Precision Radiation Oncology最新文献

Background: Reliable estimates of radiation dose to bone marrow are critical to understanding the risk of radiation-induced cancers. Although the medical internal radiation dose phantom is routinely used for dose estimation, bone marrow is not defined in the phantom. Consequently, methods of indirectly estimating bone marrow dose have been implemented based on dose to surrogate volumes or average dose to soft tissue.

Methods: In this study, new bone marrow structures were implemented and evaluated to the medical internal radiation dose phantom in geant4, offering improved fidelity. The dose equivalent to the bone marrow was calculated across medical, occupational, and space radiation exposure scenarios, and compared with results using prior indirect estimation methods.

Conclusion: Our results show that bone marrow dose may be overestimated by up to a factor of three when using the traditional methods when compared with the improved fidelity medical internal radiation dose method, specifically at clinical x-ray energies.

EBT-XD model of Gafchromic^™ films has a broader optimal dynamic dose range, up to 40 Gy, compared to its predecessor models. This characteristic has made EBT-XD films suitable for high-dose applications such as stereotactic body radiotherapy and stereotactic radiosurgery, as well as ultra-high dose rate FLASH radiotherapy. The purpose of the current study was to characterize the dependence of EBT-XD film response on linear energy transfer (LET) and dose rate of therapeutic protons from a synchrotron. A clinical spot-scanning proton beam was used to study LET dependence at three dose-averaged LET (LET_d) values of 1.0 keV/µm, 3.6 keV/µm, and 7.6 keV/µm. A research proton beamline was used to study dose rate dependence at 150 Gy/second in the FLASH mode and 0.3 Gy/second in the non-FLASH mode. Film response data from LET_d values of 0.9 keV/µm and 9.0 keV/µm of the proton FLASH beam were also compared. Film response data from a clinical 6 MV photon beam were used as a reference. Both gray value method and optical density (OD) method were used in film calibration. Calibration results using a specific OD calculation method and a generic OD calculation method were compared. The four-parameter NIH Rodbard function and three-parameter rational function were compared in fitting the calibration curves. Experimental results showed that the response of EBT-XD film is proton LET dependent but independent of dose rate. Goodness-of-fit analysis showed that using the NIH Rodbard function is superior for both protons and photons. Using the "specific OD + NIH Rodbard function" method for EBT-XD film calibration is recommended.

X-ray diffraction from a solid crystal shows the wave nature of photons. It is an important electromagnetic (EM) physics process when X-ray photons interact with a crystal. Bragg diffraction, often called Bragg reflection, is a special case of the general form of X-ray diffraction, known as Laue diffraction. When the Bragg's law is met, the incident photon beam is reflected from the crystal plane behaving as a specular reflection at the Bragg angle. However, the Bragg reflection physical process has not been integrated into the general-purpose Monte Carlo simulation toolkit Geant4 for particle physics. In the current study, we developed a new EM physical process class "G4CrystalBraggReflection" and a new EM physical model class "G4DarwinDynamicalModel" for modeling the Bragg reflection physical process within a crystal. We added the Bragg reflection physical process to the EM physics category of Geant4. The preliminary results of photon tracking in a silicon crystal slab have shown the feasibility of simulating the Bragg reflection process in addition to the standard EM processes in the framework of Geant4.

Purpose: The scientific community shows great interest in the study of DNA damage induction, DNA damage repair, and the biological effects on cells and cellular systems after exposure to ionizing radiation. Several in silico methods have been proposed so far to study these mechanisms using Monte Carlo simulations. This study outlines a Geant4-DNA example application, named "molecularDNA", publicly released in the 11.1 version of Geant4 (December 2022).

Methods: It was developed for novice Geant4 users and requires only a basic understanding of scripting languages to get started. The example includes two different DNA-scale geometries of biological targets, namely "cylinders" and "human cell". This public version is based on a previous prototype and includes new features, such as: the adoption of a new approach for the modeling of the chemical stage, the use of the standard DNA damage format to describe radiation-induced DNA damage, and upgraded computational tools to estimate DNA damage response.

Results: Simulation data in terms of single-strand break and double-strand break yields were produced using each of the available geometries. The results were compared with the literature, to validate the example, producing less than 5% difference in all cases. Conclusion: "molecularDNA" is a prototype tool that can be applied in a wide variety of radiobiology studies, providing the scientific community with an open-access base for DNA damage quantification calculations. New DNA and cell geometries for the "molecularDNA" example will be included in future versions of Geant4-DNA.

Breast cancer is the most prevalent disease for women. With advances in breast cancer screening, most breast cancers are now diagnosed in the early stages. With knowledge of different subtypes and their behavior, breast cancer treatment has become more individualized. Radiation therapy as one of the mainstays of breast cancer treatment has also been evolving. This review attempts to provide a summary of the most influential clinical studies that have driven the technological advances in radiation therapy for early-stage breast cancer.

Salvage external beam radiation therapy (EBRT) followed by interstitial brachytherapy is commonly used to treat patients with vaginal recurrence of endometrial cancer. The evidence for this is typically limited to case series treating small volumes of disease. For the present study, 12 consecutive patients with locally advanced, biopsy-proven vaginal recurrence after surgically treated endometrial cancer who received salvage EBRT (45 Gy in 25 daily fractions to microscopic disease and 55-57.5 Gy to gross nodal disease) with magnetic resonance-guided interstitial brachytherapy (20-21 Gy in 3 fractions over 2 days) were retrospectively reviewed. The median tumor size of recurrent disease on magnetic resonance imaging was 5 (3-6) cm. Three (25%) tumors involved the bladder wall, three (25%) involved the urethra, and four (33%) extended to the pelvic sidewall. Four (25%) patients had gross nodal disease. On follow-up, no (0%) patient developed local recurrence. One patient (8%) developed nodal recurrence outside of the radiotherapy treatment volume and then distant metastases, and one patient (8%) developed distant metastasis 2.5 years post-treatment and subsequently died from the disease. No (0%) other deaths were reported. Zero patients (0%) developed grade ≥4 bowel or bladder toxicity. These data support EBRT with interstitial brachytherapy using modern techniques for locally advanced, vaginal recurrences of endometrial cancer.

Objective: To determine the effect of dose calculation accuracy on inverse linear energy transfer (LET) optimization for intensity-modulated proton therapy, and to determine whether adding more beams would improve the plan robustness to different dose calculation engines.

Methods: Two sets of intensity-modulated proton therapy plans using two, four, six, and nine beams were created for 10 prostate cancer patients: one set was optimized with dose constraints (DoseOpt) using the pencil beam (PB) algorithm, and the other set was optimized with additional LET constraints (LETOpt) using the Monte Carlo (MC) algorithm. Dose distributions of DoseOpt plans were then recalculated using the MC algorithm, and the LETOpt plans were recalculated using the PB algorithm. Dosimetric indices of targets and critical organs were compared between the PB and MC algorithms for both sets of plans.

Results: For DoseOpt plans, dose differences between the PB and MC algorithms were minimal. However, the maximum dose differences in LETOpt plans were 11.11% and 15.85% in the dose covering 98% and 2% (D2) of the clinical target volume, respectively. Furthermore, the dose to 1 cc of the bladder differed by 11.42 Gy (relative biological effectiveness). Adding more beams reduced the discrepancy in target coverage, but the errors in D2 of the structure were increased with the number of beams.

Conclusion: High modulation of LET requires high dose calculation accuracy during the optimization and final dose calculation in the inverse treatment planning for intensity-modulated proton therapy, and adding more beams did not improve the plan robustness to different dose calculation algorithms.