Long-term oncological and functional follow-up in low-dose-rate brachytherapy for prostate cancer: results from the prospective nationwide Swiss registry.

OBJECTIVE: To evaluate the long-term oncological, functional and toxicity outcomes of low-dose-rate brachytherapy (LDR-BT) in relation to risk factors and radiation dose in a prospective multicentre cohort. PATIENTS AND METHODS: Data of patients from 12 Swiss centres undergoing LDR-BT from September 2004 to March 2018 were prospectively collected. Patients with a follow-up of ≥3 months were analysed. Functional and oncological outcomes were assessed at ~6 weeks, 6 and 12 months after implantation and annually thereafter. LDR-BT was performed with 125 I seeds. Dosimetry was done 6 weeks after implantation based on the European Society for Radiotherapy and Oncology recommendations. The Kaplan-Meier method was used for biochemical recurrence-free survival (BRFS). A prostate-specific antigen (PSA) rise above the PSA nadir + 2 was defined as biochemical failure. Functional outcomes were assessed by urodynamic measurement parameters and questionnaires. RESULTS: Of 1580 patients in the database, 1291 (81.7%) were evaluable for therapy outcome. The median (range) follow-up was 37.1 (3.0-141.6) months. Better BRFS was found for Gleason score ≤3+4 (P = 0.03, log-rank test) and initial PSA level of <10 ng/mL (P < 0.001). D'Amico Risk groups were significantly associated with BRFS (P < 0.001), with a hazard ratio of 2.38 for intermediate- and high-risk patients vs low-risk patients. The radiation dose covering 90% of the prostate volume (D90) after 6 weeks was significantly lower in patients with recurrence. Functional outcomes returned close to baseline levels after 2-3 years. A major limitation of these findings is a substantial loss to follow-up. CONCLUSION: Our results are in line with other studies showing that LDR-BT is associated with good oncological outcomes together with good functional results.

Design and implementation of a "cheese" phantom-based Tomotherapy TLD dose intercomparison.

BACKGROUND: The unique beam-delivery technique of Tomotherapy machines (Accuray Inc., Sunnyvale, Calif.) necessitates tailored quality assurance. This requirement also applies to external dose intercomparisons. Therefore, the aim of the 2014 SSRMP (Swiss Society of Radiobiology and Medical Physics) dosimetry intercomparison was to compare two set-ups with different phantoms. MATERIALS AND METHODS: A small cylindrical Perspex phantom, which is similar to the IROC phantom (Imaging and Radiation Oncology Core, Houston, Tex.), and the "cheese" phantom, which is provided by the Tomotherapy manufacturer to all institutions, were used. The standard calibration plans for the TomoHelical and TomoDirect irradiation techniques were applied. These plans are routinely used for dose output calibration in Tomotherapy institutions. We tested 20 Tomotherapy machines in Germany and Switzerland. The ratio of the measured (Dm) to the calculated (Dc) dose was assessed for both phantoms and irradiation techniques. The Dm/Dc distributions were determined to compare the suitability of the measurement set-ups investigated. RESULTS: The standard deviations of the TLD-measured (thermoluminescent dosimetry) Dm/Dc ratios for the "cheese" phantom were 1.9 % for the TomoHelical (19 measurements) and 1.2 % (11 measurements) for the TomoDirect irradiation techniques. The corresponding ratios for the Perspex phantom were 2.8 % (18 measurements) and 1.8 % (11 measurements). CONCLUSION: Compared with the Perspex phantom-based set-up, the "cheese" phantom-based set-up without individual planning was demonstrated to be more suitable for Tomotherapy dose checks. Future SSRMP dosimetry intercomparisons for Tomotherapy machines will therefore be based on the "cheese" phantom set-up.

Surface dose characterisation of the Varian Ir-192 HDR conical surface applicator set with a vertically orientated source.

