Non-coplanar Fields Research Articles

Going from 3D/3D to 2D/3D registration for noncoplanar setup verification in intracranial single-isocenter multiple-target hypofractionated stereotactic radiotherapy: comparison between kilo-voltage/mega-voltage image pairs and noncoplanar cone-beam computed tomography.

Single-isocenter (SI) noncoplanar volumetric modulated arc therapy (NC-VMAT) has been widely used in stereotactic radiosurgery (SRS) or hypofractionated stereotactic radiotherapy (HSRT) for multiple brain metastases (BMs). However, it is critical to verify patient positioning at a noncoplanar couch angle. This study aimed to compare the noncoplanar setup discrepancies between kilo-voltage/mega-voltage image (kV/MV) orthogonal image pairs with a 2-dimensional/3-dimensional (2D/3D) matching mode and noncoplanar cone-beam computed tomography (NC-CBCT) with a 3D/3D matching mode in SI NC-VMAT HSRT for multiple BMs. Twenty patients with multiple BMs [2-5] who underwent SI NC-VMAT HSRT were enrolled in this study. Prior to each noncoplanar field delivery, both kV/MV orthogonal image pairs and NC-CBCT were used to determine setup errors. The setup error values reported by NC-CBCT were defined as the gold standard and compared to those reported by kV/MV orthogonal image pairs. The Bland-Altman analysis method was utilized to assess the agreement of the two positioning modalities. In total, 104 kV/MV image pairs and NC-CBCT scans were acquired. The mean setup error differences (SEDs; absolute values) between the two positioning systems were 0.17 mm, 0.21 mm, 0.16 mm, 0.22°, 0.18°, and 0.17° in the vertical, longitudinal, lateral, yaw, pitch, and roll directions, respectively. The maximum SEDs regarding translation and rotation occurred in the longitudinal and yaw directions at 0.60 mm and 0.8°, respectively. Bland-Altman analysis showed excellent agreement between the two positioning modalities, and the 95% limits of agreement (LOAs) never exceeded 0.6 mm and 0.6° in the translational and rotational directions, respectively. Only 4.80% of SEDs exceeded the tolerance of 0.5 mm/0.5°. Orthogonal kV/MV image pairs with 2D/3D matching mode could provide comparable accuracy for noncoplanar positioning as NC-CBCT with 3D/3D matching mode.

Comparison of patient setup accuracy for optical surface-guided andX-ray-guided imaging with respect to the impact on intracranial stereotactic radiotherapy.

The objective of this work is to estimate the patient positioning accuracy of asurface-guided radiation therapy (SGRT) system using an optical surface scanner compared to an X‑ray-based imaging system (IGRT) with respect to their impact on intracranial stereotactic radiotherapy (SRT) and intracranial stereotactic radiosurgery (SRS). Patient positioning data, both acquired with SGRT and IGRT systems at the same linacs, serve as abasis for determination of positioning accuracy. Atotal of 35patients with two different open face masks (578 datasets) were positioned using X‑ray stereoscopic imaging and the patient position inside the open face mask was recorded using SGRT. The measurement accuracy of the SGRT system (in a"standard" and an SRS mode with higher resolution) was evaluated using both IGRT and SGRT patient positioning datasets taking into account the measurement errors of the X‑ray system. Based on these clinically measured datasets, the positioning accuracy was estimated using Monte Carlo (MC) simulations. The relevant evaluation criterion, as standard of practice in cranial SRT, was the 95th percentile. The interfractional measurement displacement vector of the SGRT system, σSGRT, in high resolution mode was estimated at 2.5 mm (68th percentile) and 5 mm (95th percentile). If the standard resolution was used, σSGRT increased by about 20%. The standard deviation of the axis-related σSGRT of the SGRT system ranged between 1.5 and 1.8 mm interfractionally and 0.5 and 1.0 mm intrafractionally. The magnitude of σSGRT is mainly due to the principle of patient surface scanning and not due to technical limitations or vendor-specific issues in software or hardware. Based on the resulting σSGRT, MC simulations served as ameasure for the positioning accuracy for non-coplanar couch rotations. If an SGRT system is used as the only patient positioning device in non-coplanar fields, interfractional positioning errors of up to 6 mm and intrafractional errors of up to 5mm cannot be ruled out. In contrast, MC simulations resulted in apositioning error of 1.6 mm (95th percentile) using the IGRT system. The cause of positioning errors in the SGRT system is mainly achange in the facial surface relative to adefined point in the brain. In order to achieve the necessary geometric accuracy in cranial stereotactic radiotherapy, use of an X‑ray-based IGRT system, especially when treating with non-coplanar couch angles, is highly recommended.

Can Optical Surface Imaging Replace Non-coplanar Cone-beam Computed Tomography for Non-coplanar Set-up Verification in Single-isocentre Non-coplanar Stereotactic Radiosurgery and Hypofractionated Stereotactic Radiotherapy for Single and Multiple Brain Metastases?

