Dosimetry impact of distinct gating strategies in cine MR image-guided breath-hold pancreatic cancer radiotherapy

PURPOSE

To investigate the dosimetry effects of different gating strategies in cine magnetic resonance imaging (MRI)-guided breath-hold pancreatic cancer radiotherapy.

METHODS

Two cine MRI-based gating strategies were investigated： a tumor contour-based gating strategy at a gating threshold of 0-5% and a tumor displacement-based gating strategy at a gating threshold of 3-5 mm. The cine MRI videos were obtained from 17 pancreatic cancer patients who received MRI-guided radiation therapy. We calculated the tumor displacement in each cine MR frame that satisfied the gating threshold and obtained the proportion of frames with different displacements. We generated IMRT and VMAT plans using a 33 Gy prescription, and motion plans were generated by adding up all isocenter-shift plans corresponding to different tumor displacements. The dose parameters of GTV, PTV, and organs at risk (OAR) were compared between the original and motion plans.

RESULTS

In both gating strategies, the difference was significant in PTV coverage but not in GTV coverage between the original and motion plans. OAR dose parameters deteriorate with increasing gating threshold. The beam duty cycle increased from 19.5±14.3% (median 18.0%) to 60.8±15.6% (61.1%) for gating thresholds from 0% to 5% in tumor contour-based gating and from 51.7±11.5% (49.7%) to 67.3±12.4% (67.1%) for gating thresholds from 3 to 5 mm in tumor displacement-based gating.

CONCLUSION

In tumor contour-based gating strategy, the dose delivery accuracy deteriorates while the dose delivery efficiency improves with increasing gating thresholds. To ensure treatment efficiency, the gating threshold might be no less than 3%. A threshold up to 5% may be acceptable in terms of the GTV coverage. The displacement-based gating strategy may serve as a potential alternative to the tumor contour based gating strategy, in which the gating threshold of approximately 4 mm might be a good choice for reasonably balancing the dose delivery accuracy and efficiency.

[Usefulness of Breath-hold DWI Focused on the Hepatic Dome in EOB-MRI]

PURPOSE

Respiratory-triggered-diffusion-weighted imaging (R-DWI) of the liver often results in poor image quality under the diaphragmatic dome on the cephalic side of the liver (hepatic dome) secondary to magnetic field inhomogeneity in liver magnetic resonance imaging (MRI). Hence, the usefulness of additional breath-hold-DWI (B-DWI) focusing on the hepatic dome was investigated.

METHODS

A total of 22 patients (14 men and 8 women; mean age 69.0±11.7 years) who underwent ethoxybenzyl (EOB)-MRI at our hospital between July and August, 2022 using a 3.0 T MRI system were included. One radiologist and three radiology technologists visually assessed the visibility of R-DWI and B-DWI in the hepatic dome on a 4-point scale (1 to 4). Additionally, the apparent diffusion coefficient (ADC) values of the hepatic parenchyma on each DWI were compared.

RESULTS

B-DWI improved visibility in the hepatic dome compared to R-DWI (2.67±0.71 vs. 3.25±0.43, p<0.05). No significant difference was found in the ADC values for each DWI.

CONCLUSION

B-DWI has excellent visibility in the hepatic dome and is expected to complement R-DWI. Therefore, B-DWI is very useful as an additional imaging in EOB-MRI.

Increased spleen volume provoked by temperate head-out-of-water immersion

This study tested the hypotheses that 1) spleen volume increases during head-out-of-water immersion (HOWI) and returns to pre-HOWI values postdiuresis, and 2) the magnitude of apnea-induced spleen contraction increases when preapnea spleen volume is elevated. Spleen volume was measured before and after a set of five apneas in 12 healthy adults (28 ± 5 yr, 3 females) before, during (at 30 and 150 min), and 20 min after temperate temperature (36 ± 1°C) HOWI. At each time point, spleen length, width, and thickness were measured via ultrasound, and spleen volume was calculated using the Pilström equation. Compared with pre-HOWI (276 ± 88 mL), spleen volume was elevated at 30 (353 ± 94 mL, P < 0.01) and 150 (322 ± 87 mL, P < 0.01) min of HOWI but returned to pre-HOWI volume at post-HOWI (281 ± 90 mL, P = 0.58). Spleen volume decreased from pre- to postapnea bouts at each time point (P < 0.01). The magnitude of reduction in spleen volume from pre- to postapneas was elevated at 30 min of HOWI (-69 ± 24 mL) compared with pre-HOWI (-52 ± 20 mL, P = 0.04) but did not differ from pre-HOWI at 150 min of HOWI (-54 ± 16 mL, P = 0.99) and post-HOWI (-50 ± 18 mL, P = 0.87). Thus, spleen volume is increased throughout 180 min of HOWI, and whereas apnea-induced spleen contraction is augmented after 30 min of HOWI, the magnitude of spleen contraction is unaffected by HOWI thereafter.

Cerebral hemodynamic response to caffeine: effect of dietary caffeine consumption

Caffeine has a significant effect on cerebrovascular systems, and the dual action of caffeine on both neural and vascular responses leads to concerns for the interpretation of blood oxygenation level-dependent (BOLD) functional MRI. However, potential differences in the brain response to caffeine with regard to consumption habits have not been fully elucidated, as BOLD responses may vary with the dietary caffeine consumption history. The main aim of this study was to characterize the acute effect of caffeine on cerebral hemodynamic responses in participants with different patterns of caffeine consumption habits. Fifteen non-habitual and 11 habitual volunteers were included in this study. The cerebral blood flow (CBF) and cerebrovascular reactivity (CVR) to the breath-hold challenge were measured before and after 200 mg caffeine administration. The non-habitual individuals exhibited a pattern of progressive reduction in CBF with time. The CVR was diminished in the caffeinated condition (P < 0.05). In the habitual group, the pattern of CBF decrease was smaller and homogeneous across the brain, and reached steady state rapidly. The CVR was not affected in the presence of caffeine (P > 0.05). Our results demonstrated that the cerebral hemodynamic response to caffeine was subject to the habitual consumption patterns of the participants. The compromised CVR following caffeine administration in the non-habitual group may partially explain the suppressed BOLD response to a visual stimulation in low-caffeine-level users.

