Fractionation effects in particle radiotherapy: implications for hypo-fractionation regimes.

The aim is to demonstrate the potential impact of changes in the value of the β parameter in the linear quadratic (LQ) model on the calculation of clinical relative biological effectiveness (RBE) values used for high linear energy transfer (LET) radiotherapy. The parameter RBE(min) is introduced into the LQ formulation to account for possible changes in the β radiosensitivity coefficient with changing LET. The model is used to fit fractionated data under two conditions, where RBE(min) = 1 and RBE(min) ≠ 1.

Accuracy of proton beam range verification using post-treatment positron emission tomography/computed tomography as function of treatment site.

Purpose: For 23 patients, an off-line positron emission tomography scan and a computed tomography scan after proton radiotherapy was performed at the Massachusetts General Hospital to assess in vivo treatment verification. A well-balanced population of patients was investigated to assess the effect of the tumor location on the accuracy of the technique.

Methods And Materials: Range verification was achieved by comparing the measured positron emission tomography activity distributions with the corresponding Monte Carlo-simulated distributions.

In vivo proton beam range verification using spine MRI changes.

Purpose: In proton therapy, uncertainty in the location of the distal dose edge can lead to cautious treatment plans that reduce the dosimetric advantage of protons. After radiation exposure, vertebral bone marrow undergoes fatty replacement that is visible on magnetic resonance imaging (MRI). This presents an exciting opportunity to observe radiation dose distribution in vivo.

Comparison of out-of-field photon doses in 6 MV IMRT and neutron doses in proton therapy for adult and pediatric patients.

The purpose of this study was to assess lateral out-of-field doses in 6 MV IMRT (intensity modulated radiation therapy) and compare them with secondary neutron equivalent dose contributions in proton therapy. We simulated out-of-field photon doses to various organs as a function of distance, patient's age, gender and treatment volumes based on 3, 6, 9 cm field diameters in the head and neck and spine region. The out-of-field photon doses to organs near the field edge were found to be in the range of 2, 5 and 10 mSv Gy(-1) for 3 cm, 6 cm and 9 cm diameter IMRT fields, respectively, within 5 cm of the field edge.

Proton radiation in the management of localized cancer.

Proton radiation therapy has been available for decades. However, until recently it was only applied to a small number of patients at approximately 20 centers worldwide. Increased clinical experience with protons, as well as extensive research in the physics, biology and clinical aspects of proton therapy, have recently led to a huge interest in proton therapy among radiation oncologists.

Proton vs carbon ion beams in the definitive radiation treatment of cancer patients.

Background And Purpose: Relative to X-ray beams, proton [(1)H] and carbon ion [(12)C] beams provide superior distributions due primarily to their finite range. The principal differences are LET, low for (1)H and high for (12)C, and a narrower penumbra of (12)C beams. Were (12)C to yield a higher TCP for a defined NTCP than (1)H therapy, would LET, fractionation or penumbra width be the basis?

Methods: Critical factors of physics, radiation biology of (1)H and (12)C ion beams, neutron therapy and selected reports of TCP and NTCP from (1)H and (12)C irradiation of nine tumor categories are reviewed.

Assessment of out-of-field absorbed dose and equivalent dose in proton fields.

Purpose: In proton therapy, as in other forms of radiation therapy, scattered and secondary particles produce undesired dose outside the target volume that may increase the risk of radiation-induced secondary cancer and interact with electronic devices in the treatment room. The authors implement a Monte Carlo model of this dose deposited outside passively scattered fields and compare it to measurements, determine the out-of-field equivalent dose, and estimate the change in the dose if the same target volumes were treated with an active beam scanning technique.

Methods: Measurements are done with a thimble ionization chamber and the Wellhofer MatriXX detector inside a Lucite phantom with field configurations based on the treatment of prostate cancer and medulloblastoma.

Extension of the NCAT phantom for the investigation of intra-fraction respiratory motion in IMRT using 4D Monte Carlo.

The purpose of this work was to create a computational platform for studying motion in intensity modulated radiotherapy (IMRT). Specifically, the non-uniform rational B-spline (NURB) cardiac and torso (NCAT) phantom was modified for use in a four-dimensional Monte Carlo (4D-MC) simulation system to investigate the effect of respiratory-induced intra-fraction organ motion on IMRT dose distributions as a function of diaphragm motion, lesion size and lung density. Treatment plans for four clinical scenarios were designed: diaphragm peak-to-peak amplitude of 1 cm and 3 cm, and two lesion sizes--2 cm and 4 cm diameter placed in the lower lobe of the right lung.

Test of the nuclear interaction model in SHIELD-HIT and comparison to energy distributions from GEANT4.

Monte Carlo codes are widely used to simulate dose distributions in ion radiotherapy. The benchmark of the implemented physical models against experimental data plays an important role in improving the accuracy of the simulations. To estimate the accuracy of the inelastic cross sections in SHIELD-HIT, the simulated charge is compared to measured data from a Multi Layer Faraday Cup.

Reduction of the secondary neutron dose in passively scattered proton radiotherapy, using an optimized pre-collimator/collimator.

Proton radiotherapy represents a potential major advance in cancer therapy. Most current proton beams are spread out to cover the tumor using passive scattering and collimation, resulting in an extra whole-body high-energy neutron dose, primarily from proton interactions with the final collimator. There is considerable uncertainty as to the carcinogenic potential of low doses of high-energy neutrons, and thus we investigate whether this neutron dose can be significantly reduced without major modifications to passively scattered proton beam lines.

