Definition of a moving gross target volume for stereotactic radiation therapy of stented coronary arteries

Quantification of coronary artery motion and internal risk volume from ECG gated radiotherapy planning scans

BACKGROUND

Radiotherapy for carcinoma of breast and thoracic structures involves inadvertent radiation to heart and coronary arteries (CA). Coronary artery stenosis in high radiation dose segments has been documented. Cardiac and respiratory motion induced displacement of CA and internal risk volume (IRV) margin remains inadequately quantified.

MATERIAL AND METHODS

Twenty cases of carcinoma breast, lung and lung metastasis were enrolled in this study. ECG gated intravenous contrast enhanced computed tomography (CECT) scans were performed in inspiratory breath hold (IBH) and expiratory breath hold (EBH). The images were segregated into inspiratory systole (IS), inspiratory diastole (ID), expiratory systole (ES) and expiratory diastole (ED) sets. Left anterior descending (LAD), limited segment of LAD close to chest wall (short LAD), right coronary artery (RCA), Left circumflex artery (LCX) and left ventricle (LV) were delineated in all four sets. Mean displacements in systole versus diastole and inspiration versus expiration were calculated in three co-ordinates [anterio-posterior (Z), left-right (X) and cranio-caudal (Y)].

RESULTS

Mean of displacement (mm) between systole and diastole (IS versus ID; and ES versus ED) in X, Y, Z co-ordinates were: LAD 3.0(±1.6), 2.8(±1.5), 3.6(±2.0); Short-LAD 3.0(±1.1), 0.8(±0.4), 2.4(±0.6); LV 2.4(±1.6), 1.7(±1), 5.0(±1.5); LCX 4.9(±1.6), 2.9(±1.3), 5.1(±1.9); RCA 6.6(±2.2), 3.6(±2.1), 5.9(±2.2). Mean displacement between inspiration and expiration (IS versus ES; and ID versus ED) in X, Y, Z axes were: LAD 3.3(±1.5), 8.0(±3.4), 3.8(±1.8); Short-LAD 2.7(±1), 12.2(±4.4), 3.3(±1.5); LV 2.9(±1.4), 9.8(±3.3), 4.7(±1.9); LCX 2.9(±.8), 9.7(±3.2), 6.2(±2.5); RCA 2.6(±1.3), 7.6(±2.5), 3.8(±1.7).

CONCLUSION

Radial (RM), cranio-caudal margin (CC) of 7mm, 4mm in breath-hold radiotherapy whereas RM, CC of 7mm, 13mm respectively in free breath radiotherapy will cover the range of motions of CA, LV and can be recommended as IRV for these structures.

Estimation of the displacement of cardiac substructures and the motion of the coronary arteries using electrocardiographic gating

Purpose

The aim of this study was to quantify the displacement of cardiac substructures, including the anterior myocardial territory (AMT), left ventricle, and coronary arteries during a normal cardiac cycle.

Materials and methods

Computed tomography (CT) images with retrospective electrocardiographic gating of 17 eligible patients were obtained. All images were reconstructed automatically for the end-diastolic and end-systolic phases. CT scanning without contrast at a random phase and a selected vertebral body were used as references to measure three-dimensionaldisplacements of the cardiac substructures.

Results

The displacement between the end-diastolic and end-systolic phases (D_d-s) was greater than that between the end-systolic and random phases and between the end-diastolic and random cardiac phases. The largest displacements for the heart were in the left, posterior, and inferior directions with an average D_d-s of approximately 4–6 mm. The average D_d-s for the AMT and left ventricle was 1.2–2.7 mm in the anterior and right directions, 4.3–7.8 mm in left and posterior directions, and 4.9–6.3 mm in superior and inferior directions. For the coronary arteries, the average D_d-s was 2.8–5.9 mm in the anterior-posterior direction, 3.5–6.6 mm in left-right direction, and 3.8–5.3 mm in the superior-inferior direction. Inter-observer agreement was excellent for the heart, AMT, and left ventricle (kappa coefficient, >0.75 for all) and good for most coronary arteries in three dimensions (kappa coefficient, 0.511–0.687). The D_d-s did not differ significantly between men and women.

