Verification of an optimizer algorithm by the beam delivery evaluation of intensity-modulated arc therapy plans.

BACKGROUND: In the case of dynamic radiotherapy plans, the fractionation schemes can have dosimetric effects. Our goal was to define the effect of the fraction dose on the plan quality and the beam delivery. MATERIALS AND METHODS: Treatment plans were created for 5 early-stage lung cancer patients with different dose schedules. The planned total dose was 60 Gy, fraction dose was 2 Gy, 3 Gy, 5 Gy, 12 Gy and 20 Gy. Additionally renormalized plans were created by changing the prescribed fraction dose after optimization. The dosimetric parameters and the beam delivery parameters were collected to define the plan quality and the complexity of the treatment plans. The accuracy of dose delivery was verified with dose measurements using electronic portal imaging device (EPID). RESULTS: The plan quality was independent from the used fractionation scheme. The fraction dose could be changed safely after the optimization, the delivery accuracy of the treatment plans with changed prescribed dose was not lower. According to EPID based measurements, the high fraction dose and dose rate caused the saturation of the detector, which lowered the gamma passing rate. The aperture complexity score, the gantry speed and the dose rate changes were not predicting factors for the gamma passing rate values. CONCLUSIONS: The plan quality and the delivery accuracy are independent from the fraction dose, moreover the fraction dose can be changed safely after the dose optimization. The saturation effect of the EPID has to be considered when the action limits of the quality assurance system are defined.

[The effects of normal tissue objective parameters on lung stereotactic body radiotherapy dose distributions]. / Normálszöveti optimalizálási paraméterek hatása tüdosztereotaxiás besugárzási tervek dóziseloszlására.

In treatment planning of small-sized lung tumors treated with stereotactic body radiotherapy (SBRT) in Eclipse treatment planning system with the Normal tissue objective (NTO) tool sharp dose gradients beyond the target volume can be achived. NTO has 5 variable parameters, so it is difficult to know which settings are optimal. The purpose of this study was to characterize the effects of changing NTO parameters on lung SBRT dose distributions. Ten lung SBRT cases were replanned using different NTO parameters. Dose calculation was performed using AAA and AXB algorithms as well. Differences between AAA and AXB plans were statistically significant. Plans were evaluated based on plan quality metrics. According to this analysis the fall-off of 0.15 and the priority of 500 have satisfied our institutional criteria best. Using NTO during planning is recommended in clinical practice.

[Dosimetric analysis of LINAC based stereotactic irradiation of brain tumours in CIRS SHANE phantom]. / Lineáris gyorsítóval végzett agyi sztereotaxiás besugárzások terveinek dozimetriai elemzése CIRS SHANE fantomban.

The aim of the study was to compare the different stereotactic treatment plans and dose calculation algorithms for small targets with film dosimetry in anthropomorphic phantom. Treatment plans were prepared for multiple targets with single setup isocenter. Plans for three different irradiation techniques were generated using conformal arc with four non-coplanar arcs, RapidArc with two coplanar full arcs and RapidArc with four non-coplanar arcs in the Varian Eclipse v13.7.16 TPS. Conformal arc and RapidArc plans were calculated using AAA, Acuros XBDm and XBDw algorithms. Conformity index, gradient index and dose maximum were calculated for all PTVs. All measurements were made on the Varian TrueBeam linear accelerator. Comparison between computed and measured dose distributions was performed with gamma evaluation criteria of 3%, 3 mm; 3%, 1 mm and 2%, 2 mm. According to our results, the Eclipse AAA and AXB algorithms provide accurate dose distributions for homogeneous cranial irradiation.

[Biological dose estimation for photons of different qualities in radiation therapy]. / Biológiai dózisbecslés a sugárterápiában alkalmazott különbözo sugárminoségu fotonnyaláboknál.

