A. Bridier

The ESTRO-QUALity assurance network (EQUAL)

BACKGROUND AND PURPOSE ESTRO has set up a Quality Assurance network (EQUAL) to check the dose delivered on axis in reference and non-reference conditions for external radiotherapy. The external audits covered by the network are based on measurements made with mailed thermoluminescent dosimeters (TLD). MATERIAL AND METHODS The TLD consist of LiF powder type DTL 937 read with a PCL 3 automatic TLD reader. The participating centres are instructed to deliver to the TLDs absorbed doses of 2 Gy calculated with the Treatment Planning System used in clinical routine. A maximum of three photon energies by participating centre have been checked with 10 on-axis points per beam. The quantities checked include the reference beam output, beam output variation with collimator opening, depth dose data and wedge transmission factor. RESULTS During the 1998 EQUAL programme 102 centres have been checked corresponding to 235 beams (28 (60)Co beams and 207 X-ray beams). About 3% of the outputs in reference conditions show deviations outside tolerance level (>+/-5%). A similar rate of deviation is noted for the percentage depth doses. A rate of deviation (6%) has been observed for the beam output variation (open and wedged beams) and the wedge transmission factor. The analysis of the results shows that for 24 out of the 102 centres, a deviation outside tolerance level is observed at least in one point, mainly for the large and rectangular field sizes and for the wedged beams. CONCLUSIONS The results for the EQUAL programme show the importance of a quality assurance network in Radiotherapy especially for the non reference points even if they are only located on the beam axis (In order to participate in this network, please contact EQUAL secretariat or download the attached application form ESTRO web site: Dr I.H. Ferreira or Mrs Aline Mechet, EQUAL-ESTRO, Physics Department, Institut Gustave-Roussy 39 Rue Camille Desmoulins, F-94805 Villejuif Cedex, France. e-mail:equal@igr.fr or http://www.estro.be/).

Définition des volumes en radiothérapie externe : rapports ICRU 50 et 62

Resume La prescription et la realisation de la radiotherapie impliquent la definition precise des volumes–cibles et des doses qui doivent y etre delivrees. La necessite d’utiliser a cet effet un vocabulaire coherent, reconnu du niveau local au niveau international, a conduit l’International Commission on Radiation Units and Measurements (ICRU) a publier, pour la radiotherapie externe, des recommandations dans deux rapports, le rapport ICRU 50 en 1993 et le rapport 62 en 1999. Cet article presente les principales propositions de l’ICRU relatives aux volumes–cibles, ainsi que des commentaires et recommandations pour leur utilisation.

Influence of high-energy photon beam irradiation on pacemaker operation

In this paper, we determine the influence of high-energy photon beam irradiation used for external radiotherapy on pacemakers, at different doses and dose rates. Ninety-six pacemakers of various origins and ages underwent in vitro high-energy photon irradiation under technical conditions close to external radiotherapy, using a linear accelerator delivering photons of high energy (18 MV). Various dose levels (up to 200 Gy for certain particularly resistant pacemakers) were delivered to pacemakers located in a water-equivalent phantom with several dose rates (from 0.05 to 8 Gy min(-1)). Observed failures were sorted into eight classes of progressive harmfulness, some of them possibly lethal. One irradiated pacemaker exhibited an important defect at a dose rate of 0.2 Gy min(-1), for a cumulative dose of 0.15 Gy. Two pacemakers showed an important defect at a cumulative dose of 1 Gy, while nine pacemakers failed at a cumulative dose lower than or equal to 2 Gy and 13 failed at a cumulative dose lower than or equal to 5 Gy. The most important failure probability (70% of irradiated pacemakers) is observed for 8 Gy min(-1), whereas no pacemakers failed at a dose rate lower than or equal to 0.2 Gy min(-1). In conclusion, warnings given by manufacturers about the maximum tolerable cumulative radiation doses for safe operation of irradiated pacemakers (5 Gy), even reduced to 2 Gy, are not reliable. The spread of cumulative doses inducing failures is very large since our observations show an important failure at 0.15 Gy, while ten pacemakers withstood more than 140 Gy of cumulative dose. The safe operation of pacemakers under irradiation depends mainly on type and model. It depends also on dose rate. From our observations, for the safe operation of pacemakers, a recommendation of a maximum dose rate of 0.2 Gy min(-1) rejecting direct irradiation of the pacemaker at a standard dose rate for tumour treatment (2 Gy min(-1)) is made.

