DEVELOPING RADIATION RESISTANT THERMAL NEUTRON DETECTORS FOR THE E_LIBANS PROJECT: PRELIMINARY RESULTS.

Radiation-resistant, gamma-insensitive, active thermal neutron detectors were developed to monitor the thermal neutron cavity of the E_LIBANS project. Silicon and silicon carbide semiconductors, plus vented air ion chambers, were chosen for this purpose. This communication describes the performance of these detectors, owing on the results of dedicated measurement campaigns.

INTENSE THERMAL NEUTRON FIELDS FROM A MEDICAL-TYPE LINAC: THE E_LIBANS PROJECT.

The e_LiBANS project aims at producing intense thermal neutron fields for diverse interdisciplinary irradiation purposes. It makes use of a reconditioned medical electron LINAC, recently installed at the Physics Department and INFN in Torino, coupled to a dedicated photo-converter, developed within this collaboration, that uses (γ,n) reaction within high Z targets. Produced neutrons are then moderated to thermal energies and concentrated in an irradiation volume. To measure and to characterize in real time the intense field inside the cavity new thermal neutron detectors were designed with high radiation resistance, low noise and very high neutron-to-photon discrimination capability. This article offers an overview of the e_LiBANS project and describes the results of the benchmark experiment.

Complete recovery from paraparesis in spinal cord compression due to extramedullary haemopoiesis in beta-thalassaemia by emergency radiation therapy.

Extramedullary haemopoiesis (EMH) is a complication commonly associated with beta-thalassaemia intermedia; it is frequently asymptomatic but can sometimes lead to symptomatic tumour-like masses. No guidelines or common consensus are available in literature regarding the different treatment strategies and only single cases have been reported. We describe a case of spinal cord compression due to intrathoracic EMH masses treated with combined radiotherapy and hydroxyurea.

[Characterization of a diode system for in vivo dosimetry with electron beams]. / Caratterizzazione di un sistema a diodi per la dosimetria in vivo con fasci di elettroni.

PURPOSE: Current quality assurance regulation stresses the basic role of in vivo dosimetry. Our study evaluates the usefulness and reliability of semiconductor diodes in determining the electron absorbed dose. MATERIAL AND METHODS: P-type EDE semiconductor detectors were irradiated with electron beams of different energies produced by a CGR Saturn Therac 20. The diode and ionization chamber response were compared, and effect of energy value, collimator opening, source skin distance and gantry angle on diode response was studied. RESULTS: Measurements show a maximum increment of about 20% in diode response increasing the beam energy (6-20 MeV). The response also increases with: collimator opening, reaching 5% with field sizes larger than 10x10 cm2 (with the exception of 20 MeV energy); SSD increase (with a maximum of 8% for 20 MeV); transversal gantry incidence, compared with the diode longitudinal axis; it does not affect the response in the interval of +/- 45 degrees. Absorbed dose attenuation at dmax, due to the presence of diode on the axis of the beam as a function of electron energy was also determined : the maximum attenuation value is 15% in 6 MeV electron beams. A dose calculation algorithm, taking into account diode response dependence was outlined. In vivo dosimetry was performed in 92 fields for 80 patients, with an agreement of +/-4 % (1 SD) between prescribed and measured dose. DISCUSSION AND CONCLUSIONS: It is possible to use the EDE semiconductor detectors on a quality control program of dose delivery for electron beam therapy, but particular attention should be paid to the beam incidence angle and diode dose attenuation.

[Absorbed doses in dental radiology]. / Dosi assorbite nella radiologia dentale.

