(P138) Dosimetric Evaluation of Parotid Dose in Whole-Brain Radiation Plans Covering C1 vs C2

OncologyOncology Vol 29 No 4_Suppl_1
Volume 29
Issue 4_Suppl_1

Clinicians who choose to cover C2 with WBRT should be aware of the increased radiation dose delivered to the parotid glands. NTCP modeling predicts an increased rate of treatment-associated xerostomia as a result.

Andrew W. Orton, MD, John D. Gordon, MS, DABR, Tyler P. Vigh, Allison E. Tonkin, MD, George M. Cannon, MD; Huntsman Cancer Institute; Intermountain Medical Center

BACKGROUND AND PURPOSE: Dosimetric analysis has demonstrated a higher-than-anticipated dose to the parotid glands during whole-brain radiation therapy (WBRT). Even in the computed tomography (CT) planning era, WBRT fields continue to be designed based on anatomic landmarks identified on digitally reconstructed radiographs (DRRs) of the skull. The dose of radiation delivered incidentally to the parotid glands is influenced by the location of the inferior border of the treatment field. The purpose of this study is to compare the dose delivered to the parotid glands and associated normal tissue complication probabilities (NTCPs) in plans covering the C1 vs C2 vertebral level.

MATERIALS AND METHODS: A total of 15 patients underwent CT simulation of the brain, followed by dosimetric evaluation of parotid dose. Two treatment plans were produced for each patient using the CT simulation images: the first extended the inferior field border to the inferior edge of the C1 vertebra, and the second extended the field to the inferior edge of C2. Two dose prescriptions were compared: 30 Gy and 37.5 Gy. NTCPs were estimated using the Lyman-Burman-Kutcher model with parameters obtained from studies published by Eisbruch, Emami, and Roesink. Mean dose to the parotids and NTCPs were compared between the two groups, and statistical significance was determined using a patient-matched two-sided t-test.

RESULTS: The mean parotid dose was significantly higher when C2 was covered. For the 30-Gy prescription, coverage to C2 increased the parotid dose from 14.3 Gy to 18.3 Gy (P < .01). For the 37.5-Gy plan, coverage to C2 increased the parotid dose from 18.5 Gy to 23.4 Gy (P < .01). NTCPs for the parotid gland were also higher when covering C2 vs C1. At 30 Gy, NTCP estimates for C1 coverage ranged from 0.0 to 0.08 compared with a range of 0.0 to 0.12 in plans covering C2. At 37.5 Gy, C1 coverage resulted in predicted rates of 0.0 to 0.12 vs 0.01 to 0.21 in plans covering C2.

CONCLUSIONS: Clinicians who choose to cover C2 with WBRT should be aware of the increased radiation dose delivered to the parotid glands. NTCP modeling predicts an increased rate of treatment-associated xerostomia as a result.

Proceedings of the 97th Annual Meeting of the American Radium Society - americanradiumsociety.org

Articles in this issue

(P005) Ultrasensitive PSA Identifies Patients With Organ-Confined Prostate Cancer Requiring Postop Radiotherapy
(P001) Disparities in the Local Management of Breast Cancer in the United States According to Health Insurance Status
(P002) Predictors of CNS Disease in Metastatic Melanoma: Desmoplastic Subtype Associated With Higher Risk
(P003) Identification of Somatic Mutations Using Fine Needle Aspiration: Correlation With Clinical Outcomes in Patients With Locally Advanced Pancreatic Cancer
(P004) A Retrospective Study to Assess Disparities in the Utilization of Intensity-Modulated Radiotherapy (IMRT) and Proton Therapy (PT) in the Treatment of Prostate Cancer (PCa)
(S001) Tumor Control and Toxicity Outcomes for Head and Neck Cancer Patients Re-Treated With Intensity-Modulated Radiation Therapy (IMRT)-A Fifteen-Year Experience
(S003) Weekly IGRT Volumetric Response Analysis as a Predictive Tool for Locoregional Control in Head and Neck Cancer Radiotherapy 
(S004) Combination of Radiotherapy and Cetuximab for Aggressive, High-Risk Cutaneous Squamous Cell Cancer of the Head and Neck: A Propensity Score Analysis
(S005) Radiotherapy for Carcinoma of the Hypopharynx Over Five Decades: Experience at a Single Institution
(S002) Prognostic Value of Intraradiation Treatment FDG-PET Parameters in Locally Advanced Oropharyngeal Cancer
(P006) The Role of Sequential Imaging in Cervical Cancer Management
(P008) Pretreatment FDG Uptake of Nontarget Lung Tissue Correlates With Symptomatic Pneumonitis Following Stereotactic Ablative Radiotherapy (SABR)
(P009) Monte Carlo Dosimetry Evaluation of Lung Stereotactic Body Radiosurgery
(P010) Stereotactic Body Radiotherapy for Treatment of Adrenal Gland Metastasis: Toxicity, Outcomes, and Patterns of Failure
(P011) Stereotactic Radiosurgery and BRAF Inhibitor Therapy for Melanoma Brain Metastases Is Associated With Increased Risk for Radiation Necrosis
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