(P128) Statistically Significant Calibration Curve for Ir-192 HDR Source Using Multichannel Gafchromic Film Analysis

OncologyOncology Vol 29 No 4_Suppl_1
Volume 29
Issue 4_Suppl_1

An accurate and robust calibration curve using the green channel of Gafchromic film can be easily created for use in validating HDR planning systems.

J. Barbiere, J. Napoli, A. Ndlovu; HUMC

PURPOSE: This work presents a unique methodology to create statistically valid calibration curves required to validate high-dose-rate (HDR)–planned dose distributions during brachytherapy treatment planning commissioning. A robust calibration curve is essential to accurately convert measured planar Gafchromic film density to dose for comparison with calculated dose distributions using standard metrics. The process presented herein is appropriate for widespread application since it can be used with any planning/analysis system that is capable of DICOM (Digital Imaging and COmmunication in Medicine) dose import/export, does not require specialized phantoms, and can be performed rapidly on the actual film sheet used for plan validation in a single exposure.

MATERIALS AND METHODS: A section of Gafchromic EBT3 film was positioned in contact with an HDR bronchial catheter surrounded by water-equivalent material. The film was irradiated for 1,350 Cisec with a Nucletron Ir-192 HDR line source and then digitized with an Epson 10000 XL color scanner. The remaining section of the film can be used for plan evaluation.

Film analysis was performed in MatLab with the imaging toolbox. Transmission values for the red, green, and blue channels were converted into optical density (OD) as a function of perpendicular distance from the center of the line source. A corresponding theoretical dose curve for each exposure was calculated using the TG43 formalism. The calculated dose was fitted to the measured OD in the clinically significant range to a fourth-order polynomial.

A single dwell position plan, normalized for the appropriate irradiation time, was created using the Oncentra treatment planning system. The three-dimensional (3D) DICOM dose matrix was imported into a Varian Eclipse external beam treatment planning system, and the two-dimensional (2D) dose in a coronal plane was extracted for comparison in MatLab with the corresponding measured film dose plane.

RESULTS: (1) The green channel had greater range, contrast scale, and accuracy than either the blue or red channel and was therefore used for analysis. (2) The calibration curve, consisting of nearly 200 points, was statistically valid and robust. (3) Agreement between the measured film and plan dose was within +/− 1.5% throughout the clinical range in 0.1-mm increments. (4) Our results provide a significant improvement in both dose and distance to agreement over current practice, which typically uses fewer than 10 calibration points.

CONCLUSION: An accurate and robust calibration curve using the green channel of Gafchromic film can be easily created for use in validating HDR planning systems.

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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