Factors Affecting Prostate Displacement During Volumetric Modulated Arc Therapy in Prone Position After High-Dose-Rate Brachytherapy for Prostate Cancer.

Purpose: In irradiating the prostate and pelvic lymph node regions, registration based on bony structures matches the pelvic lymph node regions but not necessarily the prostate position, and it is important to identify factors that influence prostate displacement. Therefore, we investigated factors influencing prostate displacement during volumetric modulated arc therapy after single-fraction high-dose-rate brachytherapy (HDR-BT) for prostate cancer and the trends in displacement for each fraction. Methods and Materials: Seventy patients who underwent pelvic volumetric modulated arc therapy of 46 Gy in the prone position 15 days after 13 Gy HDR-BT were included. Prostate displacement relative to bony structures was calculated using cone beam computed tomography. Systematic error (SE) and random error (RE) were evaluated in the right-left (RL), craniocaudal (CC), and anteroposterior (AP) directions. The association with clinical and anatomic factors on the planning computed tomography or magnetic resonance imaging was analyzed. Prostate volume change (PVC) was defined as the volume change at 2 days after HDR-BT. Displacement trends were individually examined from the first to 23rd fractions. Results: The mean SE in the RL, CC, and AP directions was -0.01 mm, -2.34 mm, and -0.47 mm, respectively. The root mean square of the RE in the RL, CC, and AP directions was 0.44 mm, 1.14 mm, and 1.10 mm, respectively. SE in the CC direction was independently associated with bladder volume (P = .021, t statistic = 2.352) and PVC (P < .001, t statistic = -8.526). SE in the AP direction was independently associated with bladder volume (P = .013, t statistic = -2.553), PVC (P < .001, t statistic = 5.477), and rectal mean area (P = .008, t statistic = 2.743). RE in the CC direction was independently associated with smoking (P = .035). RE in the AP direction was associated with PVC (P = .043). Gradual displacement caudally and posteriorly occurred during the irradiation period. Conclusions: Anatomic characteristics of the bladder, rectum, and prostate predict SE. Smoking and PVC predict RE. In particular, whether PVC is ≥140% affects setting internal margins.

Impact of pulse duration alterable laser ureterorenoscopic lithotripsy for upper urinary tract calculi.

To assess the effectiveness of a pulse duration alterable Holmium-YAG (Ho:YAG) laser on the stone-free rate (SFR) compared to a conventional pulse duration fixed laser after ureterorenoscopic lithotripsy (URSL). The medical records from patients with upper urinary tract calculi of ≥ 9 mm and < 30 mm were retrospectively investigated. URSL using a conventional Ho:YAG Laser (group C) or a pulse duration alterable Ho:YAG system (group A) was included. In total, 228 and 188 patients were enrolled in groups C and A, respectively. A 272 µm optical core bare-ended, reusable laser fiber was used, and the laser system was set to a standard 0.8 J and 10 Hz (8 W of average power) in both groups. URSL adopts active fragmentation using an extraction approach. SF was defined as the complete absence of stone fragments on computed tomography (CT) 1-2 months after URSL. Sex, BMI, stone length, stone volume, stone density, and the number of patients with positive preoperative urine cultures were not significantly different between the groups. However, age, rate of preoperative febrile urinary tract infection (fUTI), and pre-stenting were significantly higher in group A, and the operative times and incidence of postoperative fUTI were comparable. The SFRs were 71.5% and 80.3% in groups C and A, respectively (P = 0.035). Multivariate logistic regression revealed that the use of conventional laser was associated with non-SF (odds ratio [OR] 1.090, 95% confidence interval [CI] 1.01-1.18, P = 0.040). The present study revealed the superior performance of a pulse duration alterable Ho:YAG laser on the SFR after URSL compared to a conventional pulse duration fixed laser delivery system.

Sensitivity of a bone-equivalent polymer gel dosimeter for measuring the dose to bone during radiation therapy.

