. Assessment of Dose Calculation Accuracy of TiGRT Treatment Planning System for Physical Wedged fields in Radiotherapy. IJMP. 2016; 13(3):146-53.
    9. Muhammad W, Maqbool M, Shahid M, Hussain A, Tahir S, Matiullah, et al. Assessment of computerized treatment planning system accuracy in calculating wedge factors of physical wedged fields for 6 MV photon beams. Phys Med. 2011; 27(3):135-43.
    10. Fontanarosa D, Orlandini LC, Andriani I, Bernardi L. Commissioning Varian enhanced dynamic wedge in the PINNACLE treatment planning system using Gafchromic EBT film. Med Phys. 2009; 36(10):4504-10.
    11. Salomons GJ, Kerr AT, Mei X, Patel D. The accuracy of MU calculations for dynamic wedge with the Varian's Anisotropic Analytical Algorithm. Med Phys. 2008; 35(10):4289-91.
    12. Caprile PF, Venencia CD, Besa P. Comparison between measured and calculated dynamic wedge dose distributions using the anisotropic analytic algorithm and pencil-beam convolution. J Appl Clin Med Phys. 2007; 8(1):47-54.
    13. Andreo P, Burns DT, Huq MS, Kanai T, laitano F, Symth VG, et al. IAEA; TRS-398: Absorbed dose determination in external beam radiotherapy: An International code of practice for dosimetry based on standards of absorbed dose to water. Vienna: IAEA: international atomic energy agency. 2000; 10: 46-80.
    14. Behjati M, Sohrabpour M, Shirmardi SP, Mosleh-Shirazi MA, Bouzarjomehri F. Calculation of wedged dose distributions using an analytical method. IJMP. 2018;15(Special Issue-12th. Iranian Congress of Medical Physics):105.
    15. Hideki F, Nao K, Hiroyuki H, Hiroshi K, Haruyuki F. Improvement of dose distribution with irregular surface compensator in whole breast radiotherapy. JMP. 2013; 38(3):115-9.
    16. Jones AO, Das IJ, Jones FL, Jr. A Monte Carlo study of IMRT beamlets in inhomogeneous media. Med Phys. 2003; 30(3):296-300.
    17. Tyagi N, Curran BH, Roberson PL, Moran JM, Acosta E, Fraass BA. Experimental verification of a Monte Carlo-based MLC simulation model for IMRT dose calculations in heterogeneous media Journal of Physics. Journal of Physics. 2008; Conference Series 102 (2008) 012025.
    18. Verhaegen F, Das IJ. Monte Carlo modelling of a virtual wedge. Physics in medicine and biology. PMB. 1999; 44(12):N251-9.
    19. Shih R, Li XA, Chu JC. Dynamic wedge versus physical wedge: a Monte Carlo study. Med Phys. 2001; 28(4):612-9.
    20. Rogers D, Faddegon B, Ding G, Ma CM, We J, Mackie T. BEAM: a Monte Carlo code to simulate radiotherapy treatment units. Med Physs. 1995; 22(5):503-24.
    21. Fraser D, Parker W, Seuntjens J. Characterization of cylindrical ionization chambers for patient specific IMRT QA. J Appl Clin Med Phys. 2009; 10(4):2923.
    22. Chung H, Jin H, Dempsey JF, Liu C, Palta J, Suh TS, et al. Evaluation of surface and build-up region dose for intensity-modulated radiation therapy in head and neck cancer. Med Phys. 2005; 32(8):2682-9.
    23. Zhu XR, Gillin MT, Jursinic PA, Lopez F, Grimm DF, Rownd JJ. Comparison of dosimetric characteristics of Siemens virtual and physical wedges. Med Phys. 2000; 27(10):2267-77.
    24. Attalla EM, Abo-Elenein HS, Ammar H, El-Desoky I. Comparison of dosimetric characteristics of Siemens virtual and physical wedges for ONCOR linear accelerator. JMP. 2010; 35(3):164-9.
    25. Geraily G, Mirzapour M, Mahdavi SR, Allahverdi M, Mostaar A, Masoudifar M. Monte Carlo study on beam hardening effect of physical wedges. Int J Radiat Res. 2014; 12:249-56.
    26. Biglari F, Mehnati P, Jomehzadeh A. Interpretation of In-air Output Ratio of Wedged Fields in Different Measurement Conditions. IJMP. 2018;15(Special Issue-12th. Iranian Congress of Medical Physics):366.
    27. Mohammadkarim A, Nedaie HA, Allahverdi M, Esfehani M, Shirazi A, Geraily G. Experimental Evaluation of Depth Dose by Exit Surface Diode Dosimeters for Off-Axis Wedged Fields in Radiation Therapy. IJMP. 2015; 12(4):262-70.
    28. Ahmad M, Hussain A, Muhammad W, Rizvi SQ, Matiullah. Studying wedge factors and beam profiles for physical and enhanced dynamic wedges. JMP. 2010; 35(1):33-41.
    29. Cheng CW, Tang WL, Das IJ. Beam characteristics of upper and lower physical wedge systems of Varian accelerators. Physics in medicine and biology. PMB. 2003; 48(22):3667-83.
    30. Khan FM. Dosimetry of wedged fields with asymmetric collimation. Med Phys. 1993; 20(5):1447-51.
    31. Niroomand-Rad A, Haleem M, Rodgers J, Obcemea C. Wedge factor dependence on depth and field size for various beam energies using symmetric and half-collimated asymmetric jaw settings. Med Phys. 1992; 19(6):1445-50.
    32. Kemikler G. Field size and depth dependence of wedge factor for internal wedge of dual energy linear accelerator. J BUON. 2003; 8(1):55-9.


Volume 17, Issue 3
May and June 2020
Pages 213-219
  • Receive Date: 21 June 2019
  • Revise Date: 04 August 2019
  • Accept Date: 12 August 2019
  • First Publish Date: 01 May 2020