Dosimetry impact of gating latency in cine magnetic resonance image guided breath-hold pancreatic cancer radiotherapy

Objective.We investigated dosimetry effect of gating latency in cine magnetic resonance image (cine MRI) guided breath-hold pancreatic cancer radiotherapy.Approach.The gating latency was calculated based on cine MRI obtained from 17 patients who received MRI guided radiotherapy. Because of the cine MRI-related latency, beam overshoot occurs when beam remains on while the tracking target already moves out of the target boundary. The number of beam on/off events was calculated from the cine MRI data. We generated both IMRT and VMAT plans for all 17 patients using 33 Gy prescription, and created motion plans by applying isocenter shift that corresponds to motion-induced tumor displacement. The GTV and PTV coverage and dose to nearby critical structures were compared between the motion and original plan to evaluate the dosimetry change caused by cine MRI latency.Main results.The time ratio of cine MRI imaging latency over the treatment duration is 6.6 ± 3.1%, the mean and median percentage of beam-on events <4 s are 67.0 ± 14.3% and 66.6%. When a gating boundary of 4 mm and a target-out threshold of 5% is used, there is no significant difference for GTV V33Gy between the motion and original plan (p = 0.861 and 0.397 for IMRT and VMAT planning techniques, respectively). However, the PTV V33Gy and stomach Dmax for the motion plans are significantly lower; duodenum V12.5 Gy and V18Gy are significantly higher when compared with the original plans, for both IMRT and VMAT planning techniques.Significance.The cine MRI gating latency can significantly decrease the dose delivered to the PTV, and increase the dose to the nearby critical structures. However, no significant difference is observed for the GTV coverage. The dosimetry impact can be mitigated by implementing additional beam-on control techniques which reduces unnecessary beam on events and/or by using faster cine MRI sequences which reduces the latency period.

A Transdiagnostic Multilevel Examination of Interoceptive Processing in Individuals With a Remote History of Suicidal Behavior

A developing area of research suggests that there may be a relationship between interoception and suicidal behavior. For example, it was recently reported that individuals who made a suicide attempt within the previous 5 years exhibit behavioral and neural abnormalities across multiple domains of interoception relative to nonattempters. This included increased tolerance for aversive sensations of pain and dyspnea, reduced heartbeat-perception accuracy, and blunted insula activity during attention to cardiac sensations. However, the degree to which interoceptive deficits persist following a suicidal attempt is unknown. In the current study, we examined differences between individuals with a remote history of suicide attempts (greater than 5 years ago; N = 56) versus those with no history of attempts (N = 240). We found that remote suicide attempters demonstrated greater pain tolerance and lower ratings of stress during a cold-pressor challenge and lower ratings of suffocation during a breath-hold challenge, as compared to nonattempters. In contrast, there were no group differences in breath-hold duration, interoceptive accuracy on a heartbeat-tapping task, or insula activation during cardiac attention. An exploratory resting-state functional connectivity analysis of individuals with suicide attempts in the past 5 years (N = 23), individuals with more remote histories of suicide attempts (N = 39), and nonattempters (N = 232) revealed preliminary and subtle evidence of differences in insula connectivity with areas of the temporal cortex in remote suicide attempters. Taken together, these findings suggest that blunted affective responses to aversive interoceptive sensations is an enduring characteristic of suicide attempters, even when assessed many years after a suicide attempt, whereas differences in the experience of nonaversive interoceptive sensations may be less persistent.

Comparison of Cortical Autonomic Network-Linked Sympathetic Excitation by Mueller Maneuvers and Breath-Holds in Subjects With and Without Obstructive Sleep Apnea

In healthy young volunteers, acquisition of blood oxygen level-dependent (BOLD) magnetic resonance (MR) and muscle sympathetic nerve (MSNA) signals during simulation of obstructive or central sleep apnea identified cortical cardiovascular autonomic regions in which the BOLD signal changed synchronously with acute noradrenergic excitation. In the present work, we tested the hypothesis that such Mueller maneuvers (MM) and breath-holds (BH) would elicit greater concomitant changes in mean efferent nerve firing and BOLD signal intensity in patients with moderate to severe obstructive sleep apnea (OSA) relative to age- and sex-matched individuals with no or only mild OSA (Apnea Hypopnea Index, AHI, <15 events/h). Forty-six participants, 24 with OSA [59 ± 8 years; AHI 31 ± 18 events/h (mean ± SD); seven women] and 22 without (58 ± 11 years; AHI 7 ± 4; nine women), performed a series of three MM and three BH, in randomly assigned order, twice: during continuous recording of MSNA from the right fibular nerve and, on a separate day, during T2^∗-weighted echo planar functional MR imaging. MSNA at rest was greater in those with OSA (65 ± 19 vs. 48 ± 17 bursts per 100 heart beats; p < 0.01). MM and BH elicited similar heart rate, blood pressure, and MSNA responses in the two cohorts; group mean BOLD data were concordant, detecting no between-group differences in cortical autonomic region signal activities. The present findings do not support the concept that recurring episodes of cyclical apnea during sleep alter cortical or peripheral neural responsiveness to their simulation during wakefulness by volitional Mueller maneuvers or breath-holds.

