Radiochromic film (RCF) dosimetry has great potential in the procedures for the quality control of dosimetric computation of multiple beam techniques supplied by treatment planning systems (TPS). In this study the RCF MD-55-2 have been used for 62 MeV clinical proton beam dosimetry at the Clatterbridge Center for Oncology (UK). Irradiations were performed positioning the RCF directly in a water phantom. The films were irradiated both in perpendicularly and in parallel configuration with respect to the proton beam central axis, to study the change of the RCF efficiency with the film orientation. Due to the change of the RCF efficiency at Bragg peak, the dose underestimation was 8% and 52% for the RCF positioned in perpendicular and parallel configuration with respect to the central beam axis, respectively. For a modulated proton beam the dose underestimation was 8% and 60% for perpendicular and parallel irradiated film, respectively, at the end of the SOBP (spread-out Bragg peak) region. For RCF irradiated with a modulated proton beam in parallel configuration, a correction method was implemented to obtain accurate depth dose, profiles and isodose distributions. The method used an empirical factor k(E0)(RCF), that is a function of the beam residual range and is specific for a proton beam of incident effective energy, E-0. The procedure has been automatized by a dedicated software and could be useful for the dosimetric verification of the TPS computation, and accurate dosimetric characterization of small proton beams.

The calibration factor variation for a PTW natural diamond detector and a Scanditronix p-type stereotactic silicon diode (designed for use in photon beams) was studied in the 10-59 MeV range. Irradiations were performed in a water phantom with the 60 MeV ocular therapy beam at the CCO (UK). The diamond detector showed a sensitivity increase with energy, underestimating the dose by about 18% at the Bragg peak, by 7% at the centre and by 17% at the distal end of the SOBP region. The silicon diode did not show any significant sensitivity change with energy. However, a decrease in response of 24% was observed for an accumulated dose of 300 Gy.

Small dosimeters as solid state detectors can be useful for the dosimetric characterization and periodic quality control of radiotherapy proton beams. The calibration of solid state detectors for proton beams is not a solved problem especially for ophthalmologic proton beams, where these detectors present a LET-dependent signal. In this work a PTW diamond detector has been selected because of its good signal reproducibility (0.3%) and stable response with accumulated dose. A method that takes into account the LET dependence of the diamond detector signal, at 62 MeV proton beam, is here proposed. In particular an empirical correction factor, kDD(Eo) (Rres), has been determined as a function of the residual range quality index, to correct the diamond detector signal for a proton beam of incident effective energy E0= 62 MeV. A dedicated software allows us to use the diamond detector as an on-line reference dosimeter, where an ionization chamber may be difficult to use, or for periodic quality control procedures. The article also reports a comparison between the signal dependence on proton energy of silicon, diamond, and radiochromic film detectors.

The present work reports preliminary measurements on the behaviour of a new p-type stereotactic silicon diode. Hi-pSi, produced by Scanditronix and dedicated to proton dosimetry. Diode response was investigated in low-energy proton beams (26.7 MeV and 12 MeV nominal energy), mainly with attention to stability, linearity, dose rate and energy dependence of the detector response. Three different Hi-pSi diodes of the same type were investigated. The diode response was linear with dose and the standard deviation of repeated readings was less than 2.5%. A marked dependence on dose rate was observed for one of the diodes (a response increase of 47% in the 0.7-11 Gy x min(-1) range). After the dose rate and water to silicon mass collision stopping power ratio correction of the diode response in the depth dose measurements, the difference, at the Bragg peak, with respect to the reference chamber was about 4%, ascribed to poor knowledge of the materials in front of the sensitive volume. The diode response was also nearly independent of linear energy transfer (LET) in the 9.6-21.5 MeV effective energy range.

