Analysis of components of variance determining probability of setup errors in CBCT-guided stereotactic radiotherapy of lung tumors.

Purpose: Online tumor matching for SABR lung setup requires margins for inaccuracies due to intra-fraction variability of breathing-averaged tumor position (BATP) and CBCT image guidance. We studied intra-fraction variability during SABR delivery using VMAT, corrected these for measurement inaccuracies, and quantified the CBCT image-guidance uncertainties.

Materials And Methods: For 193 fractions in 38 patients positioned without immobilization devices, CBCT scans were acquired before and after 2 arcs of a RapidArc treatment.

Isotoxic radiosurgery planning for brain metastases.

Purpose/objective(s): Radionecrosis (RN) has previously been correlated with radiosurgery (RS) dose, lesion volume, and the volume of the brain receiving specific doses, i.e. V10-14Gy.

Frameless high dose rate stereotactic lung radiotherapy: intrafraction tumor position and delivery time.

Intrafraction change in tumor position (Δ) was evaluated for stereotactic lung radiotherapy delivered with flattening filter free volumetric modulated arc therapy. In 140 fractions from 32 patients mean Δ (±SD) was -0.7±1.

Dosimetric impact of intrafraction motion during RapidArc stereotactic vertebral radiation therapy using flattened and flattening filter-free beams.

Purpose: To study the dosimetric impact of relatively short-duration intrafraction shifts during a single fraction of RapidArc delivery for vertebral stereotactic body radiation therapy (SBRT) using flattened (FF) and flattening filter-free (FFF) beams.

Methods And Materials: The RapidArc plans, each with 2 to 3 arcs, were generated for 9 patients using 6-MV FF and 10-MV FFF beams with maximum dose rates of 1000 and 2400 MU/min, respectively. A total of 1272 plans were created to estimate the dosimetric consequences in target and spinal cord volumes caused by intrafraction shifts during one of the arcs.

Flattening filter free vs flattened beams for breast irradiation.

Purpose: Flattening filter free (FFF) beams offer the potential for a higher dose rate, shorter treatment time, and lower peripheral dose. To investigate their role in large-field treatments, this study compared flattened and FFF beams for breast irradiation.

Methods And Materials: Ten left breast clinical plans comprising 2 tangential beams and a medially located 3-field simultaneous integrated boost (SIB) were replanned.

Clinical application of a novel hybrid intensity-modulated radiotherapy technique for stage III lung cancer and dosimetric comparison with four other techniques.

Purpose: In large stage III lung tumors, planning delivery of doses exceeding 60 Gy can be challenging and time consuming. Intensity modulated radiation therapy (IMRT) can improve target coverage but may increase volumes receiving low-dose irradiation. We clinically implemented a novel hybrid IMRT (h-IMRT) technique that allowed plans to be produced quickly, and compared these plans with 4 other techniques.

Fast arc delivery for stereotactic body radiotherapy of vertebral and lung tumors.

Purpose: Flattening filter-free (FFF) beams with higher dose rates and faster delivery are now clinically available. The purpose of this planning study was to compare optimized non-FFF and FFF RapidArc plans for stereotactic body radiotherapy (SBRT) and to validate the accuracy of fast arc delivery.

Methods And Material: Ten patients with peripheral lung tumors and 10 with vertebral metastases were planned using RapidArc with a flattened 6-MV photon beam and a 10-MV FFF beam for fraction doses of 7.

Impact of the calculation resolution of AAA for small fields and RapidArc treatment plans.

Purpose: To investigate the impact of the calculation resolution of the anisotropic analytical algorithms (AAA) for a variety of small fields in homogeneous and heterogeneous media and for RapidArc plans.

Methods: Dose distributions calculated using AAA version 8.6.

Stereotactic radiotherapy for peripheral lung tumors: a comparison of volumetric modulated arc therapy with 3 other delivery techniques.

Purpose: Volumetric modulated arc therapy (RapidArc) allows for fast delivery of stereotactic body radiotherapy (SBRT) delivery in stage I lung tumors. We compared dose distributions and delivery times between RapidArc and common delivery techniques in small tumors.

