A Suitably Designed Lip Applicator for Radiation Therapy of Lips Carcinoma

Abstract

Background: The aim of this study was to evaluate a novel boosting technique in radiation therapy of lip carcinoma using a suitably designed lip applicator, called (in this study) internal dose enhancer tool. Methods: The internal dose enhancer tool was designed with proper thickness of lead for reducing transmission to tissues located beyond the lips. A 0.5 cm thickness of polystyrene was used to cover the lead and reduce the backscattered electron dose, while an opening in the polystyrene layer allowed electrons to reach the target. Monte-Carlo models of 6 and 8 MeV electron beams were developed using BEAMnrc code and were validated against experimental measurements. Using the developed models, dose distributions in a lip phantom were calculated and the effect of an internal dose enhancer tool on target dose enhancement was evaluated. Findings: Using the internal dose enhancer tool, the maximum dose enhancement as a percentage of dose at dmax of the unshielded field were 57.6% and 36.1% for 6 and 8 MeV beams, respectively. The best outcome was achieved for lip thickness of less than 1.5 cm and target thickness of less than 1 cm. For lateral dose coverage of planning target volume (PTV), the 80% isodose curve at the lip-internal dose enhancer tool interface showed a 12 mm expansion, compared to the unshielded field. Conclusion: This study showed that a conformal external beam radiation therapy (EBRT) of lip is possible by using an internal dose enhancer tool. This boosting method is especially applicable to cases in which other treatment modalities, such as brachytherapy, faces limitations.

Keywords

• Electron beam radiation therapy
• Lip carcinoma
• Monte Carlo simulation