Multi-institutional investigation into the robustness of intra-cranial multi-target stereotactic radiosurgery plans to patient setup errors.

PURPOSE: This study aimed to analyse correlations between planning factors including plan geometry and plan complexity with robustness to patient setup errors. METHODS: Multiple-target brain stereotactic radiosurgery (SRS) plans were obtained through the Trans-Tasman Radiation Oncology Group (TROG) international treatment planning challenge (2018). The challenge dataset consisted of five intra-cranial targets with a 20 Gy prescription. Setup error was simulated using an in-house tool. Dose to targets was assessed via dose covering 99 % (D99 %) of gross tumour volume (GTV) and 98 % of planning target volume (PTV). Dose to organs at risk was assessed using volume of normal brain receiving 12 Gy and maximum dose covering 0.03 cc of brainstem. Plan complexity was assessed via edge metric, modulation complexity score, mean multi-leaf collimator (MLC) gap, mean MLC speed and plan modulation. RESULTS: Even for small (0.5 mm/°) errors, GTV D99 % was reduced by up to 20 %. The strongest correlation was found between lower complexity plans (larger mean MLC gap and lower edge metric) and higher robustness to setup error. Lower complexity plans had 1 %-20 % fewer targets/scenarios with GTV D99 % falling below the specified tolerance threshold. These complexity metrics correlated with 100 % isodose volume sphericity and dose conformity, though similar conformity was achievable with a range of complexities. CONCLUSIONS: A higher level of importance should be directed towards plan complexity when considering plan robustness. It is recommended when planning multi-target SRS, larger MLC gaps and lower MLC aperture irregularity be considered during plan optimisation due to higher robustness should patient positioning errors occur.

Dosimetric impact of intrafraction patient motion on MLC-based 3D-conformal spatially fractionated radiation therapy treatment of large and bulky tumors.

PURPOSE: To evaluate the dosimetric impact on spatially fractionated radiation therapy (SFRT) plan quality due to intrafraction patient motion via multi-field MLC-based method for treating large and bulky (≥8 cm) unresectable tumors. METHODS: For large tumors, a cone beam CT-guided 3D conformal MLC-based SFRT method was utilized with 15 Gy prescription. An MLC GTV-fitting algorithm provided 1 cm diameter apertures with a 2 cm center-to-center distance at the isocenter. This generated a highly heterogeneous sieve-like dose distribution within an hour, enabling same-day SFRT treatment. Fifteen previously treated SFRT patients were analyzed (5 head & neck [H&N], 5 chest and lungs, and 5 abdominal and pelvis masses). For each plan, intrafraction motion errors were simulated by incrementally shifting original isocenters of each field in different x-, y-, and z-directions from 1 to 5 mm. The dosimetric metrics analyzed were: peak-to-valley-dose-ratio (PVDR), percentage of GTV receiving 7.5 Gy, GTV mean dose, and maximum dose to organs-at-risk (OARs). RESULTS: For ±1, ±2, ±3, ±4, and ±5 mm isocenter shifts: PVDR dropped by 3.9%, 3.8%, 4.0%, 4.1%, and 5.5% on average respectively. The GTV(V7.5) remained within 0.2%, and the GTV mean dose remained within 3.3% on average, compared to the original plans. The average PVDR drop for 5 mm shifts was 4.2% for H&N cases, 10% for chest and lung, and 2.2% for abdominal and pelvis cases. OAR doses also increased. The maximum dose to the spinal cord increased by up to 17 cGy in H&N plans, mean lung dose (MLD) changed was small for chest/lung, but the bowel dose varied up to 100 cGy for abdominal and pelvis cases. CONCLUSION: Due to tumor size, location, and characteristics of MLC-based SFRT, isocenter shifts of up to ±5 mm in different directions had moderate effects on PVDR for H&N and pelvic tumors and a larger effect on chest tumors. The dosimetric impact on OAR doses depended on the treatment site. Site-specific patient masks, Vac-Lok bags, and proper immobilization devices similar to SBRT/SRT setups should be used to minimize these effects.

Air inflow into vacuum-type immobilization devices impacts setup errors.

