A method for the inter-calibration of a matrix of sensors.

We present a quick and easy method for the calibration of a matrix of sensors. The algorithm is based on a three-step irradiation procedure which relies only on the constancy of the delivered fluence at each step. With this method the gain of each sensor is derived relative to a reference detector. The algorithm has been applied to a matrix of (32 x 32) ionization chambers. After the calibration coefficients have been applied, by comparing the response of the matrix of chambers to a reference detector over a large field, we determined that the fluence measurement of individual chambers is better than 0.7%. The algorithm solves the cumbersome problem of the relative gain calibration of a matrix of a large number of sensors.

Dosimetric characterization of a large area pixel-segmented ionization chamber.

A pixel-segmented ionization chamber has been designed and built by Torino University and INFN. The detector features a 24 x 24 cm2 active area divided in 1024 independent cylindrical ionization chambers and can be read out in 500 micros without introducing dead time; the digital charge quantum can be adjusted between 100 fC and 800 fC. The sensitive volume of each single ionization chamber is 0.07 cm3. The purpose of the detector is to ease the two-dimensional (2D) verifications of fields with complex shapes and large gradients. The detector was characterized in a PMMA phantom using 60Co and 6 MV x-ray photon beams. It has shown good signal linearity with respect to dose and dose rate to water. The average sensitivity of a single ionization chamber was 2.1 nC/Gy, constant within 0.5% over one month of daily measurements. Charge collection efficiency was 0.985 at the operating polarization voltage of 400 V and 3.5 Gy/min dose rate. Tissue maximum ratio and output factor have been compared with a Farmer ionization chamber and were found in good agreement. The dose profiles have been compared with the ones obtained with an ionization chamber in water phantom for the field sizes supplied by a 3D-Line dynamic multileaf collimator. These results show that this detector can be used for 2D dosimetry of x-ray photon beams, supplying a good spatial resolution and sensibly reducing the time spent in dosimetric verification of complex radiation fields.

Analysis of photoneutron spectra produced in medical accelerators.

A complete method is presented for the evaluation of photoneutron spectra produced in linear accelerators for cancer radiotherapy. It consists of a computer simulation code based on the MCNP4B Monte Carlo code, in which the new routine GAMMAN was implemented, allowing the accurate study of photoneutron production in high Z elements. In addition an experimental method based on a passive bubble spectrometer allows direct measurements of the photoneutron spectrum at the patient plane, also under the photon beam. The results are presented both for a 15 MeV linac with a traditional collimator system and for an 18 MeV linac equipped with a multileaf collimator, used in conformational radiotherapy.

Monte Carlo simulation of the photoneutron field in linac radiotherapy treatments with different collimation systems.

Bremsstrahlung photon beams produced by linac accelerators are currently the most commonly used method of radiotherapy for tumour treatments. When the photon energy exceeds 10 MeV the patient receives an undesired dose due to photoneutron production in the accelerator head. In the last few decades, new sophisticated techniques such as multileaf collimators have been used for a better definition of the target volume. In this case it is crucial to evaluate the photoneutron dose produced after giant dipole resonance (GDR) excitation of the high Z materials (mainly tungsten and lead) constituting the collimator leaves in view of the optimization of the radiotherapy treatment. A Monte Carlo approach has been used to calculate the photoneutron dose arising from the GDR reaction during radiotherapy with energetic photon beams. The simulation has been performed using the code MCNP4B-GN which is based on MCNP4B, but includes a new routine GAMMAN to model photoneutron production. Results for the facility at IRCC (Istituto per la Ricerca e la Cura del Cancro) Candiolo (Turin), which is based on 18 MV x-rays from a Varian Clinac 2300 C/D, are presented for a variety of different collimator configurations.

Two-dimensional and quasi-three-dimensional dosimetry of hadron and photon beams with the Magic Cube and the Pixel Ionization Chamber.

Two detectors for fast two-dimensional (2D) and quasi-three-dimensional (quasi-3D) verification of the dose delivered by radiotherapy beams have been developed at University and Istituto Nazionale di Fisica Nucleare (INFN) of Torino. The Magic Cube is a stack of strip-segmented ionization chambers interleaved with water-equivalent slabs. The parallel plate ionization chambers have a sensitive area of 24 x 24 cm2, and consist of 0.375 cm wide and 24 cm long strips. There are a total of 64 strips per chamber. The Magic Cube has been tested with the clinical proton beam at Loma Linda University Medical Centre (LLUMC), and was shown to be capable of fast and precise quasi-3D dose verification. The Pixel Ionization Chamber (PXC) is a detector with pixel anode segmentation. It is a 32 x 32 matrix of 1024 cylindrical ionization cells arranged in a square 24 x 24 cm2 area. Each cell has 0.4 cm diameter and 0.55 cm height, at a pitch of 0.75 cm separates the centre of adjacent cells. The sensitive volume of each single ionization cell is 0.07 cm3. The detectors are read out using custom designed front-end microelectronics and a personal computer-based data acquisition system. The PXC has been used to verify dynamic intensity-modulated radiotherapy for head-and-neck and breast cancers.

