Three-dimensional dose and LET prediction in proton therapy using artificial neural networks.

Purpose: Challenges in proton therapy include identifying patients most likely to benefit; ensuring consistent, high-quality plans as its adoption becomes more widespread; and recognizing biological uncertainties that may be related to increased relative biologic effectiveness driven by linear energy transfer (LET). Knowledge-based planning (KBP) is a domain that may help to address all three.

Methods: Artificial neural networks were trained using 117 unique treatment plans and associated dose and dose-weighted LET (LET ) distributions.

Treatment-planning approaches to intensity modulated proton therapy and the impact on dose-weighted linear energy transfer.

Purpose: We quantified the effect of various forward-based treatment-planning strategies in proton therapy on dose-weighted linear energy transfer (LETd). By maintaining the dosimetric quality at a clinically acceptable level, we aimed to evaluate the differences in LETd among various treatment-planning approaches and their practicality in minimizing biologic uncertainties associated with LETd.

Method: Eight treatment-planning strategies that are achievable in commercial treatment-planning systems were applied on a cylindrical water phantom and four pediatric brain tumor cases.

Pre- and Posttherapy Risk Factors for Vasculopathy in Pediatric Patients With Craniopharyngioma Treated With Surgery and Proton Radiation Therapy.

Purpose: Vasculopathy (VAS) is a significant complication associated with radiation therapy in patients treated for brain tumors. We studied the type, location, severity, timing, and resolution of VAS in children with craniopharyngioma treated with proton radiation therapy (PRT) and evaluated predictors of stenosis (STN) using a novel patient and imaging-based modeling approach.

Methods And Materials: Children with craniopharyngioma (n = 94) were treated with 54 Gy relative biological effectiveness PRT in a clinical trial, NCT01419067.

Monte Carlo framework for commissioning a synchrotron-based discrete spot scanning proton beam system and treatment plan verification.

This study aimed to develop a Monte Carlo (MC) framework for commissioning the narrow proton beams (spot size sigma, 5.2 mm 2 mm at isocenter for 69.4 MeV-221.

Dose perturbation caused by metallic port in breast tissue expander in proton beam therapy.

Proton beam treatment is being looked favourably now in breast treatment. Tissue expanders are often placed after mastectomy that contains metallic port for saline injection which produces dose perturbations in proton beam therapy with uncertain dosimetry. Dose perturbation for a stainless-steel injection port from a breast implant is investigated in this study.

Proton therapy delivery method affects dose-averaged linear energy transfer in patients.

The dosimetric advantages of proton therapy have led to its rapid proliferation in recent decades. This has been accompanied by a shift in technology from older units that deliver protons by passive scattering (PS) to newer units that increasingly use pencil-beam scanning (PBS). The biologic effectiveness of proton physical dose purportedly rises with increasing dose-weighted average linear energy transfer (LET).

Automation of Monte Carlo-based treatment plan verification for proton therapy.

Purpose: Independent calculations of proton therapy plans are an important quality control procedure in treatment planning. When using custom Monte Carlo (MC) models of the beamline, deploying the calculations can be laborious, time consuming, and require in-depth knowledge of the computational environment. We developed an automated framework to remove these barriers and integrate our MC model into the clinical workflow.

Technical Note: Design and characterization of a large diameter parallel plate ionization chamber for accurate integral depth dose measurements with proton beams.

Purpose: The goal was to develop and test a large diameter parallel plate ionization chamber capable of intercepting at least 98% of the proton beamlets tested with the system.

Methods: A commercial synchrotron proton therapy system was used for the study (Hitachi, Ltd, Hitachi City, Japan; Model: Probeat-V). The energies investigated were in the range of 100 to 192 MeV.

Challenges of dosimetry of ultra-short pulsed very high energy electron beams.

Very high energy electrons (VHEE) in the range from 100 to 250MeV have the potential of becoming an alternative modality in radiotherapy because of their improved dosimetric properties compared with 6-20MV photons generated by clinical linear accelerators (LINACs). VHEE beams have characteristics unlike any other beams currently used for radiotherapy: femtosecond to picosecond duration electron bunches, which leads to very high dose per pulse, and energies that exceed that currently used in clinical applications. Dosimetry with conventional online detectors, such as ionization chambers or diodes, is a challenge due to non-negligible ion recombination effects taking place in the sensitive volumes of these detectors.

Systemic mechanisms and effects of ionizing radiation: A new 'old' paradigm of how the bystanders and distant can become the players.

Exposure of cells to any form of ionizing radiation (IR) is expected to induce a variety of DNA lesions, including double strand breaks (DSBs), single strand breaks (SSBs) and oxidized bases, as well as loss of bases, i.e., abasic sites.

Feasibility of RACT for 3D dose measurement and range verification in a water phantom.

Purpose: The objective of this study is to establish the feasibility of using radiation-induced acoustics to measure the range and Bragg peak dose from a pulsed proton beam. Simulation studies implementing a prototype scanner design based on computed tomographic methods were performed to investigate the sensitivity to proton range and integral dose.