AimsTo conduct a direct comparison regarding the non-coplanar positioning accuracy between the optical surface imaging system Catalyst HDTM and non-coplanar cone-beam computed tomography (NC-CBCT) in intracranial single-isocentre non-coplanar stereotactic radiosurgery (SRS) and hypofractionated stereotactic radiotherapy (HSRT). Materials and methodsTwenty patients with between one and five brain metastases who underwent single-isocentre non-coplanar volumetric modulated arc therapy (NC-VMAT) SRS or HSRT were enrolled in this study. For each non-zero couch angle, both Catalyst HDTM and NC-CBCT were used for set-up verification prior to beam delivery. The set-up error reported by Catalyst HDTM was compared with the set-up error derived from NC-CBCT, which was defined as the gold standard. Additionally, the dose delivery accuracy of each non-coplanar field after using Catalyst HDTM and NC-CBCT for set-up correction was measured with SRS MapCHECKTM. ResultsThe median set-up error differences (absolute values) between the two positioning methods were 0.30 mm, 0.40 mm, 0.50 mm, 0.15°, 0.10° and 0.10° in the vertical, longitudinal, lateral, yaw, pitch and roll directions, respectively. The largest absolute set-up error differences regarding translation and rotation were 1.5 mm and 1.1°, which occurred in the longitudinal and yaw directions, respectively. Only 35.71% of the pairs of measurements were within the tolerance of 0.5 mm and 0.5° simultaneously. In addition, the non-coplanar field with NC-CBCT correction yielded a higher gamma passing rate than that with Catalyst HDTM correction (P < 0.05), especially for evaluation criteria of 1%/1 mm with a median increase of 12.8%. ConclusionsCatalyst HDTM may not replace NC-CBCT for non-coplanar set-up corrections in single-isocentre NC-VMAT SRS and HSRT for single and multiple brain metastases. The potential role of Catalyst HDTM in intracranial SRS/HSRT needs to be further studied in the future.

Surface guided radiation therapy with an innovative open-face mask and mouth bite: patient motion management in brain stereotactic radiotherapy.

To guarantee treatment reproducibility and stability, immobilization devices are essential. Additionally, surface-guided radiation therapy (SGRT) serves as an accurate complement to frameless stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT) by aiding patient positioning and real-time monitoring, especially when non-coplanar fields are in use. At our institute, we have developed a surface-guided SRS (SG-SRS) workflow that incorporates our innovative open-face mask (OM) and mouth bite (MB) to guarantee a precise and accurate dose delivery. This study included 40 patients, and all patients were divided into closed mask (CM) and open-face mask (OM) groups according to different positioning flow. Cone beam computed tomography (CBCT) scans were performed, and the registration results were recorded before and after the treatment. Then Bland-Altman method was used to analyze the consistency of AlignRT-guided positioning errors and CBCT scanning results in the OM group. The error changes between 31 fractions in one patient were recorded to evaluate the feasibility of monitoring during treatment. The median of translation error between stages of the AlignRT positioning process was (0.03-0.07) cm, and the median of rotation error was (0.20-0.40)°, which were significantly better than those of the Fraxion positioning process (0.09-0.11) cm and (0.60-0.75)°. The mean bias values between the AlignRT guided positioning errors and CBCT were 0.01cm, -0.07cm, 0.03cm, -0.30°, -0.08° and 0.00°. The 31 inter-fractional errors of a single patient monitored by SGRT were within 0.10cm and 0.50°. The application of the SGRT with an innovative open-face mask and mouth bite device could achieve precision positioning accuracy and stability, and the accuracy of the AlignRT system exhibits excellent constancy with the CBCT gold standard. The non-coplanar radiation field monitoring can provide reliable support for motion management in fractional treatment.

Case of the Month from the Peter MacCallum Cancer Centre, Melbourne, Australia: combination of stereotactic ablative body radiotherapy and radical nephrectomy for synchronous bilateral primary renal cell carcinoma.

Case of the Month from the Peter MacCallum Cancer Centre, Melbourne, Australia: combination of stereotactic ablative body radiotherapy and radical nephrectomy for synchronous bilateral primary renal cell carcinoma.

Highly anisotropic geometrical Hall effect via f−d exchange fields in doped pyrochlore molybdates

When a conduction electron couples with a non-coplanar localized magnetic moment, the realspace Berry curvature is exerted to cause the geometrical Hall effect, which is not simply proportional to the magnetization. So far, it has been identified in the case mostly where the non-coplanar magnetic order is present on the sublattice of conduction electrons. Here, we demonstrate that the geometrical Hall effect shows up even without long-range magnetic order of conduction electrons, as induced by non-coplanar exchange fields from the localized magnetic moments, in hole-doped phyrochlore molybdates. We find that the geometrical Hall effect is markedly anisotropic with respect to the applied magnetic field direction, which is in good accordance with the field-dependent magnitude and sign change of the real-space scalar spin chirality of local Tb moments. These results may facilitate the understanding of emergent electromagnetic responses induced by the Kondo-like coupling between conduction electrons and local spins in a broad material class.

