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 a New Method for CyberKnife Treatment for Central Lung and Mediastinal Tumors by Tracheobronchial Tracking.

BACKGROUND: CyberKnife treatment for central lung tumors and mediastinal tumors can be difficult to perform with marker less. PURPOSE: We aimed to evaluate a novel tracheobronchial-based method (ie, tracheobronchial tracking) for the purpose of minimally invasive CyberKnife treatment for central lung and mediastinal tumors. METHODS: Five verification plans were created using an in-house phantom. Each plan included five irradiation sessions. The reference plan irradiated and tracked the simulated tumor (using the target tracking volume, TTV). Trachea plans tracked the simulated tracheo-bronchus and irradiated the simulated tumor and included two types of subplans: correlated plans in which the displacement of the simulated tracheobronchial and the simulated tumor were correlated, and non-correlated plans in which these factors were not correlated. Moreover, 15 mm and 25 mm TTVs were evaluated for each plan. The sin waveform and the patient's respiratory waveform were prepared as the respiratory model. Evaluations were performed by calculating the dose difference between the radiophotoluminescent glass dosimeter (RPLD)-generated mean dose values (generated by the treatment planning system, TPS) and the actual absorbed RPLD dose. Statistical analyses were performed to evaluate findings for each plan. Correlation and prediction errors were calculated for each axis of each plan using log files to evaluate tracking accuracy. RESULTS: Dose differences were statistically significant only in comparisons with the non-correlated plan. When evaluated using the sin waveform, the mean values for correlation and prediction errors in each axis and for all plans were less than 0.6 mm and 0.1 mm, respectively. In the same manner, they were less than 1.1 mm and 0.2 mm when evaluated using the patient's respiratory waveform. CONCLUSION: Our newly-developed tracheobronchial tracking method would be useful in facilitating minimally invasive CyberKnife treatment in certain cases of central lung and mediastinal tumors.

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.

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.

Left testicular and pulmonary metastases of mucinous adenocarcinoma of the prostate after robot-assisted radical prostatectomy.

Introduction: We present a case of mucinous adenocarcinoma of the prostate with testicular and lung metastases following robot-assisted radical prostatectomy, androgen deprivation therapy, and radiotherapy. Case presentation: A 73-year-old man with a prostate-specific antigen level of 4.3 ng/mL was diagnosed with prostate cancer. Following the robot-assisted radical prostatectomy, the pathological diagnosis was mucinous adenocarcinoma of the prostate (pT3bpN0, Gleason score of 4 + 4). Salvage hormonal therapy and irradiation were performed after the prostatectomy. Enlargement of the left testis was noted, and 28 months after prostatectomy, computed tomography detected a left testicular tumor and nodular lesions in the bilateral lungs. The histopathological diagnosis of left high orchiectomy was metastasis of a mucinous adenocarcinoma of the prostate. Chemotherapy with docetaxel followed by cabazitaxel was initiated. Conclusion: Mucinous prostate adenocarcinoma with distal metastases following prostatectomy has been managed for longer than 3 years with multiple treatments.

The Ki67 index evaluation of pancreatic neuroendocrine tumors using 3D immunohistochemistry in small tissue specimens.

BACKGROUND: /Objectives: This study aimed to evaluate the usefulness of three-dimensional (3D) immunohistochemistry for the Ki67 index of small tissue specimens of pancreatic neuroendocrine tumor (PanNET). METHODS: Clinicopathological materials from 17 patients with PanNET who underwent surgical resection at Jichi Medical University Hospital were analyzed. We compared the Ki67 index of endoscopic ultrasonography-fine-needle aspiration biopsy (EUS-FNAB) specimens, surgical specimens, and small tissue specimens hollowed from paraffin blocks of surgical specimens that were substituted for EUS-FNAB specimens ("sub-FNAB"). The sub-FNAB specimens were optically cleared using LUCID (IlLUmination of Cleared organs to IDentify target molecules) and analyzed using 3D immunohistochemistry. RESULTS: The median Ki67 index in FNAB, sub-FNAB, and surgical specimens with conventional immunohistochemistry were 1.2% (0.7-5.0), 2.0% (0.5-14.6), and 5.4% (1.0-19.4), respectively. The median Ki67 index in sub-FNAB specimens with tissue clearing was calculated separately using the total number of cells on multiple images ("multiple slice"), with the image of the fewest positive cells ("coldspot"), and with the image of most positive cells ("hotspot"), which were 2.7% (0.2-8.2), 0.8% (0-4.8), and 5.5% (2.3-12.4), respectively. PanNET grade evaluated for the hotspot of the surgical specimens was significantly more consistent with those of the hotspot than multiple images of sub-FNAB specimens (16/17 vs. 10/17, p = 0.015). Hotspot evaluation using 3D immunohistochemistry of the sub-FNAB specimens showed agreement with the assessment of the surgical specimens (Kappa coefficient: 0.82). CONCLUSIONS: Tissue clearing and 3D immunohistochemistry for the Ki67 index can potentially improve the preoperative evaluation of EUS-FNAB specimens of PanNET in routine clinical practice.

