3-D conformal radiotherapy of localized prostate cancer: a subgroup analysis of rectoscopic findings prior to radiotherapy and acute/late rectal side effects.

BACKGROUND AND PURPOSE: To identify endoscopic pathological findings prior to radiotherapy and a possible correlation with acute or chronic rectal side effects after three-dimensional conformal radiotherapy (3D-CRT) for prostate cancer. PATIENTS AND METHODS: Between 03/99 and 07/02, a total of 298 patients, who consented in a voluntary rectoscopy prior to radiotherapy were included into the analysis. Patients were treated with a total dose of either 70 or 74 Gy. Pathological rectoscopic findings like hemorrhoids, polyps or diverticula were documented. Acute and late rectal side effects were scored using the EORTC/RTOG score. RESULTS: The most frequent pathological endosopic findings were hemorrhoids (35%), polyps (24%) and diverticula (13%). Rectal toxicity was mostly low to moderate. Grade 0/1 cumulative acute and late rectal side effects were 82 and 84%, grade 2 were 18 and 17%, respectively. We could not identify any correlation between preexisting pathological findings and rectal side effects by statistical analysis. CONCLUSIONS: There is no evidence that prostate cancer patients presenting with endoscopic verified pathological findings in the rectal mucosa at diagnosis are at an increased risk to develop rectal side effects when treated with 3D-CRT of the prostatic region.

3-D Conformal radiotherapy of localized prostate cancer within an Austrian-German multicenter trial: a prospective study of patients' acceptance of the rectal balloon during treatment.

PURPOSE: Patients with localized prostate cancer are treated with 3D radiotherapy using a rectal balloon catheter for internal immobilization of the prostate, thereby reducing the radiation dose to the dorsal rectal wall. The purpose of the study was to investigate clinical feasibility and the influence of acute rectal side effects and pre-existing hemorrhoids on patients' acceptance of the rectal balloon catheter. METHODS AND MATERIALS: 442 patients who underwent primary radiation therapy for localized prostate cancer were included in this prospective Austrian-German multicenter trial. The total radiation dose was either 70 Gy or 74 Gy. Acute rectal side effects were documented using the EORTC/RTOG grading score (European Organisation for Research and Treatment of Cancer/Radiation Therapy 225 Oncology Group) at weeks 2, 4 and 7 of radiation treatment. Within the same time intervals patients were interviewed about their tolerance of the rectal balloon catheter, evaluating five categories of acceptance (1 = no major complaints, 2 = pain at/during application, 3 = signs of blood at the balloon catheter after application but without any pain, 4 = signs of blood at the balloon catheter after application and pain, 5 = balloon application had to be stopped). Voluntary rectoscopy prior to radiotherapy was performed in 310 patients. RESULTS: 429/442 patients (97 %) were treated with the balloon catheter. No major complaints were reported in 79 % of the patients and no acute rectal side effects were seen in 52 % of the patients. Grade 1 side effects were seen in 31 % patients, Grade 2 in 17 % and Grade 3 in 0.5 %. Balloon use had to be stopped in only 4 % of the patients. There was significant correlation between balloon discomfort and rectal side effects (p < 0.01). The presence of hemorrhoids in 36 % patients prior to irradiation had no influence on balloon tolerance. CONCLUSIONS: The rectal balloon can be used in 3D radiotherapy of localized prostate cancer with a high degree of acceptance by the patients. Use of the balloon is safe within daily clinical treatment. Patients reporting acute rectal side effects experienced significantly more balloon discomfort, but the presence of hemorrhoids was not found to influence acceptance of the balloon.

A semi­automated FISH­based micronucleus­centromere assay for biomonitoring of hospital workers exposed to low doses of ionizing radiation.