Treatment planning systems that use the Monte Carlo algorithm can calculate the dose to the medium (Dm) in non-water-equivalent tissues such as bones. However, Dm cannot be verified using actual measurements; therefore, it is necessary to develop tissue-equivalent dosimeters. In this study, we developed a bone-equivalent polymer gel dosimeter (BPGD) that can measure the dose absorbed by the bone and investigated its sensitivity. The BPGDs were prepared by adding 3.0 mol of calcium hydrogen phosphate dihydrate as a component of bone to an improved dose-sensitive polyacrylamide gelatin and tetrakis hydroxymethyl phosphonium chloride (iPAGAT). One day after preparation, the BPGDs were irradiated with a field size of 15 × 15 cm2 using a 10 MV X-ray beam to evaluate the dose sensitivity, dose-rate dependence, and dose-integration dependence. One day after dose exposure, the BPGDs were scanned using a 0.4 T MRI APERTO Eterna (Hitachi, Tokyo, Japan) to obtain R2 values. The difference between the R2 values of 6 Gy and 0 Gy was up to 5 s-1, and the R2 curve plateaued in the high-dose region. Moreover, the BPGD did not depend on the integration of the dose and dose rates. Therefore, the BPGDs that we developed can determine the radiation dose to bones.

Multi-Institutional Study of End-to-End Dose Delivery Quality Assurance Testing for Image-Guided Brachytherapy Using a Gel Dosimeter.

PURPOSE: To quantify dose delivery errors for high-dose-rate image-guided brachytherapy (HDR-IGBT) using an independent end-to-end dose delivery quality assurance test at multiple institutions. The novelty of our study is that this is the first multi-institutional end-to-end dose delivery study in the world. MATERIALS AND METHODS: The postal audit used a polymer gel dosimeter in a cylindrical acrylic container for the afterloading system. Image acquisition using computed tomography, treatment planning, and irradiation were performed at each institution. Dose distribution comparison between the plan and gel measurement was performed. The percentage of pixels satisfying the absolute-dose gamma criterion was reviewed. RESULTS: Thirty-five institutions participated in this study. The dose uncertainty was 3.6% ± 2.3% (mean ± 1.96σ). The geometric uncertainty with a coverage factor of k = 2 was 3.5 mm. The tolerance level was set to the gamma passing rate of 95% with the agreement criterion of 5% (global)/3 mm, which was determined from the uncertainty estimation. The percentage of pixels satisfying the gamma criterion was 90.4% ± 32.2% (mean ± 1.96σ). Sixty-six percent (23/35) of the institutions passed the verification. Of the institutions that failed the verification, 75% (9/12) had incorrect inputs of the offset between the catheter tip and indexer length in treatment planning and 17% (2/12) had incorrect catheter reconstruction in treatment planning. CONCLUSIONS: The methodology should be useful for comprehensively checking the accuracy of HDR-IGBT dose delivery and credentialing clinical studies. The results of our study highlight the high risk of large source positional errors while delivering dose for HDR-IGBT in clinical practices.

Accuracy of patient setup positioning using surface-guided radiotherapy with deformable registration in cases of surface deformation.

The Catalyst™ HD (C-RAD Positioning AB, Uppsala, Sweden) is surface-guided radiotherapy (SGRT) equipment that adopts a deformable model. The challenge in applying the SGRT system is accurately correcting the setup error using a deformable model when the body of the patient is deformed. This study evaluated the effect of breast deformation on the accuracy of the setup correction of the SGRT system. Physical breast phantoms were used to investigate the relationship between the mean deviation setup error obtained from the SGRT system and the breast deformation. Physical breast phantoms were used to simulate extension and shrinkage deformation (-30 to 30 mm) by changing breast pieces. Three-dimensional (3D) Slicer software was used to evaluate the deformation. The maximum deformations in X, Y, and Z directions were obtained as the differences between the original and deformed breasts. We collected the mean deviation setup error from the SGRT system by replacing the original breast part with the deformed breast part. The mean absolute difference of lateral, longitudinal, vertical, pitch, roll, and yaw, between the rigid and deformable registrations was 2.4 ± 1.7 mm, 1.3 ± 1.2 mm, 6.4 ± 5.2 mm, 2.5° ± 2.5°, 2.2° ± 2.4°, and 1.0° ± 1.0°, respectively. Deformation in the Y direction had the best correlation with the mean deviation translation error (R = 0.949) and rotation error (R = 0.832). As the magnitude of breast deformation increased, both mean deviation setup errors increased, and there was greater error in translation than in rotation. Large deformation of the breast surface affects the setup correction. Deformation in the Y direction most affects translation and rotation errors.

