Evaluation of the impact of parameters on the gamma index for breast cancer treatments

Volumetric modulated arc radiotherapy treatments (VMAT) can achieve highly conformed dose distributions, however, due to the complexity of the technique, there may have differences between the planned and administered dose distributions, generated by the precision in the dose calculation of the treatment planning system (TPS) or by the errors associated with it. One way to quantify the difference between both dose distributions is by using the gamma index; however, there is no accord regarding the parameters that should be used in its analysis. On the other hand, this gamma index may depend on the pathology and the area to be treated. For this reason, the present work aims to evaluate different parameters of the analysis of the gamma index for breast cancer treatments, these are local and global normalization, the analysis criteria (1%/1 mm, 2%/2 mm, 3%/2 mm, 2%/3 mm, 3%/3 mm and 5%/3 mm) and the low dose threshold (LDT) of 5% and 10%. For this, 30 treatment plans performed with VMAT technique in a 6 MV Infinity linear accelerator (Elekta, Stockholm, Sweden) were analyzed, calculated with the TPS Monaco V.5.11.03 (Elekta, Stockholm, Sweden) and measured with the Octavius 4D system (PTW, Freiburg, Germany). The results of the analysis of the global gamma index were of a gamma passing rate (%GP) greater than 95% for analysis criteria of 3%/3 mm and 5%/3 mm, however, for these same parameters in the local gamma index analysis the results are 85.8% and 91.1% respectively. In addition, from the LDT evaluation, it is observed that there is a mean increase of %GP for the local gamma index analysis and a mean decrease of %GP for the global gamma index analysis, for the LDT from 5% to 10%. On the other hand, the standard deviation is lower in the global gamma index analysis than in the local one, and it decreases when the analysis criteria are less strict. It is concluded that there is not a great difference in choosing the LDT of 5% or 10%. When the gamma analysis criteria are less strict, the %GP increases both for the analysis of the local and global gamma index, taking this into account, each parameter should be used carefully according to the treatment plan to be analyzed, taking into account the advantages and disadvantages of each parameter.

Dosimetric Validation of a System to Treat Moving Tumors Using Scanned Ion Beams That Are Synchronized With Anatomical Motion

PurposeThe purpose of this study was to validate the dosimetric performance of scanned ion beam deliveries with motion-synchronization to heterogenous targets.MethodsA 4D library of treatment plans, comprised of up to 10 3D sub-plans, was created with robust and conventional 4D optimization methods. Each sub-plan corresponded to one phase of periodic target motion. The plan libraries were delivered to a test phantom, comprising plastic slabs, dosimeters, and heterogenous phantoms. This phantom emulated range changes that occur when treating moving tumors. Similar treatment plans, but without motion synchronization, were also delivered to a test phantom with a stationary target and to a moving target; these were used to assess how the target motion degrades the quality of dose distributions and the extent to which motion synchronization can improve dosimetric quality. The accuracy of calculated dose distributions was verified by comparison with corresponding measurements. Comparisons utilized the gamma index analysis method. Plan quality was assessed based on conformity, dose coverage, overdose, and homogeneity values, each extracted from calculated dose distributions.ResultsHigh pass rates for the gamma index analysis confirmed that the methods used to calculate and reconstruct dose distributions were sufficiently accurate for the purposes of this study. Calculated and reconstructed dose distributions revealed that the motion-synchronized and static deliveries exhibited similar quality in terms of dose coverage, overdose, and homogeneity for all deliveries considered. Motion-synchronization substantially improved conformity in deliveries with moving targets. Importantly, measurements at multiple locations within the target also confirmed that the motion-synchronized delivery system satisfactorily compensated for changes in beam range caused by the phantom motion. Specifically, the overall planning and delivery approach achieved the desired dose distribution by avoiding range undershoots and overshoots caused by tumor motion.ConclusionsWe validated a dose delivery system that synchronizes the movement of the ion beam to that of a moving target in a test phantom. Measured and calculated dose distributions revealed that this system satisfactorily compensated for target motion in the presence of beam range changes due to target motion. The implication of this finding is that the prototype system is suitable for additional preclinical research studies, such as irregular anatomic motion.

Measurement of Natural Radioactivity Level in Selected Phosphate Fertilizer Samples Collected from Iraqi Markets

The Gamma-ray spectrometry (spectra line Gp) and a high-purity germanium (HPGe) detector were used to determine the activity concentrations of 226Ra, 232Th, and 40K in fertilizer samples. 226Ra, 232Th, and 40K activity concentrations in fertilizers and phosphate raw. In this study the gamma index(I), Radium equivalent dose(Raeq),dose rate(DR),external hazard index(Hex) internal hazard index(Hin), annual effective dose outdoor(AEDout) and annual effective dose indoor(AEDin)were found. This study could serve as a starting point for figuring out how fertilizer radiation affects human health.