[The role of radiotherapy in the treatment of vulvar tumors]. / II ruolo della radioterapia nel trattamento del tumore della vulva.

Carcinoma of the vulva is relatively rare, making up 3% to 4% of all primary genital cancer. It is a disease of the elderly. The Authors treated from 1976 to 1987 twenty-one patients with locally advanced squamous vulvar cancer (6 T2; 12 T3; 3 T4). Nine of these patients were submitted to radiotherapy alone; the others were treated with a combination of surgery and postoperative radiation. Two and five years disease-free survival rate was 33% and 19%. The rate of radiotherapy sequelae has been low, because the patients were treated with the concentional 200 cGy per day or similar fractionation schemes. Disease-free survival rate was better in the subgroup of patients who underwent to combined surgery and post-operative radiation therapy. These results are discussed in comparison with others series in literature.

BNCT dose distribution in liver with epithermal D-D and D-T fusion-based neutron beams.

Recently, a new application of boron neutron capture therapy (BNCT) treatment has been introduced. Results have indicated that liver tumors can be treated by BNCT after removal of the liver from the body. At Lawrence Berkeley National Laboratory, compact neutron generators based on (2)H(d,n)(3)He (D-D) or (3)H(t,n)(4)He (D-T) fusion reactions are being developed. Preliminary simulations of the applicability of 2.45 MeV D-D fusion and 14.1 MeV D-T fusion neutrons for in vivo liver tumor BNCT, without removing the liver from the body, have been carried out. MCNP simulations were performed in order to find a moderator configuration for creating a neutron beam of optimal neutron energy and to create a source model for dose calculations with the simulation environment for radiotherapy applications (SERA) treatment planning program. SERA dose calculations were performed in a patient model based on CT scans of the body. The BNCT dose distribution in liver and surrounding healthy organs was calculated with rectangular beam aperture sizes of 20 cm x 20 cm and 25 cm x 25 cm. Collimator thicknesses of 10 and 15 cm were used. The beam strength to obtain a practical treatment time was studied. In this paper, the beam shaping assemblies for D-D and D-T neutron generators and dose calculation results are presented.

Neutron spectra in a tissue equivalent phantom during photon radiotherapy treatment by LINACS.

Bremsstrahlung photon beams produced by LINAC accelerators are currently the most used radiotherapy method for tumour treatments. When the photon energy exceeds the (gamma,n) reaction threshold energy, the patient receives an undesired dose due to photoneutron production both in the accelerator head and in the human body. In this paper, a method is presented for the assessment of the photoneutron spectra produced by Giant Dipole Resonance (GDR) during cancer radiotherapy with energetic photon beams. Experimental and numerical results have been obtained for the facility at Onkologik Klinik, Lund (Sweden), which is based on an ELEKTA 18 MV LINAC. Neutron spectra are evaluated both at the patient plane and inside an anthropomorphic phantom.

[The use of electrons in oncologic radiotherapy: our experience]. / L'uso degli elettroni nella radioterapia oncologica: nostra esperienza.

The authors describe the interaction of electrons with tissues, the characteristics of depth isodose curves with sharp dose fall-off. These characteristics reduce the utilization of electron therapy only for tumors situated some 5 cm depth below the skin surface and with regular surface. The authors report their experience from 1978 in the treatment of vulvar carcinoma, chest-wall recurrences from breast carcinoma, and cutaneous lymphomas. All these neoplastic diseases were treated with electron beam of adequate energy. Initially betatron was used, successively a linear accelerator (Siemens) about for two years. Results obtained in the treatment of vulvar carcinoma are reported. Two and five years disease free survival rates was respectively 33% and 19% (it is remarked the importance of prophylactic treatment on inguinal lymphnodes). Local control observed in 44 patients with cutaneous lymphomas was 85% until three years; a greater number of recurrences was observed in centrocytic-centroblastic lymphomas. Moreover, local control of breast recurrences was 65% with 5 years survival rate of 22% (34% in patients with only one skin recurrence). Only 22% of the further local failures appear within the treatment field while 78% appear out of field.

[The use of cisplatin as radiosensitizing agent in advanced tumors of the head and neck. Randomized study]. / Utilizzazione del cisplatino come radiosensibilizzante nei tumori avanzati della regione testa-collo. Studio randomizzato.

This study was aimed at assessing whether c-DDP administration immediately before radiotherapy could increase frequency and duration of objective responses, as well as survival, in patients affected with locally advanced stages of squamous carcinomas of the head and neck. All patients had already undergone two induction cycles according to the CABO schedule. Ninety-six of 108 treated patients could be evaluated. Treatment schedule consisted in: 1) randomized distribution of patients into two groups before induction chemotherapy; 2) two cycles of induction chemotherapy according to the CABO schedule in all patients; 3) radiation therapy: the patients in group A were given 5 mg/mq of i.v. cisplatin, 30-60 minutes before each session. The results from the two groups were compared and no significant differences were observed regarding objective response (82.5% in group A vs. 86% in group B), response duration and overall survival rates. Even though toxicity was higher in the patients in group A, therapeutic protocol never needed be modified.