Experience of Radiation Theapy Using Non-Coplanar Fields Angles VMAT in the Implementation of Radiotherapy for Prostata Cancer Patients

Purpose: This study explored the non-coplanar VMAT planning technique for the pelvic area and its ability to achieve targeted clinical doses to increase the likelihood of tumor control for prostate cancer patients while reducing radiation exposure to the OAR. Materials and methods: The study included 12 patients with prostate cancer of low, intermediate and high risk of progression according to NCCN. Planning for six patients was performed using the coplanar VMAT technique. For the second group, also of 6 patients, non-coplanar VMATs were used, where out of two full arches only one full arch (FULLARC 1), gantry 181°-179° CW, couch 0 was used. Results: Implemented plans in the study method showed that the use of non-coplanar VMAT therapy fields can significantly reduce doses in OAR, in particular, the reduction in the average dose to the femoral heads was 46.6 %. Conclusion: This study has demonstrated the potential for a non-standard approach to patient treatment with non-coplanar VMAT treatment planning.

Precision radiotherapy by SPECT lung functional imaging in NSCLC

Background: Single Photon Emission Computed Tomography (SPECT) could be used to avoid the non-affected perfusion areas in patients with non-small-cell lung cancer (NSCLC) and to potentially reduce lung toxicity. The aim of this study is to compare dosimetric differences between two different 3D-conformal treatment plans, with and without CT/SPECT contribution. Methods: Simulation Computed tomography (CT) scans were accurately co-registered with SPECT scans and three different areas, based on SPECT intensity perfusion, were contoured: low perfusion (LP), medium perfusion (MP) and high perfusion (HP). Two different 3D-conformal plans, with co-planar and nonco-planar fields, were generated; one without SPECT information (anatomic plan), and one using the perfusion area identified with functional imaging (functional plan). Results: 9 patients were planned and a total of 18 plans were available for analysis. Anatomical and functional plans resulted in comparable planning target volume (PTV) coverage. In the functional plans, a significant reduction of dose in high perfusion areas was reported. The reduction of HP-V20 Gy values ranged from 15% to 8% (p = 0.046), the ipsiHP-V20 Gy from 38% to 22% (p = 0.028) and ipsiHP-Dmean reduction from 16 Gy to 12 Gy (p = 0.039). No significant differences in other organs at risk (OARs) metrics were reported between anatomical and functional plans. Conclusions: Despite the few cases reported, the strength of our study lies in the reported benefit of functional lung information in 3D conformal radiation planning, without compromising target coverage or worsening dose distribution to the OARs. There is an urgent need for prospective clinical and randomized trials in order to define the role of lung functional imaging in reducing toxicity in clinical practice.

Non-Coplanar vs. Coplanar Intensity-Modulated Radiation Therapy (IMRT) for Protection of Lip and Buccal Mucosa

In this study, by comparing the coplanar and non-coplanar intensity-modulated radiation therapy (IMRT) treatment planning in treating tongue cancer, the significance of non-coplanar fields in the protection of lip and buccal mucosa was determined, and a reasonable solution was selected.48 tongue cancer patients treated from June 2019 to Feb 2021 were selected and divided into coplanar field group and non-coplanar field group randomly: the former one used divided nine fields on average while the latter one adopted seven fields meanly with two other fields which needed to turn the bed 270 degrees for making the angle of radiation ray tangent to the region of mucous membrane. The mucosal dose limit changed from 15 Gy to 45 Gy for comparison of the two treatment plans. The evaluating indicators including conformal index (CI), homogeneity index (HI), D5, D50, D98 of the target volume. The dose of normal tissues and organs including spine, throat, bilateral parotid gland, pharyngeal constrictor and oral mucosa (lip, upper and lower buccal mucosa) were calculated under different mucosal dose limit. The clinical manifestations of lip and buccal mucositis of 48 cases were recorded and graded by NCI-CTCAE 4.0. Corresponding statistical analysis were performed.The difference of CI, HI, D98, D50 and D5 between two groups in the target volume has the tendency to become smaller when the mucosal dose limit is less than 30 Gy, with significant statistical difference (P < 0.05). When the limit exceeds 30 Gy, there are still statistical differences in other indicators except CI (P < 0.05). In terms of normal tissue, a certain gap of doses on normal tissues between two groups exists when the mucosal limit is lower than 20 Gy, with significant statistical difference (P < 0.05). When the limit exceeds 20 Gy, there was no statistical difference. There are statistical differences (P < 0.05) in D98, D50, D5, CI and HI of the target area between the two groups when the mucosal function setting is less than 30 Gy. When the mucosal function setting exceeds 30 Gy, there is no statistical difference in CI, but there were still statistical differences in others (P < 0.05). In normal tissue, there is statistical difference (P < 0.05) between two treatment plans when mucosal function setting is smaller than 20 Gy; if it exceeds, there is no statistical difference. The patients of non-coplanar group showed better results in terms of the radiation-related toxicity of lip and cheek membrane: the incidence rate and classification of severity were much lower. Patients usually developed lip and buccal mucositis after the fourth week during the radiotherapy, and symptoms of most cases were classified mild. 21 cases ranked grade I while the remaining 3 ranked grade II.Compared with coplanar field, non-coplanar field radiotherapy can effectively reduce the exposure dose of lip and buccal mucosa. The application of non-coplanar treatment plan has good clinical significance and deserves to be promoted.

