Development and characterization of a dedicated dose monitor for ultrahigh-dose-rate scanned carbon-ion beams

The current monochromatic beam mode (i.e., uHDR irradiation mode) of the scanned carbon-ion beam lacks a dedicated dose monitor, making the beam control challenging. We developed and characterized a dedicated dose monitor for uHDR-scanned carbon-ion beams. Furthermore, a simple measurable dose rate (dose rate per spot (DRspot)) was suggested by using the developed dose monitor and experimentally validating quantities relevant to the uHDR scanned carbon-ion beam. A large plane-parallel ionization chamber (IC) with a smaller electrode spacing was used to reduce uHDR recombination effects, and a dedicated operational amplifier was manufactured for the uHDR-scanned carbon-ion beam. The dose linearity of the IC was within ± 1% in the range of 1.8-12.3 Gy. The spatial inhomogeneity of the dose response of the IC was ± 0.38% inside the ± 40-mm detector area, and a systematic deviation of approximately 2% was measured at the edge of the detector. uHDR irradiation with beam scanning was tested and verified for different doses at the corresponding dose rates (in terms of both the average dose rate and DRspot). We confirmed that the dose monitor can highlight the characteristics (i.e., dose, dose rate, and dose profile) of uHDR-scanned carbon-ion beams at several dose levels in the monochromatic beam mode.

Beam delivery characteristics of the Hitachi carbon ion scanning system at Osaka Heavy Ion Medical Accelerator in Kansai (HIMAK)

BACKGROUND

Using the pencil beam raster scanning method employed at most carbon beam treatment facilities, spots can be moved without interrupting the beam, allowing for the delivery of a dose between spots (move dose). This technique is also known as Dose-Driven-Continuous-Scanning (DDCS). To minimize its impact on HIMAK patient dosimetry, there's an upper limit to the move dose. Spots within a layer are grouped into sets, or "break points," allowing continuous irradiation. The beam is turned off when transitioning between sets or at the end of a treatment layer or spill. The control system beam-off is accomplished by turning off the RF Knockout (RFKO) extraction and after a brief delay the High Speed Steering Magnet (HSST) redirects the beam transport away from isocenter to a beam dump.

PURPOSE

The influence of the move dose and beam on/off control on the dose distribution and irradiation time was evaluated by measurements never before reported and modelled for Hitachi Carbon DDCS.

METHOD

We conducted fixed-point and scanning irradiation experiments at three different energies, both with and without breakpoints. For fixed-point irradiation, we utilized a 2D array detector and an oscilloscope to measure beam intensity over time. The oscilloscope data enabled us to confirm beam-off and beam-on timing due to breakpoints, as well as the relative timing of the RFKO signal, HSST signal, and dose monitor (DM) signals. From these measurements, we analyzed and modelled the temporal characteristics of the beam intensity. We also developed a model for the spot shape and amplitude at isocenter occurring after the beam-off signal which we called flap dose and its dependence on beam intensity. In the case of scanning irradiation, we measured move doses using the 2D array detector and compared these measurements with our model.

RESULT

We observed that the most dominant time variation of the beam intensity was at 1 kHz and its harmonic frequencies. Our findings revealed that the derived beam intensity cannot reach the preset beam intensity when each spot belongs to different breakpoints. The beam-off time due to breakpoints was approximately 100 ms, while the beam rise time and fall time (tdecay ) were remarkably fast, about 10 ms and 0.2 ms, respectively. Moreover, we measured the time lag (tdelay ) of approximately 0.2 ms between the RFKO and HSST signals. Since tdelay ≈ tdecay at HIMAK then the HSST is activated after the residual beam intensity, resulting in essentially zero flap dose at isocenter from the HSST. Our measurements of the move dose demonstrated excellent agreement with the modelled move dose.

CONCLUSION

We conducted the first move dose measurement for a Hitachi Carbon synchrotron, and our findings, considering beam on/off control details, indicate that Hitachi's carbon synchrotron provides a stable beam at HIMAK. Our work suggests that measuring both move dose and flap dose should be part of the commissioning process and possibly using our model in the Treatment Planning System (TPS) for new facilities with treatment delivery control systems with higher beam intensities and faster beam-off control.

Validation of robust radiobiological optimization algorithms based on the mixed beam model for intensity-modulated carbon-ion therapy

Currently, treatment planning systems (TPSs) that can compute the intensities of intensity-modulated carbon-ion therapy (IMCT) using scanned carbon-ion beams are limited. In the present study, the computational efficacy of the newly designed IMCT algorithms was analyzed for the first time based on the mixed beam model with respect to the physical and biological doses; moreover, the validity and effectiveness of the robust radiobiological optimization were verified. A dose calculation engine was independently generated to validate a clinical dose determined in the TPS. A biological assay was performed using the HSGc-C5 cell line to validate the calculated surviving fraction (SF). Both spot control (SC) and voxel-wise worst-case scenario (WC) algorithms were employed for robust radiobiological optimization followed by their application in a Radiation Therapy Oncology Group benchmark phantom under homogeneous and heterogeneous conditions and a clinical case for range and position errors. Importantly, for the first time, both SC and WC algorithms were implemented in the integrated TPS platform that can compute the intensities of IMCT using scanned carbon-ion beams for robust radiobiological optimization. For assessing the robustness, the difference between the maximum and minimum values of a dose-volume histogram index in the examined error scenarios was considered as a robustness index. The relative biological effectiveness (RBE) determined by the independent dose calculation engine exhibited a -0.6% difference compared with the RBE defined by the TPS at the isocenter, whereas the measured and the calculated SF were similar. Regardless of the objects, compared with the conventional IMCT, the robust radiobiological optimization enhanced the sensitivity of the examined error scenarios by up to 19% for the robustness index. The computational efficacy of the novel IMCT algorithms was verified according to the mixed beam model with respect to the physical and biological doses. The robust radiobiological optimizations lowered the impact of range and position uncertainties considerably in the examined scenarios. The robustness of the WC algorithm was more enhanced compared with that of the SC algorithm. Nevertheless, the SC algorithm can be used as an alternative to the WC IMCT algorithm with respect to the computational cost.