Flattening filter free mode (FFF) has been introduced in radiotherapy during the past decades, however, not much has been reported on its radiobiological effect. The purpose of our study was to compare the radiobiological effects of flattening filter and flattening filter free photon beams on chromosomal aberrations in peripheral blood lymphocytes. In our study the blood of the same healthy donor was irradiated with linear accelerator using both conventional flattening filter (FF) and FFF photon beams at dose rate of 3.57-23.08 Gy/min, using 6 or 10 MV. The dose-response calibration curves for dicentric + ring chromosomes induced by irradiation were fitted with linear-quadratic model. CABAS (Chromosomal Aberration Calculation Software) was used to prepare the curves. The coefficients and equations of the curves were calculated and compared with the results of other authors. We found significant differences in the number of aberrations at different irradiation parameters. Based on our results, FFF mode has a 10-20% higher biological effect than FF mode. These results can be used during radiotherapy or to estimate the biological doses in case of an accidental exposure to radiation.

Chromosomal Aberrations in Blood Lymphocytes as Predictors of Respiratory Function After Stereotactic Lung Irradiation.

Due to the profound difference in radiosensitivity of patients and various side effects caused by this phenomenon, a radiosensitivity marker is needed. Prediction by a marker may help personalise the treatment. In this study, we tested chromosomal aberrations (CA) of in vitro irradiated blood as predictor of pulmonary function decrease of nonsmall cell lung cancer (NSCLC) patients and also compared it with the CAs in the blood of irradiated patients. Peripheral blood samples were taken from 45 lung cancer patients before stereotactic radiotherapy (SBRT) and immediately after the last fraction and 3, 6, 9, 12, 15, 18, 21, and 24 months later. Respiratory function measurements were performed at the same time. Diffusing capacity of lung for carbon monoxide (DLCO), forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1s), and FEV1s/FVC (FEV1%) were monitored. Metaphase preparations of lymphocytes were made with standard procedures, and chromosome aberrations were analysed. In our cohort, the 36-month local relapse-free survival was 97.4%, and the distant metastasis-free survival was 71.5% at 36 months. There was no change in the mean of the pulmonary function tests (PFTs) after the therapy. However, there was a considerable variability between the patients. Therefore, we subtracted the baseline and normalised the PFT values. There were significant decreases at 12-24 months in relative FEV1s and relative FEV1%. The tendentious decrease of the PFTs could be predicted by the in vitro chromosome aberration data. We also found connections between the in vitro and in vivo CA values (i.e., dicentrics plus rings after 3 Gy irradiation predicts dicentric-plus-ring value directly after the radiotherapy/V54 Gy (p = 0.001 24.2%)). We found that-after further validation-chromosome aberrations resulted from in vitro irradiation before radiotherapy can be a predictive marker of pulmonary function decrease after lung irradiation.

Comparison of three film analysis softwares using EBT2 and EBT3 films in radiotherapy.

Introduction The purpose of the study was to compare the results of gamma value based film analysis according to the used type of self-developer film and software product. Material and methods The films were irradiated with different treatment techniques such as 3D conformal and intensity modulated radiotherapy with static and rotational delivery. Stereotactic plans with conformal and intensity modulated arc techniques, using coplanar and non-coplanar beam setup were also evaluated. The data of irradiated film were compared with the planned planar dose distribution exported from the treatment planning system. Three film analysis software programs were evaluated: PTW Mephysto (PTW), FilmQA Pro (FQP) and radiohromic.com(RC). Both EBT2 and EBT3 types of films were examined. The comparisons of dose distributions were performed with gamma analysis using 10% cut-off level. Results The results of the gamma analysis for larger fields were between 78.3% and 98.3%, 75.7% and 100%, 80.2% and 98.8% with PTW, FQP and RC, respectively. The results of evaluation in case of stereotactic measurements were 76.8%-99.2% for PTW, 95.7%-100% for FQP and 91.2%-99.9% for RC. Conclusions All the three software programs are suitable for calibrating and evaluating films, performing gamma analysis, and can be used for patient specific quality assurance measurements. There is no direct connection between gamma passing rate and absolute accuracy or software quality, it is just a feature of the software. The interpretation of own results has to be defined on an institutional level according to given workflow and preliminary results.

[Application of modern radiotherapy in lung cancer]. / A tüdorák modern sugárterápiája.