Analysis of the Physical and Radiobiological Equivalence of the Calculated and Measured Dose Distributions for Prostate Stereotactic Radiotherapy

Purpose: Carrying out the analysis of the physical and radiobiological equivalence of dose distributions obtained during the planning of hypofractionated stereotactic radiation therapy of the prostate cancer and verification using a three-dimensional cylindrical dosimeter. Material and Methods: Based on the anatomical data of twelve patients diagnosed with prostate carcinoma, stage T2N0M0 with low risk, plans were developed for stereotactic radiation therapy with volumetric modulates arc therapy (VMAT). The dose per fraction was 7,25 Gy for 5 fractions (total dose 36,25 Gy) with a normal photon energy of 10 MV. The developed plans were verified using a three-dimensional cylindrical ArcCHECK phantom. During the verification process, the three-dimensional dose distribution in the phantom was measured, based on which the values of the three-dimensional gamma index and the dose–volume histogram within each contoured anatomical structures were calculated with 3DVH software. The gamma index value γ (3 %, 2 mm, GN) at a threshold equal to 20 % of the dose maximum of the plan and the percentage of coincidence of points at least 95 % was chosen as a criterion of physical convergence of the calculated and measured dose distribution according to the recommendations of AAPM TG-218. To analyze the radiobiological equivalence of the calculated and measured dose distribution, the local control probability (TCP) and normal tissue complication probability (NTCP) criteria were used based on the calculated and measured dose–volume histograms. Contours of the target (PTV) and the anterior wall of the rectum were used for the analysis. The approach based on the concept of equivalent uniform dose (EUD) by A. Niemierko was used to calculate the values of TCP/NTCP criteria. Results: The results of physical convergence of plans for all patients on the contour of the whole body were higher than 95 % for the criteria γ (3 %, 2 mm, GN). The convergence along the PTV contour is in the range (75.5–95.2)%. The TCP and NTCP values obtained from the measured dose-volume histograms were higher than the planned values for all patients. It was found that the accelerator delivered a slightly higher dose to the PTV and the anterior wall of the rectum than originally planned. Conclusion: The capabilities of modern dosimetric equipment allow us move to the verification of treatment plans based on the analysis of TCP / NTCP radiobiological equivalence, taking into account the individual characteristics of the patient and the capabilities of radiation therapy equipment.

Radiometric analysis of micas used in many industries and evaluation of radiological hazards

Mica group minerals have been utilized in various industries such as paint, cement, rubber, plastic, paper, automotive, cosmetics, textile, etc. due to their unique electrical, thermal, and mechanical properties. In this study, the radiometric properties of 58 mica samples collected from three quarries operated commercially in Turkey were investigated using gamma-ray spectroscopy with an HPGe detector. The average activity concentrations of 226Ra, 232Th, and 40K analyzed in mica samples were found as 12, 44, and 2763 Bq kg−1, respectively. The radon emanation coefficient and radon mass exhalation rate of mica samples varied from 4 to 22% with an average of 10% and 0.4–5.9 µBq kg−1 s−1 with an average of 2.6 µBq kg−1 s−1, respectively. The radiological hazard caused by the utilization of mica samples as raw materials in the cement and concrete industry was evaluated for adults by calculating the gamma index and annual effective dose due to external exposure indoor. The study results revealed that there are no significant radiological hazards associated with the utilization of mica samples as building raw materials.

Sassi of Matera Building Material: High-Resolution Gamma-Ray Spectroscopy Characterization for Radioprotection

The Sassi of Matera (Basilicata region, southern Italy) is a peculiar site, but not unique in Italy, from a landscape point of view. Most of the buildings are excavated in rocks of calcarenite origin and used as homes and accommodation facilities. For this reason, the contribution of gamma radiation to the population due to this building material has been investigated for the first time. Even though the type of rock is not mentioned among the construction materials indicated in Italian Legislative Decree 101/2020 to be subjected to radiological characterization, the methodology indicated in the decree was applied, comparing the values with those present in the literature. The content of 226Ra, 232Th and 40K was then investigated with gamma spectroscopy, and the gamma index was calculated. The results obtained showed a low level of activity concentration of natural radionuclides in this type of stone, confirming the radiological safety. This result can also support the recovery and restoration initiatives for these buildings to conserve the architectural and landscape heritage of this village.

Green Tuff: Gamma Index in a Typical Building Material of Ciglio Area (Ischia Island)

Radiological characterization of tuff of Ciglio area in Ischia Island was performed to assess the potential radiological hazard associated with its use. For this purpose, high resolution gamma-ray spectroscopy was used. In five green tuff samples was measured the activity concentration of natural gamma-ray emitting radionuclides 226Ra, 232Th and 40K so, the mean gamma index was calculated. The mean value of the gamma index resulted lower than the reference level and it meets the dose criterion for the safety use of green tuff as building material.

