Manuel Blessing

Deep Inspiration Breath Hold-Based Radiation Therapy: A Clinical Review.

Several recent developments in linear accelerator-based radiation therapy (RT) such as fast multileaf collimators, accelerated intensity modulation paradigms like volumeric modulated arc therapy and flattening filter-free (FFF) high-dose-rate therapy have dramatically shortened the duration of treatment fractions. Deliverable photon dose distributions have approached physical complexity limits as a consequence of precise dose calculation algorithms and online 3-dimensional image guided patient positioning (image guided RT). Simultaneously, beam quality and treatment speed have continuously been improved in particle beam therapy, especially for scanned particle beams. Applying complex treatment plans with steep dose gradients requires strategies to mitigate and compensate for motion effects in general, particularly breathing motion. Intrafractional breathing-related motion results in uncertainties in dose delivery and thus in target coverage. As a consequence, generous margins have been used, which, in turn, increases exposure to organs at risk. Particle therapy, particularly with scanned beams, poses additional problems such as interplay effects and range uncertainties. Among advanced strategies to compensate breathing motion such as beam gating and tracking, deep inspiration breath hold (DIBH) gating is particularly advantageous in several respects, not only for hypofractionated, high single-dose stereotactic body RT of lung, liver, and upper abdominal lesions but also for normofractionated treatment of thoracic tumors such as lung cancer, mediastinal lymphomas, and breast cancer. This review provides an in-depth discussion of the rationale and technical implementation of DIBH gating for hypofractionated and normofractionated RT of intrathoracic and upper abdominal tumors in photon and proton RT.

Fast kilovoltage/megavoltage (kVMV) breathhold cone-beam CT for image-guided radiotherapy of lung cancer

Long image acquisition times of 60-120 s for cone-beam CT (CBCT) limit the number of patients with lung cancer who can undergo volume image guidance under breathhold. We developed a low-dose dual-energy kilovoltage-megavoltage-cone-beam CT (kVMV-CBCT) based on a clinical treatment unit reducing imaging time to < or =15 s. Simultaneous kVMV-imaging was achieved by dedicated synchronization hardware controlling the output of the linear accelerator (linac) based on detector panel readout signals, preventing imaging artifacts from interference of the linacs MV-irradiation and panel readouts. Optimization was performed to minimize the imaging dose. Single MV-projections, reconstructed MV-CBCT images and images of simultaneous 90 degrees kV- and 90 degrees MV-CBCT (180 degrees kVMV-CBCT) were acquired with different parameters. Image quality and imaging dose were evaluated and compared to kV-imaging. Hardware-based kVMV synchronization resulted in artifact-free projections. A combined 180 degrees kVMV-CBCT scan with a total MV-dose of 5 monitor units was acquired in 15 s and with sufficient image quality. The resolution was 5-6 line pairs cm(-1) (Catphan phantom). The combined kVMV-scan dose was equivalent to a kV-radiation scan dose of approximately 33 mGy. kVMV-CBCT based on a standard linac is promising and can provide ultra-fast online volume image guidance with low imaging dose and sufficient image quality for fast and accurate patient positioning for patients with lung cancer under breathhold.

Breath-Hold Target Localization With Simultaneous Kilovoltage/Megavoltage Cone-Beam Computed Tomography and Fast Reconstruction

PURPOSE Hypofractionated high-dose radiotherapy for small lung tumors has typically been based on stereotaxy. Cone-beam computed tomography and breath-hold techniques have provided a noninvasive basis for precise cranial and extracranial patient positioning. The cone-beam computed tomography acquisition time of 60 s, however, is beyond the breath-hold capacity of patients, resulting in respiratory motion artifacts. By combining megavoltage (MV) and kilovoltage (kV) photon sources (mounted perpendicularly on the linear accelerator) and accelerating the gantry rotation to the allowed limit, the data acquisition time could be reduced to 15 s. METHODS AND MATERIALS An Elekta Synergy 6-MV linear accelerator, with iViewGT as the MV- and XVI as the kV-imaging device, was used with a Catphan phantom and an anthropomorphic thorax phantom. Both image sources performed continuous image acquisition, passing an angle interval of 90° within 15 s. For reconstruction, filtered back projection on a graphics processor unit was used. It reconstructed 100 projections acquired to a 512 × 512 × 512 volume within 6 s. RESULTS The resolution in the Catphan phantom (CTP528 high-resolution module) was 3 lines/cm. The spatial accuracy was within 2-3 mm. The diameters of different tumor shapes in the thorax phantom were determined within an accuracy of 1.6 mm. The signal-to-noise ratio was 68% less than that with a 180°-kV scan. The dose generated to acquire the MV frames accumulated to 82.5 mGy, and the kV contribution was <6 mGy. CONCLUSION The present results have shown that fast breath-hold, on-line volume imaging with a linear accelerator using simultaneous kV-MV cone-beam computed tomography is promising and can potentially be used for image-guided radiotherapy for lung cancer patients in the near future.