Lung cancer is known for its outstanding incidence and mortality rates. One of the cornerstones of the treatment of this disease is radiation therapy. A remarkable development was observed in this field through the latest decades. Intensity-modulated and image-guided radiotherapy (IMRT and IGRT) are now widely accessible in Hungarian centers, and should be increasingly applied in case of thoracic irradiations as well. Application of modern radiotherapy techniques in the treatment of lung cancer allows better clinical results and lower rates of side effects. In this work the authors give an overview of this above mentioned development regarding different clinical stages.

Normal tissue sparing using different techniques for prostate irradiation.

AIM: The aim of this study was to investigate normal tissue sparing through dosimetric parameters of normal tissue volumes using different irradiation techniques for conventional (CFRT) and simultaneously integrated boost (SIB) schedules. BACKGROUND: Several dose-escalation studies for localized prostate cancer (PCa) have shown advanced biochemical relapse-free (bRFS) rates and also better local control for higher total doses using either CFRT or SIB schedules. Besides the most important organs-at-risk, absorbed dose reduction of other surrounding normal tissues are also preferable. In order to analyse the normal tissue sparing, dosimetric parameters of different normal tissue volumes were examined. MATERIALS AND METHODS: Treatment plans for 15 high risk prostate cancer patients were created using RapidArc (RA), Sliding Window (SW) IMRT and 4-field box (3D-CRT) technique. In order to evaluate normal tissue sparing, the volume of pelvic region was divided into six normal tissue cylinders with 1 cm wall thickness, located in each other. RESULTS: All plans met the criteria of target coverage (V95%>95%). All techniques provided the same results for OARs except 3D-CRT for rectum and bilateral femoral heads. The values of V5, V10 and V15 increased in cases which included RapidArc technique and decreased for V20 and V30. CONCLUSIONS: The dosimetric parameters for the cylindrical normal tissue volumes show that using RapidArc technique gives equal or slightly better normal tissue sparing and SIB provided the same normal tissue sparing as CFRT planned with RapidArc.

Acute and Late Toxicity after Moderate Hypofractionation with Simultaneous Integrated Boost (SIB) Radiation Therapy for Prostate Cancer. A Single Institution, Prospective Study.

ASBTRACT: To evaluate the acute and late toxicity using moderately hypofractionated, intensity-modulated radiotherapy (IMRT) with a simultaneous integrated boost (SIB) to prostate for patients with intermediate and high risk prostate cancer. From 2015 to 2017, 162 patients were treated with IMRT with SIB to the prostate. IMRT plans were designed to deliver 50.4Gy in 28 fractions (1.8 Gy/fraction) to the pelvic lymph nodes (whole pelvis radiotherapy, WPRT) while simultaneously delivering 57.4 Gy in 28 fractions (2.05 Gy/fraction) to the seminal vesicles and 70 Gy in 28 fractions (2.5 Gy/fraction) to the prostate for high risk patients. For intermediate risk patients the same technique was applied, without WPRT. Acute and cumulative late genitourinary (GU) and gastrointestinal (GI) toxicities were scored according to the Radiation Therapy Oncology Group (RTOG) scoring system. Of the 162 patients enrolled, 156 (96%) completed the treatment as planned. The median follow-up time was 30 months. Seventy-eight patients (48.2%) were treated with WPRT. The rate of acute grade ≥ 2 GI and GU toxicities in all patients were 22% and 58%, respectively. The rate of cumulative late grade ≥ 2 GI and GU toxicities were 11% and 17%, respectively. Acute grade 3 GI and GU toxicities occurred in 1% and 1%. Late grade 3 GI and GU side effects occurred in 5% and 4%, respectively. None of the patients developed grade ≥ 4 toxicity. IMRT with SIB technique using moderate hypofractionation to the prostate is feasible treatment option for intermediate and high risk patients, associated with low rate of severe GU and GI toxicities.

Quantifying biological effects of radiation from high-energy linear accelerators on lymphocytes.

