Yuki Otani

A comparison of the respiratory signals acquired by different respiratory monitoring systems used in respiratory gated radiotherapy

PURPOSE Respiratory monitoring systems are used to detect the respiratory phase of patients during the planning and administration of respiratory gated radiotherapy by using four-dimensional computed tomography (4DCT) or 4D positron-emission tomography/CT (4DPET/CT) and the linear accelerator (linac), respectively. Generally, identical respiratory monitoring systems are used for 4DCT, 4DPET/CT, and linac. However, different systems are sometimes used in combination because the accessibility of the respiratory monitoring systems may differ by manufacturer. The combined use of different respiratory monitoring systems in phase-based gating is of concern because the differences in the timing of tags (end-respiration signals algorithmically determined by the respiratory monitoring system), defined by the two systems, may result in phase differences, The purpose of this study is to estimate this difference and evaluate its effect on 4DCT data. METHODS Ten patients (seven men and three women) with a median age of 75 yr (range: 57-84 yr) were treated by gated stereotactic body radiation therapy between April and December 2009. Two types of respiratory monitoring systems--RPM (Varian Medical Systems) and AZ-733V (Anzai MEDICAL)--were placed on the abdominal surface of the patients, and the respiratory signals were acquired by both systems. The relationship between the amplitude peak and the tag obtained by each respiratory system was analyzed for each patient. Further, the 4DCT images were reconstructed by using the signals obtained from both the RPM and the AZ-733V systems, and the tumor volumes and the tumor centroid positions in the craniocaudal plane were analyzed for each patient. RESULTS The correlation factor between the respiratory signals from the RPM system and AZ-733V system was 0.990 (range: 0.940-0.994). The amplitude peak of the RPM system corresponded well with that of the AZ-733V system. The median +/- standard deviation of the phase difference for all the patients ranged from -4.3 +/- 7.1% to 3.5 +/- 2.2%. In the case of some patients, differences were noted between the two systems in the estimation of the tumor centroid position and tumor shape. CONCLUSIONS The estimation of the position of the tumor centroid and tumor shape may vary with the use of different respiratory monitoring systems. This implies that it is preferable to use the same respiratory monitoring system with 4DCT, 4DPET-CT, and linac.

High-dose-rate brachytherapy as monotherapy for prostate cancer: technique, rationale and perspective

High-dose-rate (HDR) brachytherapy as monotherapy is a comparatively new brachytherapy procedure for prostate cancer. Although clinical results are not yet mature enough, it is a highly promising approach in terms of potential benefits for both radiation physics and radiobiology. In this article, we describe our technique for monotherapeutic HDR prostate brachytherapy, as well as the rationale and theoretical background, with educational intent.

Monotherapeutic high-dose-rate brachytherapy for prostate cancer: A dose reduction trial

PURPOSE To report preliminary results of our second regimen with 45.5 Gy/7 fractions aiming to reduce toxicity, compared with our first regimen with 54 Gy/9 fractions, using high-dose-rate (HDR) brachytherapy as monotherapy for prostate cancer. MATERIALS AND METHODS From 2005 through 2010, 63 patients with localized prostate cancer were treated with HDR brachytherapy alone in 45.5 Gy/7 fractions for 4 days. Thirty-four patients were considered as intermediate-risk and 29 as high-risk. Thirty-seven patients also received neoadjuvant and/or adjuvant hormonal therapy. Biologically effective dose assuming α/β=1.5 Gy (BED₁.₅) was reduced from 270 Gy to 243 Gy, and BED₃.₀ from 162 Gy to 144 Gy, compared to previous 54 Gy/9 fractions for 5 days. RESULTS Median follow-up time was 42 months (range 13-72). Grade 2 acute toxicities occurred in six (9.5%), late toxicities in five (7.9%) patients, and Grade 3 or higher in none. Grade 2 late gastrointestinal toxicity rate was 1.6%, compared with 7.1% for the 54 Gy regimen. Three-year PSA failure-free rates for intermediate- and high-risk patients were 96% and 90%, which were comparable to 93% and 85% for the 54 Gy regimen. CONCLUSIONS Compared to the 54 Gy/9 fractions regimen, dose-reduced regimen of 45.5 Gy/7 fractions using HDR brachytherapy as monotherapy preliminarily showed an equivalent or lower incidence rate for acute and late toxicities without compromising the excellent PSA failure-free rate. Further studies with more patients and longer follow-up are warranted.

Source strength assay of iodine-125 seeds sealed within sterile packaging.

Early‐stage prostate cancer is widely treated by iodine‐125 (I‐125) seed implantation. While quality assurance methods are in place to assure consistency in I‐125 seed source strength, current methods involve the breaking of the sterilization package, raising issues concerning sterility and time limitations. The purpose of this study was to develop a method of characterizing the total source strength of I‐125 seeds within a cartridge that has been sealed within a sterilization package and to evaluate the probability of detecting an out‐of‐calibration seed (aberrant seed). We defined a protocol to determine the ability of a well‐type ionization chamber to detect aberrant I‐125 seeds within a cartridge sealed in the sterilization package. A novel jig for a well‐type ionization chamber was designed to accommodate the sterilization package. One seed was chosen randomly from two cartridges containing five or 15 seeds (0.544 U source strength) and was exchanged with aberrant seeds of six different source strengths. The source strength was measured at each position within the cartridge. The results indicated that the response of the well chamber was sensitive to changes in the aberrant seed position within the cartridge and the source strength of the aberrant seed. The correlation coefficient between single seed and batch assay results was high (0.998). A novel jig and a measurement method using a well ionization chamber were developed, which allowed for a batch assay characterization of the total source strength of I‐125 seeds within a cartridge sealed within sterilization package. This method is simple, time‐saving, and offers greater practical application. PACS number: D6.20.Dk

