Development of a phantom for assessing the precision of setup in skin mark-less surface-guided radiotherapy.

BACKGROUND: Surface-guided radiotherapy (SGRT) is adopted by several institutions; however, reports on the phantoms used to assess the precision of the SGRT setup are limited. PURPOSE: The purpose of this study was to develop a phantom to verify the accuracy of the irradiation position during skin mark-less SGRT. METHODS: An acrylonitrile butadiene styrene (ABS) plastic cube phantom with a diameter of 150 mm on each side containing a dummy target of 15 mm and two types of body surface-shaped phantoms (breast/face shape) that could be attached to the cube phantom were fabricated. Films can be inserted on four sides of the cubic phantom (left, right, anterior and posterior), and the center of radiation can be calculated by irradiating the dummy target with orthogonal MV beams. Three types of SGRT using a VOXELAN-HEV600M (Electronics Research&Development Corporation, Okayama, Japan) were evaluated using this phantom: (i) SGRTCT-a SGRT set-up based solely on a computed tomography (CT)-reference image. (ii) SGRTCT + CBCT-a method where cone beam computed tomography (CBCT) matching was performed after SGRTCT. (iii) SGRTScan-a resetup technique using a scan reference image obtained after completing the (ii) step. RESULTS: Both the breast and face phantoms were recognized in the SGRT system without problems. SGRTScan ensure precision within 1 mm/1° for breast and face verification, respectively. All SGRT methods showed comparable rotational accuracies with no significant disparities. CONCLUSIONS: The developed phantom was useful for verifying the accuracy of skin mark-less SGRT position matching. The SGRTScan demonstrated the feasibility of achieving skin-mark less SGRT with high accuracy, with deviations of less than 1 mm. Additional research is necessary to evaluate the suitability of the developed phantoms for use in various facilities and systems. This phantom could be used for postal surveys in the future.

Evaluation of the performance of both machine learning models using PET and CT radiomics for predicting recurrence following lung stereotactic body radiation therapy: A single-institutional study.

PURPOSE: Predicting recurrence following stereotactic body radiotherapy (SBRT) for non-small cell lung cancer provides important information for the feasibility of the individualized radiotherapy and allows to select the appropriate treatment strategy based on the risk of recurrence. In this study, we evaluated the performance of both machine learning models using positron emission tomography (PET) and computed tomography (CT) radiomic features for predicting recurrence after SBRT. METHODS: Planning CT and PET images of 82 non-small cell lung cancer patients who performed SBRT at our hospital were used. First, tumors were delineated on each CT and PET of each patient, and 111 unique radiomic features were extracted, respectively. Next, the 10 features were selected using three different feature selection algorithms, respectively. Recurrence prediction models based on the selected features and four different machine learning algorithms were developed, respectively. Finally, we compared the predictive performance of each model for each recurrence pattern using the mean area under the curve (AUC) calculated following the 0.632+ bootstrap method. RESULTS: The highest performance for local recurrence, regional lymph node metastasis, and distant metastasis were observed in models using Support vector machine with PET features (mean AUC = 0.646), Naive Bayes with PET features (mean AUC = 0.611), and Support vector machine with CT features (mean AUC = 0.645), respectively. CONCLUSIONS: We comprehensively evaluated the performance of prediction model developed for recurrence following SBRT. The model in this study would provide information to predict the recurrence pattern and assist in making treatment strategies.

Evaluation of computed tomography metal artifact and CyberKnife fiducial recognition for novel size fiducial markers.

