In Vivo Lens Dosimetry in a Case of En Face Electron Adjuvant Radiotherapy for Cutaneous Nasal Bridge Basal Cell Carcinoma: A Case Report

Abstract

"Radiation therapy represents one of the main treatment modalities for basal cell carcinoma (BCC), the most common type of skin cancer. The proximity of organs at risk (OARs) increases the risk of side effects. Treatment planning system (TPS) estimates the absorbed dose, but the real value can be determined only by in vivo dosimetry. We measured the absorbed dose at the lenses’ level in a case who received electron irradiation for a resected BCC with positive microscopic margins, located at the bridge of the nose. The thermoluminescent eye lens dosimeters (TLD) were placed under the lead protections. We compared the measured dose with the values estimated by TPS. The treatment involved delivering 50 Gy in 25 fractions. A Monaco 5.11 Treatment Planning System (TPS) was used to plan treatment with a 9 MeV electron field and a 10x10 cm applicator at a 100 cm Source-to-Skin Distance (SSD). Customized lead layers and circular lead blocks were used for protection. The TPS estimated maximum doses of 5.87 Gy for the left lens, and 2.70 Gy for the right lens, respectively. After measuring the doses for the first three fractions by TLD, we calculated that maximum dose for the left lens would get to 0.55 Gy, and to 0.30 Gy for the right lens. In this case report we show that irradiation for a BCC localised at the bridge of the nose is possible with proper shielding and can be safely delivered, without exposing the patient to long- term side effects"