Visually guided inspiration breath-hold facilitated with nasal high flow therapy in locally advanced lung cancer

BACKGROUND AND PURPOSE

Reducing breathing motion in radiotherapy (RT) is an attractive strategy to reduce margins and better spare normal tissues. The objective of this prospective study (NCT03729661) was to investigate the feasibility of irradiation of non-small cell lung cancer (NSCLC) with visually guided moderate deep inspiration breath-hold (IBH) using nasal high-flow therapy (NHFT).

MATERIAL AND METHODS

Locally advanced NSCLC patients undergoing photon RT were given NHFT with heated humidified air (flow: 40 L/min with 80% oxygen) through a nasal cannula. IBH was monitored by optical surface tracking (OST) with visual feedback. At a training session, patients had to hold their breath as long as possible, without and with NHFT. For the daily cone beam CT (CBCT) and RT treatment in IBH, patients were instructed to keep their BH as long as it felt comfortable. OST was used to analyze stability and reproducibility of the BH, and CBCT to analyze daily tumor position. Subjective tolerance was measured with a questionnaire at 3 time points.

RESULTS

Of 10 included patients, 9 were treated with RT. Seven (78%) completed the treatment with NHFT as planned. At the training session, the mean BH length without NHFT was 39 s (range 15-86 s), and with NHFT 78 s (range 29-223 s) (p = .005). NHFT prolonged the BH duration by a mean factor of 2.1 (range 1.1-3.9s). The mean overall stability and reproducibility were within 1 mm. Subjective tolerance was very good with the majority of patients having no or minor discomfort caused by the devices. The mean inter-fraction tumor position variability was 1.8 mm (-1.1-8.1 mm;SD 2.4 mm).

CONCLUSION

NHFT for RT treatment of NSCLC in BH is feasible, well tolerated and significantly increases the breath-hold duration. Visually guided BH with OST is stable and reproducible. We therefore consider this an attractive patient-friendly approach to treat lung cancer patients with RT in BH.

Enhanced Deep-Inspiration Breath Hold Superior to High-Frequency Percussive Ventilation for Respiratory Motion Mitigation: A Physiology-Driven, MRI-Guided Assessment Toward Optimized Lung Cancer Treatment With Proton Therapy

Background: To safely treat lung tumors using particle radiation therapy (PRT), motion-mitigation strategies are of critical importance to ensure precise irradiation. Therefore, we compared applicability, effectiveness, reproducibility, and subjects' acceptance of enhanced deep-inspiration breath hold (eDIBH) with high-frequency percussive ventilation (HFPV) by MRI assessment within 1 month.

Methods: Twenty-one healthy subjects (12 males/9 females; age: 49.5 ± 5.8 years; BMI: 24.7 ± 3.3 kg/m⁻²) performed two 1.5 T MRI scans in four visits at weekly intervals under eDIBH and HFPV conditions, accompanied by daily, home-based breath-hold training and spirometric assessments over a 3-week period. eDIBH consisted of 8-min 100% O₂ breathing (3 min resting ventilation, 5 min controlled hyperventilation) prior to breath hold. HFPV was set at 200–250 pulses min⁻¹ and 0.8–1.2 bar. Subjects' acceptance and preference were evaluated by questionnaire. To quantify inter- and intrafractional changes, a lung distance metric representing lung topography was computed for 10 reference points: a motion-invariant spinal cord and nine lung structure contours (LSCs: apex, carina, diaphragm, and six vessels as tumor surrogates distributed equally across the lung). To parameterize individual LSC localizability, measures of their spatial variabilities were introduced and lung volumes calculated by automated MRI analysis.

Results: eDIBH increased breath-hold duration by > 100% up to 173 ± 73 s at visit 1, and to 217 ± 67 s after 3 weeks of home-based training at visit 4 (p < 0.001). Measures of vital capacity and lung volume remained constant over the 3-week period. Two vessels in the lower lung segment and the diaphragm yielded a two- to threefold improved positional stability with eDIBH, whereby absolute distance variability was significantly smaller for five LSCs; ≥70% of subjects showed significantly better intrafractional lung motion mitigation under reproducible conditions with eDIBH compared with HFPV with smaller ranges most apparent in the anterior-posterior and cranial-caudal directions. Approximately 80% of subjects preferred eDIBH over HFPV, with “less discomfort” named as most frequent reason.

Conclusions: Both, eDIBH, and HFPV were well-tolerated. eDIBH duration was long enough to allow for potential PRT. Variability in lung volume was smaller and position of lung structures more precise with eDIBH. Subjects preferred eDIBH over HFPV. Thus, eDIBH is a very promising tool for lung tumor therapy with PRT, and further investigation of its applicability in patients is warranted.

Retrospective Study on Left-Sided Breast Radiotherapy: Dosimetric Results and Correlation with Physical Factors for Free Breathing and Breath Hold Irradiation Techniques

Objectives: In breast radiotherapy, the proximity of the target to sensitive structures together with the uncertainty introduced by respiratory movement, make this treatment one of the most studied to increase its effectiveness. Dosimetric and physical variables play an important role and the study of their correlation and impact on treatment is fundamental. This retrospective study aims to highlight the dosimetric differences of 2 different clinical data sets of patients receiving left-sided breast irradiation in free breathing (FB) or breath hold (BH). Methods: A total of 155 left breast carcinoma patients receiving whole-breast irradiation in FB (73 patients) and BH (82 patients) were enrolled in this study. The dosimetric parameters of the target, heart, left and right lung and right breast were evaluated and compared, and possible correlations were studied in both groups. Results: No significant difference (P > .05) was found in the target dosimetry; a clear advantage in BH for both high and low doses received by the heart, with reductions of the dosimetric parameters between 27.1% and 100% (P < .003); for the left lung reductions decreased with increasing dose (-22.4% and -13.4% for doses of 5 and 20 Gy, respectively, P < .003). Conclusion: Significant correlations for BH treatments were registered between the volumes of the target and left lung, and the dosimetric parameters of the heart and left lung. BH treatment brings significant dosimetric advantages to organs at risk for a wide range of patients with different anatomy, target volumes and lung capacity, with additional benefits for small-sized breasts and important lung capacity.