PURPOSE: This study aimed to compare fiducial markers used in CyberKnife treatment in terms of metal artifact intensity observed in CT images and fiducial recognition in the CyberKnife system affected by patient body thickness and type of marker. METHODS: Five markers, ACCULOC 0.9 mm × 3 mm, Ball type Gold Anchor (GA) 0.28 mm × 10 mm, 0.28 mm × 20 mm, and novel size GA 0.4 mm × 10 mm, 0.4 mm × 20 mm were evaluated. To evaluate metal artifacts of CT images, two types of CT images of water-equivalent gels with each marker were acquired using Aquilion LB CT scanner, one applied SEMAR (SEMAR-on) and the other did not apply this technique (SEMAR-off). The evaluation metric of artifact intensity (MSD ) which represents a variation of CT values were compared for each marker. Next, 5, 15, and 20 cm thickness of Tough Water (TW) was placed on the gel under the condition of overlapping the vertebral phantom in the Target Locating System, and the live image of each marker was acquired to compare fiducial recognition. RESULTS: The mean MSD of SEMAR-off was 78.80, 74.50, 97.25, 83.29, and 149.64 HU for ACCULOC, GA0.28 mm × 10 mm, 20 mm, and 0.40 mm × 10 mm, 20 mm, respectively. In the same manner, that of SEMAR-on was 23.52, 20.26, 26.76, 24.89, and 33.96 HU, respectively. Fiducial recognition decreased in the order of 5, 15, and 20 cm thickness, and GA 0.4 × 20 mm showed the best recognition at thickness of 20 cm TW. CONCLUSIONS: We demonstrated the potential to reduce metal artifacts in the CT image to the same level for all the markers we evaluated by applying SEMAR. Additionally, the fiducial recognition of each marker may vary depending on the thickness of the patient's body. Particularly, we showed that GA 0.40 × 20 mm may have more optimal recognition for CyberKnife treatment in cases of high bodily thickness in comparison to the other markers.

Reproducibility of deep inspiration breath-hold technique for left-side breast cancer with respiratory monitoring device, Abches.

PURPOSE: This study aimed to evaluate the reproducibility of deep inspiration breath-hold (DIBH) using a respiratory control device, Abches, in patients with left-sided breast cancer. MATERIAL AND METHODS: Abches comprises a main body, an indicator panel, and two fulcrums, one each on the chest and abdomen. Forty left side breast cancer patients treated with DIBH using abches were enrolled in this study. For all patients, CT images were taken three times to confirm the target position inside the body and to check the breath-hold reproducibility. Three anatomical points on the nipple, sternum, and heart were selected as measurement points on CT images. After measuring the coordinates, breath-hold reproducibility was defined as the mean of the absolute difference in the coordinates between the three CT images. The maximum differences were also investigated. In addition, the dice similarity coefficient (DSC) was calculated to examine the displacement of the heart volume in detail. Moreover, digitally reconstructed radiographs (DRRs) and linac graphs (LGs) were used to measure the positional accuracy of the chest and heart. RESULTS: The reproducibility in all patients was within 0.75 mm for the nipple, 0.78 mm for the sternum, and 2.18 mm for the heart in each direction. Similarly, the maximum displacements for all patients were within 1.90 mm, 1.69 mm, and 4.75 mm, respectively, in each direction. For heart volume, the average DSC for all cases was 0.93 ± 0.01. The differences between the DRR and LG images were 1.70 ± 1.10 mm and 2.10 ± 1.60 mm, for the chest and heart, respectively. CONCLUSION: Our study showed that DIBH using Abches can be performed with good target reproducibility of less than 3 mm with proper breath-hold practice, whereas the heartbeat-derived reproducibility of the cardiac position is poor and needs to be monitored carefully during treatment simulation.

Anatomy-based prediction method for determining ipsilateral lung doses in postoperative breast radiation therapy assisted by diagnostic computed tomography images.

Background: This study aimed to investigate whether ipsilateral lung doses (ILDs) could be predicted by anatomical indexes measured using diagnostic computed tomography (CT) prior to the planning stage of breast radiation therapy (RT). Materials and methods: The thoracic diameters and the length of lines drawn manually were measured on diagnostic CT images. The parameters of interest were the skin maximum lung distance (sMLD), central lung distance (CLD), Haller index (HI), and body mass index (BMI). Lung dose-volume histograms were created with conformal planning, and the lung volumes receiving 5-40 Gy (V5-V40) were calculated. Linear regression models were used to investigate the correlations between the anatomical indexes and dose differences and to estimate the slope and 95% confidence intervals (CIs). Results: A total of 160 patients who had undergone three-dimensional conformal RT after breast-conserving surgery were included. Univariable analysis revealed that the sMLD (p < 0.001), CLD (p < 0.001), HI (p = 0.002), and BMI (p < 0.001) were significantly correlated with the V20. However, multivariable analysis revealed that only the sMLD (slope: 0.147, p = 0.001, 95% CI: 0.162-0.306) and CLD (0.157, p = 0.005, 0.048-0.266) were strongly correlated with the V20. The p-value for the sMLD was the lowest among the p-values for all indexes, thereby indicating that the sMLD had the best predictive power for ILD. Conclusions: sMLD and CLD are anatomical markers that can be used to predict ILD in whole breast RT. An sMLD > 20.5 mm or a CLD > 24.3 mm positively correlated with a high ILD.