Treatment planning of carbon ion radiotherapy for prostate cancer based on cellular experiments with PC3 human prostate cancer cells

[Purpose] Treatment plans for carbon ion radiotherapy (CIRT) in Japan are designed to uniformly deliver the prescribed clinical dose based on the radiosensitivity of human salivary gland (HSG) cells to the planning target volume (PTV). However, sensitivity to carbon beams varies between cell lines, that is, it should be checked that the clinical dose distribution based on the cell radiosensitivity of the treatment site is uniform within the PTV. [Methods] We modeled the linear energy transfer (LET) dependence of the linear-quadratic (LQ) coefficients specific to prostate cancer, which accounts for the majority of CIRT. This was achieved by irradiating prostate cancer cells (PC3) with X-rays from a 4 MV-Linac and carbon beams with different LETs of 11.1-214.3 keV/μm. By using the radiosensitivity of PC3 cells derived from cellular experiments, we reconstructed prostate-cancer-specific clinical dose distributions on patient computed tomography (CT). [Results] The LQ coefficient, α, of PC3 cells was larger than that of HSG cells at low (<50 keV/μm) LET and smaller at high (>50 keV/μm) LET, which was validated by cellular experiments performed on rectangular SOBPs. The reconstructed dose distribution on patient CT was sloped when 1 fraction incident from the one side of the patient was considered, but remained uniform from the sum of 12 fractions of the left-right opposing beams (as is used in clinical practice). [Conclusion] Our study reveals the inhomogeneity of clinical doses in single-field plans calculated using the PC3 radiosensitivity data. However, this inhomogeneity is compensated by using the combination of left-right opposing beams.

Ultra-high Dose-rate Carbon-ion Scanning Beam With a Compact Medical Synchrotron Contributing to Further Development of FLASH Irradiation

BACKGROUND/AIM

The focus of this report is establishing an irradiation arrangement to realize an ultra-high dose-rate (uHDR; FLASH) of scanned carbon-ion irradiation possible with a compact commonly available medical synchrotron.

MATERIALS AND METHODS

Following adjustments to the operation it became possible to extract ≥1.0×10⁹ carbon ions at 208.3 MeV/u (86 mm in range) per 100 ms. The design takes the utmost care to prevent damage to monitors, particularly in the nozzle, achieved by the uHDR beam not passing through this part of the apparatus. Doses were adjusted by extraction times, using a function generator. After one scan by the carbon-ion beam it became possible to create a field within the extraction time. The Advanced Markus chamber (AMC) and Gafchromic film are then able to measure the absolute dose and field size at a plateau depth, with the operating voltage of the chamber at 400 V at the uHDR for the AMC.

RESULTS

The beam scanning utilizing this uHDR irradiation could be confirmed at a dose of 6.5±0.08 Gy (±3% homogeneous) at this volume over at least 16×16 mm² corresponding to a dose-rate of 92.3 Gy/s (±1.3%). The dose was ca. 0.7, 1.5, 2.9, and 5.4 Gy depending on dose-rate and field size, with the rate of killed cells increasing with the irradiation dose.

CONCLUSION

The compact medical synchrotron achieved FLASH dose-rates of >40 Gy/s at different dose levels and in useful field sizes for research with the apparatus and arrangement developed here.

Clinical dose assessment for scanned carbon-ion radiotherapy using linear energy transfer measurements and Monte Carlo simulations

Objective. Dosimetric commissioning of treatment planning systems (TPS) focuses on validating the agreement of the physical dose with experimental data. For carbon-ion radiotherapy, the commissioning of the relative biological effectiveness (RBE) is necessary to predict the clinical outcome based on the radiation quality of the mixed radiation field. In this study, we proposed a approach for RBE commissioning using Monte Carlo (MC) simulations, which was further strengthen by RBE validation based on linear energy transfer (LET) measurements.Approach. First, we tuned the MC simulation based on the results of dosimetric experiments including the beam ranges, beam sizes, and MU calibrations. Furthermore, we compared simulated results to measured depth- and radial-LET distributions of the 430 MeV u^-1carbon-ion spot beam with a 1.5 mm², 36μm thick silicon detector. The measured dose-averaged LET (LET_d) and RBE were compared with the simulated results. The RBE was calculated based on the mixed beam model with linear-quadratic parameters depending on the LET. Finally, TPS-calculated clinical dose profiles were validated through the tuned MC-based calculations.Main results. A 10 keVμm^-1and 0.15 agreement for LET_dand RBE, respectively, were found between simulation and measurement results obtained for a 2σlateral size of 430 MeV u^-1carbon-ion spot beam in water. These results suggested that the tuned MC simulation can be used with acceptable precision for the RBE and LET calculations of carbon-ion spot beam within the clinical energy range. For physical and clinical doses, the TPS- and MC-based calculations showed good agreements within 1.0% at the centre of the spread-out Bragg peaks.Significance. The tuned MC simulation can accurately reproduce the actual carbon-ion beams, and it can be used to validate the physical and clinical dose distributions calculated by TPS. Moreover, the MC simulation can be used for dosimetric commissioning, including clinical doses, without LET measurements.

