Accuracy evaluation of distance inverse square law in determining virtual electron source location in Siemens Primus linac

Measurement-based validation of a commercial Monte Carlo dose calculation algorithm for electron beams

PURPOSE

This work presents the clinical validation of RayStation's electron Monte Carlo Code by use of diodes and plane parallel radiation detectors in homogenous and heterogeneous tissues. Results are evaluated against international accepted criteria.

METHODS

The Monte Carlo based electron beam dose calculation code was validated using diodes, air filled and liquid filled parallel radiation detectors on a Elekta Linac with beam energies of 4,6,8,10 and 12 MeV. Treatment setups with varying SSD's, different applicators, various cut-outs and oblique beam incidences were addressed, together with dose prediction behind lung, air and bone equivalent inserts. According to NCS (Netherlands Commission of Radiation Dosimetry) report 15 for non-standard treatment setups a dose agreement of 3 % in the δ₁ region (high dose region around Z_ref ), a distance to agreement of 3 mm or a dose agreement of 10 % in the δ₂ region (regions with high dose gradients) and 4 % in the δ₄ region (photon tail/low dose region) were applied. During validation, clinical routine settings of 2×2×2 mm³ dose voxels and a statistically dose uncertainty of 0.6% (250 000 histories/cm² ) were used.

RESULTS

RayStation's electron Monte Carlo code dose prediction was able to achieve the tolerances of NCS report 15. Output predictions as function of the SDD improve with energy and applicator size. Cut-out data revealed no field size neither energy dependence on the accuracy of the dose prediction. Excellent agreement for the oblique incidence data was achieved and maximum one voxel difference was obtained for the distance to agreement behind heterogeneous inserts.

CONCLUSIONS

The accuracy of RayStation's Monte Carlo based electron beam dose prediction for Elekta accelerators is confirmed for clinical treatment planning that is not only performed within an acceptable timeframe in terms of number of histories but also addresses for homogenous and heterogeneous media. This article is protected by copyright. All rights reserved.

Determination of effective source to surface distance and cutout factor in small fields in electron beam radiotherapy: A comparison of different dosimeters

Objective: The main purpose of this study is to calculate the effective source to surface distance (SSDeff) of small and large electron fields in 10, 15, and 18 MeV energies, and to investigate the effect of SSD on the cutout factor for electron beams a linear accelerator. The accuracy of different dosimeters is also evaluated.

Materials and methods: In the current study, Elekta Precise linear accelerator was used in electron beam energies of 10, 15, and 18 MeV. The measurements were performed in a PTW water phantom (model MP3-M). A Semiflex and Advanced Markus ionization chambers and a Diode E detector were used for dosimetry. SSDeff in 100, 105, 110, 115, and 120 cm SSDs for 1.5 × 1.5 cm2 to 5 × 5 cm2 (small fields) and 6 × 6 cm2 to 20 × 20 cm2 (large fields) field sizes were obtained. The cutout factor was measured for the small fields.

Results: SSDeff in small fields is highly dependent on energy and field size and increases with increasing electron beam energy and field size. For large electron fields, with some exceptions for the 20 × 20 cm2 field, this quantity also increases with energy. The SSDeff was increased with increasing beam energy and field size for all three detectors.

Conclusion: The SSDeff varies significantly for different field sizes or cutouts. It is recommended that SSDeff be determined for each electron beam size or cutout. Selecting an appropriate dosimetry system can have an effect in determining cutout factor.

Determining the Effectivity of Infrared Distance to Eliminate Dental Pain Due to Pulpitis and Periodontitis

OBJECTIVE

 The infrared rays is one of the treatments to relief of dental pain due to pulpitis or periodontitis. The ability of infrared to increase the pain threshold which make eliminating P substance on the inflammation area and inducing Aβ and Aδ fibers to activate γ-aminobutyrate (GABA) and neuropeptides to decrease the pain. Hence, reducing or eliminating dental pain. This study to get information about effectively distance between patients and infrared rays which can reduce or eliminate dental pain.

MATERIALS AND METHODS

 The explorative experimental research to determine the effectivity of the infrared rays' distance: 45, 55, and 55 cm in reducing or eliminating dental pain. The material of infrared was tungsten with luminous light and the time for the lighting was 15 minutes.

STATISTICAL ANALYSIS

 The data were obtained and analyzed using Wilcoxon's signed rank test and Kruskal-Wallis test (α= 0.05).

RESULTS

  There were influenced of the infrared rays to reduce the dental pain as follow, distance 45 cm (p = 0.007), distance 55 cm (p = 0.026), and distance 65 cm (p = 0.007). The average scale reduction for distance 45 cm was 2.23 ± 0.83, the distance 55 cm was 3.33 ± 0.87, and the distance 65 cm was (1.78 ± 0.83). Therefore, according to Kruskal-Wallis test with p = 0.004 (p < 0.05) showed the significant difference between the scale to decrease of dental pain was the distance of 55.

CONCLUSION

 Infrared rays located at a distance of 55 cm from patients might be more effective in relieving dental pain, compared with other distances tested.

Analysis of performance factors in 240 consecutive cases of robot-assisted flexible ureteroscopic stone treatment

Flexible ureteroscopy is the keystone of modern kidney stone treatment. Although a simple surgical technique achieves good clinical results and a low complication rate, there are high demands on the surgeon's dexterity and ergonomic restrictions. Robotic-assisted flexible ureteroscopy (rfURS) could overcome these limitations. After 4 years of use of rfURS at a tertiary stone center, performance factors were analyzed to define the role of rfURS in kidney stone management. A rfURS system was installed in August 2014 at the SLK Kliniken (Heilbronn, Germany). Treatment data of N = 240 consecutive patients undergoing rfURS were prospectively collected and analyzed. The patient cohort represents typical stone formers. N = 240 renal units containing 443 stones with an average stone load of 1798 mm³ were treated. Surgical parameters as well as the peri- and postoperative complications were recorded, analyzed and compared to the current data in the literature. OR time 91 min, stone treatment time 55 min, stone treatment efficacy 33 mm³/min; perioperative complications 5.4%; robot times: preparation 5 min, docking 5 min, console time to stone contact 6 min, console time 75 min; postoperative complications 6.7%; postoperative length of stay 1.5 days; stone-free rate (residuals < 2 mm) 90% and re-treatment rate 8.75%. This consecutive series represents real-life data about the utilization of rfURS. The detailed analysis of performance factors revealed the successful utilization of the first generation of robotic systems in endourologic stone surgery, and indicates that the robot performs comparably to conventional flexible URS. Optimal ergonomics maintain the surgeon's endurance in long-lasting surgeries.