The effect and stability of MVCT images on adaptive TomoTherapy.
ABSTRACT Use of helical TomoTherapy-based MVCT imaging for adaptive planning is becoming increasingly popular. Treatment planning and dose calculations based on MVCT require an image value to electron density calibration to remain stable over the course of treatment time. In this work, we have studied the dosimetric impact on TomoTherapy treatment plans due to variation in image value to density table (IVDT) curve as a function of target degradation. We also have investigated the reproducibility and stability of the TomoTherapy MVCT image quality over time. Multiple scans of the TomoTherapy "Cheese" phantom were performed over a period of five months. Over this period, a difference of 4.7% in the HU values was observed in high-density regions while there was no significant variation in the image values for the low densities of the IVDT curve. Changes in the IVDT curves before and after target replacement were measured. Two clinical treatment sites, pelvis and prostate, were selected to study the dosimetric impact of this variation. Dose was recalculated on the MVCTs with the planned fluence using IVDT curves acquired before and after target change. For the cases studied, target replacement resulted in an overall difference of less than 5%, which can be significant for hypo-fractionated cases. Hence, it is recommended to measure the IVDT curves on a monthly basis and after any major repairs/replacements.
SourceAvailable from: Jae Hong Jung[Show abstract] [Hide abstract]
ABSTRACT: Recently, the jaw size for the TomoTherapy Hi-Art II(®) (TomoTherapy Inc., Madison, WI) was reduced from 4 mm (J4) to 1 mm (J1) to improve the longitudinal (IEC-Y) resolution in megavoltage computed tomography (MVCT) images. This study evaluated the effect of jaw size on the image quality and dose, as well as the dose delivered to the lens of the eye, which is a highly radiosensitive tissue. MVCT image quality (image noise, uniformity, contrast linearity, high-contrast resolution, and full width at half-maximum) and multiple scan average dose (MSAD) were measured at different jaw sizes. A head phantom and photoluminescence glass dosimeters (PLDs) were used to measure the exposed lens dose (cGy). Different MVCT scan modes (pitch = 1, 2, and 3) and scan lengths (108 mm, 156 mm, and 204 mm) were applied in the MSAD and PLDs measurements. The change in jaw size from J4 to J1 produced no change or only a slight improvement in image noise, uniformity, contrast linearity, and high-contrast resolution. However, the full-width at half-maximum reduced from approximately 7.2 at J4 to 4.5 mm at J1, which represents an enhancement in the longitudinal resolution. The MSAD at the center point changed from approximately 0.69-2.32 cGy (peripheral: 0.83-2.49 cGy) at J4 to 0.85-2.81 cGy (peripheral: 1.05-2.86 cGy) at J1. The measured lens dose increased from 0.92-3.36 cGy at J4 to 1.06-3.91 cGy at J1. The change in jaw size improved longitudinal resolution. The MVCT imaging dose of approximately 3.86 cGy, 1.92 cGy, and 1.22 cGy was delivered at a pitch of 1, 2, and 3, respectively, per fraction in the head and neck treatment plans. Therefore, allowance for an approximately 15% increase in lens dose over that with J4 should be provided with J1.Medical Physics 08/2012; 39(8):4976-83. DOI:10.1118/1.4736951 · 3.01 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: We have analyzed the stability of CT to density curve of kilovoltage cone-beam computerized tomography (kV CBCT) imaging modality over the period of six months. We also, investigated the viability of using image value to density table (IVDT) generated at different time, for adaptive radiotherapy treatment planning. The consequences of target volume change and the efficacy of kV CBCT for adaptive planning issues is investigated. MATERIALS AND METHODS.: Standard electron density phantom was used to establish CT to electron density calibrations curve. The CT to density curve for the CBCT images were observed for the period of six months. The kV CBCT scans used for adaptive planning was acquired with an on-board imager system mounted on a "Trilogy" linear accelerator. kV CBCT images were acquired for daily setup registration. The effect of variations in CT to density curve was studied on two clinical cases: prostate and lung. The soft tissue contouring is superior in kV CBCT scans in comparison to mega voltage CT (MVCT) scans. The CT to density curve for the CBCT images was found steady over six months. Due to difficulty in attaining the reproducibility in daily setup for the prostate treatment, there is a day-to-day difference in dose to the rectum and bladder. There is no need for generating a new CT to density curve for the adaptive planning on the kV CBCT images. Also, it is viable to perform the adaptive planning to check the dose to target and organ at risk (OAR) without performing a new kV CT scan, which will reduce the dose to the patient.Radiology and Oncology 09/2011; 45(3):220-6. DOI:10.2478/v10019-011-0024-5 · 1.60 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: HI-ART II system can generate CT images from the same megavoltage X-ray beam used for treatment. These megavoltage CT (MVCT) images not only provide verification of the patient position prior to and potentially during radiation therapy, but they are also used for dose calculation. Dose calculations based on MVCT images require an image value to electron density calibration to remain stable over the course of treatment time. In this work, we have investigated the dosimetric effects on TomoTherapy treatment plans due to variation in image value to density table (IVDT) curve, such as time, MVCT parameters, phantom material and arrangement. We also have evaluated the reliability and stability of dose calculation during adaptive radiation therapy and dose verification using MVCT images. Among the tests, dose calculation using MVCT images was well consistent with that using kVCT. The differences in dose calculation on the phantom plan were up to almost 3% and typically the dosimetric points varied by less than 2%. Hence, the reliability of dose calculation for MVCT provides a basis of adaptive radiation therapy. It is recommended to measure the IVDT curves on a regular basis.IFMBE proceedings 05/2012; DOI:10.1007/978-3-642-29305-4_308