Proton versus Photon Breath-Hold Radiation for Left-Sided Breast Cancer after Breast-Conserving Surgery: A Dosimetric Comparison

PURPOSE

Radiation to breast, chest wall, and/or regional nodes is an integral component of breast cancer management in many situations. Irradiating left-sided breast and/or regional nodes may be technically challenging because of cardiac tolerance and subsequent risk of long-term cardiac complications. Deep inspiratory breath-hold (DIBH) technique physically separates cardiac structures away from radiation target volume, thus reducing cardiac dose with either photon (Ph) or proton beam therapy (PBT). The utility of combining PBT with DIBH is less well understood.

METHODS AND MATERIALS

We compared photon-DIBH (Ph-DIBH) versus proton DIBH (Pr-DIBH) for different planning parameters, including target coverage and organ at risk (OAR) sparing. Necessary ethical permission was obtained from the institutional review board. Ten previous patients with irradiated, intact, left-sided breast and Ph-DIBH were replanned with PBT for dosimetric comparison. Clinically relevant normal OARs were contoured, and Ph plans were generated with parallel, opposed tangent beams and direct fields for supraclavicular and/or axillae whenever required. For proton planning, all targets were delineated individually and best possible coverage of planning target volume was achieved. Dose-volume histogram was analyzed to determine the difference in doses received by different OARs. Minimum and maximum dose (Dmin and Dmax ) as well as dose received by a specific volume of OAR were compared. Each patient's initial plan (Ph-DIBH) was used as a control for comparing newly devised PBT plan (Pr-DIBH). Matched, paired t tests were applied to determine any significant differences between the 2 plans.

RESULTS

Both the plans were adequate in target coverage. Dose to cardiac structure subunits and ipsilateral lung were significantly reduced with the proton breath-hold technique. Significant dose reduction with Pr-DIBH was observed in comparison to Ph-DIBH for mean dose (D mean) to the heart (0.23 Gy versus 1.19 Gy; P < .001); D mean to the left ventricle (0.25 Gy versus 1.7 Gy; P < .001); D mean, D max, and the half-maximal dose to the left anterior descending artery (1.15 Gy versus 5.54 Gy; P < .003; 7.7 Gy versus 22.15 Gy; P < .007; 1.61 Gy versus 4.42 Gy, P < .049); D max of the left circumflex coronary artery (0.13 Gy versus 1.35 Gy; P < .001) and D mean, the volume to the ipsilateral lung receiving 20 Gy and 5 Gy (2.28 Gy versus 8.04 Gy; P < .001; 2.36 Gy versus 15.54 Gy, P < .001; 13.9 Gy versus 30.28 Gy; P = .002). However, skin dose and contralateral breast dose were not significantly improved with proton.

CONCLUSION

This comparative dosimetric study showed significant benefit of Pr-DIBH technique compared with Ph-DIBH in terms of cardiopulmonary sparing and may be the area of future clinical research.

Using flattening filter free beams in electronic tissue compensation whole breast irradiation with deep inspiration breath hold

PURPOSE

In order to reduce heart dose, DIBH has become a common practice in left-sided whole breast irradiation. This technique involves a significant strain on patients due to the breath-hold requirements. We hereby investigate the dosimetric and delivery feasibility of using flattening filter free (FFF) energies with electronic tissue compensation (ECOMP) planning technique to reduce the required breath-hold lengths and increase patient compatibility.

METHODS

Fifteen left-sided, postlumpectomy patients previously receiving DIBH whole-breast radiotherapy (266cGy x 16fx) were retrospectively planned using ECOMP for both 6X and 6X-FFF. A dosimetric comparison was made between the two plans for each patient using various dosimetric constraints. Delivery feasibility was analyzed by recalculating the 6X ECOMP plan with 6X-FFF without replanning (6X-FFF QA) and delivering both plans for a one-to-one comparison using Gamma analysis. Beam-on times for the 6X and 6X-FFF plans were measured. For all tests, Wilcoxon signed-rank test was used with P < 0.05 as significant.

RESULTS

No statistical difference was observed between 6X and 6X-FFF plans for most dosimetric endpoints except contralateral breast D_max (P = 0.0008) and skin D_max (p = 0.03) and D_min (P = 0.01) for which 6X-FFF showed favorable results when compared with 6X. 6X-FFF significantly reduced beam-on times for all patients by 22%-42% (average 32%). All plan QAs passed departmental gamma criteria (10% low-dose threshold, 3%/3mm, >95% passing).

CONCLUSION

ECOMP planning with FFF was found feasible for left-sided breast patients with DIBH. Plan quality is comparable, if not better, than plans using flattened beams. FFF ECOMP could significantly reduce beam-on time and required breath-hold lengths thereby increasing patient compatibility for this treatment while offering satisfactory plan quality and delivery accuracy.