A phenomenological kV beam model for cone-beam imaging

A phenomenological kV beam model was developed to address attenuation and scatter in radiographic images for the purpose of cone-beam imaging. Characterization of a kV beam in terms of the minimal number of parameters and calculation of attenuation and scatter in radiographs of scanned objects are the main applications of this model. Model parameters are derived from radiographs of homogeneous solid water phantoms for various depths and field sizes. The response of the cone-beam detector to kV beams is factorized into different contributions such as output factor, tissue-air ratio and off-axis ratio, with each contribution having an analytical representation. The formulas which are used to characterize the beam model in uniform phantoms are then extended to arbitrary objects using the concept of the water-equivalent pathlength. A weighted sum of three Gaussians in each direction models the dose deposition kernel. Detector response arising from the first Gaussian term can be interpreted as the primary signal while the second and third Gaussians constitute short- and long-range scatter. The model is then applied to predict the primary and scatter signals for arbitrary objects. A technique of scatter removal from the measured radiographs is investigated. The model accurately predicts detector response of varying-thickness phantoms such as multi-step and cylindrical phantoms. The scatter contributes over 90% to the total signal for 20 cm thick phantoms. The calculated scatter-to-primary ratio as a function of spatial coordinates agrees with Monte Carlo studies reported in the literature. Water-equivalent thickness related to primary and scatter contributions calculated from an analysis of radiographs results in an improved calibration technique suitable for CB-CT reconstruction. The kV beam model and the associated theoretical formulations can be utilized to characterize any kV beam line; however, for the specific study the OBI system (Varian) was used to obtain experimental radiographs.

Phantom-based evaluation of dose exposure of ultrafast combined kV-MV-CBCT towards clinical implementation for IGRT of lung cancer

Purpose Combined ultrafast 90°+90° kV-MV-CBCT within single breath-hold of 15s has high clinical potential for accelerating imaging for lung cancer patients treated with deep inspiration breath-hold (DIBH). For clinical feasibility of kV-MV-CBCT, dose exposure has to be small compared to prescribed dose. In this study, kV-MV dose output is evaluated and compared to clinically-established kV-CBCT. Methods Accurate dose calibration was performed for kV and MV energy; beam quality was determined. For direct comparison of MV and kV dose output, relative biological effectiveness (RBE) was considered. CT dose index (CTDI) was determined and measurements in various representative locations of an inhomogeneous thorax phantom were performed to simulate the patient situation. Results A measured dose of 20.5mGE (Gray-equivalent) in the target region was comparable to kV-CBCT (31.2mGy for widely-used, and 9.1mGy for latest available preset), whereas kV-MV spared healthy tissue and reduced dose to 6.6mGE (30%) due to asymmetric dose distribution. The measured weighted CTDI of 12mGE for kV-MV lay in between both clinical presets. Conclusions Dosimetric properties were in agreement with established imaging techniques, whereas exposure to healthy tissue was reduced. By reducing the imaging time to a single breath-hold of 15s, ultrafast combined kV-MV CBCT shortens patient time at the treatment couch and thus improves patient comfort. It is therefore usable for imaging of hypofractionated lung DIBH patients.

Breath-Hold Target Localization with Simultaneous Kilovoltage/Megavoltage Cone-Beam CT and Fast Reconstruction

Hypofractionated high dose radiotherapy of small lung tumors is very effective and was based on stereotaxy until now. It has recently become possible to achieve a high patient positioning precision based on on-line imaging with cone-beam CT (CBCT) and breath-hold techniques. The CBCT acquisition time of roughly 60 seconds, however, is too long for one breath-hold, resulting in image degradation by respiratory motion artifacts. By using megavoltage (MV) an kilovoltage (kV) photon source (mounted perpendicularly on the Linac gantry) for volume reconstruction, we could reduce the acquisition time to 15 seconds.

Automated ultrafast kilovoltage–megavoltage cone-beam CT for image guided radiotherapy of lung cancer: System description and real-time results

PURPOSE To establish a fully automated kV-MV CBCT imaging method on a clinical linear accelerator that allows image acquisition of thoracic targets for patient positioning within one breath-hold (∼15s) under realistic clinical conditions. METHODS AND MATERIALS Our previously developed FPGA-based hardware unit which allows synchronized kV-MV CBCT projection acquisition is connected to a clinical linear accelerator system via a multi-pin switch; i.e. either kV-MV imaging or conventional clinical mode can be selected. An application program was developed to control the relevant linac parameters automatically and to manage the MV detector readout as well as the gantry angle capture for each MV projection. The kV projections are acquired with the conventional CBCT system. GPU-accelerated filtered backprojection is performed separately for both data sets. After appropriate grayscale normalization both modalities are combined and the final kV-MV volume is re-imported in the CBCT system to enable image matching. To demonstrate adequate geometrical accuracy of the novel imaging system the Penta-Guide phantom QA procedure is performed. Furthermore, a human plastinate and different tumor shapes in a thorax phantom are scanned. Diameters of the known tumor shapes are measured in the kV-MV reconstruction. RESULTS An automated kV-MV CBCT workflow was successfully established in a clinical environment. The overall procedure, from starting the data acquisition until the reconstructed volume is available for registration, requires ∼90s including 17s acquisition time for 100° rotation. It is very simple and allows target positioning in the same way as for conventional CBCT. Registration accuracy of the QA phantom is within ±1mm. The average deviation from the known tumor dimensions measured in the thorax phantom was 0.7mm which corresponds to an improvement of 36% compared to our previous kV-MV imaging system. CONCLUSIONS Due to automation the kV-MV CBCT workflow is speeded up by a factor of >10 compared to the manual approach. Thus, the system allows a simple, fast and reliable imaging procedure and fulfills all requirements to be successfully introduced into the clinical workflow now, enabling single-breath-hold volume imaging.