[A Simple Measurement Method for Verifying the Accuracy of the Displayed Dose on an Over-couch-type X-ray Fluoroscopic System].

The purpose of this study was to establish a simple measurement method to verify the accuracy of incident air kerma (Ka, r) and air kerma area product (PKA) displayed on an over-couch-type X-ray fluoroscopy system. A dosimeter was located at the patient entrance reference point, and the irradiation field size was set to 10×10 cm. A lead plate was placed on the couchtop to protect the image receptor, and the duration of fluoroscopy was set to 1 min. The Ka, r was measured with the proposed method and the Japanese Industrial Standards (JIS) method on three X-ray fluoroscopy units of different manufactures. The effect of backscattered X-rays from the lead plate was calculated using Monte Carlo methods. The errors of the displayed Ka, r and PKA to the measured Ka, r and PKA with our proposed method were calculated. There was no significant difference in the measured Ka, r between the proposed method and the JIS method in all units. The effect of backscattered X-ray was ≤0.5%. The errors of displayed Ka, r and PKA to those measured were in the range of 3.4 to 15.7% and -4.1 to 20.3%, respectively, which met the tolerance for accuracy of ±35% in accordance with the JIS method. We found that our proposed method was simple and that the accuracy of measured values was comparable to that of the JIS method.

Incidence and dosimetric predictive factors of late rectal toxicity after low-dose-rate brachytherapy combined with volumetric modulated arc therapy in high-risk prostate cancer at a single institution: Retrospective study.

PURPOSE: The purpose of this study is to investigate the incidence of rectal toxicity and to identify the associated dosimetric predictive parameters after I-125 seed low-dose-rate brachytherapy (LDR-BT) combined with volumetric modulated arc therapy (VMAT) and dose constraints. METHODS AND MATERIALS: In total, 110 patients with high-risk prostate cancer received 110 Gy LDR-BT, followed by 45 Gy VMAT. Rectal toxicity was recorded according to Common Terminology Criteria for Adverse Events v.4.03. The dosimetric factors associated with LDR-BT and VMAT were analyzed to determine their relationship with rectal toxicity. Receiver operating characteristic (ROC) curve analysis was performed for ≥ grade 2 (G2) rectal toxicity prediction. RESULTS: The follow-up duration was 10.1-115.2 months (median 60.5 months). Seven patients had G2 rectal hemorrhage, and none of the patients had grade 3 rectal hemorrhage. In the univariate analysis, the rectal volume receiving 100% of the prescribed dose (rV100) (p < 0.001), the dose covering 2 cc of the rectum (rD2cc) during LDR-BT (p = 0.002), and the combined rD2cc during LDR-BT and VMAT (p = 0.001) were identified as predictors of G2 rectal hemorrhage. In the ROC curve analysis, the cutoff value was 0.46 cc for rV100, 74.0 Gy for rD2cc, and 86.8 GyEQD2 for combined rD2cc. CONCLUSION: Predictors of late ≥ G2 rectal hemorrhage are rV100, rD2cc, and combined rD2cc. The incidence of rectal toxicity is low and acceptable in this setting and is highly dependent on the rectal dose of LDR-BT. The use of higher-quality LDR-BT and VMAT dose constraints may further reduce the rate of rectal hemorrhage.

Effect of an integral quality monitor on 4-, 6-, 10-MV, and 6-MV flattening filter-free photon beams.

