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

Introduction: Parotid gland tumors account for approximately ۳% 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 ۵-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%: ۲.۳۱ and ۲.۲۸ Gy vs ۶.۱۴ 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 (۱.۹ Gy). All techniques achieved at least ۹۵% 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.

کلیدواژه ها:

Parotid tumor radiotherapy ، Tumor Dose ، TLD ، Rando phantom