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.

Development of a dynamic motion platform with two independent drive systems for radiotherapy.

BACKGROUND: There are some motion platforms for radiotherapy quality assurance. However, no platform with two drive systems that can move along three axes is available. PURPOSE: The purpose of this study is to develop a dynamic motion platform with two drive systems capable of three-axis motion and to evaluate its motion performance. METHODS: The developed moving platform had two drive systems that use the same equipment. Each axis of the platform used can support a maximum load of 10 kg. The motors for moving the platform in each direction are capable of a drive stroke up to 40 mm. The drive speed is 30 mm/s at maximum load fluctuation. To evaluate the static positional accuracy of this system with an arbitrary input movement, the XYZ position of each axis was measured using a coordinate measuring machine operating from 0 to 40 mm at 10 mm intervals. In addition, the accuracy of dynamic motion was verified with Sine waveform inputs of different patterns to the three axes for approximately 60 s, and they were compared with the resulting detected signals by SyncTrax. RESULTS: The two drive systems were successfully operated on three axes by using independent control systems. For static position, the accuracies were within 0.2 mm, 0.05 mm, and 0.14 mm for lateral, longitudinal, and vertical directions, respectively. For dynamic motion, the mean absolute errors in the X, Y, and Z axes between the platform inputs and SyncTrax detected signals were 0.14 ± 0.10 mm, 0.16 ± 0.12 mm, and 0.16 ± 0.11 mm, respectively. CONCLUSIONS: A new dynamic platform for radiation therapy with two drive systems capable of three-axis motion was developed, and the positional accuracy of the drive axes was confirmed to be less than 0.2 mm.

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.

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.

Bile cytology diagnosis in challenging cases: Validation of diagnostic bile cytology criteria and extensive study for immunocytochemical markers.

BACKGROUND: Bile cytology is useful in diagnosing biliary tract lesions, albeit often challenging due to equivocal findings. To achieve better diagnoses for clinical decisions, we conducted cytomorphological and immunocytochemical studies of bile cytology cases. MATERIALS AND METHODS: We re-evaluated 40 bile cytology cases with initial equivocal diagnoses, taken from the cytology records of Jichi Medical University Hospital, including 1778 bile cytology specimens. First, we assessed the cases by the diagnostic bile cytology criteria of the Japanese Society of Clinical Cytology. Second, we searched for useful immunocytochemical markers by extensive immunohistochemical analyses using tissue microarray for 10 antibodies: S100P, IMP3, GLUT1, p53, S100A4, Mapsin, MUC17, CD10, MDM2, and SMAD4. Microarrays were from 257 extrahepatic bile duct carcinoma cases. To elucidate the utility of immunocytochemistry, we applied selected markers to immunocytochemical evaluation of the equivocal cases after cell transfer. RESULTS: The criteria indicated a sensitivity 60%, specificity 87%, and accuracy 70%. Irregularly overlapping (88%), arranged (96%), and shaped (76%) nuclei were more common in malignant cases, while enlarged nuclei were more frequent in benign cases (67% vs. 28%). We applied S100P and IMP3, which showed higher accuracy (88% and 77%) in tissue microarray, to immunocytochemistry. The sensitivity of S100P and IMP3 were 69% and 70%, respectively. The specificity of S100P and IMP3 were 50% and 100%, respectively. CONCLUSION: The criteria showed a certain effectiveness even in challenging cases, and some pitfalls associated with reactive changes of benign cells. Although comprehensive diagnosis including cytomorphology seems preferable, S100P and IMP3 are promising immunocytochemical 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.

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.

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.

Dose Prescription Methods in Stereotactic Body Radiotherapy for Small Peripheral Lung Tumors: Approaches Based on the Gross Tumor Volume Are Superior to Prescribing a Dose That Covers 95% of the Planning Target Volume.

