Nuklearmedizin und Strahlentherapie

A Novel Three Dimensional Conformal Radiation Therapy Technique to Decrease the Mean Parotid Gland Dose in Whole Brain Radiation Therapy

Abstract

Lara Hilal, Hana Mekdash, Paul Ramia, Mustafa Jammal, Dima Mahmoud, Bilal Shahine, Toufic Eid, Wassim Jalbout, Helena Abdul Khalek, Fady Geara, Youssef H. Zeidan and Bassem Youssef

Purpose: Whole brain radiation therapy remains standard for patients with multiple brain metastases not amenable to stereotactic irradiation. Incidental irradiation of the parotid glands can result in xerostomia. A novel technique (NT) using 3D conformal radiotherapy was used to decrease the radiation dose to the parotid glands and hence the risk of xerostomia.

Methods: CT simulations of 20 de-identified patients were randomly selected. For each patient, 3 different WBRT plans were generated. The first using the standard opposed laterals fields with the inferior border at C2, the second with the inferior border at C1 and the third using a NT. In the NT, we placed the isocenter 0.5-1 cm superior to the contoured parotid glands. Superior to the isocenter, two lateral fields were designed similar to the standard opposed laterals. Inferior to the isocenter, 2 oblique fields were used, conformal to the contoured brain, with a 1 cm collimation to the edge of the MLC. Prescription dose was 30 Gy in 10 fractions for all plans. Brain coverage and the means of the right, left and bilateral parotids were compared in each of the plans.

Results: In all three techniques of WBRT, brain coverage was adequate with 95% of the dose covering more than 95% of the brain volume. The average of the mean right parotid dose using C2, C1, and the NT were 17.7 Gy ± 4.4, 12.3 Gy ± 3.3, and 5.6 Gy ± 2.1. The average of the mean left parotid dose using C2, C1, and the NT were 18.3 Gy ± 4.2, 13.0 Gy ± 3.1, and 6.2 Gy ± 1.5. The average of the mean bilateral parotids dose using C2, C1, and the NT were 18.0 Gy ±4.0, 12.6 Gy ±2.8, and 5.8 Gy ±1.8.

Conclusion: Our simple new 3DCRT technique for WBRT significantly reduces mean parotid gland dose compared to the standard techniques.