Advanced External Beam Stereotactic Radiotherapy for Skull Base Reirradiation.

Background/objectives: Stereotactic body radiation therapy (SBRT) for skull base reirradiation is particularly challenging, as patients have already received substantial radiation doses to the region, and nearby normal organs may have approached their tolerance limit from prior treatments. In this study, we reviewed the characteristics and capabilities of four advanced external beam radiation delivery systems and four modern treatment planning systems and evaluated the treatment plan quality of each technique using skull base reirradiation patient cases.

Methods: SBRT plans were generated for sixteen skull base reirradiation patients using four modalities: the GK plan for the Elekta Leksell Gamma Knife Perfexion/ICON, the CyberKnife (CK) plan for the Accuray CyberKnife, the intensity-modulated proton therapy (IMPT) plan for the Hitachi ProBeat-FR proton therapy machine, and the volumetric-modulated arc therapy (VMAT) plan for the Varian TrueBeam STx.

Anatomic change over the course of treatment for non-small cell lung cancer patients and its impact on intensity-modulated radiation therapy and passive-scattering proton therapy deliveries.

Purpose: To quantify tumor anatomic change of non-small cell lung cancer (NSCLC) patients given passive-scattering proton therapy (PSPT) and intensity-modulated radiation therapy (IMRT) through 6-7 weeks of treatment, and analyze the correlation between anatomic change and the need to adopt adaptive radiotherapy (ART).

Materials And Methods: Weekly 4D CT sets of 32 patients (8/8 IMRT with/without ART, 8/8 PSPT with/without ART) acquired during treatment, were registered to the planning CT using an in-house developed deformable registration algorithm. The anatomic change was quantified as the mean variation of the region of interest (ROI) relative to the planning CT by averaging the magnitude of deformation vectors of all voxels within the ROI contour.

An analytical model for the upper bound estimation of respiratory motion-induced dose uncertainty in spot-scanning proton beam therapy.

Purpose: We developed an analytical model of a spot-scanning beam delivery system to estimate the upper bound of respiratory motion-induced dose uncertainty for a given treatment plan.

Methods: The effective delivery time for each spot position in the treatment plan was calculated on the basis of the parameters of the delivery system. The upper bound of the dose uncertainty was then calculated as a function of the effective delivery time.

Power-law relationship in the long-tailed sections of proton dose distributions.

The halo portion of a proton therapy dose creates a long tail in proton dose distributions, but so far study of this phenomenon has been limited. We used statistical methods and mathematical models to confirm that the long-tailed portion of proton dose distributions exhibits a power-law relationship. By analyzing 299 measured dose profiles, we found that all proton lateral dose distributions had a significant power-law scaling correlation with a high correlation coefficient in the tail.

Proton Beam Radiotherapy and Concurrent Chemotherapy for Unresectable Stage III Non-Small Cell Lung Cancer: Final Results of a Phase 2 Study.

Importance: Proton beam radiotherapy (PBT) has the potential to reduce toxic effects in the definitive management of locally advanced non-small cell lung cancer (NSCLC), but long-term prospective data are lacking.

Objective: To report the final (5-year) results of a prospective study evaluating concurrent chemotherapy and high-dose PBT to treat unresectable stage III NSCLC.

Design, Setting, And Participants: In this open-label, single-group assignment study, with median follow-up of 27.

Spot scanning proton therapy minimizes neutron dose in the setting of radiation therapy administered during pregnancy.

This is a real case study to minimize the neutron dose equivalent (H) to a fetus using spot scanning proton beams with favorable beam energies and angles. Minimum neutron dose exposure to the fetus was achieved with iterative planning under the guidance of neutron H measurement. Two highly conformal treatment plans, each with three spot scanning beams, were planned to treat a 25-year-old pregnant female with aggressive recurrent chordoma of the base of skull who elected not to proceed with termination.

Novel Hybrid Scattering- and Scanning-Beam Proton Therapy Approach.

Purpose: To determine whether a hybrid intensity-modulated proton therapy (IMPT) and passive scattered proton therapy (PSPT) technique, termed HimpsPT, could be adopted as an alternative delivery method for patients demanding scanning beam proton therapy.

Patients And Methods: We identified 3 representative clinical cases-an oropharyngeal cancer, skull base chordoma, and stage III non-small-cell lung cancer-that had been treated with IMPT at our center. We retrospectively redesigned these cases using HimpsPT.