OPAR: A Multicenter Phase II Randomized Trial of Fractionation Schedules for Once-a-Day Accelerated Partial Breast Irradiation (APBI)

<h3>Purpose/Objective(s)</h3> APBI is the delivery of radiotherapy (RT) to the tumor bed after breast conserving surgery (BCS) often given over a week or less. An attractive approach to deliver APBI is by external beam 3DCRT or IMRT. Previous studies have suggested that external beam APBI delivered twice-a-day can lead to increased late effects and poor breast cosmesis. The objective of our trial was to determine if two doses for APBI given once-a-day over 1-week result in acceptable long-term morbidity. <h3>Materials/Methods</h3> Eligible patients were > 50 years with DCIS or invasive breast cancer < 3 cm treated by BCS with negative margins and negative axillary nodes. Consenting patients were planned to receive APBI with 3-5 non-coplanar fields using a 3DCRT or IMRT and randomized to 27.5Gy or 30Gy each given in 5 fractions once-a-day over 5-8 days. Cosmetic evaluation with the EORTC Cosmetic Rating System was performed at baseline and 2 years by: a study nurse directly assessing the breast, and a group of oncologists unaware of RT regimen assessing photographs. Patient assessment of cosmesis was also performed at 3 years. Patients were followed for toxicity using the NCI CTCAE and recurrence. The primary outcome was adverse cosmesis (fair or poor global score) by photographic assessment at 2 years. The rate of adverse cosmesis with standard whole breast irradiation was 17% in our previous trial. Based on this consideration and one-sided α of 5% for each group, the upper bound of a one-sided 95% (two-sided 90%) confidence interval (CI) had to be < 23% for the treatment to be acceptable; 140 patients were required for each group. The proportion of patients with adverse cosmesis at 2 years and cosmetic deterioration from baseline to 2 years (excellent/good to fair/poor) with corresponding two-sided 90% CIs were estimated using the Wilson score method. The proportion of patients with any late breast toxicity (edema, induration, and telangiectasia) grades 2-3 at 2 years and local recurrence (LR) were also determined. <h3>Results</h3> Of the 281 patients: 139 were randomized to 27.5Gy and 142 to 30.0Gy. Median follow-up was 3 years. The mean age was 65 years; mean tumor size was 1.2cm. With respect to photographic assessment both schedules met our criteria for acceptability (Table 1). Adverse cosmesis assessed by nurse or patient and toxicity appeared to be less for 27.5Gy compared to 30Gy. No LRs were observed for 27.5Gy and one LR was observed for 30Gy. <h3>Conclusion</h3> According to the study design 27.5Gy and 30Gy resulted in acceptable cosmetic outcomes. In light of recent studies, the lower dose may be preferable in terms of late adverse effects but requires further evaluation.

Applications of various range shifters for proton pencil beam scanning radiotherapy

BackgroundA range pull-back device, such as a machine-related range shifter (MRS) or a universal patient-related range shifter (UPRS), is needed in pencil beam scanning technique to treat shallow tumors.MethodsThree UPRS made by QFix (Avondale, PA, USA) allow treating targets across the body: U-shaped bolus (UB), anterior lateral bolus (ALB), and couch top bolus. Head-and-neck (HN) patients who used the UPRS were tested. The in-air spot sizes were measured and compared in this study at air gaps: 6 cm, 16 cm, and 26 cm. Measurements were performed in a solid water phantom using a single-field optimization pencil beam scanning field with the ALB placed at 0, 10, and 20 cm air gaps. The two-dimensional dose maps at the middle of the spread-out Bragg peak were measured using ion chamber array MatriXX PT (IBA-Dosimetry, Schwarzenbruck, Germany) located at isocenter and compared with the treatment planning system.ResultsA UPRS can be consistently placed close to the patient and maintains a relatively small spot size resulting in improved dose distributions. However, when a UPRS is non-removable (e.g. thick couch top), the quality of volumetric imaging is degraded due to their high Z material construction, hindering the value of Image-Guided Radiation Therapy (IGRT). Limitations of using UPRS with small air gaps include reduced couch weight limit, potential collision with patient or immobilization devices, and challenges using non-coplanar fields with certain UPRS. Our experience showed the combination of a U-shaped bolus exclusively for an HN target and an MRS as the complimentary device for head-and-neck targets as well as for all other treatment sites may be ideal to preserve the dosimetric advantages of pencil beam scanning proton treatments across the body.ConclusionWe have described how to implement UPRS and MRS for various clinical indications using the PBS technique, and comprehensively reviewed the advantage and disadvantages of UPRS and MRS. We recommend the removable UB only to be employed for the brain and HN treatments while an automated MRS is used for all proton beams that require RS but not convenient or feasible to use UB.