The aim of the present study was to perform cytogenetic analysis by means of a semi­automated micronucleus­centromere assay in lymphocytes from medical radiation workers. Two groups of workers receiving the highest occupational doses were selected: 10 nuclear medicine technicians and 10 interventional radiologists/cardiologists. Centromere­negative micronucleus (MNCM­) data, obtained from these two groups of medical radiation workers were compared with those obtained in matched controls. The blood samples of the matched controls were additionally used to construct a 'low­dose' (0­100 mGy) MNCM­ dose­response curve to evaluate the sensitivity and suitability of the micronucleus­centromere assay as an 'effect' biomarker in medical surveillance programs. The physical dosimetry data of the 3 years preceding the blood sampling, based on single or double dosimetry practices, were collected for the interpretation of the micronucleus data. The in vitro radiation results showed that for small sized groups, semi­automated scoring of MNCM­ enables the detection of a dose of 50 mGy. The comparison of MNCM­ yields in medical radiation workers and control individuals showed enhanced MNCM­ scores in the medical radiation workers group (P=0.15). The highest MNCM­ scores were obtained in the interventional radiologists/cardiologists group, and these scores were significantly higher compared with those obtained from the matched control group (P=0.05). The higher MNCM­ scores observed in interventional radiologists/cardiologists compared with nuclear medicine technicians were not in agreement with the personal dosimetry records in both groups, which may point to the limitation of 'double dosimetry' procedures used in interventional radiology/cardiology. In conclusion, the data obtained in the present study supports the importance of cytogenetic analysis, in addition to physical dosimetry, as a routine biomonitoring method in medical radiation workers receiving the highest occupational radiation burdens.

Relative biologic effectiveness determination in mouse intestine for scanning proton beam at Paul Scherrer Institute, Switzerland. Influence of motion.

PURPOSE: To determine the relative biologic effectiveness (RBE) of the Paul Scherrer Institute (PSI) scanning proton beam in reference conditions and to evaluate the influence of intestine motion on the proton dose homogeneity. METHODS AND MATERIALS: First, RBE was determined for crypt regeneration in mice after irradiation in a single fraction. Irradiation was performed at the middle of a 7-cm spread out Bragg peak (SOBP; reference position), as well as in the proximal part of the plateau and at the distal end of the SOBP. Control gamma-irradiation was randomized with proton irradiation and performed simultaneously. Second, motion of mouse intestine was determined by radiographs after copper wire markers had been placed on the jejunum and intestinal wall. RESULTS: Proton RBE (reference (60)Co gamma) was equal to 1.16 for irradiation at the middle of the SOBP and to 1.11 and 1.21 for irradiation in the initial plateau and end of the SOBP, respectively. The confidence intervals for these RBE values were much larger than those obtained in the other proton beams we have tested so far. They exceeded +/-0.20 (compared with the usual value of +/-0.07), which resulted from the unusually large dispersion of the individual proton data. The instantaneous positions of the mice intestines varied by +/-2 mm in the course of irradiation. CONCLUSION: The results of this study have shown that the RBE of the PSI proton beam is in total accordance with the RBE obtained at the other centers. This experiment has corroborated that proton RBE at the middle of the SOBP is slightly larger than the generic value of 1.10 and that there is a slight tendency for the RBE to increase close to the end of the SOBP. Also, excessive dispersion of individual proton data may be considered to result from intestine motion, taking into account that irradiation at the PSI is delivered dynamically by scanning the target volume with a pencil proton beam ("spot scanning"). Because 2-mm movements resulted in significant variations in local dose depositions, this should be considered for moving targets. Strategies to reduce this effect for the spot scanning technique have been developed at the PSI for radiotherapy of humans.

In-vivo dosimetry for gynaecological brachytherapy: physical and clinical considerations.