BACKGROUND: Conical surface applicators with an Ir-192 high-dose-rate brachytherapy source are a common modality for the treatment of non-melanomatous skin cancer with high tumour control rates. Surface dose characterisation of the Varian Varisource GammaMed+ IX afterloader vertical type surface applicators is performed two dimensionally using high-resolution film dosimetry. AIM: The focus of this study was to determine if Varian surface applicators with a vertical source suffer from the dose distribution irregularities reported for comparable applicators. Our goal was to evaluate if the irregularities found affected treatment and dose output verification procedures. METHODS: Ionisation chamber-based verification of applicator output was established according to guidelines provided by the manufacturer. For additional measurement of surface dose Gafchromic EBT3 film dosimetry was used. The term "therapeutic dose" was defined as 85% of the prescribed dose level. RESULTS: For the 10 different applicator inserts evaluated, cold spots were observed. Mean cold spot size was 2.0 mm × 3.6 mm (± 0.6 mm). The cold spots were dosimetrically well below 85% of the prescribed dose. The cold spot was situated 2.2 mm (1.4-2.7 mm) unilaterally from the central axis and caused general asymmetry in the dose profiles intersecting the cold spot area. A source tilt of approximately 8° (± 1°) was determined for the source used for irradiation. CONCLUSIONS: A central underdosed area exceeding 15 % of the prescribed dose has not been previously reported. Source tilt was observed and found to affect clinical use and possibly treatment outcome in applicators using a vertically arranged source. Surface applicators with a vertically orientated source were subject to dose irregularities that could impact on chamber-based applicator output verification procedures. We recommend film dosimetry-backed applicator commissioning to avoid systematic errors.

Catalytic activity imperative for nanoparticle dose enhancement in photon and proton therapy.

Nanoparticle-based radioenhancement is a promising strategy for extending the therapeutic ratio of radiotherapy. While (pre)clinical results are encouraging, sound mechanistic understanding of nanoparticle radioenhancement, especially the effects of nanomaterial selection and irradiation conditions, has yet to be achieved. Here, we investigate the radioenhancement mechanisms of selected metal oxide nanomaterials (including SiO2, TiO2, WO3 and HfO2), TiN and Au nanoparticles for radiotherapy utilizing photons (150 kVp and 6 MV) and 100 MeV protons. While Au nanoparticles show outstanding radioenhancement properties in kV irradiation settings, where the photoelectric effect is dominant, these properties are attenuated to baseline levels for clinically more relevant irradiation with MV photons and protons. In contrast, HfO2 nanoparticles retain some of their radioenhancement properties in MV photon and proton therapies. Interestingly, TiO2 nanoparticles, which have a comparatively low effective atomic number, show significant radioenhancement efficacies in all three irradiation settings, which can be attributed to the strong radiocatalytic activity of TiO2, leading to the formation of hydroxyl radicals, and nuclear interactions with protons. Taken together, our data enable the extraction of general design criteria for nanoparticle radioenhancers for different treatment modalities, paving the way to performance-optimized nanotherapeutics for precision radiotherapy.

Exposure of treating physician to radiation during prostate brachytherapy using iodine-125 seeds: dose measurements on both hands with thermoluminescence dosimeters.

BACKGROUND AND PURPOSE: Only sparse reports have been made about radiation exposure of the treating physician during prostate seed implantation. Therefore, thermoluminescence dosimeter (TLD) measurements on the index fingers and the backs of both hands were conducted. MATERIAL AND METHODS: Stranded iodine-125 seeds with a mean apparent activity of 27.4 MBq per seed were used. During application, the treating physician manipulated the loaded needle with the index fingers, partially under fluoroscopic control. Four physicians with varying experience treated 24 patients. The radiation exposure was determined with TLD-100 chips attached to the index fingertips and the backs of hands. Radiation exposure was correlated with the physician's experience. RESULTS: The average brachytherapy duration by the most experienced physician was 19.2 min (standard deviation sigma = 1.2 min; novices: 34.8 min [sigma = 10.2 min]). The mean activity was 1,703 MBq (sigma = 123 MBq), applied with 16.3 needles (sigma = 2.5 needles; novices: 1,469 MBq [sigma = 229 MBq]; 16.8 needles [sigma = 2.3 needles]). The exposure of the finger of the "active hand" and the back of the hand amounted to 1.31 mSv (sigma = 0.54 mSv) and 0.61 mSv (sigma = 0.23 mSv), respectively (novices: 2.07 mSv [sigma = 0.86 mSv] and 1.05 mSv [sigma = 0.53 mSv]). CONCLUSION: If no other radiation exposure needs to be considered, an experienced physician can perform about 400 applications per year without exceeding the limit of 500 mSv/year; for novices, the corresponding figure is about 200.