The aim of this study was to investigate the radiobiological effects of flattening filter (FF) and flattening filter-free (FFF) modes of linear electron accelerators and to understand whether there is any difference between the effects of these modes. We evaluated the number of chromosome aberrations following irradiation of lymphocytes from healthy volunteers with X-ray photons at two energy levels, 6 and 10 MV; the dose rate ranged between 5.50 and 23.08 Gy/min and absorbed doses ranged between 0.5 and 8 Gy. A 60Co curve was employed for comparison. Metaphases from the lymphocyte cultures were prepared using standard cytogenetic techniques and chromosome analysis was performed. Our results allow the performance of biodosimetry at higher energies and doses than the currently used reference dosimetry. We observed significant differences in aberration frequencies when different irradiation techniques were used. FFF mode has a higher radiobiological effect than the FF mode. Linear-quadratic dose response calibration curves were constructed and relative biological effectiveness (RBE) values were calculated. Average RBE values using 6 MV (5.50 Gy/min) as a reference radiation were 1.28 for 60Co γ irradiation, 1.11 for 6 FFF and 0.79-0.92 for 10 FFF. Since there are compelling differences between radiation modalities in cases of hypofractionation, these results may be even more important in a therapeutic situation. In case of an accidental overdose of a patient, use of the appropriate calibration curves for biodosimetry are also essential for quantifying the overdose.

[Curative radiotherapy of early-stage lung cancer using respiratory motion compensation]. / Korai stádiumú tüdõdaganatok kuratív sugárkezelése légzõmozgást figyelembe vevõ technikával.

In this paper we present our early experience with a method for the management of respiratory motion in radiotherapy for early-stage lung cancer. Forty-six patients were irradiated with a total dose of 60 Gy. Tumor response on control CT, survival, local and distant progression as well as early and late side effects were registered. Complete and partial remission, stable and progressive disease was 17 (37.0%), 15 (32.6%), 11 (23.9%) and 3 (6.5%). Isolated local recurrence and distant metastasis appeared in 4 (8.7%) and 2 (4.3%) cases, while simultaneous local and distant progression was diagnosed in 3 (6.5%) patients. The probability of 2-year local recurrence-free, progression-free, and overall survival was 76.8%, 64.0%, and 83.2%. Grade 1 (G1) and G2 early side effects occurred at 15 (32.6%) and 3 (6.5%) patients without ≥G3 side effects. G1 and G2 late side effects were observed in 10 (21.7%) and 7 (15.2%) cases. G1-2 post-irradiation fibrosis occurred in 11 (23.9%) cases. Twenty months after the irradiation, G5 respiration failure was developed in one patient. The implemented technique of respiratory motion management for the radiotherapy of early-stage lung cancer resulted in promising local freedom from relapse and survival with favorable side effect profile. Further follow-up is needed to assess longterm side effects and survival results.

[Imaging protocols for the management of respiratory motions in the radiotherapy planning for early stage lung cancer patients]. / Légzomozgást figyelembe vevo képalkotó protokollok alkalmazása korai stádiumú tüdodaganatos betegek besugárzástervezésénél.

The aim of our work is to present the imaging techniques used at the National Institute of Oncology for taking into consideration the breathing motion at radiation therapy treatment planning. Internationally recommended imaging techniques, such as 4D CT, respiratory gating and ITV (Internal Target Volume) definition were examined. The different imaging techniques were analysed regarding the delivered dose during imaging, the required time to adapt the technique, and the necessary equipment. The differences in size of PTVs (Planning Target Volume) due to diverse volume defining methods were compared in 5 cases. For 4D CT breath monitoring is crucial, which requires special equipment. To decrease the relatively high exposure of 4D CT it is possible to scan only a few predefined breathing phases. The possible positions of the tumour can be well approximated with CT scans taken in the inhale maximum, the exhale maximum and in intermediate phase. The intermediate phase can be exchanged with an ordinary CT image set, and the extreme phase CT images can be ensured by given verbal instructions for the patient. This way special gating equipment is not required. Based on these 3 breathing phases an ITV can be defined. Using this ITV definition method the margin between the CTV (Clinical Target Volume) and the PTV can be reduced by 1 cm. Using this imaging protocol PTV can be reduced by 30%. A further 10% PTV reduction can be achieved with respiratory gating. In the routine clinical practice respiratory motion management with a 3-phase CT-imaging protocol the PTV for early-stage lung cancer can be significantly reduced without the use of 4D CT and/or respiratory gating. For special, high precision treatment techniques 4D CT is recommended.