Microdosimetric measurements of a monoenergetic and modulated Bragg Peaks of 62 MeV therapeutic proton beam with a synthetic single crystal diamond microdosimeter.

PURPOSE: The purpose of this study was to investigate for the first time the performance of a synthetic single crystal diamond detector for the microdosimetric characterization of clinical 62 MeV ocular therapy proton beams. METHODS: A novel diamond microdosimeter with a well-defined sensitive volume was fabricated and tested with a monoenergetic and spread-out Bragg peak (SOBP) of the CATANA therapeutic proton beam in Catania, Italy. The whole sensitive volume of the detector has an active planar-sectional area of 100 µm × 100 µm and a thickness of approximately 6.3 um. Microdosimetric measurements were performed at several water equivalent depths, corresponding to positions of clinical relevance. From the measured spectra, microdosimetric quantities such as the frequency mean lineal energy ( y ¯ F ), dose mean lineal energy ( y ¯ D ) as well as microdosimetric relative biological effectiveness (RBEµ ) values were derived for each depth along both a pristine Bragg curve and SOBP. Finally, Geant4 Monte Carlo simulations were performed modeling the detector geometry and CATANA beamline in order to calculate the average linear energy transfer (LET) values in the diamond active layer and water. RESULTS: The microdosimetric spectra acquired by the diamond microdosimeter show different shapes as a function of the water equivalent depths. No spectral distortion, due to pile-up events and polarization effects, was observed. The experimental spectra have a very low detection threshold due to the electronic noise during the irradiation of about 1 keV/µm. The y ¯ F and y ¯ D values were in agreement with expected trends, showing a sharp increase in mean lineal energy at the distal edge of the Bragg peak. In addition, a good agreement between the mean lineal energy values and the calculated average LET ones was also observed. Finally, the RBE values evaluated with the diamond microdosimeter were in excellent agreement with those obtained with a mini tissue equivalent proportional counter as well as with radiobiological measurements in the same proton beam field. CONCLUSIONS: The microdosimetric performance of the tested synthetic single crystal diamond microdosimeter clearly indicates its suitability for quality assurance in clinical proton therapy beam.

Concepts and terms for dose/volume parameters in carbon-ion radiotherapy: Conclusions of the ULICE taskforce.

PURPOSE: The Union of Light Ion Centers in Europe (ULICE) program addressed the need for uniting scientific results for carbon-ion radiation therapy obtained by several institutions worldwide in different fields of excellence, and translating them into a real benefit to the community. Particularly, the concepts for dose/volume parameters developed in photon radiotherapy cannot be extrapolated to high linear energy transfer particles. METHODS AND MATERIALS: The ULICE-WP2 taskforce included radiation oncologists involved in carbon-ion radiation therapy and International Commission on Radiation Units and Measurements, radiation biologists, expert physicists in the fields of carbon-ion radiation therapy, microdosimetry, biological modeling and image-guided radiotherapy. Consensual reports emerged from multiple discussions within both the restricted group and the wider ULICE community. Public deliverables were produced and disseminated to the European Commission. RESULTS: Here we highlight the disparity in practices between treating centers, then address the main topics to finally elaborate specific recommendations. Although it appears relatively simple to add geometrical margins around the clinical target volume to obtain the planning target volume as performed in photon radiotherapy, this procedure is not appropriate for carbon-ion radiation therapy. Due to the variation of the radiation quality in depth, there is no generic relative biological effectiveness value for carbon-ions outside of an isolated point, for a given fractionation and specific experimental conditions. Absorbed dose and "equieffective dose" for specified conditions must always be reported. CONCLUSIONS: This work contributed to the development of standard operating procedures for carbon-ion radiation therapy clinical trials. These procedures are now being applied, particularly in the first phase III international, multicenter trial (PHRC Étoile).

Miniaturized microdosimeters as LET monitors: First comparison of calculated and experimental data performed at the 62 MeV/u 12C beam of INFN-LNS with four different detectors.

PURPOSE: The aim of this paper is to investigate the limits of LET monitoring of therapeutic carbon ion beams with miniaturized microdosimetric detectors. METHODS: Four different miniaturized microdosimeters have been used at the 62 MeV/u 12C beam of INFN Southern National Laboratory (LNS) of Catania for this purpose, i.e. a mini-TEPC and a GEM-microdosimeter, both filled with propane gas, and a silicon and a diamond microdosimeter. The y-D (dose-mean lineal energy) values, measured at different depths in a PMMA phantom, have been compared withLET¯D (dose-mean LET) values in water, calculated at the same water-equivalent depth with a Monte Carlo simulation setup based on the GEANT4 toolkit. RESULTS: In these first measurements, no detector was found to be significantly better than the others as a LET monitor. The y-D relative standard deviation has been assessed to be 13% for all the detectors. On average, the ratio between y-D and LET¯D values is 0.9 ±â€¯0.3, spanning from 0.73 ±â€¯0.08 (in the proximal edge and Bragg peak region) to 1.1 ±â€¯0.3 at the distal edge. CONCLUSIONS: All the four microdosimeters are able to monitor the dose-mean LET with the 11% precision up to the distal edge. In the distal edge region, the ratio of y-D to LET¯D changes. Such variability is possibly due to a dependence of the detector response on depth, since the particle mean-path length inside the detectors can vary, especially in the distal edge region.

Radiation quality and ion-beam therapy: understanding the users' needs.

