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Objective: The recently developed V79-RBE 10 biological weighting function (BWF) model is a simple and robust tool for a fast relative biological effectiveness (RBE) assessment for comparing different exposure conditions in particle therapy. In this study, the RBE 10 derived by this model (through the Particle and Heavy Ion Transport code System (PHITS) simulated d(y) spectra) is compared with values of RBE 10 using experimentally derived d(y) spectra from a silicon-on-insulator (SOI) microdosimeter. 
 
Approach: Experimentally measured d(y) spectra are used to calculate an RBE 10 value utilizing the V79-RBE 10 BWF model as well as the modified microdosimetric kinetic model (MKM) to produce an RBE 10 -vs-y D trend for a wide range of ions. In addition, a beamline specific PHITS simulation was conducted which replicated the exact experimental conditions that were used with the SOI microdosimeter at the Heavy Ion Medical Accelerator in Chiba (HIMAC) biological beamline with 12 C ions. 
 
Main Results: The RBE 10 -vs-y D trend for 1 H, 4 He, 7 Li, 12 C, 14 N, 16 O, 20 Ne, 28 Si, 56 Fe, and 124 Xe ions is examined with good agreement found between the SOI microdosimeter derived RBE 10 values with the V79-RBE 10 BWF model and MKM, as well as the PHITS simulations for 1 H, 4 He, 7 Li, 12 C, 16 O and 56 Fe ions while some discrepancies were seen for 14 N, 20 Ne, 28 Si ions. Deviations have been attributed to the difference in the derivation of the d(y) spectra based on the different methods utilized. Good agreement was found between y D values and an over estimation was observed for RBE 10 values for the beamline specific simulation of the 12 C ion beam. 
 
Significance: Overall, this study shows that the SOI microdosimeter is a valuable tool that can be utilized for quick and accurate experimental derivation of the d(y) spectra, which can then be convoluted with the weighting function of the V79-RBE 10 BWF model to derive RBE 10 . The SOI microdosimeter is able to derive experimental values of y D and RBE 10 for various ions in any irradiation condition utilizing other radiobiological models., (Creative Commons Attribution license.)

Objective. Spot size stability is crucial in pencil beam scanning (PBS) proton therapy, and variations in spot size can disrupt dose distributions. Recently, a novel proton beam delivery method known as DynamicARC PBS scanning has been introduced. The current study investigates the dosimetric impact of spot size errors in DynamicARC proton therapy for head and neck (HNC), prostate, and lung cancers. Approach. Robustly optimized DynamicARC proton therapy plans were created for HNC ( n = 4), prostate ( n = 4), and lung ( n = 4) cancer patients. Spot size errors of ±10%, ±15%, and ±20% were introduced, and their effects on target coverage ( D 95% and D 99% ), homogeneity index (HI), and organ-at-risk doses were analyzed across different cancer sites. Main Results. HNC and lung cancer plans showed greater vulnerability to spot size errors, with reductions in target coverage of up to 4.8% under -20% spot size errors. Dose homogeneity was also more affected in these cases, with HI degrading by 0.12 in lung cancer. Prostate cancer demonstrated greater resilience to spot size variations, even under errors of ±20%. For spot size errors ±10%, the oral cavity, parotid glands, and constrictor muscles experienced D mean deviations within ±1.2%, while deviations were limited to ±0.5% for D 10% of the bladder and rectum and ±0.3% for V 20 Gy(RBE) of the lungs. The robustness analysis indicated that lung cancer plans were most susceptible to robustness reductions caused by spot size errors, while HNC plans demonstrated moderate sensitivity. Conversely, prostate cancer plans demonstrated high robustness, experiencing only minimal reductions in target coverage. Significance. While the ±10% spot size tolerance is appropriate in majority of the cases, lung cancer plans may require more stringent criteria. As DynamicARC becomes clinically available, measuring spot size errors in practice will be essential to validate these findings and refine tolerance thresholds for clinical use., (© 2024 Institute of Physics and Engineering in Medicine. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