Methods: In 18 patients who completed RapidArc SBRT for tumors measuring <70 cm(3), new treatment plans were generated using non-coplanar 3D conformal fields (conf-SBRT) and dynamic conformal arc radiotherapy (DCA).

A novel simple approach for incorporation of respiratory motion in stereotactic treatments of lung tumors.

Purpose: An internal target volume (ITV) is often used for incorporating tumor motion into radiotherapy planning but it overestimates the margins necessary for breathing motion. We describe a pragmatic approach using maximum- and minimum-intensity projections (MIP and Min-IP) only, for reducing ITVs in stereotactic radiotherapy by using dosimetric margins that compensate for motion-induced dose blurring.

Patients And Method: We studied tumor motion characteristics from 26 repeat 4DCT scans derived from 10 patients.

The accuracy of frameless stereotactic intracranial radiosurgery.

Purpose: To determine the accuracy of frameless stereotactic radiosurgery using the BrainLAB ExacTrac system and robotic couch by measuring the individual contributions such as the accuracy of the imaging and couch correction system, the linkage between this system and the linac isocenter and the possible intrafraction motion of the patient in the frameless mask.

Materials And Methods: An Alderson head phantom with hidden marker was randomly positioned 31 times. Automated 6D couch shifts were performed according to ExacTrac and the deviation with respect to the linac isocenter was measured using the hidden marker.

Quality assurance of 4D-CT scan techniques in multicenter phase III trial of surgery versus stereotactic radiotherapy (radiosurgery or surgery for operable early stage (stage 1A) non-small-cell lung cancer [ROSEL] study).

Purpose: To determine the accuracy of four-dimensional computed tomography (4D-CT) scanning techniques in institutions participating in a Phase III trial of surgery vs. stereotactic radiotherapy (SBRT) for lung cancer.

Methods And Materials: All 9 centers performed a 4D-CT scan of a motion phantom (Quasar, Modus Medical Devices) in accordance with their in-house imaging protocol for SBRT.

Dosimetric impact of interplay effect on RapidArc lung stereotactic treatment delivery.

Purpose: Volumetric modulated arc therapy (RapidArc; Varian Medical Systems, Palo Alto, CA) allows fast delivery of stereotactic radiotherapy for Stage I lung tumors. We investigated discrepancies between the calculated and delivered dose distributions, as well as the dosimetric impact of leaf interplay with breathing-induced tumor motion.

Methods And Materials: In 20 consecutive patients with Stage I lung cancer who completed RapidArc delivery, 15 had tumor motion exceeding 5 mm on four-dimensional computed tomography scan.

Rapid delivery of stereotactic radiotherapy for peripheral lung tumors using volumetric intensity-modulated arcs.

The delivery of high dose conventional stereotactic body radiotherapy (SBRT) for patients with stage I lung tumors generally takes 30-45min per fraction. The novel volumetric intensity-modulated arc therapy (RA) for planning and delivery enabled much faster treatment for three patients with different fractionation schemes. This reduces the risk of intrafraction motion and is more patient friendly.

Volumetric intensity-modulated arc therapy vs. conventional IMRT in head-and-neck cancer: a comparative planning and dosimetric study.

Purpose: Volumetric intensity-modulated arc therapy (RA) allows for rapid delivery of highly conformal dose distributions. In this study, planning and dosimetry of RA were compared with conventional intensity-modulated radiation therapy (IMRT) plans of head-and-neck cancer patients.

Materials And Methods: Computed tomography scans of 12 patients who had completed IMRT for advanced tumors of the naso-, oro- and hypopharynx were replanned using RA using either one or two arcs.

An evaluation of two internal surrogates for determining the three-dimensional position of peripheral lung tumors.

Purpose: Both carina and diaphragm positions have been used as surrogates during respiratory-gated radiotherapy. We studied the correlation of both surrogates with three-dimensional (3D) tumor position.