Prospective Randomized Comparison of Single-Dose Versus Hyperfractionated Total-Body Irradiation in Patients With Hematologic Malignancies

PURPOSE Fractionated total-body irradiation (HTBI) is considered to induce less toxicity to normal tissues and probably has the same efficacy as single-dose total-body irradiation (STBI) in patients with acute myeloid leukemia. We decided to determine whether this concept can be applied to a large number of patients with various hematologic malignancies using two dissimilar fractionation schedules. PATIENTS AND METHODS Between December 1986 and October 1994, 160 patients with various hematologic malignancies were randomized to receive either a 10-Gy dose of STBI or 14.85-Gy dose of HTBI. RESULTS One hundred forty-seven patients were assessable. The 8-year overall survival rate and cause-specific survival rate in the STBI group was 38% and 63.5%, respectively. Overall survival rate and cause-specific survival rate in the HTBI group was 45% and 77%, respectively. The incidence of interstitial pneumonitis was similar in both groups. However, the incidence of veno-occlusive disease (VOD) of the liver was significantly higher in the STBI group. In the multivariate analysis with overall survival as the end point, the female sex was an independent favorable prognostic factor. On the other hand, when cause-specific survival was considered as the end point, the multivariate analysis demonstrated that sex and TBI were independent prognostic factors. CONCLUSION The efficacy of HTBI is probably higher than that of STBI. Both regimens induce similar toxicity with the exception of VOD of the liver, the incidence of which is significantly more pronounced in the STBI group.

Radiation therapy and late mortality from second sarcoma, carcinoma, and hematological malignancies after a solid cancer in childhood.

PURPOSE To compare patterns of long-term deaths due to secondary carcinomas, sarcomas, and hematological malignancies occurring after childhood cancer in a cohort of patients followed over a median of 28 years. METHODS AND MATERIALS The study included 4,230 patients treated at eight institutions, who were at least 5-year survivors of a first cancer, representing 105,670 person-years of observation. Complete clinical, chemotherapeutic, and radiotherapeutic data were recorded, and the integral radiation dose was estimated for 2,701 of the 2,948 patients who had received radiotherapy. The integral dose was estimated for the volume inside the beam edges. The causes of death obtained from death certificates were validated. RESULTS In total, 134 events were due to second malignant neoplasm(s) (SMN). We found that the standardized mortality ratio decreased with increasing follow-up for second carcinomas and sarcomas, whereas the absolute excess risk (AER) increased for a second carcinoma but decreased for second sarcomas. There was no clear variation in SMN and AER for hematological malignancies. We found a significant dose-response relationship between the radiation dose received and the mortality rate due to a second sarcoma and carcinoma. The risk of death due to carcinoma and sarcoma as SMN was 5.2-fold and 12.5-fold higher, respectively, in patients who had received a radiation dose exceeding 150 joules. CONCLUSIONS Among patients who had received radiotherapy, only those having received the highest integral radiation dose actually had a higher risk of dying of a second carcinoma or sarcoma.

Consequences of two different doses to the lungs during a single dose of total body irradiation: Results of a randomized study on 85 patients

