Improvement of the robustness to set up error by a virtual bolus in total scalp irradiation with Helical TomoTherapy Abstract Intensity-modulated radiation therapy has recently been used for total scalp irradiation. In inverse planning, the treatment planning system increases the fluence of tangential beam near the skin surface to counter the build-up region. Consequently, the dose to the skin surface increases even with small setup errors. Replacing the electron density of the surrounding air of some thickness with a virtual bolus during optimization could suppress the extremely high fluence near the skin. We confirmed the usefulness of a virtual bolus in total scalp irradiation. For each patient, two beams were planned, one with and the other without a virtual bolus. The dose distribution was calculated using computed tomography images that were shifted to simulate setup errors. The hot spot dose was suppressed in the plans using a virtual bolus. In conclusion, using a virtual bolus improved the robustness to setup errors.

Hendee’s physics of medical imaging, fifth edition, by Ehsan Samei and Donald J. Peck

A mask method to assess the uniformity of fat suppression in phantom studies Abstract Fat suppression is a technique used to suppress the signals from adipose tissues, during clinical evaluation of the tissues near the fat–tissue boundary. However, in cases where the scan area has a complicated shape, the effect of fat suppression may demonstrate poor uniformity, resulting in diagnosis-related difficulties. To improve the uniformity of fat suppression, phantom studies are more suitable than volunteer studies. In this study, we evaluated the reliability of the region of interest (ROI) dependency using an unevenness phantom, to develop a method to assess the uniformity of fat suppression while using whole magnetic resonance imaging by masking the surrounding phantom. We modulated different ROI sizes, which were eroded from 100% to approximately 50%, and observed that the normalized absolute average deviation and error increased with decreased ROI. Using our method, more objective, concrete, and accurate data could be obtained by including the whole-body phantom (whole poor uniformity area).

Additive value of split-bolus single-phase CT scan protocol for preoperative assessment of lung cancer patients referred for video-assisted thoracic surgery Abstract We aimed to assess the additive value of the split-bolus single-phase computed tomography (CT) scan protocol to preoperatively assess patients with lung cancer, who were referred for video-assisted thoracic surgery, when compared to a standard staging CT protocol. We included 160 patients with lung cancer who underwent a split-bolus single-phase CT scan protocol (split-bolus protocol), which can acquire whole-body staging CT and pulmonary artery-vein separation CT angiography (PA–PV CTA) in a single acquisition and 160 patients who underwent whole-body staging CT (standard protocol). We compared the quality of the staging CT images of hepatic parenchyma, portal vein, and hepatic vein between both protocols. We also investigated image quality on PA–PV CTA images in the split-bolus protocol and recorded the number of patients that underwent the 3D PA–PV CTA imaging process. The split-bolus protocol for staging CT images demonstrated a slightly higher enhancement with regard to the hepatic parenchyma (p = 0.007) and hepatic vein (p = 0.006) than the standard protocol. There was no significant difference in the quality of the staging CT images between both protocols (p = 0.067). The mean CT number for the main pulmonary artery and the left atrium for the PA–PV CTA images in the split-bolus protocol were 289.1 HU and 172.8 HU, respectively. Among the images associated with the split-bolus protocol, 98.1% were of appropriate quality for 3D PA–PV CTA imaging. The split-bolus protocol is a dose-efficient protocol to acquire the staging CT and PA–PV CTA images in a single session and provides sufficient image quality for preoperative assessment in patients with lung cancer.

Technical note: improved positioning protocol for patient setup accuracy in conventional radiotherapy for lung cancer Abstract This study aimed to investigate an improved setup protocol for maintaining patient setup accuracy, with minimal or no use of image-guided radiation therapy in conventional radiotherapy for lung cancer. A coordinate value for the treatment couch in the anterior–posterior (AP) direction was obtained from the first fraction using bony anatomy image guidance. The coordinate value was invariably used for patient positioning in the second and subsequent treatment fractions. The errors of 2410 setup image sets (anterior and lateral) from 105 patients with lung cancer were analyzed. The systematic and random patient positioning errors in the AP direction were 0.6 ± 1.0 mm. Such errors accounted for 97% of all fractions within ± 2 mm. The protocol resulted in minimal patient setup errors in the AP direction using only one image for guidance; therefore, it may be applied to conventional radiotherapy for lung cancer in case of insufficient image guidance.