We aimed to determine the impact of air inflow into vacuum-type immobilization devices (VIDs) on setup errors. We assigned 70 patients undergoing radiotherapy for head and neck cancer to groups V (n = 34) or N (n = 36) according to whether the VIDs were deflated weekly or not deflated during treatment, respectively. We calculated systematic errors (Σ) as the standard deviations (SDs) of mean errors, and random errors (σ) as the root mean square of SDs in each patient. We compared overall means (µ), SDs (SDoverall), random errors and systematic errors. We also measured temporary pressure changes in VIDs to determine the influence of pressure changes in VIDs on setup errors. The µ was within 0.20 mm and 0.2° in both groups, whereas SDoverall significantly differed between them. The SDoverall differed the most in the Roll axes of groups N (0. 87°) and V (0.58°). The Σ and σ values were lower in all axes of group V than in group N. Despite the initial deflation target of - 70 kPa, the pressure in VIDs reached - 5 kPa at the end of treatment. However, weekly deflation apparently maintained pressure at - 20 kPa. Effective pressure control in VIDs can reduce patient-by-patient variation and improve setup reproducibility for individual patients, consequently resulting in small variations among overall setup errors.

Impact of setup and geometric uncertainties on the robustness of free-breathing photon radiotherapy of small lung tumors.

PURPOSE: Respiratory motion and patient setup error both contribute to the dosimetric uncertainty in radiotherapy of lung tumors. Managing these uncertainties for free-breathing treatments is usually done by margin-based approaches or robust optimization. However, breathing motion can be irregular and concerns have been raised for the robustness of the treatment plans. We have previously reported the dosimetric effects of the respiratory motion, without setup uncertainties, in lung tumor photon radiotherapy using free-breathing images. In this study, we include setup uncertainty. METHODS: Tumor positions from cine-CT images acquired in free-breathing were combined with per-fraction patient shifts to simulate treatment scenarios. A total of 14 patients with 300 tumor positions were used to evaluate treatment plans based on 4DCT. Four planning methods aiming at delivering 54 Gy as median tumor dose in three fractions were compared. The planning methods were denoted robust 4D (RB4), isodose to the PTV with a central higher dose (ISD), the ISD method normalized to the intended median tumor dose (IRN) and homogeneous fluence to the PTV (FLU). RESULTS: For all planning methods 95% of the intended dose was achieved with at least 90% probability with RB4 and FLU having equal CTV D50% values at this probability. FLU gave the most consistent results in terms of CTV D50% spread and dose homogeneity. CONCLUSIONS: Despite the simulated patient shifts and tumor motions being larger than observed in the 4DCTs the dosimetric impact was suggested to be small. RB4 or FLU are recommended for the planning of free-breathing treatments.

Assessing tumor volumetric reduction with consideration for setup errors based on mathematical tumor model and microdosimetric kinetic model in single-isocenter VMAT for brain metastases.

The volumetric reduction rate (VRR) was evaluated with consideration for six degrees-of-freedom (6DoF) patient setup errors based on a mathematical tumor model in single-isocenter volumetric modulated arc therapy (SI-VMAT) for brain metastases. Simulated gross tumor volumes (GTV) of 1.0 cm and dose distribution were created (27 Gy/3 fractions). The distance between the GTV center and isocenter (d) was set at 0-10 cm. The GTV was translated within 0-1.0 mm (Trans) and rotated within 0-1.0° (Rot) in the three axis directions using affine transformation. The tumor growth volume was calculated using a multicomponent mathematical model (MCTM), and lethal effects of irradiation and repair from damage during irradiation were calculated by a microdosimetric kinetic model (MKM) for non-small cell lung cancer (NSCLC) A549 and NCI-H460 (H460) cells. The VRRs were calculated 5 days after the end of irradiation using the physical dose to the GTV for varying d and 6DoF setup errors. The tolerance value of VRR, the GTV volume reduction rate, was set at 5%, based on the pre-irradiation GTV volume. With the exception of the only one A549 condition where (Trans, Rot) = (1.0 mm, 1.0°) was repeated for 3 fractions, all conditions met all the tolerance VRR values for A549 and H460 cells with varying d from 0 to 10 cm. Evaluation based on the mathematical tumor model suggested that if the 6DoF setup errors at each irradiation could be kept within 1.0 mm and 1.0°, there would be little effect on tumor volume regardless of the distance from the isocenter in SI-VMAT.

[Estimation of Uncertainty of the VMAT Absolute Dose Measurement Due to the Phantom Setup Error Using a Treatment Planning System].

PURPOSE: When performing single-point dose verification in VMAT, it is necessary to avoid the regions with steep dose gradient. We propose a method to obtain the estimated value ( Uplan) of uncertainty of the absolute dose measurement due to the phantom setup error by using dose gradient calculated from treatment planning system (TPS), for evaluating the appropriate measurement points. METHODS: The dose gradient was calculated from the planned dose values in the vicinity of the isocenter point using TPS. The phantom setup error was estimated. The Uplan was calculated using the proposed formula after estimating the phantom setup error. Then, the dose gradient was calculated from the measured dose values in the vicinity of the isocenter point specified by TPS using the Tough water phantom with ionization chamber (IC), and Umeas was calculated as in Uplan. RESULTS: The correlation coefficient between Uplan and Umeas was 0.984, which indicates a high correlation. The average of the difference between Umeas and Uplan was -0.24%. We considered that this result was caused by the influence of volume averaging effect of IC. CONCLUSION: The Uplan obtained from this proposed method reflects the uncertainty of the absolute dose measurement due to the phantom setup error and is useful for evaluating the appropriate measurement points for absolute dose measurement.