Telemedizinische Erfassung von „patient-reported outcomes“

ZusammenfassungPatienten können heute in Echtzeit per Software (Applikationen, kurz Apps) auf modernen (Tele‑)Kommunikationssystemen wie Smartphones oder Tablets an ihre Behandler berichten, wie sie ihren subjektiven Gesundheitszustand, ihre Stimmung und ihr Zurechtkommen im Alltag, in der Summe als „patient-reported outcomes“ (PROs) bezeichnet, einschätzen. Die zunehmende Patientenzentrierung bei der Erhebung von PROs verspricht dabei erstmals, dass aufgrund verbesserter Datenqualität (bessere Compliance, mehr Messpunkte etc.) Therapieentscheidungen auf allen Ebenen, d. h. von der Leitlinie bis zur täglichen individuellen Einschätzung, von PROs beeinflusst werden. Jedoch ist noch keine einheitliche Strategie erkennbar, wie und mit welcher Gewichtung PROs in den klinischen Alltag implementiert werden, um daraus therapeutische Konsequenzen abzuleiten. Dieser Beitrag gibt einen Überblick über die Terminologie und fasst gegenwärtige Herausforderungen auf dem Weg zur Etablierung von PROs als anerkannte Daten im klinischen Alltag zusammen.AbstractModern communication systems such as smartphones and tablets allow patients to submit real-time reports on their mood, everyday functioning, and subjective health to their care providers via software. These reports and evaluations, summarized under the umbrella term “patient-reported outcomes” (PROs), are generated by locally installed applications (or, in short, apps). Increasingly patient-centered app-based PRO collection promises to significantly contribute to care plans and therapies at all levels, from guidelines to individual evaluation, as they gather more high-quality data due to improved patient compliance and more individual measurements. However, there is no clear path regarding how and with what weighting PROs are to be implemented into daily clinical practice in order to derive consequences. Herein, we summarize the terminology and most significant challenges that have to be tackled before PROs might be established as “valid” data in clinical routine.

Intra-breath-hold residual motion of image-guided DIBH liver-SBRT: An estimation by ultrasound-based monitoring correlated with diaphragm position in CBCT

BACKGROUND AND PURPOSE Craniocaudal motion during image-guided abdominal SBRT can be reduced by computer-controlled deep-inspiratory-breath-hold (DIBH). However, a residual motion can occur in the DIBH-phases which can only be detected with intrafractional real-time-monitoring. We assessed the intra-breath-hold residual motion of DIBH and compared residual motion of target structures during DIBH detected by ultrasound (US). US data were compared with residual motion of the diaphragm-dome (DD) detected in the DIBH-CBCT-projections. PATIENTS AND METHODS US-based monitoring was performed with an experimental US-system simultaneously to DIBH-CBCT acquisition. A total of 706 DIBHs during SBRT-treatments of metastatic lesions (liver, spleen, adrenal) of various primaries were registered in 13 patients. Residual motion of the target structure was documented with US during each DIBH. Motion of the DD was determined by comparison to a reference phantom-scan taking the individual geometrical setting at a given projection angle into account. Residual motion data detected by US were correlated to those of the DD (DIBH-CBCT-projection). RESULTS US-based monitoring could be performed in all cases and was well tolerated by all patients. Additional time for daily US-based setup required 8 ± 4 min. 385 DIBHs of 706 could be analyzed. In 59% of all DIBHs, residual motion was below 2 mm. In 36%, residual motion of 2-5 mm and in 4% of 5-8 mm was observed. Only 1% of all DIBHs and 0.16% of all readings revealed a residual motion of >8 mm during DIBH. For DIBHs with a residual motion over 2 mm, 137 of 156 CBCT-to-US curves had a parallel residual motion and showed a statistical correlation. DISCUSSION AND CONCLUSION Soft-tissue monitoring with ultrasound is a fast real-time method without additional radiation exposure. Computer-controlled DIBH has a residual motion of <5 mm in >95% which is in line with the published intra-breath-hold-precision. Larger intrafractional deviations can be avoided if the beam is stopped at an US-defined threshold.