Impact of Positioning Errors on the Dosimetry of Breath-Hold-Based Volumetric Arc Modulated and Tangential Field-in-Field Left-Sided Breast Treatments

Heart diseases and cardiovascular events are well-known side effects in left-sided breast irradiation. Deep inspiration breath hold (BH) combined with fast delivery techniques such as volumetric modulated arc therapy (VMAT) or tangential field-in-field (TFiF) can serve as a valuable solution to reduce the dose to the heart. This study aims to compare the impact of positioning errors in VMAT and TFiF plans for BH left-sided breast treatments. Fifteen left-sided breast patients treated in BH with TFiF technique were included in this retrospective study. For each patient, a second plan with VMAT technique was optimized. Eighteen setup variations were introduced in each of these VMAT and TFiF reference plans, shifting the isocenter along six different directions by 3, 5, and 10 mm. A total of 540 perturbed plans, 270 for each technique, were recalculated and analyzed. The dose distributions on the target and organs at risk obtained in the different perturbed scenarios were compared with the reference scenarios, using as dosimetric endpoints the dose-volume histograms (DVH). The results were compared using the Wilcoxon test. Comparable plan quality was obtained for the reference VMAT and TFiF plans, except for low doses to organs at risk for which higher values (p < 0.05) were obtained for VMAT plans. For TFiF plans, perturbations of the isocenter position of 3, 5, or 10 mm produced mean deviations of the target DVH dosimetric parameters up to -0.5, -1.0, and -5.2%, respectively; VMAT plans were more sensitive to positioning errors resulting in mean deviations up to -0.5, -4.9, and -13.9%, respectively, for the same magnitude of the above mentioned perturbations. For organs at risk, only perturbations along the left, posterior, and inferior directions resulted in dose increase with a maximum deviation of +2% in the DVH dosimetric parameters. A notable exception were low doses to the left lung and heart for 10 mm isocenter shifts for which the mean differences ranged between +2.7 and +4.1%. Objective information on how external stresses affect the dosimetry of the treatment is the first step towards personalized radiotherapy.

Malignant Cutaneous Melanoma: Updates in PET Imaging

BACKGROUND

Cutaneous malignant melanoma is a neoplasm whose incidence and mortality are dramatically increasing. 18F-FDG PET/CT gained clinical acceptance over the past 2 decades in the evaluation of several glucose-avid neoplasms, including malignant melanoma, particularly for the assessment for distant metastases, recurrence and response to therapy.

OBJECTIVE

To describe the advancements of nuclear medicine for imaging melanoma with particular attention to 18F-FDG-PET and its current state-of-the-art technical innovations.

METHODS

A comprehensive search strategy was used based on SCOPUS and PubMed databases. From all studies published in English, we selected the articles that evaluated the technological insights of 18FFDG- PET in the assessment of melanoma.

RESULTS

State-of-the-art silicon photomultipliers based detectors ("digital") PET/CT scanners are nowadays more common, showing technical innovations that may have beneficial implications for patients with melanoma. Steady improvements in detectors design and architecture, as well as the implementation of both software and hardware technology (i.e., TOF, point spread function, etc.), resulted in significant improvements in PET image quality while reducing radiotracer dose and scanning time.

CONCLUSION

Recently introduced digital PET detector technology in PET/CT and PET/MRI yields higher intrinsic system sensitivity compared with the latest generation analog technology, enabling the detection of very small lesions with potential impact on disease outcome.

Effect of varying chemoreflex stress on sympathetic neural recruitment strategies during apnea

We sought to examine the effect of varying chemoreflex stress on sympathetic neural recruitment strategies during end-expiratory apnea. We hypothesized that increases in the firing frequency and probability of low-threshold axons at the asphyxic "break point" would be exaggerated during hypoxia and attenuated during hyperoxia. Multiunit muscle sympathetic nervous system activity (MSNA) (peroneal nerve microneurography) was measured in 10 healthy male subjects (31 ± 2 yr, 25 ± 1 kg/m²). Individuals completed maximal voluntary end-expiratory apnea under normoxic, hypoxic (inspired O₂ fraction: 0.17 ± 0.01), and hyperoxic (inspired O₂ fraction: 0.92 ± 0.03) conditions. Action potential (AP) patterns were examined from the filtered raw signal with wavelet-based methodology. Multiunit MSNA was increased (P ≤ 0.05) during normoxic apnea, because of an increase in the frequency and incidence of AP spikes (243 ± 75 to 519 ± 134 APs/min, P = 0.048; 412 ± 133 to 733 ± 185 APs/100 heartbeats, P = 0.02). Multiunit MSNA increased from baseline (P < 0.01) during hypoxic apnea, which was due to an increase in the frequency and incidence of APs (192 ± 59 to 952 ± 266 APs/min, P < 0.01; 326 ± 89 to 1,212 ± 327 APs/100 heartbeats, P < 0.01). Hypoxic apnea also resulted in an increase in the probability of a particular AP cluster firing more than once per burst (P < 0.01). Hyperoxia attenuated any increase in MSNA with apnea, such that no changes in multiunit MSNA or frequency or incidence of AP spikes were observed (P > 0.05). We conclude that increases in frequency and incidence of APs during apnea are potentiated during hypoxia and suppressed when individuals are hyperoxic, highlighting the important impact of chemoreflex stress in AP discharge patterns. The results may have implications for neural control of the circulation in recreational activities and/or clinical conditions prone to apnea.NEW & NOTEWORTHY Our results demonstrate that, compared with normoxic end-expiratory apnea, hypoxic apnea increases the frequency and incidence of action potential spikes as well as the probability of multiple firing. We further show that this response is suppressed when individuals are hyperoxic. These data highlight the potentially important role of chemoreflex stress in neural firing and recruitment and may have implications for neural control of the circulation in recreational and/or clinical conditions prone to apnea.