The growing use of dento-maxillo-facial radiographic examinations has been accompanied by the publication of a large number of studies on dosimetry. A thorough review of the literature is presented in this article. Most studies were carried out on tissue equivalent skull phantoms, while only a few were in vivo. The aim of the present study was to evaluate in vivo absorbed doses during Orthopantomography (OPT). Full Mouth Periapical Examination (FMPE) and Intraoral Tube Panoramic Radiography (ITPR). Measurements were made on 30 patients, reproducing clinical conditions, in 46 anatomical sites, with 24 intra- and 22 extra-oral thermoluminiscent dosimeters (TLDS). The highest doses were measured, in orthopantomography, at the right mandibular angle (1899 mu Gy) in FMPE on the right naso-labial fold (5640 mu Gy and in ITPR on the palatal surface of the left second upper molar (1936 mu Gy). Intraoral doses ranged from 21 mu Gy, in orthopantomography, to 4494 mu Gy in FMPE. Standard errors ranged from 142% in ITPR to 5% in orthopantomography. The highest rate of standard errors was found in FMPE and ITPR. The data collected in this trial are in agreement with others in major literature reports. Disagreements are probably due to different exam acquisition and data collections. Such differences, presented comparison in several sites, justify lower doses in FMPE and ITPR. Advantages and disadvantages of in vivo dosimetry of the maxillary region are discussed, the former being a close resemblance to clinical conditions of examination and the latter the impossibility of collecting values in depth of tissues. Finally, both ITPR and FMPE required lower doses than expected, and can be therefore reconsidered relative to their radiation risk.

[High-dose-rate brachytherapy. The indications, technic and preliminary results]. / La brachiterapia ad alto rateo di dose. Indicazioni, tecnica e risultati preliminari.

The authors report their experience of high dose brachytherapy technique (HDR), relative to the first period of work, especially regarding treatment indications and preliminary clinical results. Twenty eight patients were examined, 12 of them with esophageal carcinoma, 7 biliary tract carcinoma, 6 skin of the face and 3 head and neck carcinoma. HDR brachytherapy was the first treatment in 20 cases; the other 8 cases were recurrences after previous irradiation. The HDR treatment had a curative purpose in 15 patients and was palliative in the other 13. Brachytherapy doses ranged from 20 to 30 Gy for curative treatments, with 4-8 fractions; 1 fraction was used for palliative radiotherapy, with doses from 5 to 10 Gy. The results were satisfactory. Local control was achieved in 5/6 patients affected with cholangiocarcinoma of the biliary tract and in 6/6 patients with skin neoplasia. In esophageal cancer, 9/12 patients treated with palliative, disobstructive purpose, showed dysphagia remission in 89% of the cases; the remission was maintained in 7 patients (78%), with 9 months median follow-up. HDR brachytherapy was then proved, during this first period of clinical application, as a valid and safe therapeutic method. It also allowed to extend the application field of brachytherapy, with new indications, as in esophageal neoplasias and biliary tract carcinomas.

[Total skin therapy with electron beams. I. Physical and geometric factors]. / Terapia cutanea totale con fasci di elettroni. Parte I. Fattori fisici e geometrici.

The study pf physical and geometrical factors influencing dose distribution is necessary in performing the Total Skin Electron Therapy. The authors examined some aspects. Photographic emulsions in humanoid phantom were used for dosimetry. The techniques uses 6 dual fields at 320 cm treatment distance, with a degrading lucite filter 100 x 200 x 0.6 cm3 at 20 cm from the patient. Absorbed dose and energy were determined according TG 30 and 21 AAPM. The position of degrading filter was recognized to be the main factor influencing dose rate, penetration depth and dose homogeneity.

[Total skin therapy with electron beams. II. Clinical results in mycosis fungoides]. / Terapia cutanea totale con fasci di elettroni. Parte II. Risultati clinici nella micosi fungoide.

Between 1985 and 1989, 19 patients with mycosis fungoides were treated by Total Skin Electron Therapy (TSET). Overall and disease-free survival at 3 years were 72% and 40%. The complete remission (CR) rate was 100% in patients with plaque and 33.3% in those with tumor masses; patients with negative nodes had a 90% CR rate whereas in those with adenopathy the rate was 55%. Overall and disease free survivals were also correlated with these factors.

Lateral high abdominal ovariopexy: an original surgical technique for protection of the ovaries during curative radiotherapy for Hodgkin's disease.

