Immobilization in stereotactic radiotherapy: the head and neck localizer frame.

Stereotactic radiotherapy refers to multiple daily fractions of radiation, over days or weeks of treatment, with the patient in a relocatable stereotactic frame. The linear accelerator-based, couch-mounted system from Radionics utilizes the Gill-Thomas-Cosman (GTC) frame and the new Tarbell-Loeffler-Cosman (TLC) pediatric frame for accurate positioning reproducibility. Radionics has now made available the Head and Neck Localizer (HNL) frame to be used with its XPlan treatment planning system and the mini multileaf collimator (MMLC). This will extend the overall capability of stereotactic radiotherapy to the treatment of head and neck cancers. However, with no data available on the HNL frame, a study is being undertaken to assess the accuracy in patient position reproducibility using the frame. This report provides the preliminary findings of comparing depth-helmet readings with radiographic data, together with recommended modifications to the frame.     

Simple method of stereotactic radiotherapy without stereotactic body frame for extracranial tumors

Thirty-five patients with metastatic lung cancer(46 lesions) and twenty patients with primary lung cancer (21 lesions) have been treated with a simple method of stereotactic radiotherapy (SRT) without stereotactic body frame. Tumor size ranged from 1-4 cm in diameter. We used Vac-Lok cushion(Med-Tek) as a immobilization system. To be sure to include the respiratory movement of tumor to planning target volume(PTV), every patients were examined by fluoroscopy and radio-opaque catheters with the same length of tumor movement were attached on the anterior and lateral chest wall before CT simulation. A gold grain was implanted into a tumor that was invisible on fluoroscopy, as a radiomaker. Protocol of 60 Gy/8 fractions/2 weeks and 45 Gy/3 fractions/3-6 days were mainly used. The median follow-up period was 15 months for primary lung cancer and 19 months for metastatic lung cancer. Local control rates were 91% for metastatic lung cancer, 89% for primary lung cancer and 85% for T1, 2N0M0 cases. All patients developed mild pneumonitis or fibrosis about 4.5 months after SRT just in the treatment volume. Only three patients was symptomatic.     

Interobserver variability of patient positioning using four different CT datasets for image registration in lung stereotactic body radiotherapy

Purpose

To assess the impact of different reference CT datasets on manual image registration with free-breathing three-dimensional (3D) cone beam CTs (FB-CBCT) for patient positioning by several observers.

Methods

For 48 patients with lung lesions, manual image registration with FB-CBCTs was performed by four observers. A slow planning CT (PCT), average intensity projection (AIP), maximum intensity projection (MIP), and midventilation CT (MidV) were used as reference images. Couch shift differences between the four reference CT datasets for each observer as well as shift differences between the observers for the same reference CT dataset were determined. Statistical analyses were performed and correlations between the registration differences and the 3D tumor motion and the CBCT score were calculated.

Results

The mean 3D shift difference between different reference CT datasets was the smallest for AIPvsMIP (range 1.1–2.2?mm) and the largest for MidVvsPCT (2.8–3.5?mm) with differences >10?mm. The 3D shifts showed partially significant correlations to 3D tumor motion and CBCT score. The interobserver comparison for the same reference CTs resulted in the smallest ?3D mean differences and mean ?3D standard deviation for ?AIP (1.5 ± 0.7?mm, 0.7 ± 0.4?mm). The maximal 3D shift difference between observers was 10.4?mm (?MidV). Both 3D tumor motion and mean CBCT score correlated with the shift differences (R_s = 0.336–0.740).

Conclusion

The applied reference CT dataset impacts image registration and causes interobserver variabilities. The 3D tumor motion and CBCT quality affect shift differences. The smallest differences were found for AIP which might be the most appropriate CT dataset for image registration with FB-CBCT.

     

Evaluation of fractionation regimens in stereotactic radiotherapy using a mathematical model of repopulation and reoxygenation.

PURPOSE: Various forms of stereotactic fractionation regimens have been used in the clinic. The purpose of this article is to evaluate the influence of the number of fractions on tumor control in stereotactic radiotherapy. METHODS: The 50% curative dose (D50) is calculated using a mathematical model of reoxygenation and repopulation. A review of the literature of stereotactic fractionation regimens is also presented. RESULTS: The number of fractions required to achieve the best therapeutic ratio is strongly influenced by the pattern of reoxygenation and the potential doubling time of the tumor. In the case of rapid repopulation, well-oxygenated clonogenic cells present a greater danger than hypoxic cells in a prolonged fractionated treatment schedule. In a slowly growing tumor, repopulation is relatively unimportant and the response is dominated by the pattern of reoxygenation. For a small number of large dose fractions, the potential doubling time and the time interval between fractions have a negligible effect on the D50 values. CONCLUSION: If a small number of large dose fractions is used in stereotactic radiotherapy and if reoxygenation occurs more efficiently with the passage of time, the therapeutic ratio can be enlarged by a sufficient time interval between fractions.     