Dosimetric effects of intrafractional isocenter variation during deep inspiration breath-hold for breast cancer patients using surface-guided radiotherapy

The aim of this study was to investigate potential dose reductions to the heart, left anterior descending coronary artery (LAD), and ipsilateral lung for left‐sided breast cancer using visually guided deep inspiration breath‐hold (DIBH) with the optical surface scanning system Catalyst™, and how these potential dosimetric benefits are affected by intrafractional motion in between breath holds. For both DIBH and free breathing (FB), treatment plans were created for 20 tangential and 20 locoregional left‐sided breast cancer patients. During DIBH treatment, beam‐on was triggered by a region of interest on the xiphoid process using a 3 mm gating window. Using a novel nonrigid algorithm, the Catalyst™ system allows for simultaneous real‐time tracking of the isocenter position, which was used to calculate the intrafractional DIBH isocenter reproducibility. The 50% and 90% cumulative probabilities and maximum values of the intrafractional DIBH isocenter reproducibility were calculated and to obtain the dosimetric effect isocenter shifts corresponding to these values were performed in the treatment planning system. For both tangential and locoregional treatment, the dose to the heart, LAD and ipsilateral lung was significantly reduced for DIBH compared to FB. The intrafractional DIBH isocenter reproducibility was very good for the majority of the treatment sessions, with median values of approximately 1 mm in all three translational directions. However, for a few treatment sessions, intrafractional DIBH isocenter reproducibility of up to 5 mm was observed, which resulted in large dosimetric effects on the target volume and organs at risk. Hence, it is of importance to set tolerance levels on the intrafractional isocenter motion and not only perform DIBH based on the xiphoid process.

Voluntary apnea during dynamic exercise activates the muscle metaboreflex in humans

Voluntary apnea during dynamic exercise evokes marked bradycardia, peripheral vasoconstriction, and pressor responses. However, the mechanism(s) underlying the cardiovascular responses seen during apnea in exercising humans is unknown. We therefore tested the hypothesis that the muscle metaboreflex contributes to the apnea-induced pressor response during dynamic exercise. Thirteen healthy subjects participated in apnea and control trials. In both trials, subjects performed a two-legged dynamic knee extension exercise at a workload that elicited heart rates at ~100 beats/min. In the apnea trial, after reaching a steady state, subjects began voluntary apnea. Immediately after cessation of the apnea, arterial occlusion was initiated at both thighs and the subjects stopped exercising. The occlusion was sustained for 3 min in the postexercise period. In the control trial, the occlusion was started without subjects performing the apnea. The apnea induced marked bradycardia, pressor responses, and decreases in arterial O₂ saturation, cardiac output, and total vascular conductance. In addition, arterial blood pressure was significantly higher and total vascular conductance was significantly lower in the apnea trials than the control trials throughout the occlusion period. In separate sessions, we measured apnea-induced changes in exercising leg blood flow in the same subjects. Leg blood flow was significantly reduced by apnea and reached the resting level at the peak of the apnea response. We conclude that the muscle metaboreflex is activated by the decrease in O₂ delivery to the working muscle during apnea in exercising humans and contributes to the large pressor response. NEW & NOTEWORTHY We demonstrated that apnea during dynamic exercise activates the muscle metaboreflex in humans. This result indicates that a reduction in O₂ delivery to working muscle triggers the muscle metaboreflex during apnea. Activation of the muscle metaboreflex is one of the mechanisms underlying the marked apnea-induced pressor response.

Free Breathing versus Breath-Hold Scanning Beam Proton Therapy and Cardiac Sparing in Breast Cancer

Purpose

To assess dose errors caused by the interplay effects of free-breathing (FB) motion and to assess the value of breath-hold (BH) in terms of cardiac dose reduction for scanning beam proton therapy (SBPT).

Materials and Methods

Three patients with left-sided breast cancer previously treated with photon therapy were included in this dosimetric study: 2 following breast-conserving surgery with 2 hypothetical target volumes (whole breast alone and whole breast plus regional nodes, including supraclavicular, axillary, and internal mammary lymph nodes); and 1 postmastectomy, with the target volume including the chest wall plus regional nodes. SBPT plans were generated with various beam angles that ranged between 2 tangential directions. For treatment with FB, nominal dose and dose with interplay effects considered were calculated based on FB 4-dimensional computed tomography scans. SBPT plans on the BH computed tomography were also calculated for one of the patients, who was selected to be treated with photon therapy with BH.

Results

Dosimetric differences between nominal and interplay dose were small (average target mean dose, -0.06 Gy; range, -0.23 to 0.06 Gy; average heart mean dose, 0.001 Gy; range, -0.12 to 0.05 Gy). The largest dose deviations occurred in plans calculated with tangential beam arrangements; the smallest was noted with the en face beam. The average value of the mean heart dose with FB was <1 Gy. For the selected patient, the mean heart doses were 0.5 and 0.2 Gy for FB and BH, respectively.

Conclusion

Dose deviations caused by the interplay effects of respiratory motion during FB do not have a significant impact in SBPT with en face beam arrangement. BH does not significantly reduce cardiac dose. SBPT delivery is feasible with FB and can provide optimal target coverage and maximal sparing of the cardiopulmonary system, which can translate into improved clinical outcomes and a decrease in treatment-related morbidity in left-sided breast cancer patients or those who require internal mammary node coverage.

Exploring the Experiences of Left-Sided Breast Cancer Patients Receiving Radiation Therapy Using the Active Breathing Coordinator

BACKGROUND

The Active Breathing Coordinator (ABC) to induce breath hold during radiation therapy is used with the intent to reduce the risk of long-term, radiation-induced cardiovascular morbidity. Many studies have explored the dosimetric and toxicity benefits of using the device, but limited research has been done on the patient's perspective. The aim of this study was to explore the patient's experience using the ABC device and to evaluate the teaching provided.

METHODS AND MATERIALS

Following Research Ethics Board approval and written informed consent, paper questionnaires were used, and cross-sectional data were collected from 30 English-speaking women receiving radiation therapy for left-sided breast cancer using the ABC device. Questions were both quantitative (a 10-point Likert scale) and qualitative in nature and evaluated patient-reported anxiety levels, confidence levels, and suggestions for process improvement. Descriptive and inferential statistics were used to analyze the results, with thematic analysis of qualitative comments.