INTRODUCTION: The study aimed to estimate the dosimetric uncertainty using diodes (PTW/Germany) for a high-dose rate Iridum-192 source under clinical conditions. Finally, the role of in-vivo dosimetry for cervix cancer patients was evaluated. MATERIAL AND METHODS: First, diode calibration and factors influencing diode response were investigated and phantom studies compared doses measured and computed by the treatment planning system. Based on that, the uncertainty for diode measurements was estimated to be 7% (1 sigma). Secondly, 55 applications of patients with cervix carcinoma were evaluated. Doses in rectum and bladder were measured and compared to the computed doses and differences were calculated. If the differences exceeded 10% the corresponding shift in probe position was evaluated. Additionally, the in-vivo dosimetry data were compared to doses at the ICRU 38 [ICRU Report No. 38, dose and volume specification for reporting intracavitary therapy in gynaecology. In: Chassagne D, Dutreix A, Almond P, Burgers J, Busch M, Joslin C editors. International commissioning on radiation units and measurements. Bethesda: 1985.] reference points for rectum and bladder. RESULTS: In patients, in-vivo dosimetry resulted in differences between calculated and measured doses ranging from -31 to+90% (mean 11%) for the rectum and from -27 to+26% (mean 4%) for the bladder. Shifts in probe position of 2.5mm for the rectal probe and 3.5mm for the bladder probe caused dose differences exceeding 10%. The dose at the ICRU rectum reference point was underestimated by the calculated doses at probe position ranging from -61 to 156% (mean 29%). The dose to the ICRU bladder reference point was underestimated by the calculated dose ranging from 12 to 162% (mean 58%). CONCLUSION: The study shows that diode accuracy and reproducibility is sufficient for clinical applications. For accurate in-vivo dosimetry geometric conditions are of utmost importance. It is recommended that in-vivo dosimetry should be performed in addition to computation.

The influence of a rectal balloon tube as internal immobilization device on variations of volumes and dose-volume histograms during treatment course of conformal radiotherapy for prostate cancer.

PURPOSE: A prospective comparative study of a subset of 10 consecutive patients was performed, to describe the effects of an air-inflated rectal balloon tube that has been used for prostate immobilization in 360 patients since 1994. In particular, influences on prostate motion, rectum filling variations, and dose-volume histograms (DVHs) of the rectum during a course of conformal radiotherapy were investigated. METHODS AND MATERIALS: Computed tomographic (CT) examinations without and with rectal balloon (filled with 40 mL air) were performed at the start (t(0)), middle (t(mi)), and end of treatment (t(e)), resulting in 6 CT scans for each patient. Prostate displacement was measured from a lateral beam's-eye-view. DVHs of rectum as a solid organ, and anterior, posterior, and whole rectum wall were calculated at t(0), t(mi), and t(e), and variations during treatment were analyzed for both examinations, with and without balloon. RESULTS: By use of the balloon, rectum filling variations (p = 0.04) and maximum anterior-posterior displacements of the prostate (p = 0.008) were reduced significantly, leading to a reduction in DVH variations during treatment. Maximum displacements of posterior prostate border (>5 mm) were found in 8/10 patients without a rectum balloon and in only 2/10 patients with the balloon. The balloon led to a significant reduction in partial posterior rectal wall volumes included in the high-dose regions, without significant changes at the anterior rectum wall in cases of irradiation of the prostate only. However, when entirely irradiating the whole seminal vesicles, this advantage was lost. CONCLUSIONS: The rectal balloon catheter represents a simple technique to immobilize the prostate and to determine the position of the anterior rectal wall at daily treatment. This allows a reduction of margins, because of reduced prostate movement during treatment course.

Retrospective analysis of results of p(65)+Be neutron therapy for treatment of prostate adenocarcinoma at the cyclotron of Louvain-la-Leuve. Part II: Side effects and their influence on quality of life measured with QLQ-C30 of EORTC.

PURPOSE: Between 1978 and 1998, 533 prostate adenocarcinoma patients were treated with mixed photon-neutron radiotherapy. We report on a retrospective series of patients for whom the side effects of the treatment and their impact on quality of life were assessed by a mailed questionnaire. METHODS AND MATERIALS: The European Organization for Research and Treatment of Cancer quality-of-life core questionnaire and a prostate-specific questionnaire were used. Between 1990 and 1996, 308 consecutive patients were treated. Two protocols were used: pelvic fields (50 Gy equivalent photons, 2 Gy/fraction) followed by a prostate boost (66 Gy) or prostate alone. The neutron/photon ratio varied. The questionnaire was mailed to 262 patients presumed to be alive. RESULTS: Of the 262 patients, 230 replied. Of the 230 patients, 73% had no trouble doing strenuous activities and 4% had trouble with taking a short walk. The overall physical condition and quality-of-life questions received a mean score of 5.2 and 5.3 on a 7-point scale, respectively. Twenty-two percent had bowel movements at least four times daily, and 6% did so six times or more. Retaining stool was a problem in 26%, and only 38% reported full continence; 17% urinated four times or more nightly. Urinary incontinence was scored as "quite a bit" or "very much" in 11% and 5%, respectively. Hematuria and dysuria (pain) were reported by 7% and 16%, respectively, mainly as moderate. Only 28% reported easy erections, but 75% judged the sexual change acceptable. A greater neutron/photon ratio was significantly associated with more bowel problems (p = 0.003). CONCLUSION: Mixed photon-neutron therapy for prostate cancer was associated with significant patient-reported side effects. Their significant effect on patients' quality of life is described.