Dosimetric investigation of non-coplanar field technology in static intensity-modulated radiation therapy for gastric carcinoma

Objective To compare the dosimetric characteristics of non-coplanar and coplanar field technology in static intensity-modulated radiotherapy of gastric cancer patients, so as to provide a reference for clinical radiotherapy plan selection. Methods Thirty-six patients with gastric cancer were selected to receive intensity-modulated radiotherapy in Huanggang Central Hospital, which was designed plan A and B. Group A used 7-field coplanar technology, while Group B used 7-fleld non-coplanar technology. We compared the differences of the optimized monitor unit, the dosimetry of organs at risk and target areas between group A and group B. Results Both group A and B could meet the requirements of doctors. The homogeneity index (0.14 ± 0.02), the conformity index (0.98 ± 0.01), D min (4 315.21 ± 16.74) cGy, D mean (4 679.28 ± 28.39) cGy and D max (4 952.30 ± 33.26) cGy of target areas in group B were better than those of group A. Moreover, the monitor unit of group B was much lower than that of group A, and the difference was statistically significant ( P < 0.05). The D max, D mean, V 15, V 20 and V 30 of the left and right kidneys in group B were lower than those of group A. The D max (3 408.57 ± 46.03) cGy, D mean (1 250.32 ± 14.27) cGy and V 20 (44.91% ± 6.67%) of spinal cord and the D max (3 408.57 ± 46.03) cGy, D mean (1 720.55 ± 17.42) cGy, V 20 (25.31% ± 7.78%) and V 30 (18.52% ± 1.56%) of small intestine were also lower than those of group A. The differences were statistically significant ( P < 0.05). Conclusion The non-coplanar field radiation plan has more advantages in terms of target dose distribution and protection of organs so that it can be more considerably used in the process of planning and design. 摘要： 目的 通过比较非共面射野与共面射野计划在胃癌静态调强中的剂量学特点, 为临床放疗计划选择提供依 据。 方法 选取黄冈市中心医院接受调强放射治疗的胃癌患者 36 例, 每名患者均设计A、B 2 组计划, A 组采用 7 野 共面技术, B 组采用 7 野非共面技术, 比较 A 组和 B 组优化后机器跳数、危及器官和靶区的剂量学差异。 结果 A、B 两组计划均能满足医生要求, B 组靶区均匀性指数 HI (0.14 ± 0.02)和适形度指数 CI (0.98 ± 0.01), 靶区 D min (4 315.21 ± 16.74) cGy, D mean (4 679.28 ± 28.39) cGy 和 D max (4 952.30 ± 33.26) cGy 均优于 A 组, 且 B 组机器跳数更 少, 差异有统计学意义 ( P < 0.05)。B 组左右侧肾脏 D max、 D mean、 V 15、 V 20 和 V 30均低于A组, 脊髓的 D max (3 408.57 ± 46.03) cGy、 D mean (1 250.32 ± 14.27) cGy 和 V 20 (44.91% ± 6.67%)以及小肠的 D max (3 408.57 ± 46.03) cGy、 D mean (1 720.55 ± 17.42) cGy、 V 20 (25.31% ± 7.78%) 和 V 30 18.52% ± 1.56%)也均低于 A 组, 差异有统计学意义 ( P < 0.05)。 结论 非共面射野计划在靶区剂量分布和危及器官保护上更优, 计划设计过程中可以更多的考虑非共面布野技术。

Noncoplanar Versus Coplanar Intensity-Modulated Radiation Therapy (IMRT) for Protection of the Lip and Buccal Mucosa

Objective:In this study, by comparing coplanar and noncoplanar intensity-modulated radiation therapy (IMRT) treatment planning in treating tongue cancer, the significance of noncoplanar fields in the protection of the lip and buccal mucosa was determined, and a reasonable solution was selected.Methods:Forty-eight tongue cancer patients treated from June 2019 to February 2021 were selected and randomly divided into a coplanar field group and a noncoplanar field group. The mucosal dose limit changed from 15 Gy to 45 Gy for comparison of the two treatment plans. The evaluation indicators (conformal index (CI); homogeneity index (HI); D5, D50, and D98 of the target volume; and the dose of normal tissues) were calculated under different mucosal dose limits. The clinical observation of the lip and buccal mucosa of 48 cases was monitored and graded carefully according to NCI-CTCAE V4.0. Statistical analyses were performed.Results:The differences in CI, HI, D98, D50 and D5 between the two groups in the target volume tended to decrease when the mucosal dose limit was less than 30 Gy, with a significant difference (P < 0.05). When the limit exceeded 30 Gy, significant differences in other indicators except CI (P < 0.05) were still noted. In normal tissue, differences in doses between the two groups existed when the mucosal limit was less than 20 Gy, with a significant difference (P < 0.05). When the limit exceeded 20 Gy, no significant difference was noted. Patients in the noncoplanar group showed significantly better results than those in the other group in terms of the radiation-related toxicity of the lip and cheek membrane(P < 0.001).Conclusions:Compared with coplanar field radiotherapy, noncoplanar field radiotherapy can effectively reduce the exposure dose to the lip and buccal mucosa. The application of noncoplanar treatment plans exhibits good clinical significance and deserves to be promoted.