Commissioning a newly developed treatment planning system, VQA Plan, for fast-raster scanning of carbon-ion beams

In this study, we report our experience in commissioning a commercial treatment planning system (TPS) for fast-raster scanning of carbon-ion beams. This TPS uses an analytical dose calculation algorithm, a pencil-beam model with a triple Gaussian form for the lateral-dose distribution, and a beam splitting algorithm to consider lateral heterogeneity in a medium. We adopted the mixed beam model as the relative biological effectiveness (RBE) model for calculating the RBE values of the scanned carbon-ion beam. To validate the modeled physical dose, we compared the calculations with measurements of various relevant quantities as functions of the field size, range and width of the spread-out Bragg peak (SOBP), and depth–dose and lateral-dose profiles for a 6-mm SOBP in water. To model the biological dose, we compared the RBE calculated with the newly developed TPS to the RBE calculated with a previously validated TPS that is in clinical use and uses the same RBE model concept. We also performed patient-specific measurements to validate the dose model in clinical situations. The physical beam model reproduces the measured absolute dose at the center of the SOBP as a function of field size, range, and SOBP width and reproduces the dose profiles for a 6-mm SOBP in water. However, the profiles calculated for a heterogeneous phantom have some limitations in predicting the carbon-ion-beam dose, although the biological doses agreed well with the values calculated by the validated TPS. Using this dose model for fast-raster scanning, we successfully treated more than 900 patients from October 2018 to October 2020, with an acceptable agreement between the TPS-calculated and measured dose distributions. We conclude that the newly developed TPS can be used clinically with the understanding that it has limited accuracies for heterogeneous media.

Commissioning of carbon-ion radiotherapy for moving targets at the Osaka Heavy-Ion Therapy Center

Purpose

Herein, we report the methods and results of the Hitachi carbon‐ion therapy facility commissioning to determine the optimum values of the magnitude of movement and repaint number in respiratory‐gated irradiation.

Methods

A virtual‐cylinder target was created using the treatment‐planning system (VQA Plan), and measurements were performed to study the effects of respiratory movements using a two‐dimensional ionization‐chamber array detector and a phantom with movable wedge and stage. For simulations, we selected a 10 × 10 × 10 cm³ cubic irradiation pattern with a uniform physical dose and two actual cases of liver‐cancer treatments, whose prescribed doses were 60 Gy(RBE)/4 fraction (Case 1) and 60 Gy(RBE)/12 fraction (Case 2). We employed two types of repainting methods, one produced by the algorithm of VQA Plan (VQA algorithm) and the other by ideal repainting. The latter completely repeats all spots with set number of repaintings. We performed flatness calculations and gamma analysis to evaluate the effects of each condition.

Results

From the measurements, the gamma passing rates for which the criteria were 3%/3 mm exceeded 95% for displacements in the head‐to‐tail direction if the repaint number was greater than 3 and the magnitude of the residual motions was less than 5.0 mm. In simulations with the cubic irradiation pattern, the gamma passing rates (with criteria of 2%/2 mm) exceeded 95% when the magnitude of the residual motions was 3.0 mm and the repaint number was greater than 3. When the repaint number was set to 4 in the VQA with the actual liver cases, the flatness results for Case 2 was minimal. For ideal repainting, the flatness results for all ports fell within ∼3.0% even when the magnitude of the residual motions was 5.0 mm if the repaint number was 6. However, the flatness was less than 3.0% for almost all ports if the magnitude of the residual motions was less than 3.0 mm with a repaint number of 4 in case of both types of repaint methods.

Conclusions

At our facility, carbon‐ion radiotherapy can be provided safely to a moving target with residual motions of 3.0 mm magnitude and with a repaint number of 4.

Carbon ion radiotherapy using fiducial markers for prostate cancer in Osaka HIMAK: Treatment planning

PURPOSE

Carbon ion radiotherapy for prostate cancer was performed using two fine needle Gold Anchor (GA) markers for patient position verification in Osaka Heavy Ion Medical Accelerator in Kansai (Osaka HIMAK). The present study examined treatment plans for prostate cases using beam-specific planning target volume (bsPTV) based on the effect of the markers on dose distribution and analysis of target movements.

MATERIALS AND METHODS

Gafchromic EBT3 film was used to measure dose perturbations caused by markers. First, the relationships between the irradiated film density and absolute dose with different linear energy transfer distributions within a spread-out Bragg peak (SOBP) were confirmed. Then, to derive the effect of markers, two types of markers, including GA, were placed at the proximal, center, and distal depths within the same SOBP, and dose distributions behind the markers were measured using the films. The amount of internal motion of prostate was derived from irradiation results and analyzed to determine the margins of the bsPTV.

RESULTS

The linearity of the film densities against absolute doses was constant within the SOBP and the amount of dose perturbations caused by the markers was quantitatively estimated from the film densities. The dose perturbation close behind the markers was smallest (<10% among depths within the SOBP regardless of types of markers) and increased with depth. The effect of two types of GAs on dose distributions was small and could be ignored in the treatment planning. Based on the analysis results of internal motions of prostate, required margins of the bsPTV were found to be 8, 7, and 7 mm in left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions, respectively.

CONCLUSION

We evaluated the dose reductions caused by markers and determined the margins of the bsPTV, which was applied to the treatment using fiducial markers, using the analysis results of prostate movements.

