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.

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.

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.

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.

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.

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.

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.

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.