A retrospective study on improving the accuracy of radiotherapy for patients with breast cancer with lymph node metastasis using Styrofoam.

BACKGROUND: To retrospectively analyze the accuracy of radiotherapy using cone beam computed tomography (CBCT), Styrofoam fixation, and breast bracket fixation in the chest wall target area and supraclavicular lymphatic drainage area (supraclavicular target area) of patients with breast cancer.and compare the setting efficiency and comfort satisfaction. PATIENTS AND METHODS: A total of 65 patients with postoperative lymphatic metastasis of breast cancer, including 36 cases of Styrofoam fixation and 29 cases of breast bracket fixation, were recruited from March 2021 to August 2022 and retrospectively analyzed. All the patients underwent CBCT scans weekly, and the setup errors of the chest wall and supraclavicular target volume were compared and recorded. The planning target volume (PTV) margins of the two groups were calculated using the correlation MPTV = 2.5Σ + 0.7σ. The setup time and comfort satisfaction scores of the two groups were recorded and analyzed. The correlations among errors in each direction were analyzed using the Pearson correlation analysis. RESULTS: There was a significant difference in the left-right direction (X) axis of the chest wall target area between the Styrofoam and breast bracket groups (1.59 ± 1.47 mm vs. 2.05 ± 1.64 mm, P = 0.012). There were statistical differences in the ventrodorsal direction (Z) and bed angle of the supraclavicular target area, the data were (1.36 ± 1.27 mm vs. 1.75 ± 1.55 mm, P = 0.046; 0.47 ± 0.47° vs. 0.66 ± 0.59°, P = 0.006, respectively). In the X, Y, and Z directions, the respective PTV margins of the two groups in the chest wall target area were 5.01 mm, 5.99 mm, and 5.47 mm in the Styrofoam group, while those in the breast bracket group were 6.10 mm, 6.34 mm, and 6.10 mm, respectively. Moreover, the PTV margins of the supraclavicular target in the three directions were 3.69 mm, 3.86 mm, and 4.28 mm in the Styrofoam group, while those in the breast bracket group were 3.99 mm, 3.72 mm, and 5.45 mm, respectively. The setup time of the two groups was 3.4 ± 1.1 min and 5.5 ± 3.1 min (P = 0.007). The subjective comfort satisfaction scores of the two groups were 27.50 ± 1.24 and 25.44 ± 1.23 (P < 0.001). CONCLUSIONS: The application of Styrofoam fixation in radiotherapy of breast cancer in the supraclavicular lymph node area has several advantages as compared to breast bracket fixation, including higher positioning accuracy, smaller external expansion boundary, improved work efficiency, and patients' comfort, which might provide a reference for clinical work.

A robust treatment planning approach for chest motion in postmastectomy chest wall intensity modulated radiation therapy.

PURPOSE: Chest wall postmastectomy radiation therapy (PMRT) should consider the effects of chest wall respiratory motion. The purpose of this study is to evaluate the effectiveness of robustness planning intensity modulated radiation therapy (IMRT) for respiratory movement, considering respiratory motion as a setup error. MATERIAL AND METHODS: This study analyzed 20 patients who underwent PMRT (10 left and 10 right chest walls). The following three treatment plans were created for each case and compared. The treatment plans are a planning target volume (PTV) plan (PP) that covers the PTV within the body contour with the prescribed dose, a virtual bolus plan (VP) that sets a virtual bolus in contact with the body surface and prescribing the dose that includes the PTV outside the body contour, and a robust plan (RP) that considers respiratory movement as a setup uncertainty and performs robust optimization. The isocenter was shifted to reproduce the chest wall motion pattern and the doses were recalculated for comparison for each treatment plan. RESULT: No significant difference was found between the PP and the RP in terms of the tumor dose in the treatment plan. In contrast, VP had 3.5% higher PTV Dmax and 5.5% lower PTV V95% than RP (p < 0.001). The RP demonstrated significantly higher lung V20Gy and Dmean by 1.4% and 0.4 Gy, respectively, than the PP. The RP showed smaller changes in dose distribution affected by chest wall motion and significantly higher tumor dose coverage than the PP and VP. CONCLUSION: We revealed that the RP demonstrated comparable tumor doses to the PP in treatment planning and was robust for respiratory motion compared to both the PP and the VP. However, the organ at risk dose in the RP was slightly higher; therefore, its clinical use should be carefully considered.