Physical and biological beam modeling for carbon beam scanning at Osaka Heavy Ion Therapy Center

We have developed physical and biological beam modeling for carbon scanning therapy at the Osaka Heavy Ion Therapy Center (Osaka HIMAK). Carbon beam scanning irradiation is based on continuous carbon beam scanning, which adopts hybrid energy changes using both accelerator energy changes and binary range shifters in the nozzles. The physical dose calculation is based on a triple Gaussian pencil-beam algorithm, and we thus developed a beam modeling method using dose measurements and Monte Carlo simulation for the triple Gaussian. We exploited a biological model based on a conventional linear-quadratic (LQ) model and the photon equivalent dose, without considering the dose dependency of the relative biological effectiveness (RBE), to fully comply with the carbon passive dose distribution using a ridge filter. We extended a passive ridge-filter design method, in which carbon and helium LQ parameters are applied to carbon and fragment isotopes, respectively, to carbon scanning treatment. We then obtained radiation quality data, such as the linear energy transfer (LET) and LQ parameters, by Monte Carlo simulation. The physical dose was verified to agree with measurements to within ±2% for various patterns of volume irradiation. Furthermore, the RBE in the middle of a spread-out Bragg peak (SOBP) reproduced that from passive dose distribution results to within ±1.5%. The developed carbon beam modeling and dose calculation program was successfully applied in clinical use at Osaka HIMAK.

Radiobiological effects of flattening filter-free photon beams on A549 non-small-cell lung cancer cells

Flattening filter-free (FFF) photon beams minimize the intrafraction motion of tumors, and this feature is useful in pulmonary malignancies, such as non-small-cell lung cancer (NSCLC). However, the radiobiological effects of such beams on NSCLC cells, which are often treated with stereotactic body radiotherapy (SBRT), have not been investigated sufficiently. Although cell motility may be promoted by photon beams with a low dose, the relationship between cell motility and the dose rate of photon beams has not been evaluated. The purpose of this study was to evaluate the radiobiological effects of FFF photon beams on cell survival and motility in NSCLC. A human lung cancer cell line (A549) was irradiated with conventional flattening filter (FF) and FFF photon beams at dose rates of 300 (FF), 500 and 2000 MU/min (FFF). While cell survival was estimated using the colony formation assay, cell motility was evaluated using the Boyden chamber and Matrigel invasion assays. FFF photon beams with a high dose rate neither affected the survival of A549 cells nor caused any significant difference in their motility. On the other hand, high-dose irradiation reduced cell survival and motility regardless of the dose rate. Photon beams with a high dose rate used for radiation therapy are suitable for SBRT from the standpoint of both cell survival and motility, in addition to their physical characteristics.

Impact of time-related factors on biologically accurate radiotherapy treatment planning

BACKGROUND

The incomplete repair (IR) model expresses the cell repair effect from radiation-induced damage over time, which is given little consideration in actual treatment planning. By incorporating the IR model into the normal tissue complication probability (NTCP), the accuracy and safety of treatment plan evaluations concerning the effect of repair can be improved. This study aims to evaluate the impact of incorporating the IR model into the NTCP by varying time-related factors such as the repair half-time (T_1/2) and the junction-shift sc3hedule in craniospinal irradiation (CSI).

METHODS

CSI was planned retrospectively, and the NTCP of the spinal cord was calculated with the IR model for values of T_1/2 from 1 to 10 h. The NTCP in the case of changing the junction-shift schedule was also examined in the same manner.

RESULTS

The NTCP with the IR model increased with increasing T_1/2, which is prominent for the larger T_1/2. By changing the junction-shift schedule, the NTCP with the IR model decreased when adjacent fields overlapped.

CONCLUSIONS

The IR model is a valuable addition to treatment planning because it enables the NTCP to be evaluated including the effect of repair and differences in scheduling to be reflected in the NTCP. However, these are largely dependent on the value of the T_1/2.

Clinical Assessment of Micro-residual Tumors during Stereotactic Body Radiation Therapy for Hepatocellular Carcinoma

BACKGROUND

This study aimed to assess the need to consider microscopic invasion in terms of treatment planning in stereotactic body radiation therapy (SBRT) for hepatocellular carcinoma and elucidate the appropriate clinical target volume (CTV) margin.

PATIENTS AND METHODS

A total of 121 patients (with 146 liver tumors) who underwent SBRT between July 2007 and August 2016 were analyzed, regarding overall survival and local control (LC).

RESULTS

The 2- and 5-year LC rates were 91.5% and 89.8%, respectively. Planning target volume (PTV) margin <8 mm was associated with poor LC. Of the 77 patients with PTV margin of <8 mm, age <75 years was associated with poor LC, while alpha-fetoprotein (AFP) ≤20 ng/ml was associated with good LC.

CONCLUSION

In patients with high AFP levels, there is a possibility of microscopic invasion around the tumor, suggesting that LC may be improved by adding an additional clinical target volume margin to the gross tumor volume.

Can clinically relevant dose errors in patient anatomy be detected by gamma passing rate or modulation complexity score in volumetric-modulated arc therapy for intracranial tumors?

We investigated whether methods conventionally used to evaluate patient-specific QA in volumetric-modulated arc therapy (VMAT) for intracranial tumors detect clinically relevant dosimetric errors. VMAT plans with coplanar arcs were designed for 37 intracranial tumors. Dosimetric accuracy was validated by using a 3D array detector. Dose deviations between the measured and planned doses were evaluated by gamma analysis. In addition, modulation complexity score for VMAT (MCSv) for each plan was calculated. Three-dimensional dose distributions in patient anatomy were reconstructed using 3DVH software, and clinical deviations in dosimetric parameters between the 3DVH doses and planned doses were calculated. The gamma passing rate (GPR)/MCSv and the clinical dose deviation were evaluated using Pearson's correlation coefficient. Significant correlation (P < 0.05) between the clinical dose deviation and GPR was observed with both the 3%/3 mm and 2%/2 mm criteria in clinical target volume (D99), brain (D2), brainstem (D2) and chiasm (D2), albeit that the correlations were not 'strong' (0.38 < |r| < 0.54). The maximum dose deviations of brainstem were up to 4.9 Gy and 2.9 Gy for Dmax and D%, respectively in the case of high GPR (98.2% with 3%/3 mm criteria). Regarding MCSv, none of the evaluated organs showed a significant correlation with clinical dose deviation, and correlations were 'weak' or absent (0.01 < |r| < 0.21). The use of high GPR and MCSv values does not always detect dosimetric errors in a patient. Therefore, in-depth analysis with the DVH for patient-specific QA is considered to be preferable for guaranteeing safe dose delivery.

