A methodology for on‐board CBCT imaging dose using optically stimulated luminescence detectors

Noor Mail,Suliman M Ghamdi,Muhammad Yusuf,A Abdulrahman Kinsara,Abdelhamid Saoudi,Fahad Abdulkhaliq,Nazeeh Alothmany

doi:10.1120/jacmp.v17i5.6378

Abstract

Cone‐beam computed tomography CBCT systems are used in radiation therapy for patient alignment and positioning. The CBCT imaging procedure for patient setup adds substantial radiation dose to patient's normal tissue. This study presents a complete procedure for the CBCT dosimetry using the InLight optically‐stimulated‐luminescence (OSL) nanoDots. We report five dose parameters: the mean slice dose (DMSD); the cone beam dose index (CBDIW); the mean volume dose (DMVD); point‐dose profile, D(FOV); and the off‐field Dose. In addition, CBCT skin doses for seven pelvic tumor patients are reported. CBCT‐dose measurement was performed on a custom‐made cylindrical acrylic body phantom (50 cm length, 32 cm diameter). We machined 25 circular disks (2 cm thick) with grooves and holes to hold OSL‐nanoDots. OSLs that showed similar sensitivities were selected and calibrated against a Farmer‐type ionization‐chamber (0.6 CT) before being inserted into the grooves and holes. For the phantom scan, a standard CBCT‐imaging protocol (pelvic sites: 125 kVp, 80 mA and 25 ms) was used. Five dose parameters were quantified: DMSD, CBDIW, DMVD, D(FOV), and the off‐field dose. The DMSD for the central slice was 31.1±0.85 mGy, and CBDIW was 34.5±0.6 mGy at 16 cm FOV. The DMVD was 25.6±1.1 mGy. The off‐field dose was 10.5 mGy. For patients, the anterior and lateral skin doses attributable to CBCT imaging were 39.04±4.4 and 27.1±1.3 mGy, respectively.OSL nanoDots were convenient to use in measuring CBCT dose. The method of selecting the nanoDots greatly reduced uncertainty in the OSL measurements. Our detailed calibration procedure and CBCT dose measurements and calculations could prove useful in developing OSL routines for CBCT quality assessment, which in turn gives them the property of high spatial resolution, meaning that they have the potential for measurement of dose in regions of severe dose‐gradients.PACS number(s): 87.57.‐s, 87.57.Q, 87.57.uq

Highlights

One of the main objectives in radiation therapy is to deliver a uniform dose to the tumor whilst avoiding the organs at risk
Dose at the phantom surface The Cone-beam computed tomography (CBCT) dose at the phantom surface as a function of the superior–inferior position is shown in Fig. 3 for several FOVs
It is worth mentioning that when using the OSL dosimeter for in-phantom dosimetry, the application of depth-dependent correction factors is highly recommended to account for the energy dependence of the dosimeter due to variations in beam quality at increasing depths

Summary

Introduction

One of the main objectives in radiation therapy is to deliver a uniform dose to the tumor whilst avoiding the organs at risk. Cone-beam computed tomography (CBCT), provides a threedimensional image of the tumor, allowing the position of the patient to be adjusted prior to the start of the patient’s treatment. 144 mGy and the dose from the v1.4 system between 1 and 51 mGy. The authors measured the dose with a thermoluminescent dosimeter (TLD) and a computed tomography (CT) dose profiler. Another study[2] used an Elekta X-ray volume imaging (XVI) system (Elekta AB, Stockholm, Sweden) to calculate the CT dose index (CTDIW, a standardized measure of the radiation dose output of a CT scanner), and showed that the CBCT dose varied from 1.8 to 3.5 cGy. A TLD study by Wen et al[3] revealed a relationship between patient size and anterior–posterior skin dose and between dose and location on the body.

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