VMAT Research Articles

Optimum Treatment Planning Technique Evaluation For Synchronous Bilateral Breast Cancer With Left Side Supraclavicular Lymph Nodes

Background: the Bilateral breast cancer cases are classified as a complex in radiotherapy treatment especially those with the left side mastectomy and right-side lumpectomy with left side supraclavicular lymph nodes patients. The purpose of this study is to find the optimum treatment planning technique among the three available techniques: 3D-CRT, IMRT, and VMAT.Materials and Methods: Ten Bilateral breast cancer included in this study with left side mastectomy and right-side lumpectomy with left side supraclavicular lymph nodes. The cross-sectional clinical study conducted in Baghdad ‎radiotherapy and nuclear medicine and Al-Andalus privet radiotherapy ‎hospital, Baghdad, Iraq. The patients are delineated by oncologists and prepare for radiation planning by MONACO 5.1 treatment planning system (TPS) with an X-ray photon beam of 6 MV or 10 MV energy using ‎ELEKTA‏’‏s Agility linear accelerator. The prescribed dose set at (4005 cCy per 15 fractions. Results: The treatment with 3D-CRT, IMRT, and VMAT show a significant difference in the results. VMAT give high dose distribution for the left mastectomy breast and it’s regional supraclavicular lymph nodes while the IMRT gives a higher value for the right side breast with lumpectomy. The good homogeneity index acquired with IMRT while VMAT gives a better conformity index. The 3D-CRT planning technique lowers the dose tho the heart and lunges better than the other techniques.Conclusion: Depending on the patient health and stage, the optimum treatment planning applied. Generally, VMAT is the optimum treatment planning technique for the studied group of SBBC patients. IMRT give effective coverage results better than the 3D-CRT.

PO-1237: Assessing the role of IMRT relative to VMAT in children with medulloblastoma treated with CSI

PO-1237: Assessing the role of IMRT relative to VMAT in children with medulloblastoma treated with CSI

PO-1512: VMAT based TBI using a novel rotatable tabletop

PO-1512: VMAT based TBI using a novel rotatable tabletop

Dosimetric Comparison Between VMAT with Different Arc and dIMRT for Early-stage Peripheral Lung Adenocarcinoma

Dosimetric Comparison Between VMAT with Different Arc and dIMRT for Early-stage Peripheral Lung Adenocarcinoma

Effect of radiotherapy on ovarian function in patients undergoing radical surgery for cervical cancer

Objective The correlation between dosimetric parameters of transposed ovary and different clinical ovarian functional status was assessed in young patients with cervical cancer who needed adjuvant radiotherapy after radical resection of the ⅠB1-ⅡA2 phase of preserved and transposed ovaries. Methods The function of transposed ovary and relevant clinical symptoms in 86 patients before and 2 years after treatment between 2015 and 2017 were retrospectively analyzed, and the correlation between the dosimetric parameters and functional status of transposed ovaries during radiotherapy was evaluated. Different in vitro measures were adopted to protect the transposed ovaries during postoperative radiotherapy including 68 cases of IMRT or VMAT and 18 cases of two-dimensional and other central radiotherapy. Results The nearest distance between ovary and PTV was negatively correlated with the ovarian dose ≥V5 Gy (P=0.025). V8 Gy and Dmean were positively correlated with FSH after treatment (P=0.011, 0.020). The larger the volume of V8 Gy and the large Dmean, the higher the FSH, the worse the ovarian function. In two-dimensional technology, the ovarian dose ≥V5 Gy was significantly lower than that in three-dimensional technique. The average age of those with normal ovarian function after treatment was 33.4 years, whereas the average age of women with ovarian failure was 39.6 years (P=0.007). The number of preserved ovaries and whether synchronous chemotherapy was delivered were similar in patients with different ovarian status, which were correlated with the levels of FSH and E2 (Estradiol) before treatment, that is, the higher the level of FSH before treatment, the lower the E2 of ovarian FSH after treatment, and the higher the level of FSH after treatment, the lower the level of ovarian E2. Patients who retained their ovaries before treatment but suffered from ovarian failure received neoadjuvant chemotherapy with a slightly higher age. Conclusions Age, V8 Gy and Dmean of the transposed ovary, the shortest distance between transposed ovary and PTV, whether neoadjuvant chemotherapy was delivered before surgery and radiotherapy technique affect the protection of the function of transposed ovary. Key words: Cervical neoplasm/radiotherapy; Ovarian transposition; Ovarian function

Evaluation of different volumetric-modulated arc therapy for the large planning target volume in T3 lung cancer