Quantification of image quality of intra-fractional cone-beam computed tomography for arc irradiation with various imaging condition.

BACKGROUND: 3-dimensional intra-cone beam computed tomography (intra-CBCT ) could be a potentially powerful tool for use with arc irradiation such as volumetric modulated arc therapy. The aim of the study was to evaluate the image quality of intra-cone beam computed tomography (intra-CBCT ) for arc irradiation with various imaging condition. MATERIALS AND METHODS: Two types of intra-CBCT imaging techniques were evaluated - intra-fractional CBCT with flattening filtered (FF) beam (intra-FF CBCT ) and that with flattening filter free (FFF) beam (intra-FFF CBCT ). For the intra-MV beams, four different field sizes (2 cm × 2 cm, 5 cm × 5 cm, 10 cm × 10 cm, and 20 cm × 20 cm) were used with dose rates of 500 MU/min and 1600 MU/min, for 6 MV FF and 6 MV FFF, respectively. For all image acquisitions, two rotation angles (full-arc and half-arc) were investigated. Thereafter, the linearity, contrast-to-noise ratio (CNR), and uniformity index (UI) of intra-CBCT image were compared with those of conventional CBCT image. RESULTS: All acquisition conditions had good linearity of the CT value (R2 > 0.99). For CNR, the change rates from conventional CBCT ranged from 0.6-33.7% for a 2 cm × 2 cm beam, whereas that for a 20 cm × 20 cm beam ranged from 62.7-82.3%. Similarly, the UI increased from 1.5% to 7.0% as the field size increased. CONCLUSION: Quality of intra-CBCT image was affected by the field size and acquisition angle. Image quality of intra-CBCT was worse than that of conventional CBCT, but it was better under a smaller field and wider correction angle and would be acceptable for clinical use.

Effect of a hydrogel spacer on the intrafractional prostate motion during CyberKnife treatment for prostate cancer.

The purpose of this study was to evaluate the effect of a hydrogel spacer on intrafractional prostate motion during CyberKnife treatment. The retrospective study enrolled 24 patients (with the hydrogel spacer = 12, without the hydrogel spacer = 12) with two fiducial markers. Regarding intrafractional prostate motion, the offset values (mm) of three axes (X-axis; superior [+] to inferior [-], Y-axis; right [+] to left [-], Z-axis; posterior [+] to anterior [-]) obtained from fiducial markers position between a digitally reconstructed radiographs images and live images in the Target Locating System were used, and extracted from generated log files. The mean values of the offset and each standard deviation were calculated for each patient, and both the groups were compared. For all the patients, a total of 2204 offset values and timestamps (without the hydrogel spacer group: 1065, with the hydrogel spacer group: 1139) were recorded for the X-, Y-, and Z-axes, respectively. The offset values (mean ± standard deviation) for the X-, Y-, and Z-axes were -0.04 ± 0.92 mm, -0.03 ± 0.97 mm (P = 0.66), 0.02 ± 0.51, -0.02 ± 0.49 mm (P = 0.50), and 0.56 ± 0.97 mm, 0.34 ± 1.07 mm (P = 0.14), in patients inserted without or with the hydrogel spacer, respectively. There was no effect of a hydrogel spacer on the intrafractional prostate motion in the three axes during CyberKnife treatment for prostate cancer.

Evaluation of the target dose coverage of stereotactic body radiotherapy for lung cancer using helical tomotherapy: A dynamic phantom study.

AIM: To evaluate the target dose coverage for lung stereotactic body radiotherapy (SBRT) using helical tomotherapy (HT) with the internal tumor volume (ITV) margin settings adjusted according to the degree of tumor motion. BACKGROUND: Lung SBRT with HT may cause a dosimetric error when the target motion is large. MATERIALS AND METHODS: Two lung SBRT plans were created using a tomotherapy planning station. Using these original plans, five plans with different ITV margins (4.0-20.0 mm for superior-inferior [SI] dimension) were generated. To evaluate the effects of respiratory motion on HT, an original dynamic motion phantom was developed. The respiratory wave of a healthy volunteer was used for dynamic motion as the typical tumor respiratory motion. Five patterns of motion amplitude that corresponded to five ITV margin sizes and three breathing cycles of 7, 14, and 28 breaths per minute were used. We evaluated the target dose change between a static delivery and a dynamic delivery with each motion pattern. RESULTS: The target dose difference increased as the tumor size decreased and as the tumor motion increased. Although a target dose difference of <5 % was observed at ≤10 mm of tumor motion for each condition, a maximum difference of -9.94 % ± 7.10 % was observed in cases of small tumors with 20 mm of tumor motion under slow respiration. CONCLUSIONS: Minimizing respiratory movement is recommended as much as possible for lung SBRT with HT, especially for cases involving small tumors.

