Dose optimization of 2D X-ray image acquisition protocols in image-guided radiotherapy.

PURPOSE: In contemporary radiotherapy, patient positioning accuracy relies on kV imaging. This study aims at optimizing planar kV image acquisition protocols regarding patient dose without degrading image quality. MATERIALS AND METHODS: An image quality test-object was placed in-between PMMA plates, suitably arranged to model head or pelvis. Constructed phantoms were imaged using default protocols, the resultant image quality was assessed and the corresponding radiation dose was measured. The process was repeated using numerous kV/mAs combinations to identify those acquisition settings providing images at lower dose than the default protocols but without deterioration in image quality. Default and dose-optimized protocols were then tested on an anthropomorphic phantom and on 51 patients during two successive treatment sessions. Image quality was independently assessed by two readers. Organ and effective doses were estimated using a Monte Carlo simulation software. RESULTS: Low-contrast detectability exhibited a stronger dependence on kV/mAs settings, compared to high-contrast resolution. Dose-optimized protocols resulted in significant dose reductions (anteroposterior-head 48.0 %, lateral-head 30.0 %, anteroposterior-pelvis 28.4 %, lateral-pelvis 27.0 %) compared to the default ones, without compromising image quality. Optimized protocols decreased effective doses by 54 % and 29.6 % in head and pelvic acquisitions, respectively. Regarding image quality, anthropomorphic and patient images acquired using the dose-optimized protocols were subjectively evaluated equivalent to those obtained with the corresponding default settings, indicating that the proposed protocols may be routinely used. CONCLUSIONS: Given the potentially large number of radiotherapy fractions and the pertinent image acquisitions, dose-optimized protocols could significantly reduce patient dose associated with planar imaging without compromising positioning accuracy.

Availability of technology for managing cancer patients in the Southeast European (SEE) region.

Background: The Southeast European (SEE) region of 10 countries and about 43 million people differs from Western Europe in that most SEE countries lack active cancer registries and have fewer diagnostic imaging devices and radiotherapy (RT) units. The main objective of this research is to initiate a common platform for gathering SEE regional cancer data from the ground up to help these countries develop common cancer management strategies. Methods: To obtain detailed on-the-ground information, we developed separate questionnaires for two SEE groups: a) ONCO - oncologists regarding cancer treatment modalities and the availability of diagnostic imaging and radiotherapy equipment; and b) REG - national radiation protection and safety regulatory bodies regarding diagnostic imaging and radiotherapy equipment in SEE facilities. Results: Based on responses from 13/17 ONCO participants (at least one from each country) and from 9/10 REG participants (all countries but Albania), cancer incidence rates are higher in those SEE countries that have greater access to diagnostic imaging equipment while cancer mortality-to-incidence (MIR) ratios are higher in countries that lack radiotherapy equipment. Conclusion: By combining unique SEE region information with data available from major global databases, we demonstrated that the availability of diagnostic imaging and radiotherapy equipment in the SEE countries is related to their economic development. While immediate diagnostic imaging and radiation therapy capacity building is necessary, it is also essential to develop both national and SEE-regional cancer registries in order to understand the heterogeneity of each country's needs and to establish regional collaborative strategies for combating cancer.

The importance of the accuracy of image registration of SPECT images for 3D targeted radionuclide therapy dosimetry.

In this paper, the importance of the accuracy of image registration of time-sequential SPECT images for 3D targeted radionuclide therapy dosimetry is studied. Image registration of a series of SPECT scans is required to allow the computation of the 3D absorbed dose distribution for both tumour sites and normal organs. Three simulated 4D datasets, based on patient therapy studies, were generated to allow the effect of mis-registration on the absorbed dose distribution to be investigated. The tumour sites studied range in size, shape and position, relative to the centre of the 3D SPECT scan. Randomly generated transformations along the x-, y- and z-axes and rotations around the z-axis were employed and the maximum and average absorbed dose distribution statistics, for the tumour sites present, were computed. It was shown that even small mis-registrations, translation of less than 9 mm and rotation of less than 5 degrees might cause differences in the absorbed dose statistics of up to 90%, especially when the size of the tumour is comparable to the induced mis-registration or when the tumour is situated close to the edge of the 3D dataset.

The variation of intrinsic spatial resolution across the UFOV of scintillation cameras.

The aim of the present study was to investigate in detail the variation of the intrinsic spatial resolution across the useful field of view (UFOV) of gamma-cameras and to explore whether this variation could lead to observable effects in clinical images. Two gamma-cameras were used, without their collimators, to acquire 560 (99m)Tc point source images at different points across their UFOVs, in order to measure the intrinsic spatial resolution at each point. Possible clinical effects of the resolution variation were examined on images of a thyroid phantom using a LEHR collimator, acquired at different locations on the UFOV and at various distances from the collimator. The gamma-camera intrinsic resolution varied significantly across the UFOV, being generally lower at the central region and deteriorating at the edges. Pronounced local maxima and minima were found at points corresponding to the centers of the photomultiplier tubes (PMTs) and halfway in between. Maximum differences of more than 50% were observed between the points presenting the best and worst intrinsic resolution. Differences between neighboring points reached 17%. The effects of resolution variation were clearly observable on the thyroid phantom images. It was concluded that an appropriate correction algorithm might be necessary in order to correct for the variation of the intrinsic spatial resolution across the UFOV of gamma-cameras.

Skin doses to patients undergoing coronary angiography in a Greek hospital.

In this study, the skin dose (SD) to patients undergoing coronary angiography (CA) were measured with thermoluminescence dosemeters (TLD) attached to various anatomical locations on the patient's skin during 93 CA procedures in a Greek hospital. The dose-area product (DAP) for every radiological projection was also measured for each procedure. The SD values were measured to be in the range 2.4-427.5 mGy, lower than the 2 Gy dose threshold for transient erythema. No general correlation was observed between the SD and the total DAP.

The dependence of patient dose on factors relating to the technique and complexity of Interventional Cardiology procedures.

Dose-area product (DAP) measurements were conducted for 168 coronary angiography (CA) and 89 single vessel percutaneous transluminal coronary angioplasty (PTCA) to examine the factors influencing patient dose beyond the X-ray exposure parameters. It was found that for CA, the DAP increases with the number of catheters used and with the number of vessels with stenosis. DAP values for patients with a prior bypass surgery, were higher compared to those without such a medical record to surgery. In PTCA, the use of coronary stents did not enhance the patient radiation dose significantly. Noticeable differences were found in the percentage contribution of each projection to the total DAP between the three types of single vessel PTCA. Finally low variations in DAP were found among the cardiologists performing both procedures.

Radiation exposure to cardiologists performing interventional cardiology procedures.

Medical doctors, who practice interventional cardiology, receive a noticeable radiation dose. In this study, we measured the radiation dose to 9 cardiologists during 144 procedures (72 coronary angiographies and 70 percutaneus translumined coronary angioplasties) in two Greek hospitals. Absorbed doses were measured with TLD placed underneath and over the lead apron at the thyroid protective collar. Based on these measurements, the effective dose was calculated using the Niklason method. In addition, dose area product (DAP) was registered. The effective doses, E, were normalised to the total DAP measured in each procedure, producing the E/DAP index. The mean effective dose values were found to be in the range of 1.2-2.7 microSv while the mean E/DAP values are in the range of 0.010-0.035 microSv/Gycm2. The dependence of dose to the X-ray equipment, the exposure parameters and the technique of the cardiologist were examined. Taking under consideration the laboratories' annual workload, the maximum annual dose was estimated to be 1.9 and 2.8 mSv in the two hospitals.