Image-guidance technique comparison on respiratory reproducibility and dose indexes for stereotactic body radiotherapy in lung tumor

We investigated respiratory reproducibility from position errors of gold internal fiducial markers for breath-hold (BH) and real-time tumor tracking (RTT) techniques for stereotactic body radiotherapy in lung tumors. The relationship between position errors and dose indexes was checked for both techniques. The stereotactic body radiotherapy plan in lung tumors was planned for 29 patients. The tumor positioning was arranged using 1.5 mm diameter gold internal fiducial markers. First, CT images were acquired to analyze position errors of gold markers for BH and RTT techniques. The offset plans for both techniques were calculated by displacing the mean position errors. The dose indexes (D98, D95, D2, mean dose) in a planning target volume were evaluated from dose volume histograms for the original plan, BH, and RTT offset plans. The relationship between position errors and dose indexes was analyzed using the root mean square (RMS) for both techniques. For the BH, the RMS was 3.29 mm at the lower lobe. Similarly, it was 1.34 mm for the RTT. The difference for D98 by position error for BH was ?7.0 ± 10.8% at the lower lobe and the difference of all dose indexes for the RTT was less than 1%. The D2 and mean dose for both techniques were nearly the same as those of the original plan. In conclusion, the adaptation of the BH technique should be ≤2 mm RMS. If the position error is >2 mm RMS, the RTT technique should be used instead of the BH technique.     

Interbreath-hold reproducibility of lung tumour position and reduction of the internal target volume using a voluntary breath-hold method with spirometer during stereotactic radiotherapy for lung tumours

The purpose of this study was to evaluate the interbreath-hold reproducibility of the tumour (gross tumour volume, GTV) position and relative reduction of the internal target volume (ITV) using a voluntary breath-hold method with a spirometer in a clinical setting of stereotactic radiotherapy (SRT) for lung tumours 11 patients with 14 lung tumours were enrolled in this study. CT scans were performed once at the free breathing phase and five times at the breath holding phase before the first treatment day. Patients held their breath at the end-expiration phase under spirometer-based monitoring. All GTVs were delineated by a physician and the GTV centroid was calculated automatically. To evaluate the interbreath-hold reproducibility of the tumour position, we measured the distance of three dimensions (craniocaudal, CC; left-right, LR; anteroposterior, AP) and vectors between the GTV centroid and bony landmark. The reproducibility was defined as the average of the differences between the GTV centroid and bony landmark from the second to fifth CT scans with regard to that from the first CT scans. We also evaluated the relative reduction of ITV between the free breathing and breath-holding phase. The interbreath-hold reproducibility of the tumour position was 1.3+/-1.3 mm, 1.4+/-1.8 mm, 2.1+/-1.6 mm and 3.3+/-2.2 mm in CC, LR and AP directions and vectors, respectively. ITV at the breath-holding phase was significantly smaller than that at the free breathing phase (P<0.01). In conclusion, the voluntary breath-hold method with a spirometer is feasible, with relatively good reproducibility of the tumour position for SRT in the clinical setting.     

Treatment of metastatic liver tumors using stereotactic ablative radiotherapy Nair VJ,Pantarotto JP简

The prognosis of patients with metastatic liver disease remains dismal with a median survival of only 6-12 mo. As 80%-90% of patients are not candidates for surgical therapy, there is a need for effective non-surgical therapies that would improve outcomes in these patients. The body of evidence related to the use of stereotactic ablative radiotherapy (SABR) in metastatic liver disease has substantially grown and evolved over the past decade. This review summarizes the current evidence supporting liver SABR with particular attention given to patient selection, target delineation, organ at risk dose volume constraints, response evaluation imaging and the various SABR techniques for delivering ablative radiotherapy to the liver. Even though it is unclear what dose-fractionation scheme, delivery system, concomitant therapy or patient selection strategy yields the optimum liver SABR outcomes, clear and growing evidence is available that SABR is a safe and effective therapy for the treatment of oligometastatic liver disease.     

