In-beam PET monitoring of mono-energetic (16)O and (12)C beams: experiments and FLUKA simulations for homogeneous targets.

(16)O and (12)C ion beams will be used-besides lighter ions-for cancer treatment at the Heidelberg Ion Therapy Center (HIT), Germany. It is planned to monitor the treatment by means of in-beam positron emission tomography (PET) as it is done for therapy with (12)C beams at the experimental facility at the Gesellschaft für Schwerionenforschung (GSI), Darmstadt, Germany. To enable PET also for (16)O beams, experimental data of the beta(+)-activity created by these beams are needed. Therefore, in-beam PET measurements of the activity created by (16)O beams of various energies on targets of PMMA, water and graphite were performed at GSI for the first time. Additionally reference measurements of (12)C beams on the same target materials were done. The results of the measurements are presented. The deduction of clinically relevant results from in-beam PET data requires reliable simulations of the beta(+)-activity production, which is done presently by a dedicated code limited to (12)C beams. Because this code is not extendable to other ions in an easy way, a new code, capable of simulating the production of the beta(+)-activity by all ions of interest, is needed. Our choice is the general purpose Monte Carlo code FLUKA which was used to simulate the ion transport, the beta(+)-active isotope production, the decay, the positron annihilation and the transport of the annihilation photons. The detector response was simulated with an established software that gives the output in the same list-mode data format as in the experiment. This allows us to use the same software to reconstruct measured and simulated data, which makes comparisons easier and more reliable. The calculated activity distribution shows general good agreement with the measurements.

Comparison of PDR brachytherapy and external beam radiation therapy in the case of breast cancer.

Pulsed dose rate brachytherapy (PDR) was compared to external beam radiation therapy (EBRT) in the case of breast cancer. The benefits were figured out by evaluation of dosimetric parameters and calculating the normal tissue complication probability (NTCP). PDR plans were set up for five randomly chosen left-sided breast cancer patients delivering a total dose of 50.4 Gy to the target (dose rate 0.8 Gy h(-1)). For EBRT five left-sided breast cancer patients were planned using 3D-conformal tangential photon beams with a prescribed total dose of 50 Gy (2 Gy/fraction) to the total breast volume. For plan ranking and NTCP calculation the physical dose was first converted into the biologically effective dose (BED) and then into the normalized total dose (NTD) using the linear quadratic model with an alpha/beta ratio of 3 Gy. In PDR the relative effectiveness (RE) was calculated for each dose bin of the differential dose volume histogram to get the BED. NTCPs were calculated for the ipsilateral lung and the heart as contoured on CT slices based on the Lyman model and the Kutcher reduction scheme. Dosimetric parameters as V(th) (percentage of the total volume exceeding a threshold dose) and Jackson's f(dam) (fraction of the organ damaged) were also used to figure out the benefits. The comparison of calculated NTCPs in PDR and EBRT showed no difference between these two modalities. All values were below 0.01%. f(dam) derived from EBRT was always higher (mean value 8.95% versus 1.21% for the lung). The mean V(10) and V(20) of the lung related to BED were 6.32% and 1.72% for PDR versus 11.72% and 9.59% for EBRT. When using dosimetric parameters as V(th) and f(dam), PDR was mostly superior to EBRT in respect of sparing normal tissues. NTCP calculation as a single method of modality ranking showed a lack of information, especially when normal tissue was exposed to low radiation doses.

Targeted radionuclide therapy: theoretical study of the relationship between tumour control probability and tumour radius for a 32P/33P radionuclide cocktail.

As revealed by previous theoretical studies, targeted radionuclide therapy (TRT) that relies on a single beta-emitting radioisotope is likely to be inappropriate for clinical scenarios such as disseminated malignancy. For a patient with a vast number of tumours and metastases of largely differing sizes a high level of therapeutical efficiency might be achieved only for a restricted range of tumour sizes. This is due to the limited range of beta-electrons in human tissue, essentially causing the therapeutical impact to vary tremendously with tumour size. The dependence of curability on the tumour dimension is expected to be significantly altered if a radionuclide cocktail, consisting of a long-range and a short-range beta-emitter, such as (32)P and (33)P, is involved in the treatment. In this study, a radiation transport simulation was performed, using the MCNP4c2 Monte Carlo code, in order to investigate the relationship between tumour control probability (TCP) and tumour size, associated with concurrent use of (32)P and (33)P. Two different models of intratumoural distribution of cumulated activity were taken into account. One simulated an ideal radionuclide uptake in tumour tissue and the other referred to a limited radiotracer penetration. The results were examined in comparison to tumours targeted with pure (32)P, (33)P and (131)I. For both uptake scenarios a considerable reduction of the overall variation of TCP and thus an increasing chance of achieving tumour cure was observed for tumour sizes ranging from microscopic dimensions up to macroscopic diameters, if the targeted radionuclide treatment relies on a (32)P/(33)P cocktail. It was revealed that particular attention has to be given to the ratio of the (32)P and (33)P specific cumulated activities (SCA) in the tumour, since this is a significant determinant of the resulting behaviour of tumour control probability as the tumour diameter varies. This study suggests that a 32P/33P approach is more applicable to diseases that involve a variety of tumours and metastases differing in size.

