Respiratory-driven lung tumor motion is independent of tumor size, tumor location, and pulmonary function

Self Cite

In this study, we compared the amount of lung tissue irradiated when respiratory gating was imposed during expiration with the amount of lung tissue irradiated when gating was imposed during inspiration. Our hypothesis was that the amount of lung tissue spared increased as inspiration increased. Computed tomography (CT) image data sets were acquired for 10 patients diagnosed with primary bronchogenic carcinoma. Data sets were acquired during free breathing, during breath‐holds at 0% tidal volume and 100% tidal volume, and, when possible, at deep inspiration corresponding to approximately 60% vital capacity. Two treatment plans were developed on the basis of each of the gated data sets: one in which the treatment portals were those of the free‐breathing plan, and the other in which the treatment portals were based on the gated planning target volumes. Dose‐mass histograms of the lungs calculated at 0% tidal volume were compared to those calculated at deep inspiration and at 100% tidal volume. Data extracted from the dose‐mass histograms were used to determine the most dosimetrically beneficial point to gate, the reduction in the amount of irradiated lung tissue that resulted from gating, and any disease characteristics that might predict a greater need for gating. The data showed a reduction in the mass of normal tissue irradiated when treatment portals based on the gated planning target volume were used. More normal lung tissue was spared at deep inspiration than at the other two gating points for all patients, but normal lung tissue was spared at every point in the respiratory cycle. No significant differences in the amount of irradiated tissue by disease characteristic were identified. Respiratory gating of thoracic radiation treatments can often improve the quality of the treatment plan, but it may not be possible to determine which patients may benefit from gating prior to performing the actual treatment planning.PACS numbers 87.53 –j; 87.53.Tf

Section: Resultssupporting

confidence: 92%

Dosimetric benefits of respiratory gating: a preliminary study

Butler

Forster

Stevens

et al. 2004

Self Cite

“…As our institution does not have 4D CT, a collaborative deep inspiration/deep expiration CT scan could prove useful when attempting to estimate an upper limit to the amount and direction of tumor motion that could be useful when analyzing the necessary margins. This motion is not predictable by location, 5 , 36 as we observed in specific cases. Although intrafraction motion has been demonstrated, 4 , 6 , 27 we observed that

R_{m}

and

R_{95 %}

were stable estimators during a treatment for each patient.…”

Section: Discussioncontrasting

confidence: 51%

“…Although this step is not independent of Step 2, we considered them independent and conservatively assumed that all the uncertainty for this step was due to changes in the respiratory cycle from the external markers, variations in patient respiratory cycles, correlation between skin and internal fiducials, and unknown sources 4 , 5 , 6 , 29 , 30 . We assumed that the variation in the seed configuration during treatment had no effect on the correlation model.…”

Section: Methodsmentioning

confidence: 99%

“…During recent decades, understanding the movement of the tumor in the thorax and its reproducibility during treatment has been an area of concern 1 , 2 , 3 , 4 , 5 , 6 . A variety of methods have been proposed to manage respiratory motion, (1) and the margins necessary to compensate for geometric uncertainties have been reduced, depending on the technique 7 , 8 .…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Retrospective evaluation of CTV to PTV margins using CyberKnife in patients with thoracic tumors

Floriano

García²,

Moreno³

et al. 2014

The objectives of this study were to estimate global uncertainty for patients with thoracic tumors treated in our center using the CyberKnife VSI after placement of fiducial markers and to compare our findings with the standard CTV to PTV margins used to date. Datasets for 16 patients (54 fractions) treated with the CyberKnife and the Synchrony Respiratory Tracking System were analyzed retrospectively based on CT planning, tracking information, and movement data generated and saved in the logs files by the system. For each patient, we analyzed all the main uncertainty sources and assigned a value. We also calculated an expanded global uncertainty to ensure a robust estimation of global uncertainty and to enable us to determine the position of 95% of the CTV points with a 95% confidence level during treatment. Based on our estimation of global uncertainty and compared with our general margin criterion (5 mm in all three directions: superior/inferior [SI], anterior/posterior [AP], and lateral [LAT]), 100% were adequately covered in the LAT direction, as were 94% and 94% in the SI and AP directions. We retrospectively analyzed the main sources of uncertainty in the CyberKnife process patient by patient. This individualized approach enabled us to estimate margins for patients with thoracic tumors treated in our unit and compare the results with our standard 5 mm margin.PACS number: 87.55‐x

“…Theoretically, patients would adjust themselves to meet the requirements of treatment with elapsed time. But a single planning CT scan cannot predict the change of respiration pattern (30) . Furthermore, concomitant diseases, such as slight pleural effusion, pneumothorax and pulmonary emphysema, could exert an effect on the position of tumor during treatment.…”

Section: Discussionmentioning

confidence: 99%

Evaluation of interfractional variation of the centroid position and volume of internal target volume during stereotactic body radiotherapy of lung cancer using cone‐beam computed tomography

Sun

Cheng

et al. 2016

The purpose of this study was to determine interfractional variation of the centroid position and volume of internal target volume (ITV) during stereotactic body radiation therapy (SBRT) of lung cancer. From January 2014 to August 2014, a total of 32 patients with 37 primary or metastatic lung tumors were enrolled in our study. All patients received SBRT treatment in 4–5 fractions to a median dose of 48 Gy. Both 3D CT and 4D CT scans were used for radiotherapy treatment planning. 3D CBCT was acquired prior to treatment delivery to verify patient positioning. A total of 163 3D CBCT images were available for evaluation. 3D CBCT scans acquired for verification were registered with simulation CT scans. The ITVs were contoured on all verification 3D CBCT scans and compared to the initial gross target volume (GTV) or ITV in treatment planning system. GTV was based on 3D CT while ITV was based on both 3D CT and 4D CT. To assess the interfractional variation of ITV centroid position, we used vertebrae body adjacent to the tumor as reference point when performing the registration procedure. To eliminate the effect of time on tumor volume between simulation CT scan and the first fraction, the interfractional variation of ITV was evaluated from the first fraction to the last fraction. The overall 3D vector shift was 4.4±2.5 mm (range: 0.4−13.8 mm). The interfractional variation of ITV centroid position in superior‐inferior, anterior‐posterior, and left‐right directions were −0.7±2.7 mm, −1.4±3.4 mm, and −0.5±2.2 mm, respectively. No significant difference was observed between three directions (p=0.147). Large interfractional variations (≥5 mm) were observed in 12 fractions (9.3%) in superior‐inferior direction, 24 fractions (18.6%) in anterior‐posterior direction, and 5 fractions (3.9%) in left‐right direction. No time trend of tumor volume change measured in 3D CBCT was detected during four fractions (p=0.074). A significant (p=0.010) time trend was detected when evaluating the time trend of ITV change during 5 fractions and diameter was found to be significantly correlated with the ITV change (p=0.000). ITV did not show significant regression during SBRT treatment, but interfractional variation in the ITV centroid position was observed, especially in anterior‐posterior direction. An isotropic margin of 7 mm around ITV might be necessary for adequate coverage of interfractional variation of ITV centroid position, but only in case no soft tissue‐based setup is performed during SBRT treatment.PACS number(s): 87.55.dk