一种基于光学体表监测技术的新型摆位方法在头部放疗中的应用

目的提出一种基于光学体表监测技术的新型摆位方法,并对比分析其在头部放疗中与传统摆位方法的差异。方法通过图像引导配准结果回顾性分析2018年5月至2019年4月北京大学肿瘤医院放疗科99例头部肿瘤患者358次摆位数据,其中传统摆位方法130次(41例),新型摆位方法228次(58例)。对比摆位误差分布情况、异常摆位个数、摆位时间等指标评估新型摆位法的优势。结果新型摆位方法3个线性方向即升降(Vrt)、头脚(Lng)、左右(Lat)摆位误差绝对化后分别为(0.07±0.07)、(0.08±0.06)、(0.06±0.06)cm,3个旋转方向即偏转角(Rtn)、俯仰角(Pitch)、翻滚角(Roll)摆位误差绝对化后分别为(0.53±0.41)°、(0.59±0.44)°、(0.59±0.46)°。其摆位精度相对于传统方法组均有不同程度的改善,且差异均具有显著的统计学意义(t=3.24~6.10,P<0.001)。同时,新型摆位方法与传统摆位方法比较,异常摆位次数大幅降低,差异具有显著的统计学意义(χ^2=60.66,P<0.001),且摆位时间有所降低,但差异无统计学意义(P>0.05)。结论基于光学体表监测技术的新型摆位方法有效提高了头部肿瘤放疗患者的摆位精度,显著缩小了6自由度床修正范围,大幅度降低了异常摆位概率,提示在头部放疗中具有潜在的临床获益。     

Treatment planning for conformal stereotactic radiotherapy

Strahlentherapie und Onkologie - Due to three dimensional planning techniques it is possible to conform the high dose region precisely to a target volume inside the brain. Special patient fixation...     

Polyurethane positioning devices for radiotherapy

A simple and cheap method is described for the manufacturing of individual positioning aids made of foamed polyurethane. Some examples are given to demonstrate the applicability of these positioning aids for the irradiation of different body regions. The reproducibility of the radiation field in the head and neck area was investigated with and without positioning aid. It was proved that the field is adjusted more exactly when positioning aids are applied. The dosimetric investigations performed showed a negligible influence of foamed polyurethane on the radiation quality. So the positioning aids could be left within the radiation field when drawing the field borders.     

Evaluation of RayStation's delivered dose and accumulated dose features for spine stereotactic radiotherapy

We investigated delivered dose and dose accumulation features in the dose tracking module of RayStation version 11B before potential integration into the spine stereotactic radiosurgery (SSRS) program at our institution. End-to-end testing with a rigid Rando phantom was performed, and 10 retrospective clinical cases were selected for evaluation. Pre-treatment cone beam CTs (pCBCT) were corrected for Hounsfield unit (HU) integrity and contours were rigidly copied from the reference plan. We then calculated the delivered dose to the corrected cone beam CT (cCBCT). A deformable image registration (DIR) was generated between cCBCT and reference planning CT (rCT) using controlling region of interests. Deformed delivered dose to the rCT was summed to generate the accumulated dose for multiple fractions. The end-to-end tests of the phantom study revealed an improvement of cCBCT HU information by > 100 HU compared to the pCBCT. When compared to the reference plan, the delivered dose and deformed delivered dose were within 1.0% for the GTV and CTV and 3.0% for the spinal cord, respectively. Nearly all 10 clinical cases demonstrated delivered dose and accumulated dose deviations < 3.0% from the reference plan. However, 2 patients rendered delivered dose deviations between 3.0% and 4.0%, showing the effectiveness of the module. The dose tracking module in RayStation version 11B could potentially be utilized to aid clinical decision-making for external body shape change or positional deviation in SSRS for rigid target and critical structures. Evaluation before clinical application under one's specific practice is required, and results must be carefully analyzed specially near the high dose gradient area.     

Dosimetric evaluation of a new collimator insert system for stereotactic radiotherapy

The prototype of a stereotactic collimator set developed in our department is evaluated for clinical use. This set consists of three cylindrical blocks mounted on a tray which slides in the wedge insert of a Siemens Primus accelerator. Each block has a collimating hole along its long axis to produce radiation fields of circular cross-section at the isocentre plane with diameters of 15 mm, 20 mm and 25 mm. Different geometric and dosimetric quality assurance tests were performed and results are found within the limits set for stereotactic radiotherapy. Dosimetry results measured using Kodak EDR-2 radiographic film and a pinpoint ion chamber also show good agreement with corresponding results calculated by Monte Carlo simulation of the linear accelerator head and the collimators. Measured dosimetry data were used to adapt a conventional PLATO treatment planning system for stereotactic radiotherapy using the prototype collimator set. Treatment planning system calculations and film measurements for treatment of an intracranial lesion in an anthropomorphic head phantom using coplanar 180 degrees arcs are compared and found to agree within 2 mm. This supports the accuracy of dose delivery using the prototype stereotactic collimators. Despite their increased penumbra (2.5-3.5 mm relative to 2-2.5 mm for commercially available collimators) the ease of construction makes the proposed stereotactic collimators an interesting alternative for accomplishing cost effective stereotactic treatments.     

