Multiple-CT optimization: An adaptive optimization method to account for anatomical changes in intensity-modulated proton therapy for head and neck cancers.

PURPOSE: We aimed to determine whether multiple-CT (MCT) optimization of intensity-modulated proton therapy (IMPT) could improve plan robustness to anatomical changes and therefore reduce the additional need for adaptive planning. METHODS AND MATERIALS: Ten patients with head and neck cancer who underwent IMPT were included in this retrospective study. Each patient had primary planning CT (PCT), a first adaptive planning CT (ACT1), and a second adaptive planning CT (ACT2). Selective robust IMPT plans were generated using each CT data set (PCT, ACT1, and ACT2). Moreover, a MCT optimized plan was generated using the PCT and ACT1 data sets together. Dose distributions optimized using each of the four plans (PCT, ACT1, ACT2, and MCT plans) were re-calculated on ACT2 data. The doses to the target and to organs at risk were compared between optimization strategies. RESULTS: MCT plans for all patients met all target dose and organs-at-risk criteria for all three CT data sets. Target dose and organs-at-risk dose for PCT and ACT1 plans re-calculated on ACT2 data set were compromised, indicating the need for adaptive planning on ACT2 if PCT or ACT1 plans were used. The D98% of CTV1 and CTV3 of MCT plan re-calculated on ACT2 were both above the coverage criteria. The CTV2 coverage of the MCT plan re-calculated on ACT2 was worse than ACT2 plan. The MCT plan re-calculated on ACT2 data set had lower chiasm, esophagus, and larynx doses than did PCT, ACT1, or ACT2 plans re-calculated on ACT2 data set. CONCLUSIONS: MCT optimization can improve plan robustness toward anatomical change and may reduce the number of plan adaptation for head and neck cancers.

Wide volume versus helical acquisition using 320-detector row computed tomography for computed tomography urography in adults.

PURPOSE: To evaluate the best collimation used in wide volume (WV) mode to cover the abdomen in computed tomography (CT) urography in terms of radiation dose and image quality. MATERIALS AND METHODS: This study was performed on a 320×0.5mm detector row CT unit. The first part identified the lowest volume CT dose index (CTDIvol) by using the topograms data of 25 medium size patients (13 men and 12 women; mean age: 52±9 [SD] years; age range: 46-68 years) using different collimations on WV from 6cm to 16cm and the one of the helical mode for the same coverage length. The second part consisted of a clinical evaluation of this result including 45 medium size patients (32 men and 13 women; mean age: 68±14 [SD] years; age range: 45-72 years). The qualitative evaluation included several items based on a 5-point Likert scale. RESULTS: The first part of the study indicated that a collimation of 10cm (200×0.5mm) in WV mode with 5 volumes had the lowest CTDIvol (2.78±0.35mGy; range: 2.35-3.21mGy) compared to helical mode (4.38±0.48mGy, range: 3.75-4.95mGy). In the second part, the mean radiation dose reduction by comparison with helical mode was 44.03%±0.36% (P<0.001) and 51.16%±1.22% (P<0.005) for CTDIvol and DLP, respectively. CONCLUSION: Wide volume mode of the abdomen can be performed with a significant radiation dose reduction with a collimation of 10cm (200×0.5mm) and five volumes.

Multiple-CT optimization of intensity-modulated proton therapy - Is it possible to eliminate adaptive planning?

BACKGROUND AND PURPOSE: We hypothesized that a plan's robustness to anatomical changes can be improved by optimizing with multiple CT scans of a patient. The purpose of this study was to determine whether an intensity modulated proton therapy (IMPT) plan could be developed to meet dose criteria on both planning and adaptive CT plans. MATERIAL AND METHODS: Eight lung cancer patients who underwent adaptive IMPT were retrospectively selected. Each patient had two CTs: a primary planning CT (PCT) and an adaptive planning CT (ACT), and IMPT plans associated with the scans. PCT and ACT were then used in combination to optimize one plan (MCT plan). The doses to the target and organs at risk from the PCT plan, ACT plan, P-ACT plan (PCT plan calculated on ACT data), and MCT plans calculated on both CTs were compared. RESULTS: The MCT plan maintained the D95% on both CTs (mean, 65.99 Gy on PCT and 66.02 Gy on ACT). Target dose coverage on ACT was significantly better with the MCT plan than with the P-ACT plan (p = 0.01). MCT plans had slightly higher lung V20 (0.6%, p = 0.02) than did PCT plans. The various plans showed no statistically significant difference in heart and spinal cord dose. CONCLUSIONS: The results of this study indicate that an IMPT plan can meet the dose criteria on both PCT and ACT, and that MCT optimization can improve the plan's robustness to anatomical change.

Impact of the Adaptive Statistical Iterative Reconstruction Technique on Radiation Dose and Image Quality in Bone SPECT/CT.