Overview of JSPS Core-to-Core Program: Forming Research and Educational Hubs of Medical Physics

To foster medical physicists, we introduce the achievement we made since 2011 under the national research project of the Japan Society for the Promotion of Science (JSPS) Core-to-Core program; 'Forming Research and Educational Hubs of Medical Physics.' On this basis and under the JSPS program, we promoted research and educational exchange with Indiana University (IU) in USA, University of Groningen (The UG) in the Netherland and other cooperating institutions such as University of Minnesota (UM).A total of 23 students and researchers were sent. UG accepted the most among three institutions. In turn, 12 foreign researchers including post-doctor fellows came to Japan for academic seminars or educational lectures.Fifteen international seminars were held; 8 in Japan, 4 in USA, and 3 in the Netherland.Lots of achievement were made through these activities in 5 years. Total of 23 research topics at the international conferences were presented. Total of 12 articles were published in international journals.This program clearly promoted the establishment of international collaboration, and many young researchers and graduate students were exchanged and collaborated with foreign researchers.

Assessment with cone-beam computed tomography of intrafractional motion and interfractional position changes of resectable and borderline resectable pancreatic tumours with implanted fiducial marker

OBJECTIVE

The volume of targets to which a high radiation dose can be delivered is limited for pancreatic radiotherapy. We assessed changes in movements of pancreatic tumours between simulation and treatment and determined compensatory margins.

METHODS

For 23 patients, differences in implanted fiducial marker motion magnitude (MMM) and mean marker position (MMP) between four-dimensional CT and cone-beam CT were measured. Subsequently, residual uncertainty was simulated after no action level (NAL) and extended no action level (eNAL) protocols were adopted.

RESULTS

With no correction, respective 95th percentile of MMM were 4.5 mm, 6.2 mm and 16.0 mm and systematic (random) errors of MMP were 2.8 mm (3.3 mm), 3.2 mm (2.0 mm) and 5.9 mm (4.0 mm) in the left-right (L-R), anteroposterior (A-P) and superoinferior (S-I) directions, so that large margins were required (L-R, 10.5 mm; A-P, 11.7 mm; and S-I, 24.8 mm). NAL reduced systematic errors of MMP, but resultant margins remained large (L-R, 8.0 mm; A-P, 9.6 mm; and S-I, 18.1 mm). eNAL compensated for time trends and obtained minimal margins (L-R, 6.7 mm; A-P, 6.7 mm; and S-I, 15.2 mm).

CONCLUSION

Motion magnitude and position of pancreatic tumours during simulation are frequently not representative of that during treatment. eNAL compensated for systematic interfractional position change and would be a practical approach for improving targeting accuracy. Advances in knowledge: Considerably large margins, especially in the S-I direction, were required to compensate for intrafractional motion and interfractional position changes of the pancreatic tumour. An application of eNAL was an effective strategy to diminish these margins.

VMAT-SBRT planning based on an average intensity projection for lung tumors located in close proximity to the diaphragm: a phantom and clinical validity study

The aim of the this study was to validate the use of an average intensity projection (AIP) for volumetric-modulated arc therapy for stereotactic body radiation therapy (VMAT-SBRT) planning for a moving lung tumor located near the diaphragm. VMAT-SBRT plans were created using AIPs reconstructed from 10 phases of 4DCT images that were acquired with a target phantom moving with amplitudes of 5, 10, 20 and 30 mm. To generate a 4D dose distribution, the static dose for each phase was recalculated and the doses were accumulated by using the phantom position known for each phase. For 10 patients with lung tumors, a deformable registration was used to generate 4D dose distributions. Doses to the target volume obtained from the AIP plan and the 4D plan were compared, as were the doses obtained from each plan to the organs at risk (OARs). In both phantom and clinical study, dose discrepancies for all parameters of the dose volume (D(min), D(99), D(max), D(1) and D(mean)) to the target were <3%. The discrepancies of D(max) for spinal cord, esophagus and heart were <1 Gy, and the discrepancy of V20 for lung tissue was <1%. However, for OARs with large respiratory motion, the discrepancy of the D(max) was as much as 9.6 Gy for liver and 5.7 Gy for stomach. Thus, AIP is clinically acceptable as a planning CT image for predicting 4D dose, but doses to the OARs with large respiratory motion were underestimated with the AIP approach.