Radiobiological assessment of nasopharyngeal cancer IMRT using various collimator angles and non-coplanar fields

AbstractAim:The aim of this study was to evaluate clinical efficacy and radiobiological outcome of intensity-modulated radiation therapy (IMRT) modalities using various collimator angles and non-coplanar fields for nasopharyngeal cancer (NPC).Materials and methods:A 70-Gy planning target volume dose was administered for 30 NPC patients referred for IMRT. Standard IMRT plans were constructed based on the target and organs at risk (OARs) volume; and dose constraints recommended by Radiation Therapy Oncology Group (RTOG). Using various collimator angles and non-coplanar fields, 11 different additional IMRT protocols were investigated. Homogeneity indexes (HIs) and conformation numbers (CNs) were calculated. Poisson and relative seriality models were utilised for estimating tumour control probability (TCP) and normal tissue complication probabilities (NTCPs), respectively.Results:Various collimator angles and non-coplanar fields had no significant effect on HI, CN and TCP, while significant effects were noted for some OARs, with a maximum mean dose (Dmax). No significant differences were observed among the calculated NTCPs of all the IMRT protocols. However, the protocol with 10° collimator angle (for five fields out of seven) and 8° couch angle had the lowest NTCP. Furthermore, the standard and some of non-coplanar IMRT protocols led to the reduction in OARs Dmax.Conclusions:Using appropriate standard/non-coplanar IMRT protocols for NPC treatment could potentially reduce the dose to the OARs and the probability of inducing secondary cancer in patients.

P2.06-02 Feasibility of Intensity Modulated Radiotherapy After Pleurectomy/Decortication for Malignant Pleural Mesothelioma Patients

Treatment strategies for patients with malignant pleural mesothelioma (MPM) include pneumectomy followed by radiation with considerable efficacy, although post-surgical morbidity and mortality are frequent. Recently, more conservative surgical approaches have been implemented, including Pleurectomy/Decortication (P/D), which spares the lung tissue while removing the malignant pleura and visible tumor. Although this approach significantly reduces surgical morbidity, it poses a challenge for post-surgical radiotherapy, as the risk of developing radiation pneumonitis is high. In this feasibility study we evaluated the loco-regional control and toxicity profile in patients with MPM treated with induction chemotherapy followed by P/C and Intensity Modulated Radiotherapy (IMRT) to the entire thoracic cavity. Patients with MPM treated from October 2011 to February 2014 were screened for inclusion. All patients underwent 4 cycles of induction chemotherapy with cisplatin/gemcitabine or cisplatin/pemetrexed without progression followed by P/D. Thereafter, patients received IMRT to the thoracic cavity (50.4-54 Gy in 28-30 fractions), treated with 9-11 non-coplanar fields. A total of 20 patients were screened for inclusion, from these, 13 patients were included in the final analysis. The median age was 61.3 ±10.3 years; 69.2% (9/13) were classified as low risk according to the European Organization for Research and Treatment of Cancer prognostic group. From the 13 patients, 12 (92.3%) had a histological diagnosis of epithelioid mesothelioma, while one patient (7.7%) presented with a sarcomatoid histology. Partial response to chemotherapy was observed in 61.5% (8/13) and stable disease in 38.5% (5/13). After P/D, only 23% (3/13) had residual macroscopic disease. The median follow-up was 23.6 months (7.5-44.7). Nine patients had recurrence or progression (6 distant [67%] and 3 loco-regional recurrences [33%]). 2-year Progression Free Survival was 31.3% (95%CI [8.72-57.51]). Only one patient died due to hepatic metastases. Any grade Pneumonitis was reported in 69.2% (9/13), however only 22.2% (n=2) of patients presented grade ≥3 pneumonitis. The V5 of the contralateral lung was above 70% and the V20 of the total lung was 45% in these patients. No IMRT-related deaths were observed throughout the study. Results from this pilot study show that it is feasible to administer IMRT to patients who have undergone P/D while maintaining an adequate toxicity profile. In our study pulmonary toxicity was frequent; however there was only one event of grade 4 pneumonitis, meanwhile the loco-regional control using this treatment modality shows great promise. However, a larger study with a more robust sample size is required to draw strong conclusions.

