Extracranial Stereotactic Radiotherapy Research Articles

TU‐FF‐A4‐03: Concept and Evaluation of Averaged 4‐D CT Imaging in Determining the Internal Target Volume for Extracranial Stereotactic Radiotherapy of Lung Nodules

Purpose: To evaluate the accuracy and robustness of averaging 4‐D images to determine the internal target volume (ITV) for small lung tumors during breathing. Method and Materials: A Philips Brilliance 16‐slice CT simulator (CT‐sim) obtained axial cinematographic (cine') images (512×512 pixels, 480mm FOV) of a phantom that moved with known distance and velocity in both the longitudinal and axial planes. The CT‐sim recorded 25 cine' images in each of 16 slices, 1.5mm thick to create a 24mm slab of data at different times during a motion cycle. The images at each slice position were averaged to produce composite slices. Composite slices were assembled longitudinally to produce a composite slab. Concatenated composite slabs are called an Averaged 4‐D (4‐DAvg) image set. Patients were scanned using the protocol above. Gross tumor volume (GTV) appearing in the 4‐DAvg image set was contoured to produce an mGTV (ITV minus the margin for sub‐clinical disease) before superposition on beam's‐eye‐view DRRs and transferred to an on‐line electronic portal imager (EPI) for comparison of the mGTV position to that of the GTV as observed during treatment. Results: Phantom measurements showed key factors which govern the ability of the 4‐DAvg image set to accurately represent the location of objects during motion: slice thickness, cine' duration relative to the period of motion and the sampling frequency of the cine' relative to the duration of motion at its extremes. We determined the position of objects undergoing a 0.2Hz movement over 20mm to within approximately 1.0mm. Similar results were obtained for a patient in the stereotactic body frame using an EPI. Conclusion: For tumors with motions having a frequency about 0.2Hz over a 20mm range, one can obtain positional accuracy within approximately 1mm using the 4‐DAvg technique outlined above. Conflict of Interest: Partly funded by Elekta, Inc., Norcross, GA.

2. 能動的呼吸抑制装置を用いた体幹部定位照射法の実際(高度先進技術を駆使した放射線治療への取り組み, 第60回総会学術大会シンポジウム)

2. 能動的呼吸抑制装置を用いた体幹部定位照射法の実際(高度先進技術を駆使した放射線治療への取り組み, 第60回総会学術大会シンポジウム)

Reproducibility of organ position using voluntary breath-hold method with spirometer for extracranial stereotactic radiotherapy

To evaluate in healthy volunteers the reproducibility of organ position using a voluntary breath-hold method with a spirometer and the feasibility of this method for extracranial stereotactic radiotherapy in a clinical setting. For this study, 5 healthy volunteers were enrolled. After training sessions, they held their breath at the end-inspiration and the end-expiration phase under spirometer-based monitoring. Computed tomography (CT) scans were performed twice at each respiratory phase, with a 10-min interval, on 2 separate days. The total number of CT scans was four at each respiratory phase. After CT volume data were transferred to a three-dimensional treatment-planning system, digitally reconstructed radiographs (DRRs) were calculated for anterior-posterior and left-right beams. Verification was performed with DRRs relative to the diaphragm position, bony landmarks, and the isocenter in each healthy volunteer at each respiratory phase. To evaluate intrafraction reproducibility, we measured the distance between diaphragm position and bony landmarks. To evaluate interfraction reproducibility, we measured the distance between diaphragm position and the isocenter. Reproducibility and setup error were defined as the average value of the differences between each DRR with regard to the first DRR. Intrafraction reproducibility of the caudal-cranial direction was 4.0 +/- 3.5 mm at the end-inspiration phase and 2.2 +/- 2.0 mm at the end-expiration phase. Interfraction reproducibility of the caudal-cranial direction was 5.1 +/- 4.8 mm at the end-inspiration phase and 2.1 +/- 1.8 mm at the end-expiration phase. The end-expiration phase was more stable than the end-inspiration phase. The voluntary breath-hold method with a spirometer is feasible, with relatively good reproducibility. We are encouraged about the use of this technique clinically for extracranial stereotactic radiotherapy.