Correlation between the setting of gating window width and setup accuracy in left breast cancer radiotherapy based on deep inspiration breath hold.

Personalized precision irradiation of patients with left-sided breast cancer is possible by examining the setup errors of 3- and 4-mm gated window widths for those treated with deep inspiration breath-hold (DIBH) treatment. An observational study was performed via a retrospective analysis of 250 cone-beam computed tomography (CBCT) images of 60 left-breast cancer patients who underwent whole-breast radiotherapy with the DIBH technique between January 2021 and 2022 at our hospital. Among them, 30 patients had a gated window width of 3 mm, while the remaining 30 had a gated window width of 4 mm; both groups received radiotherapy using DIBH technology. All patients underwent CBCT scans once a week, and the setup errors in the left-right (x-axis), inferior-superior (y-axis), and anterior-posterior (z-axis) directions were recorded. The clinical-to-planning target volume (CTV-PTV) margins of the two gating windows were calculated using established methods. The setup error in the Y direction was 1.69 ± 1.33 mm for the 3-mm - wide gated window and 2.42 ± 3.02 mm for the 4-mm - wide gated window. The two groups had statistically significant differences in the overall mean setup error (Dif 0.7, 95% CI 0.15-1.31, t = 2.48, p= 0.014). The Z-direction setup error was 2.32 ± 2.12 mm for the 3-mm - wide gated window and 3.15 ± 3.34 mm for the 4-mm - wide gated window. The overall mean setup error was statistically significant between the two groups (Dif 0.8, 95% CI 0.13-1.53, t= 2.34, p = 0.020). There was no significant difference in the X-direction setup error (p > 0.05). Therefore, the CTV-PTV margin values for a 3-mm gated window width in the X, Y, and Z directions are 5.51, 5.15, and 7.28 mm, respectively; those for a 4-mm gated window width in the X, Y, and Z directions are 5.52, 8.16, and 10.21 mm, respectively. The setup errors of the 3-mm - wide gating window are smaller than those of the 4-mm - wide gating window in the three dimensions. Therefore, when the patient's respiratory gating window width is reduced, the margin values of CTV-PTV can be reduced to increase the distance between the PTV and the organs at risk (OARs), which ensures adequate space for the dose to decrease, resulting in lower dose exposure to the OARs (heart, lungs, etc.), thus sparing the OARs from further damage. However, some patients with poor pulmonary function or unstable breathing amplitudes must be treated with a slightly larger gating window. Therefore, this study lays a theoretical basis for personalized precision radiotherapy, which can save time and reduce manpower in the delivery of clinical treatment to a certain extent. Another potential benefit of this work is to bring awareness to the potential implications of a slightly larger gating window during treatment without considering the resulting dosimetric impact.

Accuracy Evaluation Trial of Mixed Reality-Guided Spinal Puncture Technology.

Purpose: To evaluate the accuracy of mixed reality (MR)-guided visualization technology for spinal puncture (MRsp). Methods: MRsp involved the following three steps: 1. Lumbar spine computed tomography (CT) data were obtained to reconstruct virtual 3D images, which were imported into a HoloLens (2nd gen). 2. The patented MR system quickly recognized the spatial orientation and superimposed the virtual image over the real spine in the HoloLens. 3. The operator performed the spinal puncture with structural information provided by the virtual image. A posture fixation cushion was used to keep the subjects' lateral decubitus position consistent. 12 subjects were recruited to verify the setup error and the registration error. The setup error was calculated using the first two CT scans and measuring the displacement of two location markers. The projection points of the upper edge of the L3 spinous process (L3↑), the lower edge of the L3 spinous process (L3↓), and the lower edge of the L4 spinous process (L4↓) in the virtual image were positioned and marked on the skin as the registration markers. A third CT scan was performed to determine the registration error by measuring the displacement between the three registration markers and the corresponding real spinous process edges. Results: The setup errors in the position of the cranial location marker between CT scans along the left-right (LR), anterior-posterior (AP), and superior-inferior (SI) axes of the CT bed measured 0.09 ± 0.06 cm, 0.30 ± 0.28 cm, and 0.22 ± 0.12 cm, respectively, while those of the position of the caudal location marker measured 0.08 ± 0.06 cm, 0.29 ± 0.18 cm, and 0.18 ± 0.10 cm, respectively. The registration errors between the three registration markers and the subject's real L3↑, L3↓, and L4↓ were 0.11 ± 0.09 cm, 0.15 ± 0.13 cm, and 0.13 ± 0.10 cm, respectively, in the SI direction. Conclusion: This MR-guided visualization technology for spinal puncture can accurately and quickly superimpose the reconstructed 3D CT images over a real human spine.