Couch height-based patient setup for abdominal radiation therapy

There are 2 methods commonly used for patient positioning in the anterior-posterior (A-P) direction: one is the skin mark patient setup method (SMPS) and the other is the couch height-based patient setup method (CHPS). This study compared the setup accuracy of these 2 methods for abdominal radiation therapy. The enrollment for this study comprised 23 patients with pancreatic cancer. For treatments (539 sessions), patients were set up by using isocenter skin marks and thereafter treatment couch was shifted so that the distance between the isocenter and the upper side of the treatment couch was equal to that indicated on the computed tomographic (CT) image. Setup deviation in the A-P direction for CHPS was measured by matching the spine of the digitally reconstructed radiograph (DRR) of a lateral beam at simulation with that of the corresponding time-integrated electronic portal image. For SMPS with no correction (SMPS/NC), setup deviation was calculated based on the couch-level difference between SMPS and CHPS. SMPS/NC was corrected using 2 off-line correction protocols: no action level (SMPS/NAL) and extended NAL (SMPS/eNAL) protocols. Margins to compensate for deviations were calculated using the Stroom formula. A-P deviation > 5mm was observed in 17% of SMPS/NC, 4% of SMPS/NAL, and 4% of SMPS/eNAL sessions but only in one CHPS session. For SMPS/NC, 7 patients (30%) showed deviations at an increasing rate of > 0.1mm/fraction, but for CHPS, no such trend was observed. The standard deviations (SDs) of systematic error (Σ) were 2.6, 1.4, 0.6, and 0.8mm and the root mean squares of random error (σ) were 2.1, 2.6, 2.7, and 0.9mm for SMPS/NC, SMPS/NAL, SMPS/eNAL, and CHPS, respectively. Margins to compensate for the deviations were wide for SMPS/NC (6.7mm), smaller for SMPS/NAL (4.6mm) and SMPS/eNAL (3.1mm), and smallest for CHPS (2.2mm). Achieving better setup with smaller margins, CHPS appears to be a reproducible method for abdominal patient setup.

Development and reproducibility evaluation of a Monte Carlo-based standard LINAC model for quality assurance of multi-institutional clinical trials

Technical developments in radiotherapy (RT) have created a need for systematic quality assurance (QA) to ensure that clinical institutions deliver prescribed radiation doses consistent with the requirements of clinical protocols. For QA, an ideal dose verification system should be independent of the treatment-planning system (TPS). This paper describes the development and reproducibility evaluation of a Monte Carlo (MC)-based standard LINAC model as a preliminary requirement for independent verification of dose distributions. The BEAMnrc MC code is used for characterization of the 6-, 10- and 15-MV photon beams for a wide range of field sizes. The modeling of the LINAC head components is based on the specifications provided by the manufacturer. MC dose distributions are tuned to match Varian Golden Beam Data (GBD). For reproducibility evaluation, calculated beam data is compared with beam data measured at individual institutions. For all energies and field sizes, the MC and GBD agreed to within 1.0% for percentage depth doses (PDDs), 1.5% for beam profiles and 1.2% for total scatter factors (Scps.). Reproducibility evaluation showed that the maximum average local differences were 1.3% and 2.5% for PDDs and beam profiles, respectively. MC and institutions' mean Scps agreed to within 2.0%. An MC-based standard LINAC model developed to independently verify dose distributions for QA of multi-institutional clinical trials and routine clinical practice has proven to be highly accurate and reproducible and can thus help ensure that prescribed doses delivered are consistent with the requirements of clinical protocols.

Respiratory monitoring with an acceleration sensor

Respiratory gating radiotherapy is used to irradiate a local area and to reduce normal tissue toxicity. There are certain methods for the detection of tumor motions, for example, using internal markers or an external respiration signal. However, because some of these respiratory monitoring systems require special or expensive equipment, respiratory monitoring can usually be performed only in limited facilities. In this study, the feasibility of using an acceleration sensor for respiratory monitoring was evaluated. The respiratory motion was represented by means of a platform and measured five times with the iPod touch® at 3, 4 and 5 s periods of five breathing cycles. For these three periods of the reference waveform, the absolute means ± standard deviation (SD) of displacement were 0.45 ± 0.34 mm, 0.33 ± 0.24 mm and 0.31 ± 0.23 mm, respectively. On the other hand, the corresponding absolute means ± SD for the periods were 0.04 ± 0.09 s, 0.04 ± 0.02 s and 0.06 ± 0.04 s. The accuracy of respiratory monitoring using the acceleration sensor was satisfactory in terms of the absolute means ± SD. Using the iPod touch® for respiratory monitoring does not need special equipment and makes respiratory monitoring easier. For these reasons, this system is a viable alternative to other respiratory monitoring systems.

Arytenoid dislocation after cardiac surgery

Occurring most usually as complications of upper aerodigestive tract instrumentation during endotracheal intubation or extubation, arytenoid cartilage dislocation and arytenoid subluxation are uncommon laryngeal injuries. Their precise cause, however, is usually difficult to determine. We encountered arytenoid dislocation following cardiac surgery requiring the use of transesophageal echocardiography (TEE). This case prompted us to review some of the mechanisms of injury to the cricoarytenoid joint. We conclude that even very subtle force may dislocate the arytenoid cartilage. We speculate that careless insertion of a TEE probe is mechanically capable of causing arytenoid dislocation and arytenoid subluxation. As ideal tools for intra-operative cardiovascular monitoring, TEE probes are increasingly being used routinely during cardiovascular surgery. So far, arytenoid cartilage dislocation and subluxation following TEE probe insertion have been reported rarely, but complications caused by TEE may increase in the near future. We wish to emphasize the pathophysiological risks of TEE monitoring and other procedures associated with anesthesia, and the need for a proper explanation to achieve informed consent before carrying out TEE monitoring during cardiac surgeries.

Removal of Two Types of Root Canal Filling Material Using Pulsed Nd:YAG Laser Irradiation

OBJECTIVE

The aim of this study was to examine the usefulness of a pulsed Nd:YAG laser in removing two types of endodontic obturation material from the root canal in vitro.

BACKGROUND DATA

Recently, a fine flexible glass fiber made of quartz has been developed to transmit the laser beam more effectively and permit its concentration in a specific area. This has increased the potential usefulness of the Nd:YAG laser in root canal treatment.

METHODS

The time required for removing the root canal obturation material (Gutta-percha cones and, Sealapex or AH26) by means of either Nd:YAG laser irradiation or a conventional method (Gates Glidden drills and K files) was measured. Contact microradiography was used to assess the radiopacity of the root canals before and after the removal of obturation material. The surfaces of the root canal after removal of the obturation materials were also observed by scanning electron microscopy.