352 oral Accuracy of patient setup for extracranial stereotactic radiotherapy for lung cancer

352 oral Accuracy of patient setup for extracranial stereotactic radiotherapy for lung cancer

1127 poster Stage I non-small cell lung cancer: treatment planning for extracranial stereotactic radiotherapy

1127 poster Stage I non-small cell lung cancer: treatment planning for extracranial stereotactic radiotherapy

Hypofractionation in non-small cell lung cancer (NSCLC): suggestions from modelling both acute and chronic hypoxia

Based on experimental estimates for acute and chronic tumour hypoxia, a speculative analysis of the therapeutic ratio dependence on the number of once-daily five-days-per-week fractions (n) for non-small cell lung cancer (NSCLC) radiotherapy is proposed. For this purpose an adapted formulation of the linear-quadratic model has been derived, including the effects of tumour repopulation, inter-tumour α-heterogeneity and oxygen enhancement ratio dependence on the dose per fraction. The relation between the curative dose D50, assuring 50% tumour control probability, and n has been computed: for (n, D50) fractionation schemes, the therapeutic ratios have been compared in terms of effective normalized total doses to the lungs (NTDeffL), estimated by a few supposed fractions of the normalized total dose to the tumour. Results suggest that D50 is dominated by chronic hypoxia for shortly hypofractionated treatments and by acute hypoxia for multifractionated treatments. Furthermore, the optimum number of fractions depends on the rapidity of the reoxygenation from chronically hypoxic cells, almost independently of the extent of both chronic and acute hypoxia. For NSCLC, both the reduction of n until about 20 fractions in hypofractionated dose-escalation trials, and the extension of extra-cranial stereotactic radiotherapy schedules to include at least 5–10 fractions, seem to be supported by this model.

Optimal treatment planning of extracranial stereotactic conformal radiotherapy for medically inoperable lung cancer

Stereotactic irradiation of extracranial targets is an emerging treatment approach in clinical radiotherapy. Unlike the situation for intracranial stereotactic irradiation or radiosurgery, hypofractionated stereotactic radiotherapy of extracranial targets is complicated by internal organ motion and difficulty regarding patient rigid fixation. Therefore, for clinical implementation of extracranial stereotactic radiotherapy, treatment planning strategies to reduce normal lung toxicity have to be analyzed and properly addressed.

Optimal treatment planning of extracranial stereotactic conformal radiotherapy for medically inoperable lung cancer

Optimal treatment planning of extracranial stereotactic conformal radiotherapy for medically inoperable lung cancer

Extracranial frameless stereotactic radiosurgery with multi-modal imaging and opto-electronic position verification

The purpose of the present work is to investigate the feasibility and develop the methods for a clinical protocol of frameless extracranial stereotactic hypo-fractioned radiotherapy and radiosurgery, for the treatment of small secondary tumours. The main concept relies on the exploitation of opto-electronic technologies and multi-modal imaging to increase the target localization accuracy in treatment planning and dose delivery. Preliminary results show that the combined use of PET/CT imaging and opto-electronic respiratory gating is a promising technique for the reduction of localization uncertainties in extracranial stereotactic irradiation. The application of moderate deep inspiration breath-hold manoeuvres, guided by an opto-electronic localizer, can provide an effective improvement in localization accuracy.