PURPOSE To evaluate the incidence of lung complications and leukemia recurrences after two different doses to the lungs during total body irradiation. METHODS AND MATERIALS Seventy-nine patients with acute leukemia (AML or ALL) in first complete remission or chronic myeloid leukemia in the chronic phase, five patients with high grade lymphoma, and one with chronic lymphocytic leukemia were entered in the study. They were given a single dose of total body irradiation (10 Gy over 4 h) with two different doses to the lungs (6 Gy or 8 Gy) prior to bone marrow transplantation. The median dose rate was 0.04 Gy/min. The median follow-up for both groups of patients was 24 months. RESULTS The actuarial 5-year overall survival rate was similar in both groups, 59% and 43% for patients given 8 Gy and 6 Gy to the lungs, respectively. The lung complication rate was similar in the two groups (28% vs. 22% for the 8 Gy and 6 Gy group, respectively). The actuarial leukemia recurrence rate was significantly higher in the group of patients given 6 Gy to the lungs (25%) vs. 0% in the 8 Gy group. Interestingly, all recurrences occurred in the group of patients who were given 6 Gy to the lungs, who had acute leukemia, and no chronic graft vs. host disease (GVHD). CONCLUSIONS Although the number of patients was not very large and the follow-up relatively short, these findings suggest that a lower dose to the lungs could lead to an increased incidence of leukemia recurrences due to a lower dose to the thoracic wall or to lower incidence of chronic GVHD.

Characteristics of contamination electrons in high energy photon beams

A simple method to estimate the contribution of contaminating electrons to the dose, and to evaluate their dosimetric characteristics is proposed. The method is based on a normalisation of the tissue--maximum ratio curves to a constant primary photon fluence. The contribution of the contaminating electrons to the dose is calculated by subtracting the dose relative to a small field from the dose relative to the field under consideration. The method includes the determination of the mean energy, the linear apparent attenuation coefficient, the 50% range and the maximum range of the contaminating electrons. The extrapolated surface dose normalised to a constant primary photon fluence has been found to be constant for a constant collimator opening whatever may be the source distance.

Secondary solid malignant tumors occurring after bone marrow transplantation for severe aplastic anemia given thoraco-abdominal irradiation

PURPOSE We have evaluated irradiation doses received at location of secondary solid tumors occurring after bone marrow transplantation (BMT) in five of 147 patients grafted for severe aplastic anaemia. RESULTS All 5 tumors occurred within the radiation field penumbra. The estimated received dose varied from 6 Gy for one inner field secondary tumor, to 2.5 Gy for the remaining secondary tumors. CONCLUSION Tumors may arise in the zone where the delivered radiation dose drops dramatically. Irradiation, with associated cofactors, may promote the development of epidermoid carcinoma in irradiated patients for BMT.

Influence of shielding blocks on the output of photon beams as a function of energy and type of treatment unit

The influence of field-defining shielding blocks on the output of a cobalt unit and of seven different accelerators (one with dual energy output) has been investigated. The quality indices range from 0.57 (cobalt-60) to 0.79. The loss in output due to shielding blocks has been calculated taking into account loss in phantom scatter only. Comparison with experimental results shows that the calculation algorithm is correct in most of the clinical conditions. However, for quality indices of 0.70 and higher, for blocks close to the central beam axis, an overestimation of the output by the algorithm has been found. The maximum deviation observed is about 5% for the highest energy and for block positions corresponding to those applied, e.g. for inverted Y-fields with narrow lumbo-aortic block spacing.

Multichannel dosemeter and Al2O3:C optically stimulated luminescence fibre sensors for use in radiation therapy: evaluation with electron beams

This article proposes an innovative multichannel optically stimulated luminescence (OSL) dosemeter for on-line in vivo dose verification in radiation therapy. OSL fibre sensors incorporating small Al(2)O(3):C fibre crystals (TLD(500)) have been tested with an X-ray generator. A reproducible readout procedure should reduce the fading-induced uncertainty ( approximately - 1% per decade). OSL readouts are temperature-dependent [ approximately 0.3% K(-1) when OSL stimulation is performed at the same temperature as irradiation; approximately 0.16% K(-1) after thermalisation (20 degrees C)]. Sensor calibration and depth-dose measurements with electron beams have been performed with a Saturne 43 linear accelerator in reference conditions at CEA-LNHB (ionising radiation reference laboratory in France). Predosed OSL sensors show a good repeatability in multichannel operation and independence versus electron energy in the range (9, 18 MeV). The difference between absorbed doses measured by OSL and an ionisation chamber were within +/-0.9% (for a dose of about 1 Gy) despite a sublinear calibration curve.