General principles for prescribing, recording and reporting a therapeutic irradiation.

Exchange of clinical information is essential for the development and progress in radiation oncology. This goal can be achieved only through a general harmonization on methods of reporting. The ICRU has been involved for several decades in a continuous effort to harmonize reporting of dose and to standardize methods used to determine the doses and points or volumes where these doses are delivered. Requirements for reporting proton and ion beam therapy should, in principle, be as similar as possible to reporting the current radiation therapy modalities. However, proton and ion therapy have their own clinical and technical uniqueness: in particular, they require definition of new clinical, radiobiological and technical concepts, and strict quality assurance programmes for efficient and safe clinical application. The current ICRU definitions of volumes are reviewed: Gross Tumour Volume (GTV), Clinical Target Volume (CTV), Planning Target Volume (PTV), Organs At Risk (OAR), Planning organ at Risk Volume (PRV), treated volume and reference volume. The irradiation conditions and the absorbed dose should always be reported together with the point(s) and/or volume(s) where the dose is delivered. In addition, the weighting factor W(RBE) introduced to take into account the RBE, and the related weighted dose D(RBE) have to be reported.

RBE and weighting of absorbed dose in ion-beam therapy.

Absorbed dose is the fundamental quantity used to quantify the exposure of any biological system to ionizing radiation. However, the relationship between dose and biological effect is not unique but varies with fractionation and time factor(s), radiation quality and irradiation conditions. In radiation therapy, weighting factors are used to correlate absorbed dose and clinical effects when altering irradiation conditions, or for combining or comparing different technical modalities. For some well established therapy modalities (e.g. fractionated photon beam therapy), a general agreement on weighting factors has been reached: it is based on the linear-quadratic model. For neutron, proton or ion therapy, the differences in radiation quality are currently accounted for using a diversity of methods (almost hospital specific). This paper reviews the current approaches used for evaluating or selecting the weighting factors and their application in clinical practice. The weighting factors take account of the RBE and other factors, such as fractionation when needed. Harmonization of these approaches will facilitate the exchange of information within the radiation oncology community and between centres using different technical modalities. In any case, when reporting the treatments, absorbed dose and irradiation conditions should always be specified in addition to the weighting factor and the weighted dose.

Radiobiological rationale and patient selection for high-LET radiation in cancer therapy.

The rationale for introducing ion beams in cancer therapy is the high level of physical selectivity that can be achieved with ions, equal or even better than with proton beams or modern photon techniques, as well as the potential advantage of high-LET radiations for some tumour types and sites. The radiobiological arguments for high-LET radiation in cancer therapy are reviewed: reduction of OER in the case of hypoxic and poorly-reoxygenating tumours, and the lesser importance of repair phenomena which are a problem in controlling repair-proficient photon-resistant tumours. Fast neutrons were the first type of high-LET radiation used clinically, and were often applied under suboptimal technical conditions. Nevertheless, useful clinical information was derived from the neutron experience. A greater benefit from neutrons than from conventional radiotherapy was found for several tumour sites. The present discussion is limited to the results for salivary gland tumours and prostatic adenocarcinoma. Based on the fast neutron experience, radiobiological arguments, and the added benefit of excellent physical selectivity of ion beams, the potential clinical indications for high-LET ions are discussed: hypoxic, slowly growing and well-differentiated photon-resistant tumours. One of the main remaining issues is the selection of individual patients for high- or low-LET radiation. Since the physical selectivity of ions now matches that obtained with other techniques, the selection of patients will be based only on the radiobiological characteristics of the tumour.