Comparison of MLC error sensitivity of various commercial devices for VMAT pre-treatment quality assurance.

The purpose of this study was to compare the MLC error sensitivity of various measurement devices for VMAT pre-treatment quality assurance (QA). This study used four QA devices (Scandidos Delta4, PTW 2D-array, iRT systems IQM, and PTW Farmer chamber). Nine retrospective VMAT plans were used and nine MLC error plans were generated for all nine original VMAT plans. The IQM and Farmer chamber were evaluated using the cumulative signal difference between the baseline and error-induced measurements. In addition, to investigate the sensitivity of the Delta4 device and the 2D-array, global gamma analysis (1%/1, 2%/2, and 3%/3 mm), dose difference (1%, 2%, and 3%) were used between the baseline and error-induced measurements. Some deviations of the MLC error sensitivity for the evaluation metrics and MLC error ranges were observed. For the two ionization devices, the sensitivity of the IQM was significantly better than that of the Farmer chamber (P < 0.01) while both devices had good linearly correlation between the cumulative signal difference and the magnitude of MLC errors. The pass rates decreased as the magnitude of the MLC error increased for both Delta4 and 2D-array. However, the small MLC error for small aperture sizes, such as for lung SBRT, could not be detected using the loosest gamma criteria (3%/3 mm). Our results indicate that DD could be more useful than gamma analysis for daily MLC QA, and that a large-area ionization chamber has a greater advantage for detecting systematic MLC error because of the large sensitive volume, while the other devices could not detect this error for some cases with a small range of MLC error.

Rib fracture after stereotactic radiotherapy for primary lung cancer: prevalence, degree of clinical symptoms, and risk factors.

BACKGROUND: As stereotactic body radiotherapy (SBRT) is a highly dose-dense radiotherapy, adverse events of neighboring normal tissues are a major concern. This study thus aimed to clarify the frequency and degree of clinical symptoms in patients with rib fractures after SBRT for primary lung cancer and to reveal risk factors for rib fracture. Appropriate α/ß ratios for discriminating between fracture and non-fracture groups were also investigated. METHODS: Between November 2001 and April 2009, 177 patients who had undergone SBRT were evaluated for clinical symptoms and underwent follow-up thin-section computed tomography (CT). The time of rib fracture appearance was also assessed. Cox proportional hazard modeling was performed to identify risk factors for rib fracture, using independent variables of age, sex, maximum tumor diameter, radiotherapeutic method and tumor-chest wall distance. Dosimetric details were analyzed for 26 patients with and 22 randomly-sampled patients without rib fracture. Biologically effective dose (BED) was calculated with a range of α/ß ratios (1-10 Gy). Receiver operating characteristics analysis was used to define the most appropriate α/ß ratio. RESULTS: Rib fracture was found on follow-up thin-section CT in 41 patients. The frequency of chest wall pain in patients with rib fracture was 34.1% (14/41), and was classified as Grade 1 or 2. Significant risk factors for rib fracture were smaller tumor-chest wall distance and female sex. Area under the curve was maximal for BED at an α/ß ratio of 8 Gy. CONCLUSIONS: Rib fracture is frequently seen on CT after SBRT for lung cancer. Small tumor-chest wall distance and female sex are risk factors for rib fracture. However, clinical symptoms are infrequent and generally mild. When using BED analysis, an α/ß ratio of 8 Gy appears most effective for discriminating between fracture and non-fracture patients.

Long-term experience in quality assurance of on-rail computed tomography systems for image-guided radiotherapy using in-house multifunctional phantoms.