Ion-beam therapy faces a growing demand of tools able to map radiation quality within the irradiated volume. Although analytical computations and simulations provide useful estimations of dose and radiation quality, the direct measure of those parameters would improve ion-beam therapy in particular when deep-seated tumours are irradiated, tissue composition and density are variable or organs at risk are near the tumour. Several ion-beam therapy facilities are studying detectors and procedures for measuring the radiation quality on a microdosimetric as well as a nanodosimetric scale. Simplicity and miniaturisation of the devices are essential for measurements first in phantoms and thereafter during therapy, particularly for intra-cavity detectors. MedAustron is studying solid-state detectors based on a single crystal chemical vapour deposition diamond. In collaboration with Italian National Institute for Nuclear Physics (INFN), Tor Vergata and Legnaro; INFN-microdosimetry and track structure project; Austrian Institute of Technology, Vienna; and Italian National agency for new technologies, energy and sustainable economic development, Rome, prototypes have been developed to characterise radiation quality in sizes equivalent to one micrometre of biological tissue.

Piloting the use of 2D barcode and patient safety-software in an Australian tertiary hospital setting.

OBJECTIVES: Errors in administration of blood products can lead to poor patient outcomes including fatal ABO incompatible transfusions. This pilot study sought to establish whether the use of two-dimensional (2D) barcode technology combined with patient identification software designed to assist in blood administration improves the bedside administration of transfusions in an Australian tertiary hospital. STUDY DESIGN AND METHODS: The study was conducted in a Haematology/Oncology Day Clinic of a major metropolitan hospital, to evaluate the use of 2D barcode technology and patient safety-software and hand-held PDAs to assist nursing staff in patient identification and blood administration. Comparative audits were conducted before and after the technology's implementation. RESULTS: The preimplementation transfusion practice audits demonstrated a poor understanding of the blood checking process, with focus on the product rather than patient identification. Following the implementation of 2D barcode technology and patient safety-software, there was significant improvement in administration practice. Positive, verbal patient identification improved from 57% (51/90) to 94% (75/80). Similarly, the cross-referencing of the patient's identification with the patient's wristband improved from 36% (32/90) to 94% (75/80), and the cross-referencing of patient ID on the compatibility tag to wristbands improved from 48% (43/90) to 99% (79/80). Importantly, the 2D barcode technology and patient safety-software saw 100% (80/80) of checks being conducted at the patient bedside, compared with 76% (68/90) in the preimplementation audits. CONCLUSION: This pilot study demonstrates that 2D barcode technology and patient safety-software significantly improves the bedside check of patient and blood product identification in an Australian setting.

Mini-TEPCs for radiation therapy.

A mini-tissue-equivalent proportional-counter (TEPC) has been constructed to study the possibility to manufacture mini-counters without field-shaping tubes for radiation therapy. The mini-TEPC can be assembled with and without field-shaping tubes. It can be equipped with a mini-alpha source for a precise lineal energy calibration. After the positive conclusions of this study, a slim TEPC has been designed and constructed. The slim TEPC has an external diameter of only 2.7 mm. It has been tested with therapeutic proton beams and gamma ray sources.

Microdosimetric analysis of radiation from a clinical mammography machine using realistic breast phantoms and a miniature proportional counter.

We have measured the microdosimetric spectra of a Senographe 600T mammography machine employing an Mo target with 0.8 mm Be inherent filtration and 0.03 mm Mo added filtration, giving a half-value layer of 0.35 mm A1 at 28 kVp. In all of our measurements a large collimator producing a 24 cm x 30 cm field at 65 cm was used. Two different phantom compositions differing in the ratio of adipose to fibroglandular tissue were compared, using simulated breast material from Nuclear Associates. Spectra were taken at various depths and locations in simulated breasts of 3.4 and 5 cm thickness. The detector used was a miniature proportional counter having outer dimensions of 5 cm x 1.8 cm diameter, with a sensitive volume 0.5 mm x 0.5 mm. The small dimensions of the counter and the cavity allowed total embedding in the breast material with minimal disturbance of the photon and secondary electron spectrum. Our results show that there can be changes in the radiation quality amounting to as much as 17% (as measured by the dose mean lineal energy. yD) between breasts of different thickness, at the same relative position within the breast. There is little difference due to breast composition.

Preoperative autologous blood donation. Linkage of the public and private hospital sectors.

OBJECTIVE: To evaluate the safety and efficacy of a preoperative autologous blood donation (PABD) program with liberal patient exclusion criteria. DESIGN: Prospective patient accrual from September 1990 to May 1992. SETTING: A PABD program in a public tertiary care hospital linked with a specialist orthopaedic practice in a private hospital. PATIENTS: One hundred and twenty patients consecutively scheduled for orthopaedic surgery were referred for PABD. There were 77 women (median age, 63 years) and 43 men (median age, 62 years). One-third of patients were 70 or more years old. Coexistent medical disease, mainly cardiovascular, was present in 46% of patients and 3% were excluded because of coexisting morbidity. Total hip or total knee replacement was performed in a private hospital with intraoperative or postoperative blood salvage in 37% of the patients. OUTCOME MEASURES: Adverse effects of PABD, autologous blood collected and used and homologous blood transfused. RESULTS: One hundred and sixteen patients donated 267 units of autologous blood. In 70 patients undergoing total hip replacement, 78% donated three and 20% donated two units, with 95% of autologous blood being used. In 38 patients undergoing total knee replacement, 42% donated two units and 55% donated one unit, with 87% of autologous blood being transfused. Seventy-eight per cent of all patients only received autologous blood. In the remaining patients, homologous blood use was confined to two units or less in 80%. Hypotensive episodes associated with phlebotomy occurred in 3% of patients, and 13% of patients had preoperative haemoglobin levels ranging from 85-100 g/L without adverse clinical effects. CONCLUSION: A hospital-based PABD program with less strict patient exclusion criteria does not prejudice the clinical status of the donors. Its linkage to private hospitals can significantly reduce the use of homologous blood in selected elective surgery.