A Retrospective Evaluation of the Benefit of Referring Pediatric Cancer Patients to an External Proton Therapy Center.

Background: Pediatric cancer patients requiring radiation therapy (RT) have been routinely assessed and referred to proton therapy (PT) at an external institution. The benefit of the delivered PT compared to the state-of-the-art intensity modulated x-ray RT (XT) at the home institution was evaluated.

Procedure: Twenty-four consecutive children referred for PT during 2010-2013 for craniospinal (CSI, n = 10), localized intracranial (IC, n = 7), head/neck (HN, n = 4) or parameningeal (PM, n = 3) lesions were included.

Evaluation and mitigation of the interplay effects of intensity modulated proton therapy for lung cancer in a clinical setting.

Purpose: The primary aim of this study was to evaluate the impact of the interplay effects of intensity modulated proton therapy (IMPT) plans for lung cancer in the clinical setting. The secondary aim was to explore the technique of isolayered rescanning to mitigate these interplay effects.

Methods And Materials: A single-fraction 4-dimensional (4D) dynamic dose without considering rescanning (1FX dynamic dose) was used as a metric to determine the magnitude of dosimetric degradation caused by 4D interplay effects.

Evaluation of the systematic error in using 3D dose calculation in scanning beam proton therapy for lung cancer.

The objective of this study was to evaluate and understand the systematic error between the planned three-dimensional (3D) dose and the delivered dose to patient in scanning beam proton therapy for lung tumors. Single-field and multifield optimized scanning beam proton therapy plans were generated for ten patients with stage II-III lung cancer with a mix of tumor motion and size. 3D doses in CT datasets for different respiratory phases and the time-weighted average CT, as well as the four-dimensional (4D) doses were computed for both plans.

On the interplay effects with proton scanning beams in stage III lung cancer.

Purpose: To assess the dosimetric impact of interplay between spot-scanning proton beam and respiratory motion in intensity-modulated proton therapy (IMPT) for stage III lung cancer.

Methods: Eleven patients were sampled from 112 patients with stage III nonsmall cell lung cancer to well represent the distribution of 112 patients in terms of target size and motion. Clinical target volumes (CTVs) and planning target volumes (PTVs) were defined according to the authors' clinical protocol.

Beyond Gaussians: a study of single-spot modeling for scanning proton dose calculation.

Active spot scanning proton therapy is becoming increasingly adopted by proton therapy centers worldwide. Unlike passive-scattering proton therapy, active spot scanning proton therapy, especially intensity-modulated proton therapy, requires proper modeling of each scanning spot to ensure accurate computation of the total dose distribution contributed from a large number of spots. During commissioning of the spot scanning gantry at the Proton Therapy Center in Houston, it was observed that the long-range scattering protons in a medium may have been inadequately modeled for high-energy beams by a commercial treatment planning system, which could lead to incorrect prediction of field size effects on dose output.

Characterization of dose impact on IMRT and VMAT from couch attenuation for two Varian couches.

In intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT), the use of posterior oblique beams has become common. Beam attenuation by the treatment couch is not negligible when the couch is in the beam portal. In this study, we established the relationship of relative dose vs.

Measurement of neutron dose equivalent and its dependence on beam configuration for a passive scattering proton delivery system.

Purpose: To measure the neutron dose equivalent per therapeutic proton dose (H/D) in a passive scattering proton therapy system and study its dependence on the proton energy, aperture-to-isocenter distance, spread-out Bragg peak (SOBP) width, and field size.

Methods And Materials: We performed four experiments of varying proton energies, aperture-to-isocenter distances, SOBP widths, and field sizes. Etched track detectors were used to measure the neutron dose equivalent at both an in-field (isocenter, beyond the protons' range) and out-of-field (30 cm lateral to the isocenter) location in air.

Blind deblurring reconstruction technique with applications in PET imaging.

We developed an empirical PET model taking into account system blurring and a blind iterative reconstruction scheme that estimates both the actual image and the point spread function of the system. Reconstruction images of high quality can be acquired by using the proposed reconstruction technique for both synthetic and experimental data. In the synthetic data study, the algorithm reduces image blurring and preserves the edges without introducing extra artifacts.