To report the long-term quality assurance (QA) experience of an on-rail computed tomography (CT) system for image-guided radiotherapy using an in-house phantom. An on-rail CT system combining the Elekta Synergy and Canon Aquilion LB was used. The treatment couch was shared by the linear accelerators and CT, and the couch was rotated by 180° when using the on-rail-CT system to ensure that the CT direction was toward the head. All QA analyses were performed by radiation technologists on CBCT or on-rail CT images of the in-house phantom. The CBCT center accuracy from the linac laser, couch rotational accuracy (CBCT center vs. on-rail CT center), horizontal accuracy by CT gantry shift, and remote couch shift accuracy were evaluated. This study reported the QA status of the system during the period 2014-2021. The absolute mean accuracy of couch rotation was 0.4 ± 0.28 mm, 0.44 ± 0.36 mm, and 0.37 ± 0.27 mm in the SI, RL, and AP directions, respectively. Horizontal and remote movement accuracies of the treatment couch were also within 0.5 mm of the absolute mean value. A decrease in the accuracy of couch rotation was also observed due to aging deterioration of related parts caused by the frequent use of couch rotation. The three-dimensional accuracy of on-rail CT systems derived mainly from treatment couches can be maintained within 0.5 mm with appropriate accuracy assurance for at least > 8 years.

Dosimetric comparison of five different radiotherapy treatment planning approaches for locally advanced non-small cell lung cancer with sequential plan changes.

BACKGROUND: The purpose of this study was to compare the dosimetric characteristics of five different treatment planning techniques for locally advanced non-small cell lung cancer (LA-NSCLC) with sequential plan changes. METHODS: A total of 13 stage III NSCLC patients were enrolled in this study. These patients had both computed tomography (CT) images for initial and boost treatment plans. The latter CT images were taken if tumor shrinkage was observed after 2 weeks of treatment. The prescription dose was 60 Gy/30 Fr (initial: 40 Gy/20 Fr, and boost: 20 Gy/10 Fr). Five techniques (forward-planed 3-dimensional conformal radiotherapy [F-3DCRT] on both CT images, inverse-planned 3DCRT [I-3DCRT] on both CT images, volumetric modulated arc therapy [VMAT] on both CT images, F-3DCRT on initial CT plus VMAT on boost CT [bVMAT], and hybrid of fixed intensity-modulated radiotherapy [IMRT] beams and VMAT beams on both CT images [hybrid]) were recalculated for all patients. The accumulated doses between initial and boost plans were compared among all treatment techniques. RESULTS: The conformity indexes (CI) of the planning target volume (PTV) of the five planning techniques were 0.34 ± 0.10, 0.57 ± 0.10, 0.86 ± 0.08, 0.61 ± 0.12, and 0.83 ± 0.11 for F-3DCRT, I-3DCRT, VMAT, bVMAT, and hybrid, respectively. In the same manner, lung volumes receiving >20 Gy (V20Gy ) were 21.05 ± 10.56%, 20.86 ± 6.45, 19.50 ± 7.38%, 19.98 ± 10.04%, and 17.74 ± 7.86%. There was significant improvement about CI and V20Gy for hybrid compared with F-3DCRT (p < 0.05). CONCLUSION: The IMRT/VMAT hybrid technique for LA-NSCLC patients improved target CI and reduced lung doses. Furthermore, if IMRT was not available initially, starting with 3DCRT might be beneficial as demonstrated in the bVMAT procedure of this study.

Real-World Results of Stereotactic Body Radiotherapy for 399 Medically Operable Patients with Stage I Histology-Proven Non-Small Cell Lung Cancer.

Surgery is the standard treatment for stage I non-small cell lung cancer (NSCLC); however, no clear randomized trial demonstrates its superiority to stereotactic body radiotherapy (SBRT) regarding survival. We aimed to retrospectively evaluate the treatment outcomes of SBRT in operable patients with stage I NSCLC using a large Japanese multi-institutional database to show real-world outcome. Exactly 399 patients (median age 75 years; 262 males and 137 females) with stage I (IA 292, IB 107) histologically proven NSCLC (adenocarcinoma 267, squamous cell carcinoma 96, others 36) treated at 20 institutions were reviewed. SBRT was prescribed at a total dose of 48-70 Gy in 4-10 fractions. The median follow-up period was 38 months. Local progression-free survival rates were 84.2% in all patients and 86.1% in the T1, 78.6% in T2, 89.2% in adenocarcinoma, and 70.5% in squamous cell subgroups. Overall 3-year survival rates were 77.0% in all patients: 90.7% in females, 69.6% in males, and 41.2% in patients with pulmonary interstitial changes. Fatal radiation pneumonitis was observed in two patients, all of whom had pulmonary interstitial changes. This real-world evidence will be useful in shared decision-making for optimal treatment, including SBRT for operable stage I NSCLC, particularly in older patients.

