Center Of Target Volume Research Articles

Experimental verification of a 3D in vivo dose monitoring system based on EPID.

PurposeTo evaluate the Edose system, a novel three-dimensional (3D) in vivo dose monitoring system based on electronic portal imaging device (EPID), prior to clinical application, we analyzed the preliminary clinical data using Edose system in patients receiving intensity-modulated radiation therapy (IMRT).Materials and methodsAfter the physical modeling, the measured results from the Edose system were examined in homogeneous and inhomogeneous phantoms, respectively. To verify the accuracy of the Edose system, we compared its results with testing results from ionization chamber, measurement matrix (Delta4) and dosimetric films. The dosimetric performance of the Edose system was evaluated in 12 randomly selected patients with IMRT and VMAT, and the measured results were compared with the treatment plans.ResultsCompared with the measured results, the dose difference at the center of target volume was (0.12±0.91)% and (0.03±0.85)%, the γ pass rate was (94.18±1.69)% and (95.24±1.62)% (3mm/3%)for homogeneous and inhomogeneous phantoms, respectively. For IMRT patients, the dose difference at the center of target volume was (0.75±1.53)%, and the γ pass rates were (89.11±3.24)% (3mm/3%) and (96.40±1.47)% (3mm/5%), respectively. Compared with the results of DVH, the maximum differences of PTVs and mostly organs at risk were all within 3%. For VMAT patients, the γ pass rates were (93.04 ± 2.62)% (3mm/3%) and (97.92 ± 1.38)% (3mm/5%), respectively.ConclusionsIn vivo dose monitoring may further improve the safety and quality assurance for radiation therapy. But rigorous clinical testing is required before putting the existing commercial systems into clinical application. In addition, more clinical experiences and better workflows for using the Edose system are needed.

SU-E-T-524: The Effect of CT Contrast on CyberKnife Treatment Planning.

To investigate the effect of CT contrast enhancement (CE) on the 3D dose distributions of non-coplanar small field beams in the CyberKnife (CK) treatment planning system. Twenty patients treated by pre-CE CT plans were recruited to this retrospective plan study. Their post-CE CT plans were based on the pre-CE CT plan data and calculated using the same MU and beam paths in either Ray-Tracing or Monte Carlo (MC) algorithms. The differences in doses of the beam path and the reference point and in DVHs of target and OARs between the pre-CE CT and the post-CE CT plans were compared. The minimum dose, the maximum dose, the mean dose, and the dose received to 50% of the target and OARs volumes, and the target volume coverage were also compared. The dose differences between the pre-CE and post-CE plans in a single beam path were less than 50 cGy in both calculation algorithms. At the center of target volume, it was 1.9% (maximum 6.2%) in Ray-Tracing and 1.5% (maximum 4.0%) in MC, with respect to the prescription dose. The post-CE plans showed on average 2% decrease in the OAR maximum dose (maximum 6.4% in Ray-Tracing and 5.8% in MC). Regardless of the algorithms, the dose to the target and the target volume coverage of post-CE plans were on average reduced by 2% and 1 %, respectively, with a maximum reduction of 6.1% (in Ray-Tracing) in the minimum target dose. The CK treatment plan using the post-CE CT could generally result in a few % dose differences from the pre-CE CT plan. However, it could be more than 6%, depending on the target positions in the body and the calculation algorithms. Thus the post-CE CT in CK treatment plans should be used with a caution.

Clinical outcomes of Cyberknife in brain metastases

Objective To retrospectively analyze clinical outcomes of brain metastases treated with Cyberknffe. Methods From Aug. 2006 to Aug. 2007, 40 patients with brain metastases treated with Cy-berknife in Tianjin Cancer Hospital were included. Totally 68 brain metastatic lesions were treated. The maximal diameter was 0.4 -7.5 cm (average 1.9 cm). The primary tumor of 35 patients was partial re-ponse or stable to the previous treatment at the diagnosis of brain metastasis. The geometric center of target volume was set as the isocenter and the nominal standard dose point. More than 95% target volume was cov-ered by 80% isodose surface. Hypofractionated radiation was 18 -36 Gy given in 1 -5 fractions of 5 -25 Gy. Results The Follow-up rate was 95%. The clinical symptom remission rate (including complete and partial remission) at one week after Cyberknife treatment was 90% (36/40). The therapeutic effective rate (CR + PR + SD) was 94% (64/68) after three months follow-up, which was evaluated by contrast-en-hanced CT or MRI. The 3-month local control and 1-year survival rates were 78% (53/68) and 68% (27/40). New brain metastatic lesions outside the radiation field occurred in 14 patients within 3 months, which was independent of age, whole brain irradiation, number or maximal diameter of original lesions, frac-tion dose, frequency or total dose of Cyberknife treatment. Conclusions Cyberknife, used as the primary treatment of brain metastases, can achieve good clinical outcomes. Key words: Neoplasm metastasis,brain/radiotherapy; Cyberknife; Treatment outcome

Ionization-cluster distributions of alpha-particles in nanometric volumes of propane: measurement and calculation.

The probability of the formation of ionization clusters by primary alpha-particles at 5.4 MeV in nanometric volumes of propane was studied experimentally and by Monte Carlo simulation, as a function of the distance between the center line of the particle beam and the center of the target volume. The volumes were of cylindrical shape, 3.7 mm in diameter and height. As the investigations were performed at gas pressures of 300 Pa and 350 Pa, the dimensions of the target volume were equivalent to 20.6 nm or 24.0 nm in a material of density 1.0 g/cm(3). The dependence of ionization-cluster formation on distance was studied up to values equivalent to about 70 nm. To validate the measurements, a Monte Carlo model was developed which allows the experimental arrangement and the interactions of alpha-particles and secondary electrons in the counter gas to be properly simulated. This model is supplemented by a mathematical formulation of cluster size formation in nanometric targets. The main results of our study are (i) that the mean ionization-cluster size in the delta-electron cloud of an alpha-particle track segment, decreases as a function of the distance between the center line of the alpha-particle beam and the center of the sensitive target volume to the power of 2.6, and (ii) that the mean cluster size in critical volumes and the relative variance of mean cluster size due to delta-electrons are invariant at distances greater than about 20 nm. We could imagine that the ionization-cluster formation in nanometric volumes might in future provide the physical basis for a redefinition of radiation quality.

Dose–Volume Analysis of Stereotactic Irradiation for Lung Tumors

Stereotactic irradiation (STI) of lung tumors may be accomplished with a linear accelerator by administering several noncoplaner arcs of a narrow beam focused at the center of target volume with a better immobilization device than conventional radiotherapy. The shape of the radiation distribution produced by this technique is affected by the field size, the number of arcs, the separation angles of the arcs, and the location of the tumor. The influence of these parameters on the resulting radiation distributions was analyzed by computing dose–volume histograms (DVH) for a typical lung. Dose–volume functions were computed for: (1) 1–12 arcs; (2) 20–45° separation angles of arc, (3) 80°–160° of gantry roration; and (4) 5 tumor locations using 4 × 4 cm2 rectangular fields. Analysis was based on the hypothetical set up without obstacles, such as the head and arms, and then extended to the practical set up, which is usable in daily practice. Dose–volume statistics showed that five non-coplanar 120° arcs and one 80° arc at different six positions of patient couch with a 30° separation between arcs may be one of the reasonable techniques for irradiation of tumors at the approximate center of the right lung. For tumors situated at more peripheral locations, smaller volume of lung receives dose of 20% to 90% of prescribed dose. Our study provides a basis for further analysis of STI for lung cancer and has the potential to be a treatment strategy for this disease.