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Underdosing of the maxillary sinus for small fields used in newer radiotherapy techniques: Comparison of thermoluminescent dosimeter and Monte Carlo data


1 Department of Radiotherapy, King George's Medical University, Lucknow, India
2 Radiological Physics and Advisory Division, Bhabha Atomic Research Center, CTCRS, Mumbai, Maharashtra, India
3 Department of Radiotherapy and Radiation Medicine, Institute of Medical Sciences, Banaras Hindu University, Varanasi, India
4 Department of Radiotherapy, U.P. Rural Institute of Medical Sciences and Research, Etawah, Uttar Pradesh, India

Correspondence Address:
Navin Singh,
Department of Radiotherapy, King George's Medical University, Lucknow, India
India
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Source of Support: None, Conflict of Interest: None

Aims: To evaluate the underdosing of the maxillary sinus at its distal end produced by air cavity in the path of the 6 MV photon beam. Materials and Methods: A cubic solid water slab phantom of dimensions 18 cm × 18 cm × 18 cm with 4 cm × 4 cm × 4 cm air cavity 3 cm away from its anterior surface was used in this study. The percentage depth dose (PDD) for 6 MV X-rays along the central axis of the cubical air cavity was measured using thermoluminescent dosimeter-100 chips. The EGSnrc/DOSXYZnrc Monte Carlo (MC) code was used to estimate the PDD values in both homogeneous and inhomogeneous conditions. The dose data were generated for 1 cm × 1 cm, 2 cm × 2 cm, 3 cm × 3 cm, and 5 cm × 5 cm field sizes. Results: Average percentage dose reductions at 1 mm beyond the distal surface of the maxillary sinus for the field sizes 1 × 1, 2 × 2, and 3 × 3 cm 2 are 42.4%, 39.5%, and 29.4%, respectively. However, for 5 cm × 5 cm field size, there is a dose enhancement (i.e., overdosing) at 1 mm from the distal surface of the maxillary sinus and the average percentage dose enhancement is 5.9%. Also, beyond 1 cm from the air-water interface, there is dose enhancement for all the field sizes. Conclusion: This study showed that the significant dose reduction occurs near the air-water interface for the treatment techniques using small photon fields such as intensity-modulated radiotherapy or other newer techniques. MC-based treatment planning calculation predicts realistic dose distribution while using small photon fields in the treatment of maxillary sinus.


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