P220] DVH-based stereotactic plan QA using Dolphin detector

Purpose QA experience on stereotactic plans with Dolphin transmission detector and compass DVH analysis program. Methods 12 spine SBRT, 20 lung SBRT and 25 SRS/SRT patients were prepared non-coplanar VMAT field plans in the Monaco 5.11 treatment planning system. Patient QA was measured with the Dolphin transmission detector and evaluated by gamma index analysis in the DVH-based Compass 4.0.27 program. Gamma index values were calculated according to the criteria of 3%-3 mm, 2%-2 mm, 1%-1 mm and 3%-1 mm as dose difference and distance to agreement in QA of stereotactic plans. For a more detailed analysis, average gamma index values were calculated. In addition,1 cm, 2 cm, 3 cm and 4 cm margins were given to the PTV to form the gamma analysis volumes. Results Differences between Monaco TPS and Dolphin in SRS/SRT plans, PTV1: 5.1%, PTVaverage: 8.1% and PTV99: 9.2%. Differences between Compass and Dolphin in SRS/SRT plans, PTV1: 2.9%, PTVaverage: 4.8% and PTV99: 6.5%. Differences between Monaco TPS and Dolphin in lung SBRT plans, PTV1: 3.5%, PTVaverage: 2.2% and PTV99: 2.6%. Differences between Compass and Dolphin in Lung SBRT plans, PTV1: 2.7%, PTVaverage: 2% and PTV99: 2.6%. Differences between Monaco TPS and Dolphin in spine SBRT plans, PTV1: −1.9%, PTVaverage: −5.8% and PTV99: −6.8%. Differences between Compass and Dolphin in spine SBRT plans, PTV1: 3.3%, PTVaverage: −0.47% and PTV99: −1.1%. When average gamma values are examined in the regions formed with 1,2,3,4 cm margins in SRS/SRT/SBRT plans: 3%–3 mm 0.34–0.6, 2%–2 mm 0.51–0.83, 1%–1 mm 0.92–1.15, 3%–1 mm 0.36–0.86. In 2D gamma analysis, SRS/SRT was 96%, lung SBRT was 88% and spine SBRT was 84.1% according to the criteria of %2–2 mm. SRS/SRT was 93%, lung SBRT was 83% and spine SBRT was 72.4% according to the criteria of %3–1 mm. Conclusions DVH-based analysis has a crucial role in validating stereotactic plans. Assessment of QA from differences in PTV and OAR doses is one of the best verification methods.It is more accurate to analyze according to the criteria of 3–1 mm and 2–2 mm because it has high heterogeneity and gradient index in stereotactic plans. We do a more comprehensive analysis with average gamma. The main reason for differences between Monaco and Compass with dolphin measurement is that the plans have high dose gradients and high dose heterogeneity. Especially differences in small volume PTVs have been increasing.

P279] Inter- and intra-fraction tumor motion in lung SBRT

Purpose In Lung SBRT treatments, inter- and intra-fraction movement management are very important. The aim of the study is to determine the tumor movement as inter-fraction and intra-fraction. Methods For 8 lung SBRT patients, CT scans were performed at 1 mm slice intervals. Breath Hold CT was performed using the Catalyst™ surface scanning system in 2 patients and 4DCT scanning was performed in all 6 patients with respiratory phases. In the Monaco 5.11 treatment planning system, plans were prepared using 4–5 non-coplanar VMAT fields. The field to be scanned for intra-fraction CBCT was set to full rotation of 360°. Pre-CBCT scanning had performed in the XVI system before the patient began treatment and the amount of deviation in the tumor was determined in three dimensions. CBCT imaging was then performed intra-fraction while the 360° field was being treated both in the treatment. CBCT imaging was performed with 3 dimensional tumor tracking until the VMAT field was completed. After the VMAT field was completed, the motion in the tumor was examined in off-line mode. According to this procedure, inter- and intra-fraction guide was performed in 45 fractions in 8 lung SBRT patients and the amount of motion in the tumor was found. Results Inter-fraction absolute (±independent) deviation amounts; Lateral axis average: 0.48 mm, maximum: 1.84 mm, longitudinal axis average: 0.29 mm, maximum 1.18 mm, vertical axis average: 0.34 mm, maximum: 1.2 mm deviation found. Intra-fraction absolute (±independent) deviation amounts; Lateral axis average: 0.07 mm, maximum: 0.24 mm, longitudinal axis average: 0.14 mm, maximum 0.35 mm, vertical axis average: 0.12 mm, maximum: 0.6 mm deviation found. Conclusions When inter- and intra-fraction motion were evaluated, it was found that there was a maximum vertical movement. We found that there may be more differences in patient and tumor position between pre-CBCT scans, with positions according to the laser before treatment. Especially in some patients with 4DCT, the maximum deviation values were found to be 1.5 mm more. Because of inter-fractional motion, CBCT scanning is absolutely necessary before treatment begins. In general, three-axis is intra-fractional motion

Automatic online and real-time tumour motion monitoring during stereotactic liver treatments on a conventional linac by combined optical and sparse monoscopic imaging with kilovoltage x-rays (COSMIK)