Stereotactic IMRT for prostate cancer: Setup accuracy of a new stereotactic body localization system

The purpose of this work is to prospectively assess the setup accuracy that can be achieved with a stereotactic body localizer (SBL) in immobilizing patients for stereotactic intensity-modulated radiotherapy (IMRT) for prostate cancer. By quantifying this important factor and target mobility in the SBL, we expect to provide a guideline for selecting planning target volume margins for stereotactic treatment planning. We analyzed data from 40 computed tomography (CT) studies (with slice thickness of 3 mm) involving 10 patients with prostate cancer. Each patient had four sets of CT scans during the course of radiotherapy. For the purpose of this study, all four sets of CT scans were obtained with the patients immobilized in a customized body pillow formed by vacuum suction. Unlike other immobilization devices, this system consists not only of a customized body pillow, but also of a fixation sheet used to suppress patient respiratory motion, a stereotactic body frame to provide stereotaxy, and a carbon fiber base board to which both the body cushion and the frame are affixed. We identified four bony landmarks and measured their coordinates in the stereotactic body frame on each set of CT scans. The displacements of the bony landmarks from their corresponding positions on the simulation scan (first CT scan) were analyzed in three dimensions in terms of overall, systematic, and random categories. The initial planned isocenter was also marked on the patients' skin with fiducials for each CT study. The distance from each bony landmark to the fiducial-based isocenter was measured and compared among the four sets of CT scans. The deviations in distances were also compared to those measured from the landmarks to the stereotactic frame center, in order to determine the effectiveness of the rigid body frame in positioning patients with prostate cancer. Target inter-fraction motion in this system was also studied for five patients by measuring the deviations in distances from the target geometric center to the bony landmarks. Our results showed that the overall setup accuracy had standard deviations (SDs) of 2.58 mm, 2.41 mm, and 3.51 mm in lateral (LAT), anterior-posterior (AP), and superior-inferior (SI) directions, respectively. The random component had SDs of 1.72 mm, 2.06 mm, and 2.79 mm, and the systematic component showed SDs of 0.92 mm, –0.27 mm, and 0.90 mm in these three directions. In terms of three-dimensional vector, the mean displacement over 116 measurements was 3.0 mm with an SD of 1.29 mm. Compared to the rigid reference, the skin-mark-based reference was less reliable for patient repositioning in terms of reproducing known bony landmark positions. The mean target mobility relative to the bony landmarks was , and in the AP, LAT, and SI directions, respectively. In conclusion, the body immobilization system has the ability to immobilize prostate cancer patients with satisfactory setup accuracy for fractionated extracranial stereotactic radiotherapy. A rigid frame system serves as a reliable alignment reference in terms of repositioning patients into the planning position, while skin-based reference showed larger deviations in repositioning patients. PACS number: 87.53Ly

Stereotactic IMRT for prostate cancer: Setup accuracy of a new stereotactic body localization system

