Document Type: Original Research


1 MSc, Medical Physics Department, Students Research Committee, Kermanshah University of Medical Sciences, Kermanshah, Iran

2 MD, Radiation oncologist, Faculty of Medicine, Hamedan University of Medical Sciences, Hamedan, Iran

3 PhD, Department of Medical Physics, Faculty of Medicine, Kermanshah University of Medical Sciences, Kermanshah, Iran

4 PhD, Medical Physicist of Radiotherapy, Mahdieh Radiotherapy and Brachytherapy Charity Center, Hamedan, Iran


Background: The use of small fields has increased by the emergence of advanced radiotherapy. Dose calculations of these fields are complex and challenging for many reasons such as lack of electrical equilibrium even in homogeneous environments, and this complexity will increase in presence of heterogeneity. According to the importance of delivery the accurate prescription dose to the target volume in the patient’s body, the dose calculation accuracy of used commercial algorithms in clinical treatment planning systems (TPS) should be evaluated.
Objective: The present study aims to evaluate the accuracy of Collapsed-Cone dose measurement algorithm in Isogray treatment planning system.
Material and Methods: In this analytical study, the measurements were made in tissue equivalent solid water phantom with lung and bone heterogeneities by Pinpoint dosimeter (0.015 cm3 sensitive volume) in several radiation fields (1×1 to 5×5 cm2). The phantoms were irradiated with 6, 10 and 18 MV photon beams and finally, the results of experimental calculations were compared with treatment planning outputs.
Results: In all setups, the maximum deviation occurred in the field of 1×1 cm2. Then, the maximum deviation was observed for 2×2 cm2 field size; however, it was up to 5% for homogeneous water phantom and lung heterogeneity. In 3×3 cm2 and larger fields, there was a good agreement between the results of the TPS and experimental dosimetry. The maximum deviation was observed in water-bone heterogeneity.
Conclusion: This algorithm was able to pass the standard audit criteria, but it is better to be used more cautiously in bone heterogeneity, especially in low energies.


  1. Golestani A, Houshyari M, Mostaar A, Arfaie AJ. Evaluation of dose calculation algorithms of Isogray treatment planning system using measurement in heterogeneous phantom. Reports of Radiotherapy and Oncology. 2015;2(3):e5320. doi: 10.17795/rro-5320.
  2. Falahati F, Nickfarjam A, Shabani M. A Feasibility Study of IMRT of Lung Cancer Using Gafchromic EBT3 Film. J Biomed Phys Eng. 2018;8:347-56. doi: 10.31661/jbpe.v0i0.791. PubMed PMID: 30568924. PubMed PMCID: PMC6280119.
  3. Laub WU, Wong T. The volume effect of detectors in the dosimetry of small fields used in IMRT. Med Phys. 2003;30:341-7. doi: 10.1118/1.1544678. PubMed PMID: 12674234.
  4. Alagar AG, Mani GK, Karunakaran K. Percentage depth dose calculation accuracy of model based algorithms in high energy photon small fields through heterogeneous media and comparison with plastic scintillator dosimetry. J Appl Clin Med Phys. 2016;17:132-42. doi: 10.1120/jacmp.v17i1.5773. PubMed PMID: 26894345. PubMed PMCID: PMC5690200.
  5. Jones AO, Das IJ. Comparison of inhomogeneity correction algorithms in small photon fields. Med Phys. 2005;32:766-76. doi: 10.1118/1.1861154.
  6. Andreo P. The physics of small megavoltage photon beam dosimetry. Radiother Oncol. 2018;126:205-13. doi: 10.1016/j.radonc.2017.11.001. PubMed PMID: 29191457.
  7. Svensson GK. Quality assurance in radiation therapy: physics efforts. Int J Radiat Oncol Biol Phys. 1984;10 Suppl 1:23-9.doi: 10.1016/0360-3016(84)90441-3. PubMed PMID: 6735791.
  8. Wambersie A. The role of the ICRU in quality assurance in radiation therapy. Int J Radiat Oncol Biol Phys. 1984;10 Suppl 1:81-6. doi: 10.1016/0360-3016(84)90454-1. PubMed PMID: 6429103.
  9. Fippel M. Fast Monte Carlo dose calculation for photon beams based on the VMC electron algorithm. Med Phys. 1999;26:1466-75. doi: 10.1118/1.598676. PubMed PMID: 10501045.
  10. Jabbari K, Bagher Tavakoli M, Mojtaba Hosseini S. Development and Implementation of the Convolution Method for Photon Dose Calculation in Radiation Therapy. Journal of Isfahan Medical School. 2012;30(198):11.
  11. Fogliata A, Nicolini G, Clivio A, Vanetti E, Cozzi L. Accuracy of Acuros XB and AAA dose calculation for small fields with reference to RapidArc® stereotactic treatments. Med Phys. 2011;38:6228-37.
  12. Singh N, Painuly NK, Chaudhari LN, Chairmadurai A, Verma T, Shrotiya D, et al. Evaluation of AAA and XVMC Algorithms for Dose Calculation in Lung Equivalent Heterogeneity in Photon Fields: A Comparison of Calculated Results with Measurements. J Biomed Phys Eng. 2018;8:223-30. PubMed PMID: 30320026. PubMed PMCID: PMC6169117.
  13. Fogliata A, Lobefalo F, Reggiori G, Stravato A, Tomatis S, Scorsetti M, et al. Evaluation of the dose calculation accuracy for small fields defined by jaw or MLC for AAA and Acuros XB algorithms. Med Phys. 2016;43:5685. doi: 10.1118/1.4963219. PubMed PMID: 27782735.
  14. Mesbahi A, Dadgar H. Dose calculations accuracy of TiGRT treatment planning system for small IMRT beamlets in heterogeneous lung phantom. Int J Radiat Res. 2015;13:345-54.
  15. Han T, Mikell JK, Salehpour M, Mourtada F. Dosimetric comparison of Acuros XB deterministic radiation transport method with Monte Carlo and model-based convolution methods in heterogeneous media. Med Phys. 2011;38:2651-64. doi: 10.1118/1.3582690. PubMed PMID: 21776802. PubMed PMCID: PMC3107831.
  16. Bagheri H, Soleimani A, Gharehaghaji N, Mesbahi A, Manouchehri F, Shekarchi B, et al. An overview on small-field dosimetry in photon beam radiotherapy: Developments and challenges. J Cancer Res Ther. 2017;13:175-85. doi: 10.4103/0973-1482.199444. PubMed PMID: 28643730.
  17. Würfel JU. Dose measurements in small fields. Med Phys. 2013;1:81-90.