Curtailing patient-specific IMRT QA procedures from 2D dose error distribution

A patient-specific quality assurance (QA) test is conducted to verify the accuracy of dose delivery. It generally consists of three verification processes: the absolute point dose difference, the planar dose differences at each gantry angle, and the planar dose differences by 3D composite irradiation. However, this imposes a substantial workload on medical physicists. The objective of this study was to determine whether our novel method that predicts the 3D delivered dose allows certain patient-specific IMRT QAs to be curtailed. The object was IMRT QA for the pelvic region with regard to point dose and composite planar dose differences. We compared measured doses, doses calculated in the treatment planning system, and doses predicted by in-house software. The 3D predicted dose was reconstructed from the per-field measurement by incorporating the relative dose error distribution into the original dose grid of each beam. All point dose differences between the measured and the calculated dose were within ±3%, whereas 93.3% of them between the predicted and the calculated dose were within ±3%. As for planar dose differences, the gamma passing rates between the calculated and the predicted dose were higher than those between the calculated and the measured dose. Comparison and statistical analysis revealed a correlation between the predicted and the measured dose with regard to both point dose and planar dose differences. We concluded that the prediction-based approach is an accurate substitute for the conventional measurement-based approach in IMRT QA for the pelvic region. Our novel approach will help medical physicists save time on IMRT QA.

Neutron intensity monitor with activation foil for p-Li neutron source for BNCT--Feasibility test of the concept.

Proton-lithium (p-Li) reaction is being examined worldwide as a candidate nuclear production reaction for accelerator based neutron source (ABNS) for BNCT. In this reaction, the emitted neutron energy is not so high, below 1 MeV, and especially in backward angles the energy is as low as about 100 keV. The intensity measurement was thus known to be difficult so far. In the present study, a simple method was investigated to monitor the absolute neutron intensity of the p-Li neutron source by employing the foil activation method based on isomer production reactions in order to cover around several hundreds keV. As a result of numerical examination, it was found that (107)Ag, (115)In and (189)Os would be feasible. Their features found out are summarized as follows: (107)Ag: The most convenient foil, since the half life is short. (115)In: The accuracy is the best at 0°, though it cannot be used for backward angles. And (189)Os: Suitable nuclide which can be used in backward angles, though the gamma-ray energy is a little too low. These would be used for p-Li source monitoring depending on measuring purposes in real BNCT scenes.

Impact of different Ir-192 source models on dose calculations in high-dose-rate brachytherapy

Highlights • In HDR brachytherapy, the geometry of the radioactive source is sometimes updated.• Some institutions use a different source model for the dose calculation and treatment.• The effects of this discrepancy were examined for four types of treatment plans.• The impact of source models depended on the types of treatment plan, patients, and dose index.

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

Abstract 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.

Case report of a dose-volume histogram analysis of rib fracture after accelerated partial breast irradiation: interim analysis of a Japanese prospective multi-institutional feasibility study

We initiated the first multi-institutional prospective study of accelerated partial breast irradiation for early breast cancer in Japan. Our early clinical results showed that the treatment methods were technically reproducible between institutions and showed excellent disease control at a median follow-up of 26 months in our previous report. At present, total 46 patients from six institutions underwent the treatment regimen from October 2009 to December 2011, and the median follow-up time was 60 months (range, 57-67 months). In 46 patients, we experienced one patient who had rib fracture as a late complication. The dose-volume histogram (DVH) result of this patient was analyzed. The D0.01cc, D0.1cc, and D1cc values of the patient were 913, 817, and 664 cGy per fraction, respectively. These values were the highest values in 46 patients. The average D0.01cc, D0.1cc, and D1cc values of the other 45 patients were 546, 500, and 419, respectively, cGy per fraction. From this result, DVH values showing high-dose irradiated volume (D0.01cc, D0.1cc, and D1cc) seem to be a good predictive factor of rib fracture for accelerated partial breast irradiation. However, further investigation is necessary because of the small number of patients investigated.

High‐dose rate intracavitary brachytherapy pretreatment dwell position verification using a transparent applicator

Abstract Purpose The major errors in HDR brachytherapy are related to treatment distance, almost all of which are caused by incorrect applicator information. The aim of this study is to propose a quick pretreatment verification method to evaluate channel length and dwell position with a transparent applicator, which, in addition, is suitable as an education tool to assist in the understanding of the applicator structure. Methods A transparent applicator model was fabricated using a three‐dimensional printer and transparent resin. Its aim is to be a replica of a real gynecological applicator. The pretreatment verification is performed by observing the planned dwell positions of a check cable inside a transparent applicator. A digital camera acquired images and the dwell positions of the radioactive source and check cable were evaluated by comparing them with respect to the theoretical dwell positions marked by the proper x‐ray marker. The potential effectiveness of verification using a transparent applicator was also evaluated using brachytherapy events reported in the literature. Results The transparent applicator closely resembles the real applicator in shape and had an error of less than 0.2 mm. The average dwell position displacement between the radioactive source and check cable was 0.4 mm. The analysis of brachytherapy events showed that channel‐length, dwell‐position, and step‐size errors made up 50% of all events, but affected 64% of all patients. Conclusions The transparent applicator model enables a noninvasive, repeatable verification of the channel length and dwell positions to be performed before treatment. This verification has the potential to help prevent common errors in treatment delivery. In addition, the transparent applicator model can be used as a teaching tool to help clinicians understand the operation of the applicator, lowering the risk of events.