RESULTS

Although none of the methods used in this study resulted in complete removal of debris from the root canal wall, the time required for the removal of any of the root canal obturation materials using laser ablation was significantly shorter than that required using the conventional method (p < 0.05). It appeared that some orifices of the dentinal tubules were blocked with melted dentin following laser irradiation.

CONCLUSIONS

Nd:YAG laser irradiation is an effective tool for the removal of root canal obturation materials, and may offer advantages over the conventional method.

Infrared transmission of electronic information via LAN in the operating room

Recent advances in technology have brought many kinds of monitoring devices into the operating room (OR). The information gathered by monitors can be channeled to the operating ward information system via a local area network (LAN). Connecting patients to monitors and monitors to the LAN, however, requires a large number of cables. This wiring is generally inconvenient and particularly troublesome if the layout of the OR is rearranged. From this point of view, wireless transmission seems ideally suited to clinical settings. Currently, two modes of wireless connectivity are available: radio-frequency (RF) waves or infrared (IR) waves. Some reports suggest that RF transmission is likely to cause electromagnetic interference (EMI) in medical devices such as cardiac pacemakers or infusion pumps. The risk of malfunctioning life-sustaining devices and the catastrophic consequences this would have on seriously ill patients rules out the use of RF. Here, we report an IR system using IR modems for LAN connectivity in the OR. In this study, we focused on the possible detrimental effects of EMI during wireless connectivity. In our trial, we found no evidence of EMI of IR modems with any of the medical devices we tested. Furthermore, IR modems showed similar performance to a wired system even in an electrically noisy environment. We conclude that IR wireless connectivity can be safely and effectively used in ORs.

The possibility of dowel removal by pulsed Nd:YAG laser irradiation

BACKGROUND AND OBJECTIVES

Nd:YAG laser is one of the popularly used laser, in dentistry for treatment and technologic processing. Removal of dowel from root canal is very troublesome at endodontic retreatment. This study aimed to examine the possibility and efficiency of dowel removal from the root canal using the Nd:YAG laser in vitro.

STUDY DESIGN/MATERIALS AND METHODS

Irradiation time and energies required for complete removal of the dowel set in the root canal using the laser were measured. The dowel ablation was observed by contact microradiographs (CMRs). The surface of the root canal after lasing was observed by a scanning electron microscope (SEM).

RESULTS

A significant difference existed in irradiation times and energies to remove dowels among various combinations of metal and cement (P < 0.05). The CMRs showed that both dowel and dentin were ablated, and the SEM observation demonstrated that root canal surface was melted.

CONCLUSIONS

The Nd:YAG laser irradiation could remove set dowels from the root canal.

Overexpression of haem oxygenase 1 protects allogeneic thyroid grafts from rejection in naive mice

Background

Endocrine allografts are an option for the treatment of endocrine failure. This study examined whether anti-CD4 monoclonal antibody (mAb) could induce survival of allogeneic thyroid grafts and investigated the mechanisms involved in graft survival.

Methods and Results

One lobe of thyroid was transplanted under the kidney capsule and graft survival was examined histologically. C57BL/10 (H2b) thyroids were rejected in naive CBA (H2k) mice within 14 days after transplantation. When mice were treated with a depleting anti-CD4 mAb (YTA 3·1; 100 μg on day −1, 0 and 3), all C57BL/10 thyroid grafts survived for over 30 days. In order to determine if donor-specific tolerance had been induced, mice with the surviving C57BL/10 thyroid grafts were transplanted with second C57BL/10 or Balb/c (H2d) thyroids under the left kidney capsule at 30 days. Interestingly, all of the second grafts were rejected in the left kidney capsule but the first C57BL/10 thyroid grafts continued to survive in the right kidney capsule for a further 30 days. These findings suggest that grafts themselves were modified under anti-CD4 mAb treatment. To confirm this hypothesis, C57BL/10 thyroid grafts in mice treated with anti-CD4 mAb were resected and retransplanted into naive mice 30 days after transplantation. All of the grafts survived when retransplanted to naive mice and this was found to correlate with overexpression of haem oxygenase 1 in the thyroid grafts. In an attempt to demonstrate the pivotal role of haem oxygenase 1 on graft survival, an inhibitor of haem oxygenase 1 (zinc protoporphyrin) or control compound (copper protoporphyrin) that did not inhibit the enzyme was injected intraperitoneally (30 mmol l−1 every day) after transplantation of C57BL/10 thyroid grafts into the primary CBA recipients treated with anti-CD4 mAb. The grafts in mice treated with zinc protoporphyrin but not copper protoporphyrin were rejected when retransplanted to naive recipients.

Conclusion

Overexpression of haem oxygenase 1 protects allogeneic thyroid grafts from rejection in recipients treated with anti-CD4 mAb. This observation may be applied for clinical endocrine grafts using gene transfer of haem oxygenase 1.

Practical issues in bispectral analysis of electroencephalographic signals

IMPLICATIONS

The aim of this report was to confirm the methodology of bispectral analysis of electroencephalogram. In developing a software for real-time bispectral analysis, we encountered several practical problems in bispectrum calculation. We settled those and concluded that 3 min of monitoring are required to obtain reliable and reproducible bicoherence values.

Overexpression of heme oxygenase-1 protects allogeneic thyroid grafts from rejection in naive mice

BACKGROUND

Endocrine allografts are an option for the treatment of endocrine failure.

METHODS

One lobe of the thyroid was transplanted under the kidney capsule.

