Benefits and considerations in using a novel computed tomography system optimized for radiotherapy planning.

In this study, we evaluated a novel 16-bit computed tomography (CT) system optimized for radiotherapy planning. Over six months, using various protocols, we conducted 616 scans, with an average of four CT series per session imported into our treatment planning software (TPS). The direct density (DD) reconstruction enabled a single CT number calibration curve for multiple tube voltages. Metal artifacts could be effectively reduced. The 16-bit character permitted dose calculation in high-density regions, while TPS integration challenges remained. In conclusion, our findings emphasize the system's potential benefits and considerations in radiotherapy workflows.

Risk management patterns in radiation oncology-results of a national survey within the framework of the Patient Safety in German Radiation Oncology (PaSaGeRO) project.

PURPOSE: Risk management (RM) is a key component of patient safety in radiation oncology (RO). We investigated current approaches on RM in German RO within the framework of the Patient Safety in German Radiation Oncology (PaSaGeRO) project. Aim was not only to evaluate a status quo of RM purposes but furthermore to discover challenges for sustainable RM that should be addressed in future research and recommendations. METHODS: An online survey was conducted from June to August 2021, consisting of 18 items on prospective and reactive RM, protagonists of RM, and self-assessment concerning RM. The survey was designed using LimeSurvey and invitations were sent by e­mail. Answers were requested once per institution. RESULTS: In all, 48 completed questionnaires from university hospitals, general and non-academic hospitals, and private practices were received and considered for evaluation. Prospective and reactive RM was commonly conducted within interprofessional teams; 88% of all institutions performed prospective risk analyses. Most institutions (71%) reported incidents or near-events using multiple reporting systems. Results were presented to the team in 71% for prospective analyses and 85% for analyses of incidents. Risk conferences take place in 46% of institutions. 42% nominated a manager/committee for RM. Knowledge concerning RM was mostly rated "satisfying" (44%). However, 65% of all institutions require more information about RM by professional societies. CONCLUSION: Our results revealed heterogeneous patterns of RM in RO departments, although most departments adhered to common recommendations. Identified mismatches between recommendations and implementation of RM provide baseline data for future research and support definition of teaching content.

Scattering effects of irradiation on surroundings calculated for a small dental implant.

A fundamental improvement of restorative dentistry is the compensation of missing teeth by insertion of artificial dental roots allowing retention of dental prosthesis. The function of dental implants conserves a permanent perforation of the mucosa and upholds a non-physiological contact of bone with foreign material and oral micro-organisms. Occasionally head and neck cancer patients are scheduled to receive radiotherapy but are wearing dental implants. An earlier study had shown that the distribution of x-rays is noteworthily changed when dental implants are present in the irradiation field. New implants of smaller size are currently being designed that allow sufficient retention for dental prosthesis. The aim of this consecutive study was to calculate alterations in the irradiated bone caused by a foreign body, representing an implant of reduced size and physical qualities equivalent to titanium, using a stochastic (Monte Carlo) simulation. A clinical linear accelerator was simulated using BEAM/EGS4. The calculations showed that the presence of a dimension-reduced implant results in remarkable differences of the dose distribution all around the implant. Titanium dental implants of reduced size located in the field of irradiation were capable of causing significant radiation scattering. Similar to standard implants, the risk for dose enhancement was notably important for the bone in direct contact with the implant. All therapists involved in the therapy of cancer patients undergoing head and neck radiotherapy should consider the impact of dental implants on the radiation beam as a catalyst of osteoradionecrosis.

Simulation of scattering effects of irradiation on surroundings using the example of titanium dental implants: a Monte Carlo approach.

Occasionally, head and neck cancer patients treated with high-energy X-rays and gamma rays have titanium dental implants. The aim of this study was to calculate alterations in the irradiated bone caused by a foreign body, representing a titanium implant in size and physical qualities, using a stochastic (Monte Carlo) simulation. A clinical linear accelerator was simulated using BEAM/EGS4. The calculations showed that the presence of an implant results in differences of the dose distribution all around the implant. Titanium dental implants in the field of irradiation were capable of causing significant radiation scattering. The risk for dose enhancement was notably important for the bone in direct contact with the foreign body. Therapists involved in radiation planning should consider the impact of dental implants on the radiation beam as a putative cause of osteoradionecrosis.

Commissioning of a double-focused micro multileaf collimator (muMLC).

Double-focused muMLCs are able to create fields with steeper dose gradients at the field edges and are, therefore, an advancement in delivering stereotactic treatments. A double-focused muMLC has been installed at a Siemens Primus linear accelerator (linac) as a first research installation in Europe. The basic dosimetric parameters, such as leakage, output factors, depth-dose curves and penumbra, have been measured in 6 and 15 MV-mode by use of radiochromic films (GafChromic EBT), ionization chambers and our solid water QA-phantom (Easy Cube). The leakage between the leaves is minimal and lower than that of most commercially available MLCs. Therefore, the field size of the linac can be kept constant while the leaves of the muMLC are creating different aperture shapes. Percentage depth doses (PDDs) generated by the double-focused muMLC are equal to depth-dose curves of the original linac. That means the muMLC affects only the off-axis ratio (OAR). Based on the fact that the muMLC is double-focused and the source-to-collimator distance is larger, the penumbra is sharper than that for fields defined by the original linac MLC. The mechanical and dosimetric investigations show the benefit of the double-focused muMLC attached to a Siemens Primus linear accelerator.