Field size dependence of the output factor in passively scattered proton therapy: influence of range, modulation, air gap, and machine settings.

At the Francis H. Burr Proton Therapy Center field specific output factors (i.e.

Neutron equivalent doses and associated lifetime cancer incidence risks for head & neck and spinal proton therapy.

In this work we have simulated the absorbed equivalent doses to various organs distant to the field edge assuming proton therapy treatments of brain or spine lesions. We have used computational whole-body (gender-specific and age-dependent) voxel phantoms and considered six treatment fields with varying treatment volumes and depths. The maximum neutron equivalent dose to organs near the field edge was found to be approximately 8 mSv Gy(-1).

Systematic analysis of biological and physical limitations of proton beam range verification with offline PET/CT scans.

The clinical use of offline positron emission tomography/computed tomography (PET/CT) scans for proton range verification is currently under investigation at the Massachusetts General Hospital (MGH). Validation is achieved by comparing measured activity distributions, acquired in patients after receiving one fraction of proton irradiation, with corresponding Monte Carlo (MC) simulated distributions. Deviations between measured and simulated activity distributions can either reflect errors during the treatment chain from planning to delivery or they can be caused by various inherent challenges of the offline PET/CT verification method.

Dose to water versus dose to medium in proton beam therapy.

Dose in radiation therapy is traditionally reported as the water-equivalent dose, or dose to water. Monte Carlo dose calculations report dose to medium and thus a methodology is needed to convert dose to medium into dose to water (or vice versa) for comparison of Monte Carlo results with results from planning systems. This paper describes the development of a formalism to convert dose to medium into dose to water for proton fields when simulating the dose with Monte Carlo techniques.

Breathing interplay effects during proton beam scanning: simulation and statistical analysis.

Treatment delivery with active beam scanning in proton radiation therapy introduces the problem of interplay effects when pencil beam motion occurs on a similar time scale as intra-fractional tumor motion. In situations where fractionation may not provide enough repetition to blur the effects of interplay, repeated delivery or 'repainting' of each field several times within a fraction has been suggested. The purpose of this work was to investigate the effectiveness of different repainting strategies in proton beam scanning.

Spread-out antiproton beams deliver poor physical dose distributions for radiation therapy.

Background And Purpose: Antiprotons have been suggested as a possibly superior modality for radiotherapy, due to the energy released when they annihilate, which enhances the Bragg peak and introduces a high-LET component to the dose. Previous studies have focused on small-diameter near-monoenergetic antiproton beams. The goal of this work was to study more clinically relevant beams.

Design and testing of a simulation framework for dosimetric motion studies integrating an anthropomorphic computational phantom into four-dimensional Monte Carlo.

We have designed a simulation framework for motion studies in radiation therapy by integrating the anthropomorphic NCAT phantom into a 4D Monte Carlo dose calculation engine based on DPM. Representing an artifact-free environment, the system can be used to identify class solutions as a function of geometric and dosimetric parameters. A pilot dynamic conformal study for three lesions ( approximately 2.

Clinical implementation of full Monte Carlo dose calculation in proton beam therapy.

The goal of this work was to facilitate the clinical use of Monte Carlo proton dose calculation to support routine treatment planning and delivery. The Monte Carlo code Geant4 was used to simulate the treatment head setup, including a time-dependent simulation of modulator wheels (for broad beam modulation) and magnetic field settings (for beam scanning). Any patient-field-specific setup can be modeled according to the treatment control system of the facility.

Sensitivity of different dose scoring methods on organ-specific neutron dose calculations in proton therapy.

Scattered doses, e.g. neutron doses in proton therapy, are of concern in radiation therapy.

Quantitative assessment of the physical potential of proton beam range verification with PET/CT.

A recent clinical pilot study demonstrated the feasibility of offline PET/CT range verification for proton therapy treatments. In vivo PET measurements are challenged by blood perfusion, variations of tissue compositions, patient motion and image co-registration uncertainties. Besides these biological and treatment specific factors, the accuracy of the method is constrained by the underlying physical processes.

Risk of developing second cancer from neutron dose in proton therapy as function of field characteristics, organ, and patient age.

Purpose: To estimate the risk of a second malignancy after treatment of a primary brain cancer using passive scattered proton beam therapy. The focus was on the cancer risk caused by neutrons outside the treatment volume and the dependency on the patient's age.

Methods And Materials: Organ-specific neutron-equivalent doses previously calculated for eight different proton therapy brain fields were considered.

A review of dosimetry studies on external-beam radiation treatment with respect to second cancer induction.

It has been long known that patients treated with ionizing radiation carry a risk of developing a second cancer in their lifetimes. Factors contributing to the recently renewed concern about the second cancer include improved cancer survival rate, younger patient population as well as emerging treatment modalities such as intensity-modulated radiation treatment (IMRT) and proton therapy that can potentially elevate secondary exposures to healthy tissues distant from the target volume. In the past 30 years, external-beam treatment technologies have evolved significantly, and a large amount of data exist but appear to be difficult to comprehend and compare.

Dosimetric impact of motion in free-breathing and gated lung radiotherapy: a 4D Monte Carlo study of intrafraction and interfraction effects.

The purpose of this study was to investigate if interfraction and intrafraction motion in free-breathing and gated lung IMRT can lead to systematic dose differences between 3DCT and 4DCT. Dosimetric effects were studied considering the breathing pattern of three patients monitored during the course of their treatment and an in-house developed 4D Monte Carlo framework. Imaging data were taken in free-breathing and in cine mode for both 3D and 4D acquisition.