The purpose of this study was to develop, validate and clinically demonstrate fully automatic tumour motion monitoring on a conventional linear accelerator by combined optical and sparse monoscopic imaging with kilovoltage x-rays (COSMIK).COSMIK combines auto-segmentation of implanted fiducial markers in cone-beam computed tomography (CBCT) projections and intra-treatment kV images with simultaneous streaming of an external motion signal. A pre-treatment CBCT is acquired with simultaneous recording of the motion of an external marker block on the abdomen. The 3-dimensional (3D) marker motion during the CBCT is estimated from the auto-segmented positions in the projections and used to optimize an external correlation model (ECM) of internal motion as a function of external motion. During treatment, the ECM estimates the internal motion from the external motion at 20 Hz. KV images are acquired every 3 s, auto-segmented, and used to update the ECM for baseline shifts between internal and external motion. The COSMIK method was validated using Calypso-recorded internal tumour motion with simultaneous camera-recorded external motion for 15 liver stereotactic body radiotherapy (SBRT) patients. The validation included phantom experiments and simulations hereof for 12 fractions and further simulations for 42 fractions. The simulations compared the accuracy of COSMIK with ECM-based monitoring without model updates and with model updates based on stereoscopic imaging as well as continuous kilovoltage intrafraction monitoring (KIM) at 10 Hz without an external signal. Clinical real-time tumour motion monitoring with COSMIK was performed offline for 14 liver SBRT patients (41 fractions) and online for one patient (two fractions).The mean 3D root-mean-square error for the four monitoring methods was 1.61 mm (COSMIK), 2.31 mm (ECM without updates), 1.49 mm (ECM with stereoscopic updates) and 0.75 mm (KIM).COSMIK is the first combined kV/optical real-time motion monitoring method used clinically online on a conventional accelerator. COSMIK gives less imaging dose than KIM and is in addition applicable when the kV imager cannot be deployed such as during non-coplanar fields.

Linear energy transfer distributions in the brainstem depending on tumour location in intensity-modulated proton therapy of paediatric cancer

Background: For tumours near organs at risk, there is concern about unintended increase in biological dose from elevated linear energy transfer (LET) at the distal end of treatment fields. The objective of this study was therefore to investigate how different paediatric posterior fossa tumour locations impact LET and biological dose to the brainstem during intensity-modulated proton therapy (IMPT).Material and methods: Multiple IMPT plans were generated for four different simulated tumour locations relative to the brainstem for a five-year-old male patient. A prescribed dose of 59.4 Gy(RBE) was applied to the planning target volumes (PTVs). Plans with two lateral and one posterior non-coplanar fields were created, along with plans with modified field arrangements. The dose-averaged LET (LETd) and the physical dose × RBELET (D × RBELET), where RBELET=1+c × LETd, were calculated using the FLUKA Monte Carlo code. A scaling parameter c was applied to make the RBELET represent variations in the biological effect due to LET.Results: High LETd values surrounded parts of the PTV and encompassed portions of the brainstem. Mean LETd values in the brainstem were 3.2–6.6 keV/μm. The highest absolute brainstem LETd values were seen with the tumour located most distant from the brainstem, whereas lower and more homogeneous LETd values were seen when the tumour invaded the brainstem. In contrast, the highest mean D × RBELET values were found in the latter case (54.0 Gy(RBE)), while the case with largest distance between tumour and brainstem had a mean D × RBELET of 1.8 Gy(RBE).Conclusions: Using IMPT to treat posterior fossa tumours may result in high LETd values within the brainstem, particularly if the tumour volume is separated from the brainstem. However, the D × RBELET was greater for tumours that approached or invaded the brainstem. Changing field angles showed a reduction of LETd and D × RBELET in the brainstem.

OUT-OF-FIELD DOSE MEASUREMENTS FOR 3D CONFORMAL AND INTENSITY MODULATED RADIOTHERAPY OF A PAEDIATRIC BRAIN TUMOUR.

The purpose of this study was to measure out-of-field organ doses in clinical conditions in anthropomorphic paediatric phantoms which received a simulated treatment of a brain tumour with intensity modulated radiotherapy (IMRT) and 3D conformal radiotherapy (3D CRT). Organ doses measured with radiophotoluminescent and thermoluminescent dosemeters were on average 1.6 and 3.0 times higher for the 5 y-old than for the 10 y-old phantom for IMRT and 3D CRT, respectively. A larger 5-y to 10-y organ dose ratio for 3D CRT can be explained because the use of a mechanical wedge for the 5-y-old 3D CRT phantom treatment increased out-of-field doses. Due to different configurations of the radiation fields, for both phantoms, the IMRT technique resulted in a higher non-target brain dose and higher eye doses but lower thyroid doses compared to 3D CRT. For 3D CRT (which used a non-coplanar field configuration), eye doses were 3-6% and for IMRT (which used a coplanar field configuration) 27-30% of the treatment dose, respectively. For thyroid and more distant organs, doses were less than 1% of the treatment dose. Comparison of measured doses and doses calculated by the treatment planning system (TPS) showed that the TPS underestimated out-of-field doses both for IMRT and 3D CRT.