[MLC positioning checks and calibration with a portal imaging system]. / Prüfung und Kalibration der MLC-Positionierung mit einem portalen Bildgebungssystem.

For checking the leaf positions of a MLC (Multi Leaf Collimator) images are acquired with an EPID (Electronic Portal Imaging Device) and then evaluated with a programme (MLC check) developed in-house. During image acquisition a Perspex tray with two metal markers of known position (in the radiation field) is inserted in the satellite tray holder. After determination of the marker positions within the image coordinate system, the image can be transformed to the radiation field coordinate system. This allows the exact determination of the leaf tip positions relative to the radiation field. This evaluation can be applied to images of arbitrary field shapes, provided they were acquired in the same geometry (EPID position, gantry and collimator angles). The entire measurement procedure is based on images in bmp (Windows Bitmap) format, with a 1024 x 1024 matrix and a pixel depth of 24 bit (8 bit per color channel). A suitable marker plate can be manufactured without sophisticated workload; thus the method may be easily and cost effectively adapted at other locations.

Basic dosimetric verification in water of the anisotropic analytical algorithm for Varian, Elekta and Siemens linacs.

Since early 2007 a new version of the Anisotropic Analytical Algorithm (AAA) for photon dose calculations was released by Varian Medical Systems for clinical usage on Elekta linacs and also, with some restrictions, for Siemens linacs. Basic validation studies were performed and reported for three beams. 4,6 and 15 MV for an Elekta Synergy, 6 and 15 MV for a Siemens Primus and, as a reference, for 6 and 15 MV from a Varian Clinac 2100C/D. Generally AAA calculations reproduced well measured data and small deviations were observed for open and wedged fields. PDD curves showed in average differences between calculation and measurement smaller than 1% or 1.2 mm for Elekta beams, 1% or 1.8 mm for Siemens beams and 1% or 1 mm for Varian beams. Profiles in the flattened region matched measurements with deviations smaller than 1% for Elekta and Varian beams, 2% for Siemens. Percentage differences in Output Factors were observed as small as 1% in average.

A treatment planning study comparing Elekta VMAT and fixed field IMRT using the varian treatment planning system eclipse.

BACKGROUND: The newest release of the Eclipse (Varian) treatment planning system (TPS) includes an optimizing engine for Elekta volumetric-modulated arc therapy (VMAT) planning. The purpose of this study was to evaluate this new algorithm and to compare it to intensity-modulated radiation therapy (IMRT) for various disease sites by creating single- and double-arc VMAT plans. METHODS: A total of 162 plans were evaluated in this study, including 38 endometrial, 57 head and neck, 12 brain, 10 breast and 45 prostate cancer cases. The real-life IMRT plans were developed during routine clinical cases using the TPS Eclipse. VMAT plans were generated using a preclinical version of Eclipse with tumor-region-specific optimizing templates without interference of the operator: with one full arc (1A) and with two full arcs (2A), and with partial arcs for breast and prostate with hip implant cases. All plans were evaluated based on target coverage, homogeneity and conformity. The organs at risk (OARs) were analyzed according to plan objectives, such as the mean and maximum doses. If one or more objectives were exceeded, the plan was considered clinically unacceptable, and a second VMAT plan was created by adapting the optimization penalties once. RESULTS: Compared to IMRT, single- and double-arc VMAT plans showed comparable or better results concerning the target coverage: the maximum dose in the target for 1A is the same as that for IMRT; for 2A, an average reduction of 1.3% over all plans was observed. The conformity showed a statistically significant improvement for both 1A (+3%) and 2A (+6%). The mean total body dose was statistically significant lower for the considered arc techniques (IMRT: 16.0 Gy, VMAT: 15.3 Gy, p < 0.001). However, the sparing of OARs shows individual behavior that depends strongly on the different tumor regions. A clear difference is found in the number of monitor units (MUs) per plan: VMAT shows a reduction of 31%. CONCLUSION: These findings demonstrate that based on optimizing templates with minimal interaction of the operator, the Eclipse TPS is able to achieve a plan quality for the Elekta VMAT delivery technique that is comparable to that of fixed-field IMRT. Plans with two arcs show better dose distributions than plans with one arc.