用MRI进行立体定向放射治疗定位的精确性

CT和MRI是SRT(立体定向放射治疗)定位经常采用的方法,二者各有优势。对MRI而言,由于存在着影像扭曲的问题,因此影响了SRT定位的精确性,并进一步影响了剂量分布的准确性。因此,MRI能否用于SRT定位,还存在着较大的争议。本文对近几年来的一些研究进行综述,以了解MRI用于SRT定位的原理、影像扭曲的来源、误差的大小及影响因素,相应的解决方法等。     

Independent dose verification for brain stereotactic radiotherapy using different add-on micro multi-leaf collimators

An add-on micro multi-leaf collimator (mMLC) is used for stereotactic radiosurgery (SRS) and brain stereotactic radiotherapy (SRT), in which rotational radiotherapy may make more complex and time-consuming. We performed a retrospective study of an independent dose calculation verification for brain SRS and SRT in two institutions to show the accuracy of the verification system and propose a tolerance value for the verification. Several comparisons of static plans and patients’ plans were conducted using a phantom measurement, and patients’ plans using the patients’ own computed tomography image. We evaluated the accuracy of the Clarkson-based dose calculation based on either the equivalent square field formed by the mMLC or by the collimator jaws to determine the collimator scatter factor (S _c). The results for the static plans showed good agreement (<1%), except when we used a 1 cm² field size (<4%). The phantom measurements for the patients’ plans showed deviations of 0.1 ± 2.3 and 1.2 ± 1.6% (2 SD) for the treatment planning system and the verification system, respectively. The patients’ plans showed a deviation of 2.0 ± 2.1% (2 SD). Depending on the mMLC system, the S _c was calculated using the equivalent field size formed by the mMLC. In this study, we suggest a tolerance level for the brain SRS and SRT of 2–3.5%. However, beam modeling in the treatment planning system would affect the deviation. The S _c should be computed according to the size of the collimator fitted to the MLC.     

Definition of stereotactic body radiotherapy

This report from the Stereotactic Radiotherapy Working Group of the German Society of Radiation Oncology (Deutschen Gesellschaft für Radioonkologie, DEGRO) provides a definition of stereotactic body radiotherapy (SBRT) that agrees with that of other international societies. SBRT is defined as a method of external beam radiotherapy (EBRT) that accurately delivers a high irradiation dose to an extracranial target in one or few treatment fractions. Detailed recommendations concerning the principles and practice of SBRT for early stage non-small cell lung cancer (NSCLC) are given. These cover the entire treatment process; from patient selection, staging, treatment planning and delivery to follow-up. SBRT was identified as the method of choice when compared to best supportive care (BSC), conventionally fractionated radiotherapy and radiofrequency ablation. Based on current evidence, SBRT appears to be on a par with sublobar resection and is an effective treatment option in operable patients who refuse lobectomy.     

再程立体定向放射治疗的应用

肿瘤经放射治疗或者多种方法联合治疗后,局部复发经常出现,但局部再程放疗仅适用于少数病人,因其会引起潜在的严重并发症,特别是对大体积的肿瘤进行再程放疗时。采用立体定向放射治疗(SBRT)对复发的椎体转移瘤、头颈部肿瘤、盆腔肿瘤进行再程放疗,不仅能够提高局部控制率并减轻症状,同时还能够减少正常组织不良反应。SBRT在临床上是一种安全有效的方法,建议将SBRT作为控制局部症状的重要治疗手段。     

Re-irradiation of recurrent anaplastic ependymoma using radiosurgery or fractionated stereotactic radiotherapy

Purpose

Recurrent ependymomas were retreated with stereotactic radiosurgery (SRS) or fractionated stereotactic radiotherapy (FSRT). The efficacy, toxicities, and differences between SRS and FSRT were analyzed.

Methods

Eight patients with recurrent ependymomas fulfilling the criteria described below were evaluated. Inclusion criteria were: (1) the patient had previously undergone surgery and conventional radiotherapy as first-line treatment; (2) targets were located in or adjacent to the eloquent area or were deep-seated; and (3) the previously irradiated volume overlapped the target lesion.

Results

FSRT was delivered to 18 lesions, SRS to 20 lesions. A median follow-up period was 23 months. The local control rate was 76 % at 3 years. No significant differences in local control were observed due to tumor size or fractionation schedule. Lesions receiving >25 Gy/5 fr or 21 Gy/3 fr did not recur within 1 year, whereas no dose–response relationship was observed in those treated with SRS. No grade ≥2 toxicity was observed.

Conclusion

Our treatment protocol provided an acceptable LC rate and minimal toxicities. Because local recurrence of tumors may result in patient death, a minimum dose of 21 Gy/3 fr or 25 Gy/5 fr or higher may be most suitable for treatment of these cases.

     

A simple computerized tomography adapter for conventional stereotactic frame

This paper introduces a new technique to convert a conventional Leksell stereotactic frame into a computerized tomography compatible system. Accurate calculation of the tumour coordinates can be made by means of two adapter plates with double diagonal lines on each side thus obviating the requirement of careful alignment of the scanner. The adapter plates are of simple design and easy to prepare.