RESULTS

Fifty-three percent of patients reported higher than 5 on the Likert scale for anxiety related to using the ABC device. Half the sample indicated that they were equally anxious about using the ABC as they were about receiving radiation therapy, a third reported being more anxious about using ABC than they were about receiving radiation therapy. Participants under 50 years were significantly more likely to feel "highly" anxious about using ABC than those older than 50 years (37% vs. 5%; P = 0.001). Half the participants indicated that their confidence level increased as treatment progressed, and suggested that the inclusion of a training video, practice sessions and constant communication via the treatment unit intercom would be helpful in reducing their anxiety.

CONCLUSIONS

This hypothesis generating study suggests that moderate-to-high levels of anxiety were common for left-sided breast cancer patients using the ABC device, particularly for patients younger than 50 years. As treatment progressed, patients seemed to become less anxious and more confident using the device. These preliminary findings support the need for further research in this area, using formal validated anxiety scoring tools.

Detecting Pulmonary Nodules in Lung Cancer Patients Using Whole Body FDG PET/CT, High-resolution Lung Reformat of FDG PET/CT, or Diagnostic Breath Hold Chest CT

RATIONALE AND OBJECTIVES

Pulmonary nodules can be missed on the non-breath hold computed tomography (CT) portion of 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT), and for this reason prior studies have advocated for routinely performing dedicated breath hold CT of the chest in addition to PET/CT for routine staging of malignancy. We evaluated the rate of pulmonary nodule detection on standard CT images from whole body PET/CT studies (WB-PET/CT), high-resolution lung reconstruction CT images from PET/CT studies (HR-PET/CT), and diagnostic breath hold chest CT (BH-CT).

MATERIALS AND METHODS

A cohort of 25 patients was identified who had a history of lung cancer as well as a PET/CT staging or restaging scan and BH-CT within 30 days of each other. All PET/CTs included a set of CT images using a soft tissue algorithm filter and 3.75- to 5-mm slice thickness, as well as high-resolution reformats with a sharp reconstruction filter and 2-mm slice thickness. The CT images from WB-PET/CT, HR-PET/CT, and BH-CT were reviewed by three radiologists. Significance was analyzed by two-way repeated measures analysis of variance.

RESULTS

There were 2.84 nodules found per patient with WB-PET/CT, 3.85 nodules with HR-PET/CT, and 3.91 nodules with BH-CT. When only nodules less than or equal to 8 mm in size were considered, WB-PET/CT also demonstrated significantly fewer nodules (1.98) compared to the HR-PET/CT (2.94) or a BH-CT (2.86) (P < 0.001). No difference in detection rate was noted between the two higher resolution modalities.

CONCLUSIONS

More pulmonary nodules are detected on the CT portion of PET/CT studies when high-resolution reformatted images are created and reviewed. The ability to detect nodules with the reformatted images was indistinguishable from dedicated BH-CT. Overall, high-resolution reformats of PET/CT images of the lungs can increase the sensitivity for pulmonary nodule detection, approaching that of dedicated BH-CT. These data suggest that if HR-PET/CT reformats are used, additional dedicated BH-CT is unnecessary for routine staging of lung cancer.

Peripheral chemoreflex inhibition with low-dose dopamine: new insight into mechanisms of extreme apnea

The purpose of this study was to determine the impact of peripheral chemoreflex inhibition with low-dose dopamine on maximal apnea time, and the related hemodynamic and cerebrovascular responses in elite apnea divers. In a randomized order, participants performed a maximal apnea while receiving either intravenous 2 μg·kg(-1)·min(-1) dopamine or volume-matched saline (placebo). The chemoreflex and hemodynamic response to dopamine was also assessed during hypoxia [arterial O2 tension, (PaO2 ) ∼35 mmHg] and mild hypercapnia [arterial CO2 tension (PaCO2 ) ∼46 mmHg] that mimicked the latter parts of apnea. Outcome measures included apnea duration, arterial blood gases (radial), heart rate (HR, ECG), mean arterial pressure (MAP, intra-arterial), middle (MCAv) and posterior (PCAv) cerebral artery blood velocity (transcranial ultrasound), internal carotid (ICA) and vertebral (VA) artery blood flow (ultrasound), and the chemoreflex responses. Although dopamine depressed the ventilatory response by 27 ± 41% (vs. placebo; P = 0.01), the maximal apnea duration was increased by only 5 ± 8% (P = 0.02). The PaCO2 and PaO2 at apnea breakpoint were similar (P > 0.05). When compared with placebo, dopamine increased HR and decreased MAP during both apnea and chemoreflex test (P all <0.05). At rest, dopamine compared with placebo dilated the ICA (3.0 ± 4.1%, P = 0.05) and VA (6.6 ± 5.0%, P < 0.01). During apnea and chemoreflex test, conductance of the cerebral vessels (ICA, VA, MCAv, PCAv) was increased with dopamine; however, flow (ICA and VA) was similar. At least in elite apnea divers, the small increase in apnea time and similar PaO2 at breakpoint (∼31 mmHg) suggest the apnea breakpoint is more related to PaO2 , rather than peripheral chemoreflex drive to breathe.

Effects of thoracic pressure changes on MRI signals in the brain

Cerebrovascular stressors, such as breath holding or CO2 inhalation, cause global magnetic resonance imaging (MRI) signal changes. In this study, we show that intrathoracic pressure changes cause rapid MRI signal alterations that have similar spatial patterns to the changes associated with breath holding or CO2 inhalation. Nine subjects performed the Valsalva maneuver during functional MRI data collection. Expiratory pressures ranged from 10 to 40 mm Hg. Breath holds ending on either inhalation or exhalation were also collected. The maximal and minimal functional MRI (fMRI) signal scaled with thoracic pressure load, and the overall amplitude of responses to the Valsalva varied, depending on brain tissue. Additionally, a Valsalva effort as short as 5 seconds yielded signal changes similar in spatial distribution and magnitude to a 20-second breath hold, suggesting potential applications of the Valsalva maneuver for calibrated fMRI experiments.