The purpose of this work is to prospectively assess the setup accuracy that can be achieved with a stereotactic body localizer (SBL) in immobilizing patients for stereotactic intensity‐modulated radiotherapy (IMRT) for prostate cancer. By quantifying this important factor and target mobility in the SBL, we expect to provide a guideline for selecting planning target volume margins for stereotactic treatment planning. We analyzed data from 40 computed tomography (CT) studies (with slice thickness of 3 mm) involving 10 patients with prostate cancer. Each patient had four sets of CT scans during the course of radiotherapy. For the purpose of this study, all four sets of CT scans were obtained with the patients immobilized in a customized body pillow formed by vacuum suction. Unlike other immobilization devices, this system consists not only of a customized body pillow, but also of a fixation sheet used to suppress patient respiratory motion, a stereotactic body frame to provide stereotaxy, and a carbon fiber base board to which both the body cushion and the frame are affixed. We identified four bony landmarks and measured their coordinates in the stereotactic body frame on each set of CT scans. The displacements of the bony landmarks from their corresponding positions on the simulation scan (first CT scan) were analyzed in three dimensions in terms of overall, systematic, and random categories. The initial planned isocenter was also marked on the patients' skin with fiducials for each CT study. The distance from each bony landmark to the fiducial‐based isocenter was measured and compared among the four sets of CT scans. The deviations in distances were also compared to those measured from the landmarks to the stereotactic frame center, in order to determine the effectiveness of the rigid body frame in positioning patients with prostate cancer. Target inter‐fraction motion in this system was also studied for five patients by measuring the deviations in distances from the target geometric center to the bony landmarks. Our results showed that the overall setup accuracy had standard deviations (SDs) of 2.58 mm, 2.41 mm, and 3.51 mm in lateral (LAT), anterior‐posterior (AP), and superior‐inferior (SI) directions, respectively. The random component had SDs of 1.72 mm, 2.06 mm, and 2.79 mm, and the systematic component showed SDs of 0.92 mm, –0.27 mm, and 0.90 mm in these three directions. In terms of three‐dimensional vector, the mean displacement over 116 measurements was 3.0 mm with an SD of 1.29 mm. Compared to the rigid reference, the skin‐mark‐based reference was less reliable for patient repositioning in terms of reproducing known bony landmark positions. The mean target mobility relative to the bony landmarks was 2.22±3.45 mm,0.17±1.11 mm, and 0.11±2.69 mm in the AP, LAT, and SI directions, respectively. In conclusion, the body immobilization system has the ability to immobilize prostate cancer patients with satisfactory setup accuracy for fractionated extracranial stereotactic radiotherapy. A rigid frame system serves as a reliable alignment reference in terms of repositioning patients into the planning position, while skin‐based reference showed larger deviations in repositioning patients.PACS number: 87.53Ly

Reproducibility of patient positioning for fractionated extracranial stereotactic radiotherapy using a double-vacuum technique.

Precise reproducible patient positioning is a prerequisite for conformal fractionated radiotherapy. A fixation system based on double-vacuum technology is presented which can be used for conventional as well as hypofractionated stereotactic extracranial radiotherapy. To form the actual vacuum mattress, the patient is pressed into the mattress with a vacuum foil which can also be used for daily repositioning and fixation. A stereotactic frame can be positioned over the region of interest on an indexed base plate. Repositioning accuracy was determined by comparing daily, pretreatment, orthogonal portal images to the respective digitally reconstructed radiographs (DRRs) in ten patients with abdominal and pelvic lesions receiving extracranial fractionated (stereotactic) radiotherapy. The three-dimensional (3-D) vectors and 95% confidence intervals (CI) were calculated from the respective deviations in the three axes. Time required for initial mold production and daily repositioning was also determined. The mean 3-D repositioning error (187 fractions) was 2.5 +/- 1.1 mm. The largest single deviation (10 mm) was observed in a patient treated in prone position. Mold production took an average of 15 min (10-30 min). Repositioning times are not necessarily longer than using no positioning aid at all. The presented fixation system allows reliable, flexible and efficient patient positioning for extracranial stereotactic radiotherapy.

Reproducibility of organ position using voluntary breath hold method with spirometer during extracranial stereotactic radiotherapy

Reproducibility of organ position using voluntary breath hold method with spirometer during extracranial stereotactic radiotherapy

Hypofractionated extracranial stereotactic radiotherapy for liver tumors

Hypofractionated extracranial stereotactic radiotherapy for liver tumors

328 poster Hypofractionation in extracranial stereotactic radiotherapy: implications of modelling acute hypoxia

328 poster Hypofractionation in extracranial stereotactic radiotherapy: implications of modelling acute hypoxia

113 oral Extracranial stereotactic radiotherapy of lung and liver cancer — a clinical comparison of two treatment planning systems

113 oral Extracranial stereotactic radiotherapy of lung and liver cancer — a clinical comparison of two treatment planning systems

Extracranial stereotactic radiation delivery: expansion of technology beyond the brain.