Assessment of Solid Mineral to Soil Radioactivity Contamination Index in Selected Mining Sites and their Radiological Risk Indices to the Public

This study examined the radioactivity levels of soil samples within selected solid mining sites in Nigeria using high purity germanium (HpGe) detector. Sixty soil samples in all were collected from the ten solid mineral mining sites investigated and six samples were collected as control samples from non-mining environment for analyses. The results of the activity concentration values obtained for 40K, 226Ra and 232Th are 100.22 Bq kg-1, 33.15 Bq kg-1 and 77.31 Bq kg-1 respectively. The 226Ra and 40K activities were found to be within the United Nation Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) acceptable permissible limit, but the 232Th mean value was above the permissible limit of 30 Bq kg-1 for the public. In comparison, 40K, 226Ra and 232Th soil samples mean activity concentrations were higher than the control soil samples values by 48.6%, 43.7% and 62.3% respectively. The results of estimated radiation hazard indices indicate average values of 150.72 Bq kg-1, 68.40T, 83.65µSvy-1 and 454.70µSvy-1 for the Radium Equivalent (h), iDose Equivalent (AEDE) and Annual Gonadal Equivalent Dose (AGED) respectively. The mean values for External Hazard Indices (Hex, Hin), Representative Gamma index (s) and Excess Life Cancer Risk (ELCR) were 0.41, 0.50, 1.06 and 0.29 x10-3 respectively. The statistical analysis shows positive skewness.

Split-VMAT technique to control the deep inspiration breath hold time for breast cancer radiotherapy

Background To improve split-VMAT technique by optimizing treatment delivery time for deep-inspiration breath hold (DIBH) radiotherapy in left-sided breast cancer patients, when automatic beam-interruption devices are not available. Methods Ten consecutive patients were treated with an eight partial arcs (8paVMAT) plan, standard of care in our center. A four partial arcs (4paVMAT) plan was also created and actual LINAC outputs were measured, to evaluate whether there was a dosimetric difference between both techniques and potential impact on the delivered dose. Subsequently, ten other patients were consecutively treated with a 4paVMAT plan to compare the actual treatment delivery time between both techniques. The prescribed dose was 40.05 Gy/15 fractions on the PTV breast (breast or thoracic wall), lymph nodes (LN) and intramammary lymph node chain (IMN). Treatment delivery time, PTVs coverage, conformity index (CI), organs at risk (OAR) dose, monitor units (MU), and gamma index were compared. Results Both split-VMAT techniques resulted in similar dose coverage for the PTV Breast and LN, and similar CI. For PTV IMN we observed a 5% increased coverage for the volume receiving ≥ 36 Gy with 4paVMAT, with an identical volume receiving ≥ 32 Gy. There was no difference for the OAR sparing, with the exception of the contralateral organs: there was a 0.6 Gy decrease for contralateral breast mean (p ≤ 0.01) and 1% decrease for the volume of right lung receiving ≥ 5 Gy (p = 0.024). Overall, these results indicate a modest clinical benefit of using 4paVMAT in comparison to 8paVMAT. An increase in the number of MU per arc was observed for the 4paVMAT technique, as expected, while the total number of MU remained comparable for both techniques. All the plans were measured with the Delta4 phantom and passed the gamma index criteria with no significant differences. Finally, the main difference was seen for the treatment delivery time: there was a significant decrease from 8.9 to 5.4 min for the 4paVMAT plans (p < .05). Conclusions This study is mainly of interest for centers who are implementing the DIBH technique without automatic beam-holding devices and who therefore may require to manually switch the beam on and off during breast DIBH treatment. Split-VMAT technique with 4 partial arcs significantly reduces the treatment delivery time compared to 8 partial arcs, without compromising the target coverage and the OAR sparing. The technique decreases the number of breath holds per fraction, resulting in a shorter treatment session.

Significance of Uranium Series Disequilibrium and Their Radiological Impacts In Abu Garadi Altered Granites.

Radioactivity of U, Th series and 40K in the collected samples from Abu Garadi area were measured using Hyper Pure Germanium detector Gamma spectrometer (HPGe). 232Th, 226Ra, 40K and 238U contents were determined in the different samples that indicating high uranium high thorium type of these granites. The activity concentrations of 232Th, 238U, 234U/238U activity ratio of the studied altered granites ranged between 1.98 to 4.25 with 2.89 as an average, indicating that the samples passed from the incipience of the oxidation-reduction zone (234U/238U=1.98) to the reduction zone (234U/238U= 4.52). 238U/235U activity ratios showed broad range as a result of the alteration processes. 226Ra and 40K are very important in determination of different environmental hazard impacts. The activity concentrations average of 238U, 232Th, 226Ra and 40K were 6553.7 ± 3.1 Bq kg− 1, 3944 ± 0.9 Bq kg− 1 201.3 ± 1.1 Bq kg− 1 and 619.4 ± 0.02 Bq kg− 1. The absorbed gamma dose rate (D), external hazard index (Hex), annual effective dose rate equivalent, radium equivalent (Raeq), internal hazard index (Hin), gamma index (Iγ) as well as Excess Lifetime Cancer Risk (ELCR) were applied based on the measured radionuclide concentration of the 238U, 232Th, 226Ra and 40K.