Optimal fractionation and timing of weekly cone-beam CT in daily surface-guided radiotherapy for breast cancer.

PURPOSE: Surface-guided radiotherapy (SGRT) has been demonstrated to be a promising supplement to cone-beam computed tomography (CBCT) in adjuvant breast cancer radiotherapy, but a rational combination mode is lacking in clinical practice. The aim of this study was to explore this mode and investigate its impact on the setup and dose accuracy. METHODS AND MATERIALS: Daily SGRT and weekly CBCT images were acquired for 23 patients with breast cancer who received conventional fractionated radiotherapy after lumpectomy. Sixteen modes were acquired by randomly selecting one (CBCT1), two (CBCTij), three (CBCTijk), four (CBCTijkl), and five (CBCT12345) images from the CBCT images for fusion with the SGRT. The CTV-PTV margins, OAR doses, and dose coverage (V95%) of PTV and CTV was calculated based on SGRT setup errors with different regions of interest (ROIs). Dose correlations between these modalities were investigated using Pearson and Spearman's methods. Patient-specific parameters were recorded to assess their impact on dose. RESULTS: The CTV-PTV margins decreased with increasing CBCT frequencies and were close to 5 mm for CBCTijkl and CBCT12345. For the ipsilateral breast ROI, SGRT errors were larger in the AP direction, and target doses were higher in all modes than in the whole breast ROI (P < 0.05). In the ipsilateral ROI, the target dose correlations between all modes increased with increasing CBCT time intervals, decreased, and then increased with increasing CBCT frequencies, with the inflection point being CBCT participation at week 5. The dose deviations in CBCT123, CBCT124, CBCT125, CBCTijkl, and CBCT12345 were minimal and did not differ significantly (P > 0.05). There was excellent agreement between CBCT124 and CBCT1234, and between (CBCTijkl, CBCT12345) and CBCT125 in determining the classification for the percentage of PTV deviation (Kappa = 0.704-0.901). In addition, there were weak correlations between the patient's Dips_b (ipsilateral breast diameter with bolus) and CTV doses in modes with CBCT participation at week 4 (R = 0.270 to 0.480). CONCLUSIONS: Based on weekly CBCT, these modes with ipsilateral ROI and a combination of daily SGRT and a CBCT frequency of ≥ 3 were recommended, and CBCT was required at weeks 1 and 2 for CBCTijk.

Assessment of dosimetric impact of interfractional 6D setup error in tongue cancer treated with IMRT and VMAT using daily kV-CBCT.

Background: This study aimed to evaluate the dosimetric influence of 6-dimensional (6D) interfractional setup error in tongue cancer treated with intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) using daily kilovoltage cone-beam computed tomography (kV-CBCT). Materials and methods: This retrospective study included 20 tongue cancer patients treated with IMRT (10), VMAT (10), and daily kV-CBCT image guidance. Interfraction 6D setup errors along the lateral, longitudinal, vertical, pitch, roll, and yaw axes were evaluated for 600 CBCTs. Structures in the planning CT were deformed to the CBCT using deformable registration. For each fraction, a reference CBCT structure set with no rotation error was created. The treatment plan was recalculated on the CBCTs with the rotation error (RError), translation error (TError), and translation plus rotation error (T+RError). For targets and organs at risk (OARs), the dosimetric impacts of RError, TError, and T+RError were evaluated without and with moderate correction of setup errors. Results: The maximum dose variation ΔD (%) for D98% in clinical target volumes (CTV): CTV-60, CTV-54, planning target volumes (PTV): PTV-60, and PTV-54 was -1.2%, -1.9%, -12.0%, and -12.3%, respectively, in the T+RError without setup error correction. The maximum ΔD (%) for D98% in CTV-60, CTV-54, PTV-60, and PTV-54 was -1.0%, -1.7%, -9.2%, and -9.5%, respectively, in the T+RError with moderate setup error correction. The dosimetric impact of interfractional 6D setup errors was statistically significant (p < 0.05) for D98% in CTV-60, CTV-54, PTV-60, and PTV-54. Conclusions: The uncorrected interfractional 6D setup errors could significantly impact the delivered dose to targets and OARs in tongue cancer. That emphasized the importance of daily 6D setup error correction in IMRT and VMAT.

Automated review of patient position in DIBH breast hybrid IMRT with EPID images.