A fit method for the determination of inherent filtration with diagnostic x-ray units.

A method for the determination of total inherent filtration for clinical x-ray units using attenuation curves was devised. A model for the calculation of x-ray spectra is used to calculate kerma values which are then adjusted to the experimental data in minimizing the sum of the squared relative differences in kerma using a modified simplex fit process. The model considers tube voltage, voltage ripple, anode angle and additional filters. Fit parameters are the thickness of an additional inherent Al filter and a general normalization factor. Nineteen sets of measurements including attenuation data for three tube voltages and five Al-filter settings each were obtained. Relative differences of experimental and calculated kerma using the data for the additional filter thickness are within a range of -7.6% to 6.4%. Quality curves, i.e. the relationship of additional filtration to HVL, are often used to determine filtration but the results show that standard quality curves do not reflect the variety of conditions encountered in practice. To relate the thickness of the additional filter to the condition of the anode surface, the data fits were also made using tungsten as the filter material. These fits gave an identical fit quality compared to aluminium with a tungsten filter thickness of 2.12-8.21 microm which is within the range of the additional absorbing layers determined for rough anodes.

The FLUKA code: new developments and application to 1 GeV/n iron beams.

The modeling of ion transport and interactions in matter is a subject of growing interest, driven by the continuous increase of possible application fields. These include hadron therapy, dosimetry, and space missions, but there are also several issues involving fundamental research, accelerator physics, and cosmic ray physics, where a reliable description of heavy ion induced cascades is important. In the present work, the capabilities of the FLUKA code for ion beams will be briefly recalled and some recent developments presented. Applications of the code to the simulation of therapeutic carbon, nitrogen and oxygen ion beams, and of iron beams, which are of direct interest for space mission related experiments, will be also presented together with interesting consideration relative to the evaluation of dosimetric quantities. Both applications involve ion beams in the AGeV range.

Dose-volume histograms based on serial intravascular ultrasound: a calculation model for radioactive stents.

BACKGROUND AND PURPOSE: Radioactive stents are under investigation for reduction of coronary restenosis. However, the actual dose delivered to specific parts of the coronary artery wall based on the individual vessel anatomy has not been determined so far. Dose-volume histograms (DVHs) permit an estimation of the actual dose absorbed by the target volume. We present a method to calculate DVHs based on intravascular ultrasound (IVUS) measurements to determine the dose distribution within the vessel wall. MATERIALS AND METHODS: Ten patients were studied by intravascular ultrasound after radioactive stenting (BX Stent, P-32, 15-mm length) to obtain tomographic cross-sections of the treated segments. We developed a computer algorithm using the actual dose distribution of the stent to calculate differential and cumulative DVHs. The minimal target dose, the mean target dose, the minimal doses delivered to 10 and 90% of the adventitia (DV10, DV90), and the percentage of volume receiving a reference dose at 0.5 mm from the stent surface cumulated over 28 days were derived from the DVH plots. Results were expressed as mean+/-SD. RESULTS: The mean activity of the stents was 438+/-140 kBq at implantation. The mean reference dose was 111+/-35 Gy, whereas the calculated mean target dose within the adventitia along the stent was 68+/-20 Gy. On average, DV90 and DV10 were 33+/-9 Gy and 117+/-41 Gy, respectively. Expanding the target volume to include 2.5-mm-long segments at the proximal and distal ends of the stent, the calculated mean target dose decreased to 55+/-17 Gy, and DV 90 and DV 10 were 6.4+/-2.4 Gy and 107+/-36 Gy, respectively. CONCLUSIONS: The assessment of DVHs seems in principle to be a valuable tool for both prospective and retrospective analysis of dose-distribution of radioactive stents. It may provide the basis to adapt treatment planning in coronary brachytherapy to the common standards of radiotherapy.

The use of a high-purity germanium detector for routine measurements of 125I in radiation workers.

A high-purity germanium detector was calibrated for the assessment of 125I uptake in the thyroid gland of radiation workers. A cylindrical water phantom (perspex walls) with high flexibility for position and size of the thyroid was constructed. Within a massive shielding chamber built for a whole-body counter, an activity of 2.2 Bq was detectable (MDA). This is well below the very restrictive limiting value of 20 Bq for inhalation specified by Austrian law. An activity of 128 Bq was measured with a statistical uncertainty of 5% in a counting period of 10 min. Various parameters influencing the result are investigated as well as the performance of two other measurement geometries outside the shielding chamber.