Yu Kumazaki

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.

Guidelines for respiratory motion management in radiation therapy

Respiratory motion management (RMM) systems in external and stereotactic radiotherapies have been developed in the past two decades. Japanese medical service fee regulations introduced reimbursement for RMM from April 2012. Based on thorough discussions among the four academic societies concerned, these Guidelines have been developed to enable staff (radiation oncologists, radiological technologists, medical physicists, radiotherapy quality managers, radiation oncology nurses, and others) to apply RMM to radiation therapy for tumors subject to respiratory motion, safely and appropriately.

Validation of Nomogram-based Prediction of Survival Probability after Salvage Re-irradiation of Head and Neck Cancer

OBJECTIVE Treatment outcomes after salvage re-irradiation in patients with recurrent head and neck cancer vary widely due to heterogeneous patient characteristics, and it is difficult to evaluate optimal re-irradiation schedules. This study aimed to validate a nomogram, originally developed by Tanvetyanon et al., used to predict the survival probability of patients with recurrent head and neck cancer after re-irradiation. METHODS Twenty-eight patients with recurrent head and neck cancer who underwent salvage re-irradiation between June 2007 and November 2011 were evaluated. The median total dose used for initial radiotherapy was 60 Gy (range, 22-72). Re-irradiation sites included the nasopharynx or Rouvieres node (n = 14), external ear (n = 4), neck lymph node (n = 3) and other sites (n = 7). Overall survival after re-irradiation was calculated using the Kaplan-Meier method, and the 2-year survival probability was estimated using Tanvetyanons nomogram. RESULTS Twenty-two patients were treated with stereotactic body radiotherapy using a median total dose of 30 Gy (range, 15-40) in 1-7 fractions and six patients were treated with conventional external beam radiotherapy using 45 Gy (range, 23.4-60) in 10-30 fractions. The 2-year overall survival was 21.7% (95% confidence interval: 9.3-41.3), and the 2-year survival probability was 16.8% (95% confidence interval: 9.9-23.6). The 2-year overall survival in 20 patients with unfavorable prognosis (median 2-year survival probability, 5.5%) and in 8 patients with favorable prognosis (median 2-year survival probability, 45%) were 11.0 and 45.7%, respectively (P = 0.05). CONCLUSIONS Our findings show that Tanvetyanons nomogram accurately estimates the survival probability in patients with recurrent head and neck cancer after re-irradiation.

Japanese Structure Survey of High-precision Radiotherapy in 2012 Based on Institutional Questionnaire about the Patterns of Care

OBJECTIVE The purpose of this study was to clarify operational situations, treatment planning and processes, quality assurance and quality control with relevance to stereotactic radiotherapy, intensity-modulated radiotherapy and image-guided radiotherapy in Japan. METHODS We adopted 109 items as the quality indicators of high-precision radiotherapy to prepare a questionnaire. In April 2012, we started to publicly open the questionnaire on the website, requesting every institution with radiotherapy machines for response. The response ratio was 62.1% (490 out of 789 institutions responded). RESULTS Two or more radiotherapy technologists per linear accelerator managed linear accelerator operation in ∼90% of the responded institutions while medical physicists/radiotherapy quality managers were engaged in the operation in only 64.9% of the institutions. Radiotherapy certified nurses also worked in only 18.4% of the institutions. The ratios of the institutions equipped for stereotactic radiotherapy of lung tumor, intensity-modulated radiotherapy and image-guided radiotherapy were 43.3, 32.6 and 46.8%, respectively. In intensity-modulated radiotherapy planning, radiation oncologists were usually responsible for delineation while medical physicists/radiotherapy quality managers or radiotherapy technologists set up beam in 33.3% of the institutions. The median time required for quality assurance of intensity-modulated radiotherapy at any site of brain, head and neck and prostate was 4 h. Intensity-modulated radiotherapy quality assurance activity had to be started after clinical hours in >60% of the institutions. CONCLUSIONS This study clarified one major issue in the current high-precision radiotherapy in Japan. A manpower shortage should be corrected for high-precision radiotherapy, especially in the area relevant to quality assurance/quality control.