A comparative study of radiation doses between phantom and patients via CT angiography of the intra-/extra-cranial, pulmonary, and abdominal/pelvic arteries Abstract This study aimed to evaluate effective dose and size-specific dose estimate (SSDE) of computed tomography angiography (CTA) examination using an anthropomorphic phantom. We included three CTA examination protocols to evaluate the intra- and extra-cranial arteries, pulmonary artery (CTPA), and abdominal vessels. Patient SSDEs were measured retrospectively to estimate patient dose, relative to the bodyweight of the patient and volume CT dose index (CTDIvol). Our findings revealed that the highest dose was absorbed by the left lobe of the thyroid gland during intra-/extra-cranial CTA and CTPA, that is, 14.11 ± 0.24 mGy and 16.20 ± 3.95 mGy, respectively. However, the highest absorbed dose in abdominal/pelvic CTA was the gonads (8.98 ± 0.30 mGy), while other radiosensitive organs in intra- and extra-cranial CTA, CTPA, and abdominal/pelvic CTA did not demonstrate significant differences between organs/structures with p value 0.88, 0.11, and 0.54, respectively. The estimated effective dose in intra-/extra-cranial CTA was lower in patients (0.80 ± 0.60 mSv) than in the phantom (0.83 mSv), but it was the opposite for CTPA, with the effective dose being higher in patients (7.54 ± 3.09 mSv) than in the phantom (6.68 mSv). Similar to the effective dose, only CTPA SSDEs were significantly higher in men than in women (19.74 ± 4.79 mGy versus 7.9 mGy). Effective dose and SSDE are clinically relevant parameters that can help estimate a more accurate patient dose based on a patient’s size.

Error evaluation of the D-shuttle dosimeter technique in positron emission tomography study Abstract The D-shuttle dosimeter technique is a convenient approach for estimating the radiation dosimetry in a positron emission tomography (PET) study that employs multiple D-shuttle dosimeters attached to the body surface of a patient. To bring this technique into clinical usage, it is very important to evaluate its performance by investigating the bias associated with D-shuttle dosimeter positioning and by comparing the estimates with those of the whole-body dynamic PET imaging technique. The torso cavity and six spheres of the NEMA body phantom were filled with 18F-FDG solution, and then, the phantom was imaged for 1 h. We assumed the mislocated positioning of the D-shuttle dosimeters by shifting them in the z-direction (upper) in a range of 1–5 cm from the original positions. The cumulative radioactivities, absorbed doses, and effective dose were estimated using accurate and mislocated positions of the D-shuttle dosimeters. For comparison, the cumulative radioactivities were also estimated from the PET images, and then, the absorbed doses and effective dose were computed. The maximum bias of the average estimated cumulated radioactivities and the effective doses was − 15.0% and − 19.7% for the 1 cm shifted positions, respectively. The ratios of absorbed doses obtained from D-shuttle and PET measurement against the actual values were between 0.9 and 1.3, and 0.7 and 1.0, respectively. The bias associated with the D-shuttle dosimeter positions was significant and probably consistent, and both dosimetric techniques exhibited good performance in this phantom study.

Usefulness of the frontal lobe bottom and cerebellum tuber vermis line as an alternative clue to set the axial angle parallel to the AC–PC line in I-123 IMP SPECT imaging: a retrospective study Abstract We aimed to investigate whether the frontal lobe bottom and cerebellum tuber vermis (FLB–CTV) line on brain perfusion scintigraphy, using iodine-123 isopropyl iodoamphetamine single photon emission computed tomography (I-123 IMP SPECT) images, is useful to determine an axial angle parallel to the anterior commissure-posterior commissure (AC–PC) line. We measured the angular differences between the AC–PC line and the FLB–CTV line on midsagittal brain magnetic resonance imaging (MRI) scans of 100 patients. We also evaluated the angular differences of the FLB–CTV line between the IMP SPECT images and the computed tomography for attenuation correction (CTAC) images in the same 100 patients, using a reference line on the CTAC images. Furthermore, the inter-reader reproducibility of the FLB–CTV line measurements on IMP SPECT images of 50 patients between two readers was evaluated using the intra-class correlation coefficient (ICC) and 95% confidence interval (CI). The mean and standard deviation of the angular differences between the AC–PC and FLB–CTV lines on midsagittal brain MRI scans were − 1.24° and 1.14°, respectively. The mean and the standard deviation of the angular differences of the FLB–CTV line in the IMP SPECT and CTAC images were 0.87° and 0.48°, respectively. The ICC of the FLB–CTV line measurements on IMP SPECT images was 0.99 (95% CI 0.98–0.99). We demonstrated that the FLB–CTV line was almost parallel to the AC–PC line and could be reconstructed using IMP SPECT images. The FLB–CTV line can be used as additional evidence to set the axial angle parallel to the AC–PC line.

Angular dependence of shielding effect of radiation protective eyewear for radiation protection of crystalline lens Abstract Radiation protective (RP) eyewear effectively protects crystalline lenses from radiation exposure. A drawback of RP eyewear is the angular dependence of the shielding effect, which results from the design of the eyewear. In this study, 21 models of RP eyewear with different designs and lead equivalences were assessed. Each piece of RP eyewear was hung on a Styrofoam phantom that imitated the head, and a 0.125-cc ionization chamber dosimeter was placed at the position of the crystalline lens. The differences in angular dependence of the shielding effect were evaluated by changing the irradiation angle, and parameters that improved the angular dependence of the shielding effect—sufficient lead equivalence, large coverage design, and minimum gap between the crystalline lens and the RP eyewear—were identified. Thus, the findings highlight the importance of selecting RP eyewear according to the angular distribution and the nature of radiation exposure in the workplace for radiation workers.