PURPOSE: To investigate the effect of an integral quality monitor (IQM; iRT Systems GmbH, Koblenz, Germany) on 4, 6, 10, and 6-MV flattening filter-free (FFF) photon beams. METHODS: We assessed surface dose, PDD20,10 , TPR20,10 , PDD curves, inline and crossline profiles, transmission factor, and output factor with and without the IQM. PDD, transmission factor, and output factor were measured for square fields of 3, 5, 10, 15, 20, 25, and 30 cm and profiles were performed for square fields of 3, 5, 10, 20, and 30 cm at 5-, 10-, and 30-cm depth. RESULTS: The differences in surface dose of all energies for square fields of 3, 5, 10, 15, 20, and 25 cm were within 3.7% whereas for a square field of 30 cm, they were 4.6%, 6.8%, 6.7%, and 8.7% for 4-MV, 6-MV, 6-MV-FFF, and 10-MV, respectively. Differences in PDD20,10 , TPR20,10 , PDD, profiles, and output factors were within ±1%. Local and global gamma values (2%/2 mm) were below 1 for PDD beyond dmax and inline/crossline profiles in the central beam region, respectively. The gamma passing rates (10% threshold) for PDD curves and profiles were above 95% at 2%/2 mm. The transmission factors for 4-MV, 6-MV, 6-MV-FFF, and 10-MV for field sizes from 3 × 3 to 30 × 30 cm2 were 0.926-0.933, 0.937-0.941, 0.937-0.939, and 0.949-0.953, respectively. CONCLUSIONS: The influence of the IQM on the beam quality (in particular 4-MV X-ray has not verified before) was tested and introduced a slight beam perturbation at the surface and build-up region and the edge of the crossline/inline profiles. To use IQM in pre- and intra-treatment quality assurance, a tray factor should be put into treatment planning systems for the dose calculation for the 4-, 6-, 10-, and 6-MV flattening filter-free photon beams to compensate the beam attenuation of the IQM detector.

Evaluation of technical performance of optical surface imaging system using conventional and novel stereotactic radiosurgery algorithms.

The Catalyst HD (C-RAD Positioning AB, Uppsala, Sweden) optical surface imaging (OSI) system is able to manage interfractional patient positioning, intrafractional motion monitoring, and non-contact respiratory gating without x-ray exposure for radiation therapy. In recent years, a novel high-precision surface registration algorithm for stereotactic radiosurgery (SRS algorithm) has been released. This study aimed to evaluate the technical performance of the OSI system using rigid phantoms, by comparing the conventional and SRS algorithms. To determine the system's technical performance, isocenter displacements were calculated by surface image registration via the OSI system using head, thorax, and pelvis rigid phantoms. The reproducibility of positioning was evaluated by the mean value calculated by repeating the registration 10 times, without moving each phantom. The accuracy of positioning was evaluated by the mean value of the residual error, where the 10 offset values given to each phantom were subtracted from the isocenter displacement values. The stability of motion monitoring was evaluated by measuring isocenter drift during 20 min and averaging it over 10 measurements. For the head phantom, all tests were compared with the mask types and algorithms. As a result, for all sites and both algorithms, the reproducibility, accuracy, and stability for translation and rotation were <0.1 mm and <0.1°, <1.0 mm and <1.0°, and <0.1 mm and <0.1°, respectively. In particular, the SRS algorithm had a small absolute error and standard deviation of calculated isocenter displacement, and a significantly higher reproducibility and accuracy than the conventional algorithm (P < 0.01). There was no difference in the stability between the algorithms (P = 0.0280). The SRS algorithm was found to be suitable for the treatment of rigid body sites with less deformation and small area, such as the head and face.

[Improvement Prediction on Contour Deformation Accuracy Using Deformable Image Registration Results Compared to Rigid Image Registration Results].

PURPOSE: The aim of this study was to analyze improvement prediction on contour deformation accuracy using deformable image registration (DIR) results compared to rigid image registration (RIR) results. METHOD: Radiotherapy plans for 31 cases (seven head and neck cases, 10 chest cases, six abdomen cases and eight female pelvis cases) from the privately open database for DIR were used. These cases used at least two radiotherapy plans, and registration was performed using two plans, not only for one case but also for different cases. The DIR and RIR were performed using the DIR software MIM Maestro (MIM software Inc., Cleveland, USA). The registration results for the following organs were analyzed: eye balls, optic nerves, brain stem, spinal cord and right and left parotid glands for head and neck; right and left lungs for chest; liver and right and left kidneys for abdomen; and rectum and bladder for pelvis. Dice similarity coefficient (DSC) for the organs was calculated from the results of RIR and DIR. The improvement in the DSC was observed. RESULTS AND DISCUSSION: DIR improved the DSC values by more than 0.2 for simple shapes, well-defined boundaries and large volumes such as eye balls, brain stem, lungs and liver. The minimum DSC for these organs was approximately 0.7. The improvement in DSC for the organs eye balls, brain stem, lungs and liver had ceiling values 0.95, 0.90, 1.0 and 1.0, respectively. DSC for the spinal cord, parotid gland, bladder and kidney also improved by DIR compared to RIR; however, DIR could not improve the DSC value for rectum compared to RIR because of a large difference in the position, shape and size due to stool and gas.