Evaluation of the detection accuracy of set-up for various treatment sites using surface-guided radiotherapy system, VOXELAN: a phantom study.

The purpose of this study is to evaluate the detection accuracy of a 3-dimensional (3D) body scanner, VOXELAN, in surface-guided radiotherapy (SGRT) of each part of the human body using a whole-body human phantom. We used A Resusci Anne was used as the whole-body phantom. The detection accuracy of VOXELAN in a radiotherapy treatment room with a linear accelerator (LINAC) was evaluated for two reference images: reconstruction of the planning computed tomography (CT) image (CT reference) and scanning by VOXELAN before the treatment (scan reference). The accuracy of the translational and rotational directions was verified for four treatment sites (open face shell, breast, abdomen, and arm), using the magnitude of the 6D robotic couch movement as the true value. Our results showed that the detection accuracy improved as the displacement from the reference position decreased for all the sites. Using the scan reference, the average accuracy of the translational and rotational axes was within 1.44 mm and 0.41°, respectively, for all sites except the arms. Similarly, using the CT reference, the average accuracy was within 2.45 mm and 1.35°, respectively. Additionally, it was difficult for both reference images to recognize misalignment of the arms. In conclusion we discovered that VOXELAN achieved a high detection accuracy for the head with an open face shell, chest, and abdomen, indicating that the system is useful in a clinical setting. However, it is necessary to pay attention to location matching for areas with few features, such as surface irregularities and potential errors, when the reference image is created from CT.

Minimum Required Interval Between Hydrogel Spacer Injection and Treatment Planning for Stereotactic Body Radiation Therapy for Prostate Cancer.

PURPOSE: The present study evaluated the short-term characteristics (<3 days) of a hydrogel spacer from the time of injection during stereotactic body radiation therapy (SBRT) for prostate cancer. METHODS AND MATERIALS: Fifteen patients treated with SBRT via the CyberKnife system (36.25 Gy/5 fractions) were enrolled in this retrospective study. Two magnetic resonance (MR) images were obtained with a hydrogel spacer: one on a computed tomography (CT) simulation day (MR pretreatment [MRpre]) and the other on the last treatment day (MR posttreatment [MRpost]). Two medical physicists contoured the hydrogel spacer on each MR image. The changes of the shapes and the volume for the hydrogel spacer between 2 MR images were evaluated. RESULTS: The median period between hydrogel spacer injection and CT simulation was 1 day (range, 1-9 days). The median period between CT simulation and the last treatment was 17 days (range, 14-25 days). Regarding the volume change of the hydrogel spacer, the 2 observers observed significant differences between the volumes of the hydrogel spacer on the MRpre and MRpost. However, the average volume difference between them was less than 1 cm3. The average dice similarity coefficient between the MRpre and MRpost to compare the shape was more than 0.83. In addition, no clear correlation was confirmed between the volume change and the period from hydrogel spacer injection to CT simulation. CONCLUSIONS: A single day is an acceptable interval between hydrogel spacer injection and treatment planning for SBRT for prostate cancer.

Dosimetric Effects of Differences in Multi-Leaf Collimator Speed on SBRT-VMAT for Central Lung Cancer Patients.

Purpose: We aimed to investigate the effects of different multi-leaf collimator (MLC) speed constraints in volumetric modulated radiotherapy (VMAT) on the robustness of treatment plans for central lung cancer patients. Method and Materials: Twenty patients with central lung tumor who underwent stereotactic body radiotherapy (SBRT) with the VMAT technique at our hospital were included in this retrospective study. The reference plans were created with 3 different MLC speed constraints (Plan A: 0.1 cm/deg., Plan B: 0.3 cm/deg., and Plan C: 0.5 cm/deg.) with a 50-Gy/8Fr, planning target volume (PTV) D95% prescription. In each of these plans, setup errors from 1 to 5 mm were intentionally added in the direction of the central organ at 1-mm intervals (300 plans [20 cases × 3 MLC speeds × 5 error plans] were created in total). Each plan was then calculated by the same beam conditions as each reference plan. The actual average MLC speed and dose difference between the reference plan and the error-added plan were then calculated and compared among the 3 MLC speeds. Results: In the reference plans, the actual average MLC speeds were 0.25 ± 0.04, 0.34 ± 0.07, and 0.39 ± 0.12 cm/deg. for Plan A, Plan B, and Plan C, respectively (P < .05). For PTV and OARs, many dose indices tended to improve as the MLC speed increased, while no significant differences were observed among the 3 MLC speed constraints. However, in assessments of robustness, no significant differences in dose difference were observed among the 3 MLC speed constraints for most of the indices. Conclusions: When necessary, increasing the MLC speed constraint with a priority on improving the quality of the dose distribution is an acceptable approach for central lung cancer patients.