Deep Inspiration Breath Hold (DIBH) is a respiratory-gating technique adopted in radiation therapy to lower cardiac irradiation. When performing DIBH treatments, it is important to have a monitoring system to ensure the patient's breath hold level is stable and reproducible at each fraction. In this retrospective study, we developed a system capable of monitoring DIBH breast treatments by utilizing cine EPID images taken during treatment. Setup error and intrafraction motion were measured for all fractions of 20 left-sided breast patients. All patients were treated with a hybrid static-IMRT technique, with EPID images from the static fields analyzed. Ten patients had open static fields and the other ten patients had static fields partially blocked with the multileaf collimator (MLC). Three image-processing algorithms were evaluated on their ability to accurately measure the chest wall position (CWP) in EPID images. CWP measurements were recorded along a 61-pixel region of interest centered along the midline of the image. The median and standard deviation of the CWP were recorded for each image. The algorithm showing the highest agreement with manual measurements was then used to calculate intrafraction motion and setup error. To measure intrafraction motion, the median CWP of the first EPID frame was compared with that of the subsequent EPID images of the treatment. The maximum difference was recorded as the intrafraction motion. The setup error was calculated as the difference in median CWP between the MV DRR and the first EPID image of the lateral tangential field. The results showed that the most accurate image-processing algorithm can identify the chest wall within 1.2 mm on both EPID and MV DRR images, and measures intrafraction motion and setup errors within 1.4 mm.

A prospective study to assess and quantify the setup errors with cone-beam computed tomography in head-and-neck cancer image-guided radiotherapy treatment.

Introduction: This study was done to quantify the translational setup errors with cone-beam computed tomography (CBCT) in the image-guided radiation therapy (IGRT) treatment of head-and-neck cancer (HNC) patients. Aims: The objective was to quantify the setup errors by CBCT. Methodology: One hundred patients of HNC were enrolled from March 2020 to March 2021 for IGRT treatment. Pretreatment kV-CBCT images were obtained at the first 3 days of irradiations, and setup error corrections were done in the mediolateral (ML), superior-inferior (SI), and anterior-posterior (AP) directions. Subsequently, a weekly kV-CBCT was repeated for whole duration of radiotherapy for the next 6-7 weeks. Adequacy of planning target volume (PTV) margins was assessed by van Herk's formula. Results: Total 630 CBCT scans of 100 patients were analyzed. Setup errors greater than 3 mm and 5 mm were seen in 11.4% and 0.31% of the patients, respectively. Systematic errors and random errors before correction in ML, SI, and AP directions were 0.10 cm, 0.11 cm, and 0.12 cm and 0.24 cm, 0.20 cm, and 0.21 cm, respectively. Systematic errors and random errors after correction in ML, SI, and AP directions were 0.06 cm, 0.07 cm, and 0.07 cm and 0.13 cm, 0.10 cm, and 0.12 cm, respectively. Conclusion: CBCT at the first 3 fractions and then weekly during radiotherapy is effective to detect the setup errors. An isotropic PTV margin of 5 mm over clinical target volume is safe to account for setup errors, however, in the case of close organ at risk, or with IGRT, a PTV margin of 3 mm can be considered.

Clinical value of styrofoam fixation in intracranial tumor radiotherapy.

Objective: To analyze the application value of two postural fixation techniques.(styrofoam combined with head mask and fixed headrest combined with head mask) in intracranial tumor radiotherapy via cone beam computed tomography (CBCT). Methods: This study included 104 patients with intracranial tumors undergoing radiotherapy. The patients were divided into two groups: Group A (54 cases with styrofoam fixation) and Group B (50 cases with fixed headrest fixation). The positional deviation in 3D space between the two groups was compared using CBCT. The set-up errors were expressed as median (25th percentile, 75th percentile)or M(p25, p75) since the set-up errors in all directions were not normally distributed,The Mann-Whitney U test was performed. Results: The age and gender of patients in the two groups were not significantly different. The set-up errors of A in lateral (X), longitudinal (Y), vertical (Z), and yaw(Rtn) axes were 1.0 (0,1) mm, 1.0 (0,1) mm, 1.0 (0,2) mm, and 0.4 (0.1, 0.8) degrees, respectively while the set-up errors of B were 1.0 (0,1) mm, 1.0 (1,2) mm, 1.0 (0,2) mm, and 0.5 (0.15,0.9) degrees, respectively. Moreover, patients in the styrofoam group had significantly smaller set-up errors in the Y-axis than patients in the headrest group (p=0.001). However, set-up errors in the X, Z, and Rtn axes were not significantly different between the two groups. The expansion boundaries of the target area in the X, Y, and Z directions were 1.77 mm, 2.45 mm, and 2.47 mm, respectively. The outer expansion boundaries of the headrest group were 2.03 mm, 3.88 mm, and 2.57 mm in X, Y, and Z directions, respectively. The set-up times of groups A and B were (32.71 ± 5.21) seconds and (46.57 ± 6.68) seconds, respectively (p=0.014). Patients in group A had significantly better comfort satisfaction than patients in group B (p=0.001). Conclusion: Styrofoam plus head thermoplastic mask body fixation technique has a higher positional accuracy in intracranial tumor radiotherapy than headrest plus head thermoplastic mask fixation. Besides, styrofoam plus head thermoplastic mask body fixation technique is associated with improved positioning efficiency, and better comfort than headrest plus head thermoplastic mask fixation, and thus can be effectively applied for intracranial tumor radiotherapy positioning.