The development of improved immobilization systems, and a greater understanding of the radiobiologic considerations associated with stereotactic radiotherapy has recently led to the clinical implementation of this technology to extracranial sites. The shared principles of targeting and treatment delivery has led to a greater understanding of the potential role this therapy may have in the management of extracranial disease. This article will review, the radiobiologic considerations and the basic principles of physics and dosimetry that help govern the utilization of extracranial stereotactic radiotherapy. In addition, this article will summarize the data that exists in the literature to date, that has documented the rationale, and efficacy of this novel therapeutic approach.

Impact of target reproducibility on tumor dose in stereotactic radiotherapy of targets in the lung and liver.

Previous analyses of target reproducibility in extracranial stereotactic radiotherapy have revealed standard security margins for planning target volume (PTV) definition of 5mm in axial and 5-10mm in longitudinal direction. In this study the reproducibility of the clinical target volume (CTV) of lung and liver tumors within the PTV over the complete course of hypofractionated treatment is evaluated. The impact of target mobility on dose to the CTV is assessed by dose-volume histograms (DVH). Twenty-two pulmonary and 21 hepatic targets were treated with three stereotactic fractions of 10 Gy to the PTV-enclosing 100%-isodose with normalization to 150% at the isocenter. A conformal dose distribution was related to the PTV, which was defined by margins of 5-10mm added to the CTV. Prior to each fraction a computed tomography (CT)-simulation over the complete target volume was performed resulting in a total of 60 CT-simulations for lung and 58 CT-simulations for hepatic targets. The CTV from each CT-simulation was segmented and matched with the CT-study used for treatment planning. A DVH of the simulated CTV was calculated for each fraction. The target coverage (TC) of dose to the simulated CTV was defined as the proportion of the CTV receiving at least the reference dose (100%). A decrease of TC to <95% was found in 3/60 simulations (5%) of pulmonary and 7/58 simulations (12%) of hepatic targets. In two of 22 pulmonary targets (9%) and in four of 21 hepatic targets (19%) a TC of <95% occurred in at least one fraction. At risk for a decreased TC <95% were pulmonary targets with increased breathing mobility and hepatic targets with a CTV exceeding 100 cm(3). Target reproducibility was precise within the reference isodose in 91% of lung and 81% of liver tumors with a TC of the complete CTV >or=95% at each fraction of treatment. Pulmonary targets with increased breathing mobility and liver tumors >100 cm(3) are at risk for target deviation exceeding the standard security margins for PTV-definition at least for one fraction and require individual evaluation of sufficient margins.

Extracranial stereotactic radiotherapy: Evaluation of PTV coverage and dose conformity

During the past few years the concept of cranial stereotactic radiotherapy has been successfully extended to extracranial tumoral targets. In our department, hypofractionated treatment of tumours in lung, liver, abdomen, and pelvis is performed in the Stereotactic Body Frame (ELEKTA Instrument AB) since 1997. We present the evaluation of 63 consecutively treated targets (22 lung, 21 liver, 20 abdomen/pelvis) in 58 patients with respect to dose coverage of the planning target volume (PTV) as well as conformity of the dose distribution. The mean PTV coverage was found to be 96.3% ± 2.3% (lung), 95.0% ± 4.5% (liver), and 92.1% ± 5.2% (abdomen/pelvis). For the so-called conformation number we obtained values of 0.73 ± 0.09 (lung), 0.77 ± 0.10 (liver), and 0.70 ± 0.08 (abdomen/pelvis). The results show that highly conformal treatment techniques can be applied also in extracranial stereotactic radiotherapy. This is primarily due to the relatively simple geometrical shape of most of the targets. Especially lung and liver targets turned out to be approximately spherically/cylindrically shaped, so that the dose distribution can be easily tailored by rotational fields.

Extracranial stereotactic radiotherapy: evaluation of the ptv to compensate target mobility and set-up inaccuracy over the complete target volume measured by dvh from repeated ct-simulation

Extracranial stereotactic radiotherapy: evaluation of the ptv to compensate target mobility and set-up inaccuracy over the complete target volume measured by dvh from repeated ct-simulation