An original surgical method for gonadal protection in young women given pelvic radiation for Hodgkin's disease is presented. Lateral high ovarian transposition (LHAO) consists of the transposition of the ovaries into the paracolic gutter during staging laparotomy, after disconnecting the gonads from the fallopian tubes by dividing the tubo-ovarian vessels. The technique's effectiveness was assessed by a study using clinical investigation, radioimmunoassay (RIA) determination of sex hormones, and dosimetry; of 18 patients treated, 10 participated in the study. All but one have normal menses and hormone values, and one pregnancy occurred. We also calculated the doses absorbed by the ovaries and proved that, during inverted Y irradiation following LHAO, the ovaries are exposed to nearly one-half the dose they receive after traditional medial transposition. During subtotal nodal irradiation after LHAO, the irradiation dose is higher than after medialisation, but absolute values are minimal and castration is not induced.

[Total cutaneous irradiation with low energy electrons and mycosis fungoides. Technic and dosimetry]. / Irradiazione cutanea totale con elettroni di bassa energia e micosi fungoide. Tecnica e dosimetria.

Mycosis fungoides initially involves the epidermis and the superficial layers of derma at a depth of about 1 cm. Wide field irradiation with low energy electrons is therefore the treatment of choice in the initial stages of the disease. In our Institute, total skin electron beam irradiation is delivered with Therac 20 linear accelerator: the lowest available energy is 6 MeV. A lucite sheet of 0.6 cm thickness is used to decrease the energy of the beam. We used film dosimetry to evaluate the homogeneity of dose distribution in an Alderson-Rando phantom with different arrangements of the fields and the lucite sheet: 4 and 6 fields techniques have been compared with different positions of the lucite filter, near the phantom and near the collimator. Six fields yield a better dose distribution: homogeneity is within +/- 3.7%, while with four fields it is within +/- 6%. X-rays contamination is less than 2%. "In vivo" dosimetry has been performed using thermoluminescent dosimeters: homogeneity is within +/- 15%.

[Technic and dosimetry in total body irradiation with 18 MeV photons]. / Tecnica e dosimetria nell'irradiazione corporea totale con fotoni da 18 MeV.

Total body irradiation (TBI) is used in our Institution in the conditioning regimen for bone marrow transplantation. The fractionation pattern consists of two daily fractions of 1.65 Gy repeated for 4 days (total dose 13.20 Gy in 8 fractions). Lung dose is reduced by means of lead custom shaped shields directly strapped to the patient surface. TBI is delivered by a THERAC 20 linear accelerator with two opposing AP-PA photon beams with a maximum energy of 18 MeV. Treatment distance is 340 cm and the patient is treated in a semi-standing position. Dosimetry studies in a homogeneous phantom were performed in the treatment geometry and consisted in the determination of: tissue maximum ratios (TMR) at different depths, absorbed dose along the median axis and the diagonal of the field, variation of the absorbed dose in the prescription point with different volumes of scattering material, and transmission of shielding and compensating material. A semi-empiric formula for the calculation of absorbed dose in a point has been obtained. A subsequent study in a Rando phantom with termoluminescent dosimeters (TLD) has shown a +/- 5% agreement between calculated and measured values and a +/- 7% homogeneity.

[Comparison of dosimetric protocols for beams of photons and electrons]. / Confronto di protocolli dosimetrici per fasci di fotoni ed elettroni.

In this work we utilize different methods for the calculus of the absorbed dose at different photon and electron energies and we evaluate the difference between their yields. One of these methods is based on the consideration of the factors C lambda e CE (ICRU, HPA, AAPM protocols before 1980); by means of the others (AAPM-Task Group 21, NACP) we seek to obtain a better accuracy introducing new conversion factors. Our measurements were performed using cylindrical and flat ionisation chambers. In the considered energy range we obtained the following results: the new conversion factors have a higher value than C lambda and always smaller than CE.

[Mantle irradiation with 18 MeV photons. Measurement and calculation of dose distribution]. / L'irradiazione a mantellina con fotoni da 18 MeV. Misura e calcolo della distribuzione della dose.

Dose distribution in mantle fields irradiated with 18 MeV photons has been studied in an Alderson-Rando phantom with thermoluminescent dosimeters. The treatment was also simulated on an RT-plan 7000 computer; calculated and measured doses in anatomical sites of major interest were compared. Doses in all significant points were within +/- 7% of the doses at the reference point. Calculated and measured doses agreed within +/- 5% except points situated near unhomogeneous tissues. The authors discuss their results and present conclusions about algorithms for computer dose calculation in irregular field treatments.