In response to needs expressed by the scientific and medical communities, the United States Congress passed the National Cancer Act in 1971. Through this legislation, Congress committed the resources necessary to assure a continuing national program of research into the causes and treatment of cancer. The vehicle of implementation chosen by Congress was the establishment of regional comprehensive cancer centers, to be selected by the National Cancer Institute on the basis of competitive grants and located at major academic research institutions across the country. These 20 centers serve as the backbone of the national research effort and provide a regional focus for all aspects of cancer prevention, detection, and care. Through the leadership of Dr. A. H. Owens, Jr., a comprehensive oncology center was established at The Johns Hopkins University in 1973. The Johns Hopkins Oncology Center is located at the East Baltimore campus and is an integral part of the Johns Hopkins Medical Institutions. The physical plant, dedicated in April 1977, includes three floors of research laboratories where basic cancer research is carried out, a 56-bed inpatient wing that also supports clinical studies, and a major radiation therapy wing, perhaps the most modern and comprehensive radiation therapy facility on the east coast. The Center also maintains a major outpatient service and an outreach program in support of nearby community hospitals. The Applied Physics Laboratory played an important role during the early planning phases of the Oncology Center. It was evident that the quality of research and patient care could be enhanced by introducing certain high-technology equipment and systems into the Center. Through J. T. Massey, then Director of Biomedical Programs at the Laboratory, and R. J. Johns, Director of the Department of Biomedical Engineering at the School of Medicine, a number of important initiatives were set in motion. A major physiologic monitoring system serving the entire patient wing was conceptualized, procured, and implemented by J. B. Oakes, L. Raum, and me. This · activity ultimately broadened substantially and led to the formation of the Oncology Center Clinical Engineering Group under my direction. Further, a com-

The dosimetric properties of two PTW Riga diamond detectors type 60003 were studied in high-energy photon and electron therapy beam. Properties under study were current-voltage characteristic, polarization effect, time stability of response, dose response, dose-rate dependence, temperature stability, and beam quality dependence of the sensitivity factor. Differences were shown between the two detectors for most of the previous properties. Also, the observed behavior was, to some extent, different from what was reported in the PTW technical specifications. The necessity to characterize each diamond detector individually was addressed.

Thin solid state detectors are attractive for relative and absolute dosimetry of therapeuticy proton beams complementing ionisation chamber measurements. In the framework of a wide collaboration, we have been studying dosimetric properties of p-type stereotactic silicon diode detectors (Scanditronix, 60 min, 0.06 mm, thick) and natural diamond detectors (PTW, 260 mm, 0.26 mm thick). Here we report preliminary results on depth dose measurements performed with both dosimetry systems in a low energy beam (26.7 MeV nominal energy available at LNS) and in a therapyeutic proton beam (62 MeV available at CCO). Results seem to be in favour of silicon diode even if care must be taken for its proper use.

The authors present a novel method for processing T(1)-weighted images acquired with Inversion-Recovery (IR) sequence. The method, developed within the Bayesian framework, takes into account a priori knowledge about the spatial regularity of the parameters to be estimated. Inference is drawn by means of Markov Chains Monte Carlo algorithms. The method has been applied to the processing of IR images from irradiated Fricke-agarose gels, proposed in the past as relative dosimeter to verify radiotherapeutic treatment planning systems. Comparison with results obtained from a standard approach shows that signal-to noise ratio (SNR) is strongly enhanced when the estimation of the longitudinal relaxation rate (R1) is performed with the newly proposed statistical approach. Furthermore, the method allows the use of more complex models of the signal. Finally, an appreciable reduction of total acquisition time can be obtained due to the possibility of using a reduced number of images. The method can also be applied to T(1) mapping of other systems.

The dosimetric behaviour of a Scanditronix p-type silicon diode and a PTW natural diamond detector was studied in low-energy proton beams in the 8.3-21.5 MeV range. The properties investigated were linearity, reproducibility, dose rate dependence, energy and linear energy transfer (LET) dependence. The influence of detector thickness on the results of depth dose measurements was also demonstrated. A Markus parallel plate ionization chamber was used for reference dosimetry. Silicon diode and diamond detectors showed linearity at therapeutic dose level, reproducibility better than 1% (1 sigma) and sensitivity variation with dose rate and proton energy.

In this work some dosimetric characteristics of MD-55-2 GafChromic films were studied in a low energy proton beam (21.5 MeV) directly in a water phantom. The nonlinearity of the optical density was quantified by a factor P(lin). A correction factor P(en), that accounts for optical density dependence on the energy, was empirically determined. The effects of detector thickness in depth dose measurements and of the film orientation with respect to beam direction were investigated. The results show that the MD-55-2 films provide dose measurements with the films positioned perpendicularly to the proton beam. A dosimetric formalizm is proposed to determine the dose to water at depth d, with films oriented perpendicularly to the beam axis. This formalism uses a calibration factor of the radiochromic film determined directly on the proton beam at a reference depth in water, and the P(lin) factor, that takes into account the nonlinearity of the calibration curve and the P(en) factor that, in turn takes into account the change of proton beam energy in water. The MD-55-2 films with their high spatial resolution and the quasiwater equivalent material are attractive, positioned perpendicularly along the beam axis, for the absolute dose determination of very small beam sizes and modulated proton beams.