BACKGROUND AND PURPOSE: We aimed to validate the usefulness of prescriptions based on gross tumor volume for stereotactic body radiotherapy for small peripheral lung tumors. MATERIALS AND METHODS: Radiotherapy treatment planning data of 50 patients with small peripheral lung tumors (adenocarcinoma: 24, squamous cell carcinoma: 10, other: 1, unknown: 15) receiving breath-hold computed tomography-guided stereotactic body radiotherapy at our institution during 2013-2016 were analyzed. For each case, 3 dose prescription methods were applied: one based on 95% (PTVD95%) of the planning target volume, one based on 50% of the gross tumor volume (GTVD50%), and one based on 98% (GTVD98%) of the gross tumor volume. The maximum (GTVDmax), minimum (GTVDmin), and mean gross tumor volume dose (GTVDmean) and the dose covering 98% of the gross tumor volume were calculated to evaluate variations in the gross tumor volume dose. RESULTS: Upon switching to GTVD50%, the variations in GTVDmax and GTVDmean decreased significantly, compared with variations observed for PTVD95% (p < 0.01), but the variation in GTVDmin increased significantly (p < 0.01). Upon switching to the GTVD98%, the variation in GTVDmean decreased significantly compared with that observed for PTVD95% (p < 0.01). CONCLUSION: Switching from prescriptions based on 95% of the planning target volume to those based on 98% of the gross tumor volume decreased variations among cases in the overall gross tumor volume dose. Overall, prescriptions based on 98% of the gross tumor volume appear to be more suitable than those based on 95% of the planning target volume in cases of small peripheral lung tumors treated with stereotactic body radiotherapy.

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.

Tumor volume shrinkage during stereotactic body radiotherapy is related to better prognoses in patients with stage I non-small-cell lung cancer.

The purpose of the study was to investigate the association between tumor volume changes during stereotactic body radiation therapy (SBRT) and prognoses in stage I non-small-cell lung cancer (NSCLC). This retrospective review included stage I NSCLC patients in whom SBRT was performed at a total dose of 48.0-50.5 Gy in four or five fractions. The tumor volumes observed on computed tomography (CT) simulation and on the CT performed at the last treatment session using a CT-on-rails system were measured and compared. Then, the tumor volume changes during the SBRT period were measured and assessed for their association with prognoses (overall survival, local control, lymph node metastases and distant metastases). A total of 98 patients with a mean age of 78.6 years were enrolled in the study. The T-stage was T1a in 42%, T1b in 32% and T2a in 26% of the cases. The gross tumor volume (GTV) shrank and increased ≥10% in 23 (23.5%) and 36 (36.7%) of the cases, respectively. The 5-year local control and overall survival rates in the groups with a tumor shrinkage of ≥10% vs the group with a shrinkage of <10% were 94.7 vs 70.8% and 85.4 vs 47.6%, respectively; these differences were significant, with a P-value < 0.05. During a short SBRT period, the tumor shrank or enlarged in a small number of cases. A decrease of ≥10% in the GTV during SBRT was significantly related to better overall survival and local control.

Comparison of rectal dose reduction by a hydrogel spacer among 3D conformal radiotherapy, volumetric-modulated arc therapy, helical tomotherapy, CyberKnife and proton therapy.

This study aimed to evaluate the rectal dose reduction with hydrogel spacer in 3D conformal radiotherapy (3DCRT), volumetric modulated arc therapy (VMAT), helical tomotherapy (HT), CyberKnife (CK) and proton therapy. Twenty patients who had hydrogel spacer for prostate radiotherapy were retrospectively enrolled. Computed tomography (CT) images with or without hydrogel spacer were used to evaluate rectal dose reduction. In total, 200 plans (20 patients × 2 CT images × 5 techniques) were created using the following criteria: 3DCRT, VMAT and HT [76 Gy/38 fractions (Fr), planning target volume (PTV) D50%], CK (36.25 Gy/5 Fr, PTV D95%) and proton therapy (63 GyE/21 Fr, PTV D50%). Rectal dose reduction was evaluated using low-/middle-dose (D20%, D50% and D80%) and high-dose (D2%) ranges. Rectal dose reduction of each dose index was compared for each technique. Significant rectal dose reduction (P < 0.001) between the treatment plans on pre- and post-CT images were achieved for all modalities for D50%, D20% and D2%. In particular, the dose reduction of high-dose (D2%) ranges were -40.61 ± 11.19, -32.44 ± 5.51, -25.90 ± 9.89, -13.63 ± 8.27 and -8.06 ± 4.19%, for proton therapy, CK, HT, VMAT and 3DCRT, respectively. The area under the rectum dose-volume histogram curves were 34.15 ± 3.67 and 34.36 ± 5.24% (P = 0.7841) for 3DCRT with hydrogel spacer and VMAT without hydrogel spacer, respectively. Our results indicated that 3DCRT with hydrogel spacer would reduce the medical cost by replacing the conventional VMAT without spacer for prostate cancer treatment, from the point of view of the rectal dose. For the high-dose gradient region, proton therapy and SBRT with CK showed larger rectal dose reduction than other techniques.