Optimal values of the Electron Monte Carlo dose engine parameters.

Background: The aim of this study was to indicate the most favorable - in terms of to the time of calculation and the uncertainty of determining the dose distribution - values of the parameters for the Electron Monte Carlo (eMC) algorithm in the Eclipse treatment planning system. Materials and methods: Using the eMC algorithm and the variability of the values of its individual parameters, calculations of the electron dose distribution in the full-scattering virtual water phantom were performed, obtaining percentage depth doses, beam profiles, absolute dose values in points and calculation times. The reference data included water tank measurements such as relative dose distributions and absolute point doses. Results: For 63 sets of calculation data created from selected values of the parameters for the eMC algorithm, calculation times were analyzed and the absolute calculated and measured doses were compared. Performing a statistical analysis made it possible to determine whether the differences in the values of deviations between the actual dose and the calculated dose in individual regions of the percentage depth dose curve and the beam profile are statistically significant between the analyzed sets of parameters. Conclusions: Taking into account obtained results from the analysis of the discrepancy between the distribution of the calculated and measured dose, the correspondence of the absolute value of the calculated and measured dose and the duration of the calculation of the dose distribution, the optimal set of parameters was indicated for the eMC algorithm which allows obtaining the dose distribution and the number of monitor units in an acceptable time.

The Price of Success-The Long-Term Outcomes of Children with Craniopharyngioma-Two Institutions' Experience.

An analysis of patients below 21 years old treated due to craniopharyngioma in the years 1979-2022 was performed with the aim of evaluating the long-term outcome and treatment side-effects. The standard statistical tests were used, and 56 patients with a median age of 11 years were evaluated. Surgery was the primary treatment in 55 patients; however, in only 29 it was the only neurosurgical intervention. Eighteen children were treated with radiotherapy (RTH) in primary treatment. The most common neurosurgical side effects observed were visual and endocrine deficits and obesity, which were diagnosed in 27 (49%), 50 (91%), and 25 (52%) patients, respectively. Complications after RTH were diagnosed in 14 cases (32%). During the median follow-up of 8.4 years (range: 0.4-39.8 years), six patients died and the 5- and 10-year overall survival was 97% and 93%, respectively. Five-year progression-free survival for gross total resection, resection with adjuvant RTH, and non-radical resection alone was 83%, 68%, and 23%, respectively (p = 0.0006). Surgery combined with RTH provides comparable results to gross tumor resection in terms of oncologic outcome in craniopharyngioma patients. Adjuvant irradiation applied in primary or salvage treatment improves disease control. The rate of complications is high irrespective of improved surgical and radiotherapeutic management.

Influence of optional measurement parameters in the Eclipse treatment planning system on the quality of the dosimetric model of the biomedical accelerator using the Acuros XB algorithm.

Background: To properly configure a treatment planning system, a measurement data set is needed, which consists of the values required for its configuration. The aim is to obtain a dosimetric model of the beam that is as compatible as possible with the measured values. The set of required data can be supplemented with optional values. The aim of the study was to assess the influence of optional measurement data on the compliance of the calculations with the measurements. Materials and methods: Dosimetric measurements, model configuration and dose distribution calculations were performed for the photon radiation beams generated by the VMS TrueBeam® linear accelerator. Beams were configured on an Eclipse™ v. 15.6 system using the Acuros v. 15.6 algorithm. The measured and calculated data were entered into the Alfard™ software for comparison with the calculated dose distributions. In the last stage, the absolute dose values at the designated points were also compared. The obtained data were statistically analysed with Statistica™ v. 13.3. Results: The work showed that the differences in the shape of the beam profile, depth dose and the dose value in points were not related to the use of optional data. Differences in dose distributions are within the tolerance. It cannot be determined under which conditions the use of optional data has a more favourable effect on the reflection of the actual dose values. Conclusions: The use of optional data in modelling photon radiation beams does not significantly improve the compliance of the calculated and measured dose values.

Using beam profile inflection point in process of treatment planning system verification.

BACKGROUND: The comparison between profiles during the commissioning of the treatment planning system is an essential procedure. It is impossible to designate a field size for off-axis, wedged, and FFF beams directly by using the definition of the on-axis symmetric field size. This work proposes the use of different characteristic points as indicators of the field size for commissioning and QA purposes. This work aimed to search for the beam profile's characteristic points and use them for the TPS commissioning purposes. MATERIALS AND METHODS: The proposal is to use profile inflection points as the beam profile characteristic points. The usage of dedicated software allowed for comparing distances between inflection points and between points of 50% intensity. For the off-axis, wedged, and FFF fields, comparisons were made to the nominal field sizes. RESULTS: Distances between inflection points proved to be different by less than 1 mm from nominal field sizes for all kinds of investigated beams. CONCLUSIONS: Inflection points are convenient for comparing the off-axis, wedged, and FFF field sizes because of their independence from profile normalization. With finite accuracy, the inflection points could be used for the above kind of beam sizes designation.

Portal dosimetry in radiotherapy repeatability evaluation.