RESULTS

C57BL/10 (H2(b)) thyroids were rejected in naive CBA (H2(k)) mice within 14 days after transplantation. When mice were treated with anti-CD4 monoclonal antibodies (mAb), all grafts survived for more than 60 days. The first grafts still survived after second C57BL/10 or Balb/c (H2(d)) thyroid grafts that were transplanted into the same recipients were rejected acutely, which suggests that the primary grafts were modified under anti-CD4 mAb treatment. To confirm this hypothesis, C57BL/10 thyroid grafts from anti-CD4 mAb-treated mice were retransplanted. All grafts survived in naive mice; this correlated with the overexpression of heme oxygenase-1 (HO-1) in the grafts. Next, an inhibitor of HO-1 (zinc protoporphyrin) or control compound (copper protoporphyrin) was injected intraperitoneally after transplantation of C57BL/10 thyroid grafts into the primary CBA recipients that had been treated with anti-CD4 mAb. The grafts in mice that had been treated with zinc protoporphyrin, but not copper protoporphyrin, were rejected when retransplanted to naive recipients.

CONCLUSIONS

Overexpression of HO-1 correlated with the protection of fully allogeneic thyroid grafts from rejection when retransplanted into naive recipients.

Experimental parathyroid transplantation: human parathyroid grafts survived and functioned in mice treated with anti-CD4 monoclonal antibody

Permanent hypoparathyroidism is one of the most difficult of all endocrine disorders to treat medically. To examine the possibility that xenotransplantation can be used to treat hypoparathyroidism, human parathyroid tissues were transplanted into mice. Human parathyroid tissue was taken from specimens excised from patients with hyperparathyroidism. Fresh human parathyroid tissue was implanted under kidney capsule of CBA (H2k) mice. Some mice were treated intraperitoneally with depleting anti-CD4 monoclonal antibody (mAb, YTA 3.1, 100 microg/dose, days -1. 0. 1, 2, 3, and 5). Mice were killed 30 days after transplantation. Survival of parathyroid grafts was examined microscopically and human parathyroid hormone in serum was measured by ELISA. All parathyroid grafts survived under kidney capsule and human parathyroid hormone was strongly detected in serum (621 +/- 576 pg/mL) when recipients were treated with short-course treatment of anti-CD4 mAb. Conversely, no parathyroid tissue was seen microscopically in any recipient mice without anti-CD4 mAb treatment. Human parathyroid hormone was undetectable by ELISA in naive mice and mice transplanted with human parathyroid tissue without short-course treatment of anti-CD4 mAb. Xenogeneic human parathyroid tissue survived and functioned in mice treated with short-course treatment of anti-CD4 mAb.

[Anesthetic management of heart transplantation]

We anesthetized a 47-yr-old man with end-stage hypertrophic cardiomyopathy for heart transplantation. This is the first case of heart transplantation from a patient with brain death, since the organ transplantation law had become valid in Japan. Anesthesia was induced and maintained with fentanyl and diazepam. Aseptic technique was used in inserting and securing all catheters. The patient was assisted by left ventricular assist system, and hemodynamic suppression at anesthetic induction was trivial. Since complete AV block was present at the termination of cardiopulmonary bypass (CPB), VVI pacing and infusion of isoproterenol were started. In addition, nitroglycerin was given for pulmonary vasodilation. The cardiovascular support used for weaning from CPB included dobutamine, isoprote-renol, dopamine and milrinone. Following weaning from CPB sinus rhythm appeared spontaneously and function of the transplanted heart was satisfactory. When the patient was transported to ICU reduction in doses of catecholamines was possible, and dopamine and milrinone were infused. The patient was extubated 10 hours after admission to ICU.

Aeration time following ethylene oxide sterilization for reusable rigid sterilization containers: concentration of gaseous ethylene oxide in containers

Because ethylene oxide (EO) gas is toxic to humans, restrictions have been imposed on its use for sterilization, specifying allowable levels of residual EO remaining in sterilized apparatus and materials. However, the aeration time that optimizes the removal of the remaining EO when a rigid sterilizing container is used for a vessel had not been identified. Therefore, polyvinyl chloride, which easily adsorbs EO, was placed in rigid sterilizing containers, and aeration was carried out after 1, 8, 12, 17, and 24 hours. After standard EO sterilization, the EO concentrations remaining in the air in the rigid containers were measured. The results indicate that a period of 17 hours of aeration is appropriate when a rigid sterilizing container is used.

The effects of propofol, isoflurane, and sevoflurane on oxygenation and shunt fraction during one-lung ventilation

Propofol's effect on hypoxic pulmonary vasoconstriction during one-lung ventilation (OLV) has not been determined. Twenty patients who had long-term OLV for esophageal surgery were allocated randomly to one of two study groups; one in which isoflurane administration preceded propofol, and another in which sevoflurane administration preceded propofol. Arterial and mixed venous blood samples and hemodynamics were measured as follows: before OLV, during OLV, OLV at 4 cm of positive end-expiratory pressure (PEEP), OLV after conversion from volatile anesthetics to propofol, OLV at 4 cm of PEEP, and after OLV. After the application of 4 cm of PEEP during propofol anesthesia, PaO2 increased significantly in both groups. The shunt fraction (Qs/Qt) increased significantly after the initiation of OLV in both groups and decreased significantly after the conversion from volatile anesthetics to propofol in both groups. Propofol can be used safely during OLV because PaO2 increased after the application of 4 cm of PEEP during propofol anesthesia, and Qs/Qt decreased significantly after the conversion from inhaled anesthetics to propofol anesthesia.

IMPLICATIONS

During one-lung ventilation, the arterial partial pressure of oxygen values with propofol were greater than those with isoflurane and sevoflurane, and shunt fraction values with propofol were lower than those with both volatile anesthetics. Propofol improved oxygenation and shunt fraction during one-lung ventilation compared with volatile anesthetics.