Intestinal crypt regeneration in mice: a biological system for quality assurance in non-conventional radiation therapy.

BACKGROUND AND PURPOSE: The Relative Biological Effectiveness (RBE) of 8 fast-neutron beams, 5 proton beams and 1 carbonion beam was determined using as biological criterion intestinal crypt regeneration in mice, i.e. an in vivo system. These beams are used or planned for clinical cancer therapy applications. In addition, the RBE of 6 epithermal neutron beams, used or planned for Boron Neutron Capture Therapy (BNCT), was determined; no boron was administered. The goal of the program was to improve the exchange of information between the centers, facilitate the interpretation of the results and increase the safety of the clinical applications. MATERIALS AND METHODS: In all visited centers, the same technique was applied in the same conditions by the same radiobiology team. The number of regenerating crypts per circumference was scored 3.5 days after single fraction total body irradiation. The control irradiations were performed locally using cobalt-60 units. The mice were randomized according to radiation quality and dose level. RESULTS: (1) For fast neutron beams, the RBE (Ref. cobalt-60 gamma rays) increases with decreasing energy (from approximately 1.7 for p(65)+Be neutrons to approximately 2.4 for d(14.5)+Be neutrons). In addition, it is specific to each facility and depends on the nuclear reaction (p or d + Be), target and collimation type. (2) For proton beams, the RBEs (Ref cobalt-60 gamma rays) at the reference position (middle of a 7-cm Spread Out Bragg Peak, SOBP) range between 1.08 and 1.18. They might differ by approximately 6-8% according to the mode of beam production or delivery. The RBEs at the end of the SOBP are always 5-10 % higher than at the middle of the SOBP. (3) For the carbon ion beam studied at NIRS in Chiba, Japan, the RBE significantly increases with depth. Relative to gamma rays, it ranges from 1.3 in the initial plateau, 1.6 at the beginning, 1.7 at the middle and 1.9 at the end of a 6-cm SOBP. 4) In BNCT beams, the radiation quality (in particular the relative contribution of the different dose components) varies rapidly with depth and depends strongly on the arrangement of the irradiation set-up (e.g. presence or not of back scattering material). Moreover, the (total) dose rates are highly variable (from 0.05 to approximately 0.5 Gy/min) according to the power of the reactors. Wide range of RBE values (Ref. gamma rays) was thus obtained (RBE = 1.4 - 2.2) at shallow depths of 1.5 - 2.5 cm. DISCUSSION AND CONCLUSION: Intestinal crypt regeneration in mice is an in vivo system perfectly suitable to perform intercomparisons between centers applying different types of non-conventional radiation qualities. It was proven to be reproducible, reliable and accurate, and becomes progressively recognized worldwide as part of the Quality Control (QA) procedures for new beams. It should be stressed that the observed RBE for intestinal crypt cells after a single high dose provide some radiobiological characterization of the radiation quality but cannot be used as the RBE weighting factor in clinical prescriptions.

Bladder and rectum dose defined from MRI based treatment planning for cervix cancer brachytherapy: comparison of dose-volume histograms for organ contours and organ wall, comparison with ICRU rectum and bladder reference point.