Conclusion

Most average displacements of the cardiac substructures and coronary arteries were 3–8 mm in three dimensions. These findings will be useful to accurately estimate the radiation dose to cardiac substructures during thoracic radiation and to evaluate the risk of radiation-related heart disease.

Small animal radiation research platform: imaging, mechanics, control and calibration

In cancer research, well characterized small animal models of human cancer, such as transgenic mice, have greatly accelerated the pace of development of cancer treatments. The goal of the Small Animal Radiation Research Platform (SARRP) is to make those same models available for the development and evaluation of novel radiation therapies. In combination with advanced imaging methods, small animal research allows detailed study of biological processes, disease progression, and response to therapy, with the potential to provide a natural bridge to the clinical environment. The SARRP will realistically model human radiation treatment methods in standard animal models. In this paper, we describe the mechanical and control structure of the system. This system requires accurate calibration of the x-ray beam for both imaging and radiation treatment, which is presented in detail in the paper.

Four-dimensional multislice computed tomography for determination of respiratory lung tumor motion in conformal radiotherapy

PURPOSE

We used four-dimensional multislice spiral computed tomography (MSCT) to determine respiratory lung-tumor motion and compared this strategy to common clinical practice in conformal radiotherapy treatment-planning imaging.

METHODS AND MATERIALS

The entire lung volume of 10 consecutive patients with 14 lung metastases were scanned by a 16-slice MSCT. During the scans, patients were instructed to breathe through a spirometer that was connected to a laptop computer. For each patient, 10 stacks of 1.5-mm slices, equally distributed throughout the respiratory cycle, were reconstructed from the acquired MSCT data. The lung tumors were manually contoured in each data set. For each patient, the tumor-volume contours of all data sets were copied to 1 data set, which allowed determination of the volume that encompassed all 10 lung-tumor positions (i.e., the tumor-traversed volume [TTV]) during the respiratory cycle. The TTV was compared with the 10 tumor volumes contoured for each patient, to which an empiric respiratory-motion margin was added. The latter target volumes were designated internal-motion included tumor volume (IMITV).

RESULTS

The TTV measurements were significantly smaller than the reference IMITV measurements (5.2 +/- 10.2 cm(3) and 10.1 +/- 13.7 cm(3), respectively). All 10 IMITVs for 2 of the 4 tumors in 1 subject completely encompassed the TTV. All 10 IMITVs for 3 tumors in 2 patients did not show overlap with up to 35% of the corresponding TTV. The 10 IMITVs for the remaining tumors either completely encompassed the corresponding TTV or did not show overlap with up to 26% of the corresponding TTV.

CONCLUSIONS

We found that individualized determination of respiratory lung-tumor motion by four-dimensional respiratory-gated MSCT represents a better and simple strategy to incorporate periodic physiologic motion compared with a generalized approach. The former strategy can, therefore, improve common and state-of-the-art clinical practice in conformal radiotherapy.

A biplane angiographic study on cardiac motion of coronary artery stents: options to minimize the target volume for high-precision external beam radiotherapy of coronary artery in-stent restenosis

PURPOSE

High-precision external beam radiotherapy (EBRT) has been suggested as a potential alternative to endovascular brachytherapy for the treatment of coronary artery in-stent restenosis. The purpose of our study was to investigate and compare different options to define a smallest feasible target volume.

METHODS AND MATERIALS

The cardiac motion of 17 coronary artery stents in 17 patients was studied by use of biplane conventional angiography, recorded during breath-hold. Each stent was reconstructed in three dimensions by use of biplane sets of frames covering an entire cardiac cycle. The volume traversed by the stent during the entire or part of the cardiac cycle was determined. Four options to define the stent-traversed volume (STV) as a target for high-precision EBRT were investigated.