UNLABELLED: The purpose of this study was to compare a routine bone SPECT/CT protocol using CT reconstructed with filtered backprojection (FBP) with an optimized protocol using low-dose CT images reconstructed with adaptive statistical iterative reconstruction (ASiR). METHODS: In this prospective study, enrolled patients underwent bone SPECT/CT, with 1 SPECT acquisition followed by 2 randomized CT acquisitions: FBP CT (FBP; noise index, 25) and ASiR CT (70% ASiR; noise index, 40). The image quality of both attenuation-corrected SPECT and CT images was visually (5-point Likert scale, 2 interpreters) and quantitatively (contrast ratio [CR] and signal-to-noise ratio [SNR]) estimated. The CT dose index volume, dose-length product, and effective dose were compared. RESULTS: Seventy-five patients were enrolled in the study. Quantitative attenuation-corrected SPECT evaluation showed no inferiority for contrast ratio and SNR issued from FBP CT or ASiR CT (respectively, 13.41 ± 7.83 vs. 13.45 ± 7.99 and 2.33 ± 0.83 vs. 2.32 ± 0.84). Qualitative image analysis showed no difference between attenuation-corrected SPECT images issued from FBP CT or ASiR CT for both interpreters (respectively, 3.5 ± 0.6 vs. 3.5 ± 0.6 and 3.6 ± 0.5 vs. 3.6 ± 0.5). Quantitative CT evaluation showed no inferiority for SNR between FBP and ASiR CT images (respectively, 0.93 ± 0.16 and 1.07 ± 0.17). Qualitative image analysis showed no quality difference between FBP and ASiR CT images for both interpreters (respectively, 3.8 ± 0.5 vs. 3.6 ± 0.5 and 4.0 ± 0.1 vs. 4.0 ± 0.2). Mean CT dose index volume, dose-length product, and effective dose for ASiR CT (3.0 ± 2.0 mGy, 148 ± 85 mGy⋅cm, and 2.2 ± 1.3 mSv) were significantly lower than for FBP CT (8.5 ± 3.7 mGy, 365 ± 160 mGy⋅cm, and 5.5 ± 2.4 mSv). CONCLUSION: The use of 70% ASiR blending in bone SPECT/CT can reduce the CT radiation dose by 60%, with no sacrifice in attenuation-corrected SPECT and CT image quality, compared with the conventional protocol using FBP CT reconstruction technique.

Lens dose in routine head CT: comparison of different optimization methods with anthropomorphic phantoms.

OBJECTIVE: The purpose of this study was to study different optimization methods for reducing eye lens dose in head CT. MATERIALS AND METHODS: Two anthropomorphic phantoms were scanned with a routine head CT protocol for evaluation of the brain that included bismuth shielding, gantry tilting, organ-based tube current modulation, or combinations of these techniques. Highsensitivity metal oxide semiconductor field effect transistor dosimeters were used to measure local equivalent doses in the head region. The relative changes in image noise and contrast were determined by ROI analysis. RESULTS: The mean absorbed lens doses varied from 4.9 to 19.7 mGy and from 10.8 to 16.9 mGy in the two phantoms. The most efficient method for reducing lens dose was gantry tilting, which left the lenses outside the primary radiation beam, resulting in an approximately 75% decrease in lens dose. Image noise decreased, especially in the anterior part of the brain. The use of organ-based tube current modulation resulted in an approximately 30% decrease in lens dose. However, image noise increased as much as 30% in the posterior and central parts of the brain. With bismuth shields, it was possible to reduce lens dose as much as 25%. CONCLUSION: Our results indicate that gantry tilt, when possible, is an effective method for reducing exposure of the eye lenses in CT of the brain without compromising image quality. Measurements in two different phantoms showed how patient geometry affects the optimization. When lenses can only partially be cropped outside the primary beam, organ-based tube current modulation or bismuth shields can be useful in lens dose reduction.

Introduction of an effective method for the optimization of CT protocols using iterative reconstruction algorithms: comparison with patient data.

OBJECTIVE: The purpose of this study is to introduce an efficient method for the optimization of iterative reconstruction CT protocols based on phantom image analysis and the comparison of obtained results with actual patient data. MATERIALS AND METHODS: We considered chest, abdomen, and pelvis CT examinations before the installation of an iterative reconstruction algorithm (iDose4) to define the exposure parameters used in clinical routine with filtered back projection (FBP). The body area of a CT phantom was subsequently scanned with various tube voltages and tube currents-exposure time products, and acquired data were reconstructed with FBP and different levels of iDose4. The contrast-to-noise ratio (CNR) for FBP with the original exposure parameters was calculated to define the minimum acceptable CNR value for each tube voltage. Then, an optimum tube current-exposure time products for each tube voltage and level of iterative reconstruction was estimated. We also compared findings derived by the phantom with real patient data by assessing dosimetric and image quality indexes from a patient cohort scanned with exposure parameters gradually adjusted during 1 year of adoption of iDose4. RESULTS: By use of the proposed phantom method, dose reduction up to 75% was achievable, whereas for an intermediate level of iteration (level 4), the dose reduction ranged between 50% and 60%, depending on the tube voltage. For comparison, with the gradual adjustment of exposure settings, the corresponding dose reduction for the same level of iteration was about 35%. CONCLUSION: The proposed method provides rapid and efficient optimization of CT protocols and could be used as the first step in the optimization process.