PURPOSE: To analyze the correlation between dose-volume histograms based on organ contour and organ wall delineation for bladder and rectum, and to compare the doses to these organs with the absorbed doses at the ICRU bladder and rectum reference points. MATERIAL AND METHODS: Individual MRI based brachytherapy treatment planning was performed in 15 patients as part of a prospective comparative trial. The external contours and the organ walls were delineated for the bladder and rectum in order to compute the corresponding dose-volume histograms. The minimum dose in 2 cm(3), 5 cm(3) and 10 cm(3) volumes receiving the highest dose were referred to as [D2], [D5] and [D10] and compared with the absorbed dose at the ICRU rectum and bladder reference point. RESULTS: The bladder (bext) and rectal (rext) doses derived from external contours and computed for volumes of 2 cm(3) [D2], provided a good estimate for the doses computed for the organ walls (bw and rw) only (mean ratio [D2](bext)/[D2](bw)=1.1+/-0.2 and [D2](rext)/[D2](rw)=1.2+/-0.1, respectively). This correspondence was no longer true when larger volumes were considered (5 and 10 cm(3)). The dose at the ICRU rectum reference point did overestimate the dose computed for 2 cm(3) of the rectum wall (mean ratio: 1.5+/-0.4). In contrast, the dose at the ICRU bladder reference point did-in the case of inappropriate topographic location of the balloon-underestimate the dose computed for 2 cm(3) of the bladder wall (overall mean ratio: 0.9+/-0.4). CONCLUSION: For clinical applications, when volumes smaller than 5 cm(3) are considered, the dose-volume histograms computed from external organ contours for the bladder and rectum can be used instead of dose-volume histograms computed for the organ walls only. External organ contours are indeed easier to obtain. The dose at the ICRU rectum reference point provides a good estimate of the rectal dose computed for volumes smaller than 2 cm(3) [D2] only for a midline position of the rectum. The ICRU bladder reference point provides a good estimate of the dose computed for the bladder wall [D2] only in cases of appropriate balloon position.

Possible impact of iridium-192 source centering on restenosis rate after femoro-popliteal angioplasty and endovascular brachytherapy in Vienna-2 study.

PURPOSE: Endovascular brachytherapy (EVBT) has been proven to significantly reduce restenosis after percutaneous transluminal angioplasty (PTA). The object of this analysis was to assess the possible correlation between iridium-192 source non-centering and angiographic-determined restenosis. MATERIALS AND METHODS: A total of 113 patients with long-segment lesions of the superficial femoro-popliteal artery (SFA) were randomized to receive either PTA alone or PTA followed by EVBT in the Vienna-2 study. This analysis was performed on a subgroup of 34 out of 57 patients, who received PTA+EVBT. Angiographic restenosis was defined as lumen reduction of more than 50%. Angiograms taken immediately after PTA (34 patients) and at follow-up (25 patients) were analyzed. The distance between the vessel wall and the actual position of the source at the time of EVBT was measured (in mm) and correlated with the follow-up vessel lumen diameter. Measurements were performed at points at a distance of 10 mm from each other. The dose was determined at the luminal surface and at the reference depth of 2 mm into the vessel wall for different distances from the source. RESULTS: Among the 622 measured points, 62 (10.0%) were within restenotic areas; 560 (90.0%) were in arterial segments without proven angiographic restenosis. As far as source centering is concerned, 7.9% of restenotic points were observed when the maximum distance to the arterial wall was <3 mm and 9.6% for 4 mm, respectively. The percentage of restenotic points increased up to 15.9% when the maximum distance to the arterial wall was 5 mm and reached 22.2% when it was >5 mm. CONCLUSIONS: The proportion of restenotic points significantly increased with source non-centering. This observation was interpreted as being related to a decrease in dose at the target. When the maximum distance between the source and the vessel surface was >5 mm, the dose at the reference depth (2 mm into the vessel wall) decreased to values lower than 5 Gy.

Bioeffect modeling and equieffective dose concepts in radiation oncology--terminology, quantities and units.

The International Commission on Radiation Units and Measurements (ICRU) Report Committee on "Bioeffect Modeling and Biologically Equivalent Dose Concepts in Radiation Therapy" is currently developing a comprehensive and consistent framework for radiobiological effect modeling based on the equieffective dose, EQDX(α/ß), a concept encompassing BED and EQD2 as special cases.

PTV margins should not be used to compensate for uncertainties in 3D image guided intracavitary brachytherapy.