RESULTS

The mean STV during the entire cardiac cycle was 3.5 cm3; the STV represented less than 1% of the heart volume in all patients. The STV during the diastolic and systolic phase resulted in a mean reduction of 26.6% and 29.1%, respectively, compared with the STV during the entire cardiac cycle. The smallest STV, measured during a 160-ms interval within the cardiac cycle, resulted in a mean maximal reduction of 75.9% compared with the STV during the entire cardiac cycle.

CONCLUSIONS

The STV during the entire cardiac cycle represents a small potential target volume for high-precision EBRT. A significant reduction of this target volume is possible in case of definition during a selected interval within the cardiac cycle.

Dosimetric comparison between high-precision external beam radiotherapy and endovascular brachytherapy for coronary artery in-stent restenosis

PURPOSE

Several drawbacks of endovascular brachytherapy for the treatment of coronary artery in-stent restenosis may be addressed by high-precision external beam radiotherapy (EBRT). The dosimetric characteristics of both treatment techniques were compared.

METHODS AND MATERIALS

The traversed volume of 10 coronary artery stents during the cardiac cycle was determined by electrocardiographically gated multislice spiral CT in 10 patients. By use of this traversed volume, high-precision EBRT treatment plans were generated for stents in the left circumflex (LCx), left anterior descending (LAD), and right coronary artery (RCA). The maximum dose to the nontargeted major coronary arteries was determined and compared to similar data calculated for endovascular brachytherapy.

RESULTS

High-precision EBRT targeted at LCx stents contributed a mean maximum dose (D(max)) of 83.5% (range: 71.6-95.3%) and 16.3% to the LAD and RCA, respectively. Targeted LAD stents contributed a mean D(max) of 39.3% (range: 14.5-94.8%) and 5.2% (range: 0-13.4%) to the LCx and RCA, respectively. Targeted RCA stents contributed a mean D(max) of 6.2% (range: 0-12.4%) and 5.8% (range: 0-11.5%) to the LCx and LAD, respectively. Endovascular brachytherapy targeted at LCx stents contributed a mean D(max) of 1.7% (range: 0.7-2.7%) and 1.0% (range: 0.6-1.4%) to the LAD and RCA, respectively. Targeted LAD stents contributed a mean D(max) of 5.2% (range: 0.5-11.4%) and 0.7% (range: 0.4-1.1%) to the LCx and RCA, respectively; targeted RCA stents contributed a mean D(max) of 0.3% (range: 0.2-0.5%) and 0.2% (range: 0.1-0.3%) to the LCx and LAD, respectively.

CONCLUSIONS

Although the doses distributed throughout the heart were higher for high-precision EBRT compared to endovascular brachytherapy, they are expected to be clinically irrelevant when nontargeted major coronary arteries are not closely situated to the targeted vessel segment. These encouraging results warrant further investigation of high-precision EBRT as a potential alternative to endovascular brachytherapy for the treatment of coronary artery in-stent restenosis.

Comparison of different methods to define a target volume for external beam radiation therapy of restenotic coronary arteries

PURPOSE

Different methods have been described to define a target volume for the treatment of restenotic (stented) coronary arteries by external beam radiation therapy (EBRT). The purpose of this study was to explore two methods to define a target for such therapy, and to compare these with previously investigated methods.

MATERIALS AND METHODS

The 3-D position of a stent throughout the cardiac cycle in the three major epicardial coronary arteries was measured in three patients by single-breathhold multislice spiral CT and breathhold biplane conventional X-ray angiography, both indexed in time with the ECG. The volume through which the stent traversed (STV) during the cardiac cycle was determined by use of displacement measurements.

RESULTS

For multislice CT and biplane angiography, respectively, the mean STV was 1.23 cm(3) (range 0.65-2.22 cm(3)) and 2.81 cm(3) (range 1.60-4.99 cm(3)). The STV represented only a fraction of the whole heart volume in all patients, that is, equal to or less than 0.4%.

CONCLUSIONS

Multislice CT and biplane angiography allowed the measurement of a relatively small potential target, that is the STV, for EBRT of restenotic stented coronary arteries. Both studied imaging modalities are instrumental for targeting the STV by highly conformal radiation therapy in case of restenotic stented coronary arteries.