Characterization of a flexible a-Si:H detector for in vivo dosimetry in therapeutic x-ray beams.

BACKGROUND: The increasing use of complex and high dose-rate treatments in radiation therapy necessitates advanced detectors to provide accurate dosimetry. Rather than relying on pre-treatment quality assurance (QA) measurements alone, many countries are now mandating the use of in vivo dosimetry, whereby a dosimeter is placed on the surface of the patient during treatment. Ideally, in vivo detectors should be flexible to conform to a patient's irregular surfaces. PURPOSE: This study aims to characterize a novel hydrogenated amorphous silicon (a-Si:H) radiation detector for the dosimetry of therapeutic x-ray beams. The detectors are flexible as they are fabricated directly on a flexible polyimide (Kapton) substrate. METHODS: The potential of this technology for application as a real-time flexible detector is investigated through a combined dosimetric and flexibility study. Measurements of fundamental dosimetric quantities were obtained including output factor (OF), dose rate dependence (DPP), energy dependence, percentage depth dose (PDD), and angular dependence. The response of the a-Si:H detectors investigated in this study are benchmarked directly against commercially available ionization chambers and solid-state diodes currently employed for QA practices. RESULTS: The a-Si:H detectors exhibit remarkable dose linearities in the direct detection of kV and MV therapeutic x-rays, with calibrated sensitivities ranging from (0.580 ± 0.002) pC/cGy to (19.36 ± 0.10) pC/cGy as a function of detector thickness, area, and applied bias. Regarding dosimetry, the a-Si:H detectors accurately obtained OF measurements that parallel commercially available detector solutions. The PDD response closely matched the expected profile as predicted via Geant4 simulations, a PTW Farmer ionization chamber and a PTW ROOS chamber. The most significant variation in the PDD performance was 5.67%, observed at a depth of 3 mm for detectors operated unbiased. With an external bias, the discrepancy in PDD response from reference data was confined to ± 2.92% for all depths (surface to 250 mm) in water-equivalent plastic. Very little angular dependence is displayed between irradiations at angles of 0° and 180°, with the most significant variation being a 7.71% decrease in collected charge at a 110° relative angle of incidence. Energy dependence and dose per pulse dependence are also reported, with results in agreement with the literature. Most notably, the flexibility of a-Si:H detectors was quantified for sample bending up to a radius of curvature of 7.98 mm, where the recorded photosensitivity degraded by (-4.9 ± 0.6)% of the initial device response when flat. It is essential to mention that this small bending radius is unlikely during in vivo patient dosimetry. In a more realistic scenario, with a bending radius of 15-20 mm, the variation in detector response remained within ± 4%. After substantial bending, the detector's photosensitivity when returned to a flat condition was (99.1 ± 0.5)% of the original response. CONCLUSIONS: This work successfully characterizes a flexible detector based on thin-film a-Si:H deposited on a Kapton substrate for applications in therapeutic x-ray dosimetry. The detectors exhibit dosimetric performances that parallel commercially available dosimeters, while also demonstrating excellent flexibility results.

Hydrogenated amorphous silicon high flux x-ray detectors for synchrotron microbeam radiation therapy.

Objective. Microbeam radiation therapy (MRT) is an alternative emerging radiotherapy treatment modality which has demonstrated effective radioresistant tumour control while sparing surrounding healthy tissue in preclinical trials. This apparent selectivity is achieved through MRT combining ultra-high dose rates with micron-scale spatial fractionation of the delivered x-ray treatment field. Quality assurance dosimetry for MRT must therefore overcome a significant challenge, as detectors require both a high dynamic range and a high spatial resolution to perform accurately.Approach. In this work, a series of radiation hard a-Si:H diodes, with different thicknesses and carrier selective contact configurations, have been characterised for x-ray dosimetry and real-time beam monitoring applications in extremely high flux beamlines utilised for MRT at the Australian Synchrotron.Results. These devices displayed superior radiation hardness under constant high dose-rate irradiations on the order of 6000 Gy s-1, with a variation in response of 10% over a delivered dose range of approximately 600 kGy. Dose linearity of each detector to x-rays with a peak energy of 117 keV is reported, with sensitivities ranging from (2.74 ± 0.02) nC/Gy to (4.96 ± 0.02) nC/Gy. For detectors with 0.8µm thick active a-Si:H layer, their operation in an edge-on orientation allows for the reconstruction of micron-size beam profiles (microbeams). The microbeams, with a nominal full-width-half-max of 50µm and a peak-to-peak separation of 400µm, were reconstructed with extreme accuracy. The full-width-half-max was observed as 55 ± 1µm. Evaluation of the peak-to-valley dose ratio and dose-rate dependence of the devices, as well as an x-ray induced charge (XBIC) map of a single pixel is also reported.Significance. These devices based on novel a-Si:H technology possess a unique combination of accurate dosimetric performance and radiation resistance, making them an ideal candidate for x-ray dosimetry in high dose-rate environments such as FLASH and MRT.

Listening understanding and acting (lung): focus on communicational issue in thoracic oncology.

BACKGROUND: In the field of oncological assistance, nowadays we have to deal with a complex scenario where patients got used to obtain a huge amount of information through internet or social media and to apply them in performing their health-related decisions. This landscape requires that clinicians become able to handle therapeutical approaches and adequate skills in communication tools to satisfy the current needs. Our project aimed to build a communication model based on clinical oncologists' real experiences in order to find a simple way to share with patients all the innovative therapeutical opportunities today available in lung cancer. The final goal is to design a flexible and personalized model adaptable to clinician's personal characteristics and to the specific patient he is facing. We applied both traditional educational tools and innovative techniques in order to make the results effective and applicable to support peer learning. METHODS: The first step consisted in a Board synthesized the definition of the diagnostic process, the identification of treatment strategies and any potential communication barrier clinicians may face dealing with patients. The second step consisted in teamwork including a theoretical part and a training part. In the third step we produce five training videos and video interviews regarding communication praxis and a "Small communication manual". The last step consisted in the publication of the produced material on website and its diffusion through the social media. RESULTS: In medicine, the universal application of a single model of communication does not represent the optimal solution. By contrary, the availability of simple and practical suggestions to improve the communicative style could allow clinicians to abandon stereotyped formulas identically repurposed to all patients. The "from bottom to top" training, starting from real-life to take advantage of the clinician's experience, give the clinicians the possibility to meditate about their own communicative style and to train in the context of a protected environment. Applying these rules, we design an effective communication model, based on healthcare humanization, which could represent a fundamental support for the patient in order to be gently driven by the clinician to the most appropriate therapeutical choice, balancing efficacy and quality of life. The relational training may improve the quality of clinician-patient communication and could be widespread to other clinicians through the media. CONCLUSIONS: Considering the innovative therapeutical options available, particularly for lung cancer patients, and the increasing access of health-related information through internet or social media the clinician-patient communication has become crucial to support the achievement of the most appropriate therapeutical choice for the patient, facing the intricate illness experience. Building a shareable and easy-to-apply communication model represents a challenge aimed to help clinicians and including technology not as a threat, but as a positive tool.