The planning target volume (PTV) concept has been created within the context of external beam radiotherapy (EBRT). It would be ideal to have a similar approach in brachytherapy (BT) to compensate for uncertainties. However, the BT and EBRT dose distributions are profoundly different, and the role of a PTV concept in BT needs a distinct discussion. The EBRT PTV concept is based on expanding the dose distribution into a homogeneous plateau reaching beyond the CTV. According to basic BT physics, there are significant dose gradients around radioactive source positions, and it is impossible to create homogeneous dose plateaus. This means that PTV margins cannot be directly applied in BT. Application of PTV margins in lateral and anterior-posterior directions can even lead to a significant and overall dose escalation (∼8% per mm margin applied) for the individual patient and for the entire patient population. In the specific direction along the intrauterine tandem, safety margins can partly account for uncertainties, though. In conclusion, safety margins can only be partially applied in intracavitary BT, and it is not recommended to perform PTV delineation. The PTV seems not to be useful for dose reporting, and dose normalisation to PTV is strongly discouraged since it can lead to dose escalation.

Comparison of the Methods of Specifying Carbon Ion Doses at NIRS and GSI.

Due to the RBE variations, the carbon-ion doses (in Gy) are no longer sufficient to monitor adequately the biological effect of these radiations. Therefore, "RBE dose weighting factors" - W(RBE) - allowing for the RBE variations with energy, dose and biological system have to be introduced in the treatment plans in order to provide the physician with interpretable information. This paper compares the methods employed for this purpose at NIRS and GSI, which are specific of the beam delivery system of these institutions. NIRS has a "passive" beam delivery system where the dose distribution in the SOBP is determined by a Ridge filter. The dose distribution - and thus, the shaping of the filter - is chosen according to the clinical situation and determined with respect to W(RBE) factors in order to yield a biologically iso-effective SOBP. W(RBE )factors in the SOBP are at first derived from a RBE/LET function for HSG cells, then normalized to 3 at a LET of 80 keV/mum. The latter value of 3 corresponds to the clinical RBE of NIRS-neutrons, which were found to exhibit the same radiobiological properties as 80 keV/mum carbon-ions. GSI has a "dynamic" beam delivery system ("spot" or "voxel" scanning) making it possible to irradiate irregular volumes and to modulate the radiation intensity according to the radiosensitivity of different tissues and/or different sub-volumes. Due to the "power" and the resulting complexity of the system, W(RBE )factors are determined through an integrated calculation code allowing iterative interaction of both physical and radiobiological parameters. The "Local Effect Model" (LEM) was developed in this view with the aim of deriving carbon-ion W(RBE )factors from the parameters determining the response to photons. Advantages and weaknesses of the respective methods will be discussed.

[Radiologic exposure of the dental patient: comparison of the doses delivered by different techniques]. / Exposition radiologique du patient en Médecine Dentaire: comparaison des doses délivrées par différentes techniques.

This paper evaluates the doses delivered to the patient during several radiological procedures in dentistry: intraoral, panoramic and cephalometric radiography. Different digital techniques now available are compared to the AgBr film and film-screen technique. Absorbed doses at different organs are derived from measurements on dental radiological phantoms. The largest dose reductions are observed for intraoral radiography (31-84%). Significant dose reductions are also found for panoramic and cephalometric radiography (25-70% and 30-60%, respectively). By optimizing the exposure parameters and according to the ALARA principle, the smallest doses should be delivered to the patient that are needed to achieve the required quality of the images. Independently on the technique, the beam size should match as closely as possible the size of the detector. Collimation is particularly important for intraoral radiography. The dose at the thyroid should be kept as low as possible especially for children. For some beam incidences, a thyroid shield is especially efficient. The development of digital radiography and the related advantages should not lead to increasing the number of radiographs. The prescribed and performed types of examinations, and their number, should always be selected based on the clinical situation and on sound clinical judgment and experience in order to solve the raised medical problem.

What's new in target volume definition for radiologists in ICRU Report 71? How can the ICRU volume definitions be integrated in clinical practice?

The optimal definition of the size, shape and location of gross tumour volume is one of the most important steps in the planning of radiation therapy, and necessitates a proper understanding of the procedure from both the oncologic radiologist and the radiation oncologist. This overview reports on the different terms and concepts that have been recommended in the ICRU Reports for this purpose; the latest Report 71 focuses on both previously given recommendations, and especially on electron beam therapy. This paper also highlights some of the problems that are encountered in the use of the International Commission on Radiation Units and Measurements (ICRU) recommendations in clinical practice, and at the interface between the radiation oncologist and the diagnostic oncologist.