Methods And Materials: A total of 59 repeat artifact-free four-dimensional (4D) computed tomography (CT) scans, acquired during uncoached breathing, were identified in 23 patients with Stage I lung cancer.

Recommendations for implementing stereotactic radiotherapy in peripheral stage IA non-small cell lung cancer: report from the Quality Assurance Working Party of the randomised phase III ROSEL study.

Background: A phase III multi-centre randomised trial (ROSEL) has been initiated to establish the role of stereotactic radiotherapy in patients with operable stage IA lung cancer. Due to rapid changes in radiotherapy technology and evolving techniques for image-guided delivery, guidelines had to be developed in order to ensure uniformity in implementation of stereotactic radiotherapy in this multi-centre study.

Methods/design: A Quality Assurance Working Party was formed by radiation oncologists and clinical physicists from both academic as well as non-academic hospitals that had already implemented stereotactic radiotherapy for lung cancer.

Analysis of reproducibility of respiration-triggered gated radiotherapy for lung tumors.

Purpose: Respiration-gated radiotherapy (RGRT) can decrease the toxicity of chemo-radiotherapy (CT-RT) by allowing use of smaller treatment fields. RGRT requires a predictable relationship between tumor position and external surrogate, which must be verified during treatment. Time-integrated electronic portal imaging (TI-EPI) identifies mean intra-fractional positions of moving structures, and was used to study reproducibility of anatomy during RGRT for lung tumors.

Impact of audio-coaching on the position of lung tumors.

Purpose: Respiration-induced organ motion is a major source of positional, or geometric, uncertainty in thoracic radiotherapy. Interventions to mitigate the impact of motion include audio-coached respiration-gated radiotherapy (RGRT). To assess the impact of coaching on average tumor position during gating, we analyzed four-dimensional computed tomography (4DCT) scans performed both with and without audio-coaching.

Verifying 4D gated radiotherapy using time-integrated electronic portal imaging: a phantom and clinical study.

Background: Respiration-gated radiotherapy (RGRT) can decrease treatment toxicity by allowing for smaller treatment volumes for mobile tumors. RGRT is commonly performed using external surrogates of tumor motion. We describe the use of time-integrated electronic portal imaging (TI-EPI) to verify the position of internal structures during RGRT delivery

Methods: TI-EPI portals were generated by continuously collecting exit dose data (aSi500 EPID, Portal vision, Varian Medical Systems) when a respiratory motion phantom was irradiated during expiration, inspiration and free breathing phases.

Is adaptive treatment planning required for stereotactic radiotherapy of stage I non-small-cell lung cancer?

Purpose: Changes in position or size of target volumes have been observed during radiotherapy for lung cancer. The need for adaptive treatment planning during stereotactic radiotherapy of Stage I tumors was retrospectively analyzed using repeat four-dimensional computed tomography (4DCT) scans.

Methods And Materials: A planning study was performed for 60 tumors in 59 patients using 4DCT scans repeated after two or more treatment fractions.

Reproducibility of target volumes generated using uncoached 4-dimensional CT scans for peripheral lung cancer.

Background: 4-dimensional CT (4DCT) scans are increasingly used to account for mobility during radiotherapy planning. As variations in respiratory patterns can alter observed motion, with consequent changes in the generated target volumes, we evaluated the reproducibility of 4D target volumes generated during repeat uncoached quiet respiration.

Methods: A retrospective analysis was performed on two successive scans (4DCT1 and 4DCT2) generated at the same scanning session for 26 patients with peripheral lung cancer treated with stereotactic radiotherapy (SRT).

Time trends in target volumes for stage I non-small-cell lung cancer after stereotactic radiotherapy.

Purpose: To identify potential time trends in target volumes and tumor mobility after stereotactic radiotherapy (SRT) for Stage I non-small-cell lung cancer.

Patients And Methods: Repeat planning computed tomography (CT) scans were performed for 40 tumors during fractionated SRT delivered in either three (n = 21), five (n = 14), or eight fractions (n = 5). The planning CT scans used to define internal target volumes (ITVs) consisted of either six multislice CT scans or a single four-dimensional CT scan.