The use of trans-applicator intracavitary ultrasonography in brachytherapy for cervical cancer: phantom study of a novel approach to 3D image-guided brachytherapy

Purpose To assess the feasibility of applying trans-applicator intracavitary ultrasonography to image-guided brachytherapy for cervical cancer. Material and methods For this experiment, a phantom was created and included a polyethylene tube, intended to simulate a tandem applicator, which was inserted into chicken meat and embedded in agar, along with magnetic resonance imaging (MRI)-compatible ovoid applicators. Three-dimensional images of the phantom were obtained using computed tomography (CT), MRI (T2-weighted), and intracavitary ultrasonography sectional images acquired at 1 mm slice intervals. Intracavitary ultrasonography images were acquired from within the simulated tandem applicator using a radial transducer. Magnetic resonance imaging and intracavitary ultrasonography images were manually registered onto CT images. The chicken meat was contoured as the target volume independently on the CT, MRI, and intracavitary ultrasonography images, and the Dice similarity coefficient was used to compare the target volumes. The dose distributions of a sample brachytherapy plan were also evaluated. Results Computed tomography, MRI, and intracavitary ultrasonography all visualized the three-dimensional phantom volumes. Intracavitary ultrasonography images depicted the meat with high echoic signals and a border clearly distinguishable from the surrounding agar. The Dice similarity coefficient values for the target volumes on CT vs. MRI, CT vs. intracavitary ultrasonography, and MRI vs. intracavitary ultrasonography were 0.966, 0.965, and 0.971, respectively, indicating similar contouring with the three modalities. Among the modalities, the differences in D50, D90, D98, and D100 values were 1.8%, 2.9%, 3.7%, and 2.9%, respectively. Conclusions Three-dimensional reconstructed trans-applicator intracavitary ultrasonographic images clearly depicted meat tissue within the phantom, and could thus be used for brachytherapy planning. This study proves the concept of trans-applicator intracavitary ultrasonography for intracavitary brachytherapy. Further research such as development of intracavitary ultrasonography system, 3D reconstruction method, ultrasonography-compatible applicators, and ultrasonography-based target concept is warranted to assess the potential clinical application.

SU-E-T-80: Development of IMRT Postal Audit Phantom Using Radiophotoluminescence Glass Dosimeter

Purpose: The purpose of this study is to develop IMRT postal audit phantom using radiophotoluminescence glass dosimeter, and to report initial experiences of the phantom. Method and Materials:We developed the IMRT postal audit phantom. The phantom can be inserted with both RPL glass dosimeter, GD‐302M (Asahi Techno Glass) for point dose verification and Radiochromic film, EBT2 (ISP) for relative planar dose verification. In the dedicated phantom, RPL glass dosimeter can be placed in 4 positions corresponding to target and 1 position to OAR. The EBT2 film can be inserted on the central transverse plane in the phantom. The phantom was made of water substitute material, Tough Water WE‐211 (Kyoto kagaku). for the initial experiences, 7 fields segmental MLCIMRT was planned with XiO (Elekta) using 6 & 10 MV from Clinac iX‐S. In addition, to evaluate the measurement accuracy of RPL glass dosimeter, point doses with ionization chamber (PTW 30013 Farmer type and PTW 31016 Pinpoint 3D) were measured under the same conditions. Results: Differences between the point dose with RPL glass dosimeter and that with Pinpoint 3D chamber agreed within 2% at all positions (high and low dose regions). Point dose differences between with Farmer chamber and with Pinpoint 3D chamber agreed within 1% at target (high dose region). At OAR (low dose and steep dose gradient region), however, the dose difference was exceeded by 5%. This is due to volume averaging effect of Farmer chamber.Conclusion: Feasibility study of IMRT postal audit phantom was performed. The measurement dose with RPL glass dosimeter was good agreement with Pinpoint 3D ionization chamber. Therefore, the dedicated phantom using RPL glass dosimeter shows considerable potential for the IMRT postal audit. To establish IMRT postal audit in Japan, we are starting dummy run now.