Methods: Derived from thermodynamic wave equation, the pressure signals generated from the dose deposited from a pulsed proton beam with a 1 cm lateral beam width and a range of 16, 20, and 27 cm in water using Monte Carlo methods were simulated.

Proton Therapy Facility Planning From a Clinical and Operational Model.

This paper provides a model for planning a new proton therapy center based on clinical data, referral pattern, beam utilization and technical considerations. The patient-specific data for the depth of targets from skin in each beam angle were reviewed at our center providing megavoltage photon external beam and proton beam therapy respectively. Further, data on insurance providers, disease sites, treatment depths, snout size and the beam angle utilization from the patients treated at our proton facility were collected and analyzed for their utilization and their impact on the facility cost.

Effect of Scanning Beam for Superficial Dose in Proton Therapy.

Proton beam delivery technology is under development to minimize the scanning spot size for uniform dose to target, but it is also known that the superficial dose could be as high as the dose at Bragg peak for narrow and small proton beams. The objective of this study is to explore the characteristics of dose distribution at shallow depths using Monte Carlo simulation with the FLUKA code for uniform scanning (US) and discrete spot scanning (DSS) proton beams. The results show that the superficial dose for DSS is relatively high compared to US.

Variability of physics education in radiation oncology medical residency programs.

Purpose: The aim of this study was to compare the quality of medical physics education for radiation oncology medical residents.

Methods: An independent survey regarding physics education was carried out using e-mail. The survey contained 12 questions addressing the duration, length, and quality of education.

A semi-empirical model for the therapeutic range shift estimation caused by inhomogeneities in proton beam therapy.

The purpose of this study was to devise a simple semi-empirical model to estimate the range shift in clinical practices with high-Z inhomogeneity in proton beam. A semi-empirical model utilizing the logarithmic dependence on Z in stopping power from Bohr's classical approach has been developed to calculate the range shift due to the presence of inhomogeneity. Range shift from metallic plates of atomic number Z of various thicknesses were measured in water using a parallel plate ionization chamber and calculated with the FLUKA Monte Carlo code.

Pitfalls of tungsten multileaf collimator in proton beam therapy.

Purpose: Particle beam therapy is associated with significant startup and operational cost. Multileaf collimator (MLC) provides an attractive option to improve the efficiency and reduce the treatment cost. A direct transfer of the MLC technology from external beam radiation therapy is intuitively straightforward to proton therapy.

Analysis of treatment planning time among systems and planners for intensity-modulated radiation therapy.

Radiation oncology is a technologically advanced health care specialty in which numerous innovations, such as intensity-modulated radiation therapy (IMRT), require significant manpower and resources. For 3 main disease sites (prostate, head and neck, and lung), the authors investigated IMRT planning time across the United States among commonly used treatment planning systems (TPS). Treatment planning time was investigated in different components of IMRT: data transfer, contouring, beam arrangements, optimization, dose calculation, and phantom plans.

Evaluation of underdosage in the external photon beam radiotherapy of glottic carcinoma: Monte Carlo study.

Purpose: Underdosage in the human larynx may be the true factor behind the decrease in local control rates.

Patients And Methods: To evaluate underdosage with Monte Carlo a CT-based geometrical model of the patient's neck (mathematical neck) was created. Dose was calculated for a pair of 6 Me V parallel-opposed photon beams modulated with 15 degree steel wedges.

Monte carlo simulation of the Leksell Gamma Knife: II. Effects of heterogeneous versus homogeneous media for stereotactic radiosurgery.

The absence of electronic equilibrium in the vicinity of bone-tissue or air-tissue heterogeneity in the head can misrepresent deposited dose with treatment planning algorithms that assume all treatment volume as homogeneous media. In this paper, Monte Carlo simulation (PENELOPE) and measurements with a specially designed heterogeneous phantom were applied to investigate the effect of air-tissue and bone-tissue heterogeneity on dose perturbation with the Leksell Gamma Knife. The dose fall-off near the air-tissue interface caused by secondary electron disequilibrium leads to overestimation of dose by the vendor supplied treatment planning software (GammaPlan) at up to 4 mm from an interface.

Lung cancer radiation therapy: Monte Carlo investigation of "under dose" by high energy photons.

Loss of electronic equilibrium in lung tissue causes a build-up region in the tumor. Increasing the photon energy increases the depth at which electronic equilibrium is reestablished within the lung tumor. This study uses the Monte Carlo code PENELOPE for simulations of radiation treatment of tumor surrounded by lung.

Use of the Leksell Gamma Knife for localized small field lens irradiation in rodents.

For most basic radiobiological research applications involving irradiation of small animals, it is difficult to achieve the same high precision dose distribution realized with human radiotherapy. The precision for irradiations performed with standard radiotherapy equipment is +/-2 mm in each dimension, and is adequate for most human treatment applications. For small animals such as rodents, whose organs and tissue structures may be an order of magnitude smaller than those of humans, the corresponding precision required is closer to +/-0.