Impact of Systemic Autoimmune Diseases on Treatment Outcomes and Radiation Toxicities in Patients with Stage I Non-Small Cell Lung Cancer Receiving Stereotactic Body Radiation Therapy: A Matched Case-Control Analysis.

We aimed to evaluate the impact of systemic autoimmune diseases (SADs) on treatment outcomes and radiation toxicities following stereotactic body radiation therapy (SBRT) for stage I non-small cell lung cancer (NSCLC). We queried an institution-based database on patients with SADs treated with SBRT for lung cancer between 2001 and 2016 (SAD group). Each patient was matched to three controls without SADs. The primary outcomes of interest were the overall survival (OS) and local control rate (LCR). The secondary outcomes were radiation toxicities of grades ≥2 (≥G2). Twelve patients with SADs were matched to 36 controls. The median follow-up duration was 3.6 years. There was a significant intergroup difference in the OS (hazard ratio [HR]: 4.11, 95% confidence incidence [CI]: 1.82−9.27, p < 0.001) and LCR (HR: 15.97, 95% CI: 2.89−88.29, p < 0.001). However, there were no significant intergroup differences in the odds of acute (odds ratio [OR]: 0.38, 95% CI: 0.02−8.91, p = 0.550) and late (OR: 2.20, 95% CI: 0.32−15.10, p = 0.422) ≥G2 radiation pneumonitis. No other ≥G2 toxicities were identified. In conclusion, although radiation toxicities are not enhanced by SADs, SADs are risk factors of poor prognosis following SBRT for stage I NSCLC.

Spacers with boluses applied to various sites of oral squamous cell carcinoma: Technical note and retrospective case series.

The present report describes a case series in which spacers with boluses were used at various sites in the oral cavity to enhance the therapeutic effect of radiation therapy in oral squamous cell carcinoma. In radiotherapy, the surface dose is reduced due to the build-up region of X-rays. In the present study, a bolus was used to complement the build-up region and increase the surface dose effect. A total of 7 patients with oral cancer from a primary care hospital underwent radiation therapy using spacers and added boluses to improve the surface dose effect. The spacer was made from a plastic splint and the bolus was connected to the splint with a quick self-curing resin. There were no complaints of pain or adverse events from the patients while wearing the intraoral splint. A total of 2 of the 7 patients were subsequently confirmed as having progressed disease, and the remaining 5 are currently being managed following a complete response to treatment. The spacers used at various sites of oral squamous cell carcinoma were safe and effective and did not cause any severe adverse effects.

New method for measurement of chest surface motion in lung cancer patients: Quantification using a technique of deformable image registration.

The purpose of this study was to measure the motion of the chest surface during breath-holding treatment for lung cancer using deformable image registration (DIR). Forty non-small-cell lung cancer patients treated with breath-holding stereotactic body radiation therapy were retrospectively examined. First, intensity-based DIR between 2 breath-holding computed tomography (CT) images was performed. Subsequently, deformation vector field (DVF) for all dimensions (left-right, anterior-posterior, and superior-inferior) was calculated from the result. For the analysis of chest surface, the DVF value of the only chest surface area was extracted after the chest surface was divided into 12 regions of interest (ROI) based on anatomy. Additionally, for the analysis of the correlation with the internal tumor motion, the median value of DVF for each surface ROI and the motion of the center of gravity of the tumor volume were used. It was possible to calculate the motion of chest surface without any outliers for all patients. For the average of 12 surface ROIs, the motion of 3D chest surface was within 2 mm (30 cases), 3 mm (8 cases), and 4 mm (2 cases). There was no correlation between the motion of the chest surface and that of the tumor for all 12 surface ROIs. We proposed a technique to evaluate the surface motion using DIR between multiple CT images. It could be a useful tool to calculate the motion of chest surface.