A deep learning-based approach for statistical robustness evaluation in proton therapy treatment planning: a feasibility study.

Objective. Robustness evaluation is critical in particle radiotherapy due to its susceptibility to uncertainties. However, the customary method for robustness evaluation only considers a few uncertainty scenarios, which are insufficient to provide a consistent statistical interpretation. We propose an artificial intelligence-based approach that overcomes this limitation by predicting a set of percentile dose values at every voxel and allows for the evaluation of planning objectives at specific confidence levels.Approach. We built and trained a deep learning (DL) model to predict the 5th and 95th percentile dose distributions, which corresponds to the lower and upper bounds of a two-tailed 90% confidence interval (CI), respectively. Predictions were made directly from the nominal dose distribution and planning computed tomography scan. The data used to train and test the model consisted of proton plans from 543 prostate cancer patients. The ground truth percentile values were estimated for each patient using 600 dose recalculations representing randomly sampled uncertainty scenarios. For comparison, we also tested whether a common worst-case scenario (WCS) robustness evaluation (voxel-wise minimum and maximum) corresponding to a 90% CI could reproduce the ground truth 5th and 95th percentile doses.Main results. The percentile dose distributions predicted by DL yielded excellent agreements with the ground truth dose distributions, with mean dose errors below 0.15 Gy and average gamma passing rates (GPR) at 1 mm/1% above 93.9, which were substantially better than the WCS dose distributions (mean dose error above 2.2 Gy and GPR at 1 mm/1% below 54). We observed similar outcomes in a dose-volume histogram error analysis, where the DL predictions generally yielded smaller mean errors and standard deviations than the WCS evaluation doses.Significance. The proposed method produces accurate and fast predictions (∼2.5 s for one percentile dose distribution) for a given confidence level. Thus, the method has the potential to improve robustness evaluation.

Impact of dose distribution on rotational setup errors in radiotherapy for prostate cancer.

This study aimed to assess the impact of rotational setup errors on the target volume's dose distribution during radiotherapy for prostate cancer. A 6D robotic couch was used to describe the rotational setup error, and the dosage change in the target volume was analyzed using the planning evaluation factors. Treatment plans for three-dimensional conformal radiotherapy (3DCRT), intensity-modulated radiotherapy (IMRT), and volumetric modulated arc radiotherapy (VMAT) were established after contouring the target volume and surrounding normal tissues on tomography obtained from the humanoid phantom. A 6D robotic couch was employed in the radiation room to describe the rotational setup errors of ±1° to ±5° in roll, yaw, and pitch, and cone beam computed tomography (CBCT) images were obtained. Furthermore, the dose distribution was extracted from the 3DCRT, IMRT, and VMAT treatment plans, dose mapping was performed on CBCT that depicts the rotational setup error. Target coverage(TC) decreased by 0.39% to 2.17% in roll, 0.43% to 2.59% in yaw, and 0.70% to 4.12% in pitch, respectively. In the comparison using the Radiation Therapy Oncology Group (RTOG) protocol criteria, when the rotational setup error of VMAT pitch was -2° or more, more than +1°, a target coverage of 95% or lower was shown, indicating the greatest effect among rotational setup errors. Furthermore, in 3DCRT, IMRT, and VMAT, the rotational setup error showed the greatest effect in pitch, and the dose change was larger in VMAT than in 3DCRT and IMRT. Therefore, specific rotational error due to pitch during radiotherapy for prostate cancer requires special consideration. Moreover, the more sophisticated and complex algorithms, such as VMAT, applied, the greater the dose change of target coverage due to rotational error; therefore, caution is required.

Multicomponent mathematical model for tumor volume calculation with setup error using single-isocenter stereotactic radiotherapy for multiple brain metastases.