Objective. This study aims to design, manufacture, and test 3D printed quality assurance (QA) dosimetry phantoms for synchrotron brain cancer radiation therapy at the Australian synchrotron. Approach. Fabricated 3D printed phantoms from simple slab phantoms, a preclinical rat phantom, and an anthropomorphic head phantom were fabricated and characterized. Attenuation measurements of various polymers, ceramics and metals were acquired using synchrotron monochromatic micro-computed tomography (CT) imaging. Polylactic acid plus, VeroClear, Durable resin, and tricalcium phosphate were used in constructing the phantoms. Furthermore, 3D printed bone equivalent materials were compared relative to ICRU bone and hemihydrate plaster. Homogeneous and heterogeneous rat phantoms were designed and fabricated using tissue-equivalent materials. Geometric accuracy, CT imaging, and consistency were considered. Moreover, synchrotron broad-beam x-rays were delivered using a 3 Tesla superconducting multipole wiggler field for four sets of synchrotron radiation beam qualities. Dose measurements were acquired using a PinPoint ionization chamber and compared relative to a water phantom and a RMI457 Solid Water phantom. Experimental depth doses were compared relative to calculated doses using a Geant4 Monte Carlo simulation. Main results. Polylactic acid (PLA+) shows to have a good match with the attenuation coefficient of ICRU water, while both tricalcium phosphate and hydroxyapatite have good attenuation similarity with ICRU bone cortical. PLA+ material can be used as substitute to RMI457 slabs for reference dosimetry with a maximum difference of 1.84%. Percent depth dose measurement also shows that PLA+ has the best match with water and RMI457 within ±2.2% and ±1.6%, respectively. Overall, PLA+ phantoms match with RMI457 phantoms within ±3%. Significance and conclusion. The fabricated phantoms are excellent tissue equivalent equipment for synchrotron radiation dosimetry QA measurement. Both the rat and the anthropomorphic head phantoms are useful in synchrotron brain cancer radiotherapy dosimetry, experiments, and future clinical translation of synchrotron radiotherapy and imaging., (Creative Commons Attribution license.)

Silicon microdosimetry is a promising technology for heavy ion therapy (HIT) quality assurance, because of its sub-mm spatial resolution and capability to determine radiation effects at a cellular level in a mixed radiation field. A drawback of silicon is not being tissue-equivalent, thus the need to convert the detector response obtained in silicon to tissue. This paper presents a method for converting silicon microdosimetric spectra to tissue for a therapeutic 12 C beam, based on Monte Carlo simulations. The energy deposition spectra in a 10 μm sized silicon cylindrical sensitive volume (SV) were found to be equivalent to those measured in a tissue SV, with the same shape, but with dimensions scaled by a factor κ equal to 0.57 and 0.54 for muscle and water, respectively. A low energy correction factor was determined to account for the enhanced response in silicon at low energy depositions, produced by electrons. The concept of the mean path length [Formula: see text] to calculate the lineal energy was introduced as an alternative to the mean chord length [Formula: see text] because it was found that adopting Cauchy's formula for the [Formula: see text] was not appropriate for the radiation field typical of HIT as it is very directional. [Formula: see text] can be determined based on the peak of the lineal energy distribution produced by the incident carbon beam. Furthermore it was demonstrated that the thickness of the SV along the direction of the incident 12 C ion beam can be adopted as [Formula: see text]. The tissue equivalence conversion method and [Formula: see text] were adopted to determine the RBE 10 , calculated using a modified microdosimetric kinetic model, applied to the microdosimetric spectra resulting from the simulation study. Comparison of the RBE 10 along the Bragg peak to experimental TEPC measurements at HIMAC, NIRS, showed good agreement. Such agreement demonstrates the validity of the developed tissue equivalence correction factors and of the determination of [Formula: see text].

Rectal balloons are used in external beam prostate radiotherapy to provide reproducible anatomy and rectal dose reductions. This is an investigation into the combination of a MOSFET radiation detector with a rectal balloon for realtime in vivo rectal wall dosimetry. The MOSFET used in the study is a radiation detector that provides a water equivalent depth of measurement of 70 microm. Two MOSFETs were combined in a face-to-face orientation. The reproducibility, sensitivity and angular dependence were measured for the dual MOSFET in a 6 MV photon beam. The dual MOSFET was combined with a rectal balloon and irradiated with hypothetical prostate treatments in a phantom. The anterior rectal wall dose was measured in real time and compared with the planning system calculated dose. The dual MOSFET showed angular dependence within +/-2.5% in the azimuth and +2.5%/-4% in the polar axes. When compared with an ion chamber measurement in a phantom, the dual MOSFET agreed within 2.5% for a range of radiation path lengths and incident angles. The dual MOSFET had reproducible sensitivity for fraction sizes of 2-10 Gy. For the hypothetical prostate treatments the measured anterior rectal wall dose was 2.6 and 3.2% lower than the calculated dose for 3DCRT and IMRT plans. This was expected due to limitations of the dose calculation method used at the balloon cavity interface. A dual MOSFET combined with a commercial rectal balloon was shown to provide reproducible measurements of the anterior rectal wall dose in real time. The measured anterior rectal wall dose agreed with the expected dose from the treatment plan for 3DCRT and IMRT plans. The dual MOSFET could be read out in real time during the irradiation, providing the capability for real-time dose monitoring of the rectal wall dose during treatment.