Six-year experience routinely using moderate deep inspiration breath-hold for the reduction of cardiac dose in left-sided breast irradiation for patients with early-stage or locally advanced breast cancer

PURPOSE

Moderate deep inspiration breath-hold (mDIBH), using an Active Breathing Control device, has been used in our clinic since 2002 to reduce cardiac dose for patients receiving left-sided breast irradiation. We report our routine use of the mDIBH technique in clinically localized breast cancer, treated to the intact breast, reconstructed breast, or chest wall.

MATERIALS AND METHODS

Ninety-nine patients with left-sided breast cancer were evaluated for Active Breathing Control treatment, of which, 87 patients were treated with mDIBH. Plans for both the free-breathing (FB) and mDIBH computed tomography scans were evaluated. Dose-volume histograms (DVHs) were analyzed for the heart and ipsilateral lung, comparing results for mDIBH versus FB plans.

RESULTS

Eighty-seven patients were included for analysis. Of those, 66% received adjuvant chemotherapy with cardiotoxic agents. The mean dose for the whole breast was 47.6 Gy. There was a statistically significant decrease in all DVH parameters evaluated, favoring the delivery of mDIBH over FB plans. mDIBH plans significantly reduced cardiac mean dose (4.23 vs. 2.54 Gy; P<0.001), a relative reduction of 40%. In addition, there were significant reductions in all other heart parameters evaluated (ie, volume of heart treated, V30, V25, V20, V15, V10, and V5). mDIBH also significantly reduced lung dose, including a reduction of the left lung mean dose (9.08 vs. 7.86 Gy; P<0.001), a relative reduction of 13%, as well as significant reduction of all lung DVH parameters evaluated.

CONCLUSIONS

To date, this series represents the largest experience utilizing mDIBH to reduce cardiac irradiation during left-sided breast cancer treatment. Statistically significant reductions in all heart and lung DVH parameters were achieved with mDIBH over FB plans. mDIBH, for the treatment of left-sided breast cancer, is a proven technique for reducing cardiac dose that may lead to reduced cardiotoxicity and can be routinely integrated into the clinic.

Prediction of Task-Related BOLD fMRI with Amplitude Signatures of Resting-State fMRI

Blood oxygen contrast-functional magnetic resonance imaging (fMRI) signals are a convolution of neural and vascular components. Several studies indicate that task-related (T-fMRI) or resting-state (R-fMRI) responses linearly relate to hypercapnic task responses. Based on the linearity of R-fMRI and T-fMRI with hypercapnia demonstrated by different groups using different study designs, we hypothesized that R-fMRI and T-fMRI signals are governed by a common physiological mechanism and that resting-state fluctuation of amplitude (RSFA) should be linearly related to T-fMRI responses. We tested this prediction in a group of healthy younger humans where R-fMRI, T-fMRI, and hypercapnic (breath hold, BH) task measures were obtained form the same scan session during resting state and during performance of motor and BH tasks. Within individual subjects, significant linear correlations were observed between motor and BH task responses across voxels. When averaged over the whole brain, the subject-wise correlation between the motor and BH tasks showed a similar linear relationship within the group. Likewise, a significant linear correlation was observed between motor-task activity and RSFA across voxels and subjects. The linear rest-task (R-T) relationship between motor activity and RSFA suggested that R-fMRI and T-fMRI responses are governed by similar physiological mechanisms. A practical use of the R-T relationship is its potential to estimate T-fMRI responses in special populations unable to perform tasks during fMRI scanning. Using the R-T relationship determined from the first group of 12 healthy subjects, we predicted the T-fMRI responses in a second group of 7 healthy subjects. RSFA in both the lower and higher frequency ranges robustly predicted the magnitude of T-fMRI responses at the subject and voxel levels. We propose that T-fMRI responses are reliably predictable to the voxel level in situations where only R-fMRI measures are possible, and may be useful for assessing neural activity in task non-compliant clinical populations.

Detection and scaling of task-induced fMRI-BOLD response using resting state fluctuations

This study evaluated a calibration technique for scaling the fMRI-BOLD response during a simple motor task. A novel scaling parameter, resting state physiological fluctuation amplitude (RSFA), was tested using previously established scaling factors such as breath hold or 5% CO(2). RSFA was hypothesized to contain vascular reactivity information present in the resting state fMRI signal. Subjects were scanned under various stimulus conditions: (a) rest while breathing room air, (b) bilateral fingertapping, (c) breath holding and (d) moderate hypercapnia (breathing 5% CO(2)+air). In all subjects who breathed 5% CO(2), RSFA correlated highly with the BOLD response amplitude during 5% CO(2) inhalation. Also, RSFA correlated highly with the amplitude of the BOLD response elicited by breath hold. RSFA was therefore used as a hemodynamic scaling factor to calibrate both the amplitude and spatial extent of the fMRI-BOLD response during the motor task (fingertapping). Results revealed that amplitude scaling using RSFA was similar to that using breath hold or 5% CO(2), where the spatial extent of activation diminished by 20-37% over all subjects. Spatial extent of activation changed significantly after scaling and only 30-40% of the activated area overlapped with the unscaled activation. RSFA-scaled task-induced fMRI-BOLD response in both amplitude and spatial extent was comparable to that obtained using breath hold or 5% CO(2). We conclude that RSFA may be used to hemodynamically scale the fMRI-BOLD response and does not require the use of a hypercapnic challenge (which may not be purely non-neural), which can be difficult to implement in special populations.