We evaluated the tumor residual volumes considering six degrees-of-freedom (6DoF) patient setup errors in stereotactic radiotherapy (SRT) with multicomponent mathematical model using single-isocenter irradiation for brain metastases. Simulated spherical gross tumor volumes (GTVs) with 1.0 (GTV 1), 2.0 (GTV 2), and 3.0 (GTV 3)-cm diameters were used. The distance between the GTV center and isocenter (d) was set at 0-10 cm. The GTV was simultaneously translated within 0-1.0 mm (T) and rotated within 0°-1.0° (R) in the three axis directions using affine transformation. We optimized the tumor growth model parameters using measurements of non-small cell lung cancer cell lines' (A549 and NCI-H460) growth. We calculated the GTV residual volume at the irradiation's end using the physical dose to the GTV when the GTV size, d, and 6DoF setup error varied. The d-values that satisfy tolerance values (10%, 35%, and 50%) of the GTV residual volume rate based on the pre-irradiation GTV volume were determined. The larger the tolerance value set for both cell lines, the longer the distance to satisfy the tolerance value. In GTV residual volume evaluations based on the multicomponent mathematical model on SRT with single-isocenter irradiation, the smaller the GTV size and the larger the distance and 6DoF setup error, the shorter the distance that satisfies the tolerance value might need to be.

Verification of patient-setup accuracy using a surface imaging system with steep measurement angle.

PURPOSE: We evaluate an SGRT device (Voxelan HEV-600 M/RMS) installed with Radixact, with the view angle of the Voxelan's camera at 74 degrees. The accuracy of Voxelan with this steep angle was evaluated with phantom experiments and inter-fractional setup errors of patients. METHODS: In the phantom experiments, the difference between the measured values of Voxelan from the truth was evaluated for translations and rotations. The inter-fractional setup error between the setup using skin markers with laser localizer (laser setup: LS) and the setup using Voxelan (surface setup: SS) was compared for head and neck (N = 19), chest (N = 7) and pelvis (N = 9) cases. The inter-fractional setup error was calculated by subtracting from bone matching by megavoltage computed tomography (MVCT) as ground truth. RESULTS: From the phantom experiments, the average difference between the measured values of Voxelan from the truth was within 1 mm and 1 degree. In all cases, inter-fractional setup error based on MVCT was not significantly different between LS and SS by Welch's t-test (P > 0.05). The vector offset of the LS for head and neck, chest, and pelvis were 6.5, 9.6, and 9.6 mm, respectively, and that of the SS were 5.8, 8.6, and 12.6 mm, respectively. Slight improvement was observed for the head and neck, and chest cases, however, pelvis cases were not improved because the umbilical region could not be clearly visualized as a reference. CONCLUSION: The results show that SS in Voxelan with an installation angle of 74 degrees is equal to or better than LS.

Clinical application of optical surface monitoring system in radiotherapy after radical mastectomy for left breast cancer / 中国辐射卫生

@#<b>Objective</b> To study the setup error under deep inspiration breath hold (DIBH) guided by optical surface monitoring system (OSMS) and free breathing (FB) FB1 and FB2 (without OSMS guidance, directly set up the body marker line by laser lamp) in radiotherapy after radical mastectomy for left breast cancer, and to provide a basis for individualized clinical target volume-planning target volume (CTV-PTV) expansion for the doctor in charge to delineate the target volume. <b>Methods</b> A total of 36 patients with left breast cancer after radical mastectomy were selected and divided into three groups, in which cone beam computed tomography (CBCT) images were taken in three states: DIBH, FB1, and FB2, respectively. CBCT and CT images were analyzed for registration; the absolute error data of linear displacement in the ventro-dorsal, cranio-caudal, and left-right directions were recorded, and the expanding margin was calculated. <b>Results</b> The translation errors in the ventro-dorsal, cranio-caudal, and left-right directions were (0.06 ± 0.22) cm, (0.05 ± 0.23) cm, and (0.01 ± 0.24) cm in the DIBH group, (0.07 ± 0.21) cm, (0.02 ± 0.23) cm, and (0.02 ± 0.21) cm in the FB1 group, and (0.07 ± 0.24) cm, (0.07 ± 0.34) cm, and (0.25 ± 0.09) cm in the FB2 group. The statistical results of the DIBH group and FB1 group in the ventro-dorsal, RTN, and ROLL directions were significantly different (<i>P</i> < 0.05). The statistical results of the FB1 group and FB2 group in the ventro-dorsal direction were significantly different. The relation of three groups in the value of margin of planning target volume was DIBH < FB1 < FB2 in the ventro-dorsal and cranio-caudal directions and FB1 < DIBH < FB2 in the left-right direction. <b>Conclusion</b> OSMS-guided DIBH radiotherapy in patients with left breast cancer after radical mastectomy can reduce the setup error and provide an important basis for individualized CTV-PTV expansion for the doctor in charge to delineate the target volume.