Experiences with a new high-dose-rate brachytherapy (HDR-BT) boost technique for T3b prostate cancer.

PURPOSE: Experiences with a new high-dose-rate brachytherapy (HDR-BT) boost technique in 41 patients with stage T3b prostate cancer are presented. PATIENTS AND METHODS: The patients received 18 Gy of HDR-BT (9 Gy on days 1 + 8) plus 50.4 Gy of EBRT. 20 patients (group A) had BT applicators placed into the prostate alone resulting in 18 Gy to prostate and 0 Gy (tip) to 12 Gy (base) to seminal vesicles (SV). The cumulative EQD2 (equivalent dose in 2-Gy fractions, alpha/beta 1.5 Gy) to the SV was 47.5-73.3 Gy. 21 patients (group B) had BT applicators placed into both prostate and SV resulting in 18 Gy to prostate and to > 80% (but not 100%) of the SV (cumulative EQD2 81.5-101.5 Gy). Both groups were compared for acute and late toxicity and for biochemical relapse-free survival (bRFS). RESULTS: The 3-year bRFS was 57% for group A and 79% for group B patients (p = 0.29). A grade 3 acute toxicity (CTC 2.0) was not observed. Grade 2 acute toxicity (proctitis, cystitis, skin toxicity) was comparable in both groups. A grade 3 late toxicity did not occur. Impotence rates were 35% in group A and 24% in group B, respectively (p = 0.73). CONCLUSION: The new HDR-BT technique (group B) was associated only with minor acute and late toxicity and appears to result in better bRFS than the conventional HDR-BT technique (group A). The results must be confirmed in a prospective trial.

Beta dosimetry with microMOSFETs for endovascular brachytherapy.

The aim of this study was to investigate if microMOSFETs are suitable for the dosimetry and quality assurance of beta sources. The microMOSFET dosimeters have been tested for their angular dependence in a 6 MeV electron beam. The dose rate dependence was measured with an iridium-192 afterloading source. By varying the source-to-surface distance (SSD) in a 12 MeV electron beam the dose rate dependence in an electron beam was also investigated. To measure a depth dose curve the dose rate at 2, 5, 8 and 12 mm distance from the beta source train axis was determined with the OPTIDOS and the microMOSFET detector. A comparison between the two detector types shows that the microMOSFET is suitable for quality assurance of beta sources for endovascular brachytherapy (EVBT). The homogeneity of the source is checked by measurements at five points (for the 60 mm source at 10, 20, 30, 40 and 50 mm) along the source train. The microMOSFET was then used to evaluate the influence of a common stent type (single layer stainless steel) on the dose distribution in water. The stent led to a dose inhomogeneity of +/-8.5%. Additionally the percentage depth dose curves with and without a stent were compared. The depth dose curves show good agreement which means that the stent does not change the beta spectrum significantly.

[Investigations of beta-dosimetry at two different sources for the cardiovascular brachytherapy]. / Untersuchungen zur beta-Dosimetrie an zwei unterschiedlichen Quellen für die kardiovaskuläre Brachytherapie.

The intracoronary brachytherapy is used at the Hamburg University Hospital as a method to treat in-stent restenosis. Two different radiochromic film types were applied to obtain dosimetric information of the beta-sources used (32P and 90Sr/90Y). First, these films were analyzed for their suitability for dosimetry. Within the investigated dose range (MD-55-2: 0 to 33 Gy, HD-810: 0 to 105 Gy), both films showed a linear behavior between the dose and the optical density (OD). Because radiochromic films are subject to time-based changes in OD, a method for colour stabilization was investigated (RCS-method). This method allowed to greatly shorten the time between irradiation and evaluation from 24 hours (time necessary for the film to reach a quasi-stable status) to 2.5 hours. Colour-stabilized films can also be stored for a long time and reanalyzed with almost the same results. Within the limits of the measurements error, both film types showed an energy independent response. Within the dose profiles, analyses of the two source types resulted in differences of 13.5% (32P) and 21% (90Sr/90Y). These inhomogenities are consistent with the fabrication tolerances given by the manufactures.

Emergency localization of radioactive seeds lost during intracoronary brachytherapy.

Recently, it has been reported that brachytherapy catheters ruptured in vivo. Localization of lost beta-radiation-emitting seeds is a problem because no appropriate technique is available that is rapid and precise. We developed a technique to localize beta-emitting seeds utilizing the effect that beta-radiation induces bremsstrahlung. The loss of a single radioactive source was simulated in an Alderson Phantom representing a human body. The beta-induced bremsstrahlung could be detected selectively by a gamma-camera. The position of the radioactive seed could be located within 5 min with an accuracy of +/- 0.5 cm. The result of this study suggests that in an emergency case of loss of a brachytherapy source, a commercially available gamma-camera can be a valuable tool to detect lost beta-radiation-emitting seeds rapidly and precisely. In addition, the technique minimizes the patient's as well as the surgeon's exposure to radiation and reduces the extent of surgical trauma.