An end-to-end postal audit test to examine the coincidence between the imaging isocenter and treatment beam isocenter of the IGRT linac system for Japan Clinical Oncology Group (JCOG) clinical trials

PURPOSE The aim of this study was to develop an end-to-end postal audit test to examine the coincidence between the imaging isocenter and treatment beam isocenter of the image guided radiotherapy (IGRT) linac system for Japan Clinical Oncology Group (JCOG) trials, as a part of IGRT credentialing of institutions participating in JCOG trials. METHODS We developed an end-to-end postal audit test to verify radiation positional errors associated with IGRT techniques. This test is intended for simulating a clinical IGRT flow and uses a static cubic phantom measuring 15 × 15 × 15 cm3 and weighing approximately 3.4 kg. The phantom has four gold fiducial markers and a spherical dummy target for setup, with known shift values from the phantom center. Two pairs of Gafchromic RTQA2 films were inserted 5 mm from the phantoms anterior-posterior and right-left surfaces. Radiation positional errors at the isocenter were determined by analyzing the center of the radiation field on the films and the known shift values of the dummy target. The test was performed on 47 IGRT devices at 35 institutions. RESULTS Radiation positional errors were within acceptance levels (1 mm/1°) for 42 IGRT devices (89.4%) in the first check. Median time to complete IGRT credentialing was 11.5 days. This audit method was applicable for any radiotherapy machine with an IGRT device. CONCLUSIONS A postal audit test to verify radiation positional errors for JCOG trials was successfully developed. In the postal audit, all but one institution passed this credentialing item within two trials.

Dosimetric comparison of three-dimensional conformal radiotherapy versus volumetric-arc radiotherapy in cervical cancer treatment: applying the central-shielding principle to modern technology

Abstract This study evaluated the feasibility of applying volumetric-arc radiotherapy (VMAT) in standard curative radiotherapy for non-bulky cervical cancer using the central-shielding principle. Whole-pelvis irradiation of 20 Gy and central-shielding pelvis irradiation of 30 Gy, both in 2 Gy fractions, were created using 3D conformal radiotherapy (3DCRT) with a standard midline block or VMAT. Composite dose distributions and DVH parameters were compared first in a simple phantom model and then in 10 clinical cases of Stage I–II cervical cancer. Whole-pelvis clinical target volumes (CTVs) were created from published guidelines for primary disease and lymph node regions, and CTVs for central-shielding irradiation were created by subtracting uterus corpus and 4 cm-wide regions centered at the cervical canal and vagina. In a phantom model, VMAT provided adequate dose coverage to the PTVs without excessive doses to the rectum or bladder compared with the 3DCRT plan. In the clinical cases, VMAT plans resulted in slightly but significantly better coverage of PTVs. The DVH parameters for the rectum and bladder were equivalent or lower for VMAT plans compared with the 3DCRT plans. In the bowel, V30Gy, V40Gy, and V50Gy were significantly lower in VMAT plans compared with in the 3DCRT plans (47.6% vs 61.0%, 29.8% vs 56.2% and 6.8% vs 21.1%, respectively). Based on these results, VMAT may be used in external-beam radiotherapy for early-stage cervical cancer by adopting the principle of central-shielding pelvis irradiation. Furthermore, VMAT is likely to reduce doses to the small bowel and may reduce gastrointestinal toxicities for these patients.

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.

SU-E-T-254: Development of a HDR-BT QA Tool for Verification of Source Position with Oncentra Applicator Modeling.

Purpose: To develop a High Dose Rate Brachytherapy (HDR-BT) quality assurance (QA) tool for verification of source position with Oncentra applicator modeling, and to report the results of radiation source positions with this tool. Methods: We developed a HDR-BT QA phantom and automated analysis software for verification of source position with Oncentra applicator modeling for the Fletcher applicator used in the MicroSelectron HDR system. This tool is intended for end-to-end tests that mimic the clinical 3D image-guided brachytherapy (3D-IGBT) workflow. The phantom is a 30x30x3 cm cuboid phantom with radiopaque markers, which are inserted into the phantom to evaluate applicator tips and reference source positions; positions are laterally shifted 10 mm from the applicator axis. The markers are lead-based and scatter radiation to expose the films. Gafchromic RTQA2 films are placed on the applicators. The phantom includes spaces to embed the applicators. The source position is determined as the distance between the exposed source position and center position of two pairs of the first radiopaque markers. We generated a 3D-IGBT plan with applicator modeling. The first source position was 6 mm from the applicator tips, and the second source position was 10 mm from the first source position. Results: All source positions were consistent with the exposed positions within 1 mm for all Fletcher applicators using in-house software. Moreover, the distance between source positions was in good agreement with the reference distance. Applicator offset, determined as the distance from the applicator tips at the first source position in the treatment planning system, was accurate. Conclusion: Source position accuracy of applicator modeling used in 3D-IGBT was acceptable. This phantom and software will be useful as a HDR-BT QA tool for verification of source position with Oncentra applicator modeling.