Tumor and Critical Organ Dose Assessment in Parotid Gland Radiotherapy: Comparison of Calculated and Measured Dose Using Different Techniques

Document Type : Original Paper

Authors

1 Medical Physics Research Centre, Mashhad University of Medical Sciences, Mashhad, Iran

2 Department of Medical Physics, School of Medicine, University of Medical Sciences, Mashhad, Iran

3 Department of Radiotherapy Oncology, Omid Hospital, Cancer Research Center, School of Medicine Mashhad University of Medical Sciences, Mashhad, Iran

4 Student Research Committee, Babol University of Medical Sciences, Babol, Iran

5 Cancer Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, I.R.Iran

10.22038/ijmp.2026.90428.2598

Abstract

Introduction: Parotid gland tumors account for approximately 3% of head and neck malignancies. Surgery is the primary treatment modality, while postoperative radiotherapy is recommended for high-grade tumors to reduce local recurrence. Several radiotherapy techniques have been used for postoperative parotid irradiation, each with different dosimetric characteristics. Among the most common approaches are angled wedged photon beams and ipsilateral mixed photon–electron beams. This study aimed to compare commonly used parotid radiotherapy techniques dosimetrically and propose clinical optimization strategies.
Material and Methods: A head-and-neck anthropomorphic Rando phantom was scanned using computed tomography with 5-mm slice thickness. Imaging data were transferred to the Isogray treatment planning system (TPS). Target volume and organs at risk (OARs) were contoured, and thermoluminescent dosimeters (TLDs) were used for dose measurements. Three radiotherapy techniques were evaluated regarding dose homogeneity, target coverage, organ sparing, and agreement between calculated and measured doses.
Results: Wedged-pair photon techniques with and without multileaf collimator (MLC) showed better dose homogeneity within the planning target volume (PTV) than the mixed photon–electron technique (ΔD₅%–D₉₅%: 2.31 and 2.28 Gy vs 6.14 Gy). The MLC-based wedged-pair technique provided superior sparing of tissues beyond the target volume, while the mixed beam technique resulted in the lowest oral cavity dose (1.9 Gy). All techniques achieved at least 95% PTV coverage. Measured and calculated doses showed acceptable agreement, although some discrepancies were observed in heterogeneous regions such as the mandible.
Conclusion: No single radiotherapy technique was optimal for all dosimetric objectives. Combining techniques may improve normal tissue sparing while maintaining adequate and homogeneous tumor dose coverage.

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Main Subjects

References

  1. Yaparpalvi R, Fontenla DP, Tyerech SK, Boselli LR, Beitler JJ. Parotid gland tumors: a comparison of postoperative radiotherapy techniques using three dimensional (3D) dose distributions and dose-volume histograms (DVHS). Int J Radiat Oncol Biol Phys. 1998;40(1):43-9.
  2. Vejdani Noghreiyan V, Naseri S, Momennezhad M. Utilization of Electronic Portal Imaging Device (EPID) For Setup Verification and Determination of Setup Margin in Head and Neck Radiation Therapy. Iranian Journal of Medical Physics. 2020;17(3):197-204.
  3. Blasi O, Fontenot JD, Fields RS, Gibbons JP, Hogstrom KR. Preliminary comparison of helical tomotherapy and mixed beams of unmodulated electrons and intensity modulated radiation therapy for treating superficial cancers of the parotid gland and nasal cavity. Radiat Oncol. 2011;6:178.
  4. Cozzi L, Fogliata A, Bolsi A, Nicolini G, Bernier J. Three-dimensional conformal vs. intensity-modulated radiotherapy in head-and-neck cancer patients: comparative analysis of dosimetric and technical parameters. Int J Radiat Oncol Biol Phys. 2004;58(2):617-24.
  5. Soleymanifard S, Toossi MT, Khosroabadi M, Noghreiyan AV, Shahidsales S, Tabrizi FV. Assessment of skin dose modification caused by application of immobilizing cast in head and neck radiotherapy. Australas Phys Eng Sci Med. 2014;37(3):535-40.
  6. Kudchadker RJ, Hogstrom KR, Garden AS, McNeese MD, Boyd RA, Antolak JA. Electron conformal radiotherapy using bolus and intensity modulation. Int J Radiat Oncol Biol Phys. 2002;53(4):1023-37.
  7. Nutting CM, Rowbottom CG, Cosgrove VP, Henk JM, Dearnaley DP, Robinson MH, et al. Optimisation of radiotherapy for carcinoma of the parotid gland: a comparison of conventional, three-dimensional conformal, and intensity-modulated techniques. Radiother Oncol. 2001;60(2):163-72.
  8. Nutting CM, Morden JP, Harrington KJ, Urbano TG, Bhide SA, Clark C, et al. Parotid-sparing intensity modulated versus conventional radiotherapy in head and neck cancer (PARSPORT): a phase 3 multicentre randomised controlled trial. Lancet Oncol. 2011;12(2):127-36.
  9. Mali SB. Adaptive Radiotherapy for Head Neck Cancer. J Maxillofac Oral Surg. 2016;15(4):549-54.
  10. Emami B, Lyman J, Brown A, Coia L, Goitein M, Munzenrider JE, et al. Tolerance of normal tissue to therapeutic irradiation. Int J Radiat Oncol Biol Phys. 1991;21(1):109-22.
  11. Bentzen SM, Constine LS, Deasy JO, Eisbruch A, Jackson A, Marks LB, et al. Quantitative Analyses of Normal Tissue Effects in the Clinic (QUANTEC): an introduction to the scientific issues. Int J Radiat Oncol Biol Phys. 2010;76(3 Suppl):S3-9.
  12. Bahreyni TMT, Gholamhosseinian H, Vejdani NA. Assessment of the Effects of Radiation Type and Energy on the Calibration of TLD-100. 2018.
  13. Luo L. Extensive fade study of Harshaw LiF TLD materials. Radiation Measurements - RADIAT MEAS. 2008;43:365-70.
  14. Van Dyk J. QA of computerized radiation treatment planning systems. Book of Extended Synopses. 2006:214.
Iranian Journal of Medical Physics
Volume 23, Issue 1
January and February 2026
Pages 1-8

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History

  • Receive Date: 14 August 2025
  • Revise Date: 24 February 2026
  • Accept Date: 09 February 2026

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