The accuracy of radiotherapy is the subject of continuous discussion, and dosimetry methods, particularly in dynamic techniques, are being developed. At the same time, many oncology centers develop quality procedures, including pretreatment and online dose verification and proper patient tracking methods. This work aims to present the possibility of using portal dosimetry in the assessment of radiotherapy repeatability. The analysis was conducted on 74 cases treated with dynamic techniques. Transit dosimetry was made for each collision-free radiation beam. It allowed the comparison of summary fluence maps, obtained for fractions with the corresponding summary maps from all other treatment fractions. For evaluation of the compatibility in the fluence map pairs (6798), the gamma coefficient was calculated. The results were considered in four groups, depending on the used radiotherapy technique: stereotactic fractionated radiotherapy, breath-hold, free-breathing, and conventionally fractionated other cases. The chi2 or Fisher's exact test was made depending on the size of the analyzed set and also Mann-Whitney U-test was used to compare treatment repeatability of different techniques. The aim was to test whether the null hypothesis of error-free therapy was met. The patient is treated repeatedly if the P-value in all the fluence maps sets is higher than the level of 0.01. The best compatibility between treatment fractions was obtained for the stereotactic technique. The technique with breath-holding gave the lowest percentage of compliance of the analyzed fluence pairs. The results indicate that the repeatability of the treatment is associated with the radiotherapy technique. Treated volume location is also an essential factor found in the evaluation of treatment accuracy. The EPID device is a useful tool in assessing the repeatability of radiotherapy. The proposed method of fluence maps comparison also allows us to assess in which therapeutic session the patient was treated differently from the other fractions.

In silico assessment of the dosimetric quality of a novel, automated radiation treatment planning strategy for linac-based radiosurgery of multiple brain metastases and a comparison with robotic methods.

BACKGROUND: To appraise the dosimetric features and the quality of the treatment plan for radiosurgery of multiple brain metastases optimized with a novel automated engine and to compare with plans optimized for robotic-based delivery. METHODS: A set of 15 patients with multiple brain metastases was selected for this in silico study. The technique under investigation is the recently introduced HyperArc. For all patients, three treatment plans were computed and compared: i: a HyperArc; ii: a standard VMAT; iii) a CyberKnife. Dosimetric features were computed for the clinical target volumes as well as for the healthy brain tissue and the organs at risk. RESULTS: The data showed that the best dose homogeneity was achieved with the VMAT technique. HyperArc allowed to minimize the volume of brain receiving 4Gy (as well as for the mean dose and the volume receiving 12Gy, although not statistically significant). The smallest dose on 1 cm3 volume for all organs at risk is for CK techniques, and the biggest for VMAT (p < 0.05). The Radiation Planning Index coefficient indicates that, there are no significant differences among the techniques investigated, suggesting an equivalence among these. CONCLUSION: At treatment planning level, the study demonstrates that the use of HyperArc technique can significantly improve the sparing of the healthy brain while maintaining a full coverage of the target volumes.

Beam rate influence on dose distribution and fluence map in IMRT dynamic technique.

AIM: To examine the impact of beam rate on dose distribution in IMRT plans and then to evaluate agreement of calculated and measured dose distributions for various beam rate values. BACKGROUND: Accelerators used in radiotherapy utilize some beam rate modes which can shorten irradiation time and thus reduce ability of patient movement during a treatment session. This aspect should be considered in high conformal dynamic techniques. MATERIALS AND METHODS: Dose calculation was done for two different beam rates (100 MU/min and 600 MU/min) in an IMRT plan. For both, a comparison of Radiation Planning Index (RPI) and MU was conducted. Secondly, the comparison of optimal fluence maps and corresponding actual fluence maps was done. Next, actual fluence maps were measured and compared with the calculated ones. Gamma index was used for that assessment. Additionally, positions of each leaf of the MLC were controlled by home made software. RESULTS: Dose distribution obtained for lower beam rates was slightly better than for higher beam rates in terms of target coverage and risk structure protection. Lower numbers of MUs were achieved in 100 MU/min plans than in 600 MU/min plans. Actual fluence maps converted from optimal ones demonstrated more similarity in 100 MU/min plans. Better conformity of the measured maps to the calculated ones was obtained when a lower beam rate was applied. However, these differences were small. No correlation was found between quality of fluence map conversion and leaf motion accuracy. CONCLUSION: Execution of dynamic techniques is dependent on beam rate. However, these differences are minor. Analysis shows a slight superiority of a lower beam rate. It does not significantly affect treatment accuracy.

EPID in vivo dosimetry in RapidArc technique.

AIM: The aim of the study was to estimate the dose at the reference point applying an aSi-EPID device in the course of patient treatment. MATERIALS AND METHODS: The method assumes direct proportionality between EPID signal and dose delivered to the patient reference point during the treatment session. The procedure consists of treatment plan calculation for the actual patient in the arc technique. The plan was realized with an elliptic water-equivalent phantom. An ionization chamber inside the phantom measured the dose delivered to the reference point. Simultaneously, the EPID matrix measured the CU distribution. EPID signal was also registered during patient irradiation with the same treatment plan. The formula for in vivo dose calculation was based on the CU(g) function, EPID signal registered during therapy and the relation between the dose and EPID signal level measured for the phantom. In vivo dose was compared with dose planned with the treatment planning system. Irradiation was performed with a Clinac accelerator by Varian Medical Systems in the RapidArc technique. The Clinac was equipped with an EPID matrix (electronic portal image device) of aSi-1000. Treatment plans were calculated with the Eclipse/Helios system. The phantom was a Scanditronix/Wellhöfer Slab phantom, and the ionization chamber was a 0.6 ccm PTW chamber. RESULTS: In vivo dose calculations were performed for five patients. Planned dose at the reference point was 2 Gy for each treatment plan. Mean in vivo dose was in the range of 1.96-2.09. CONCLUSIONS: Our method was shown to be appropriate for in vivo dose evaluation in the RapidArc technique.