Objective To investigate the feasibility and dosimetric characteristics of using dual-arc volumetric modulated arc therapy and multiple partial-arc VMAT for T3 lung cancer. Methods From June 2016 to May 2018, thirteen lung cancer patients with large planning target volume were replanned with dual full arcs VMAT(F-VMAT) and six partial-arc s VMAT(P-VMAT)on RayStation v4.5 RayArc function.PTV volume median was 550.9cm3(ranged 402.2-834.8cm3) and to a prescribed dose of 60 Gy in 30 fractions.Equivalent target coverage was required for all plans, and clinical goals were evaluated using various dose-volume metrics.These included PTV dose conformity, mean lung/heart dose, lung V5, V10, V20, V30, heart V30 and V40, and Dmax of spinal canal.The total monitor units (MUs) were also examined. Results All VMAT plans satisfied the treatment criteria.F-VMAT achieved better homogeneity index(HI) and MUs than P-VMRT(t=-3.904, P=0.002), and the conformal number(CN) of tumor volumes was likely clinically indistinguishable.However, F-VMAT significantly reduced lung V5, V10 and mean lung dose[V5: (51.31±5.36)% vs.(43.44±5.28)%, t=6.908, P=0.00; V10: (38.34±3.26)% vs.(34.05±3.74)%, t=4.632, P=0.001; Dmean: (1 449±117.19)cGy vs.(1 375.38±148.98)cGy, t=4.93, P=0.00], and heart dosimetric parameters were also observed in favor of P-VMRT[V30: (20.6±10.4)% vs.(16.4±8.9)%, t=3.822, P=0.02; V40: (14.6±7.5)% vs.(11.88±7.1)%, t=3.096, P=0.009; Dmean: (1 442.9±651.2)cGy vs.(1 263.5±605.6)cGy, t=3.986, P=0.02], and there were no statistically significant differences in lung V20, V30 and spinal cord Dmax between the two groups(all P>0.05). Conclusion VMAT is an effective treatment for stage T3 lung cancer patients.The primary advantage of P-VMAT was the reduction in low dose area and decreased risk of symptomatic radioactive lung injury.It may be a priority for pulmonary malignancy patients with the large planning target volume. Key words: Lung neoplasms; Radiotherapy; Radiotherapy, intensity-modulated; Radiometry; Radiotherapy dosage; Radiation injuries; Organs at risk; Comparative study

Study on the correlation between acute radionuclitidis and improved body mass index in intensity-modulated radiation therapy after cervical cancer surgery

Objective To investigate the relationship between the body mass index (BMI)/ body mass index improved (BMIIMPd) and the dose of the small intestine as well as the acute radiation colitis in the intensity-modulated radiation therapy after cervical cancer surgery. Methods Thirty-nine cervical cancer patients underwent postoperative adjuvant radiotherapy. All patients received Philips large bore CT scan for enhanced CT scan, target delineation and organ at risk. All patients were treated with a single arc 10 MV VMAT plan. The correlation between the radiation dose of the small intestine and the acute radiation enteritis and BMI/BMIIMPd was analyzed. Results The BMI was calculated as (22.23±2.80) kg/m2, BMIIMPd was (21.49±3.95) kg/m2, the small intestine volume VSI was (1 155.71 ± 419.33 )cc3. The volume of the small intestine received more than 10 Gy(V10_SI) VMAT was (66.50±27.01)%, and the equivalent uniform dose (EUD) and normal tissue complication probability (NTCP) were (4098.87±184.93) cGy and (7.98±8.73)%. One way ANOVA demonstrated that under the VMAT technology, the BMIIMPd, V30, V40, EUD (α=50) and NTCP in the small intestine were the influencing factors of the occurrence of acute radiation enteritis. Conclusions If the improved BMIIMPd is utilized to distinguish the BMI, the high dose area of the small intestine will be larger and the incidence of acute radiation enteritis will be higher for patients with BMIIMPd between 10.1 and 16.9(normal and thin). Conventional BMI cannot be utilized as a basis for the prediction of the incidence of acute radiation enteritis in patients with cervical carcinoma. Key words: Cervical neoplasms/radiotherapy; Acute radiation enteritis; Body mass index

Evaluation of a fast method of EPID-based dosimetry for IMRT and Comparison with 3D EPID-based dosimetry system using conventional two- and three-dimensional detectors for VMAT

Introduction: Electronic portal imaging devices (EPIDs) could potentially be useful for intensity-modulated radiation therapy (IMRT) and VMAT QA. The data density, high resolution, large active area, and efficiency of the MV EPID make it an attractive option. However, EPIDs were designed as imaging devices, not dosimeters, and as a result they do not inherently measure dose in tissue equivalent media. EPIDose is a tool designed for the use of EPIDs in IMRT and VMAT QA that uses raw MV EPID images to estimate absolute dose planes normal to the beam axis in a homogeneous medi. However, because of the inherent challenges of the EPID-based dosimetry, validating and commissioning such a system must be done very carefully, by exploring the range of use cases and using well-proven “standards” for comparison. Converted EPID images were compared to 2D diode array absolute dose. To provide a 3D dosimetric evaluation of a commercial portal dosimetry system using 2D/3D detectors under ideal conditions using VMAT. Material & Method: A 2D ion chamber array, radiochromic film and gel dosimeter were utilized to provide a dosimetric evaluation of transit phantom and pre-treatment fluence’ EPID back-projected dose distributions for a standard IMRT & VMAT plan. In house 2D and 3D gamma methods compared pass statistics relative to each dosimeter and TPS dose distributions. Results: Fluence mode and transit EPID dose distributions back-projected onto phantom geometry produced 2D gamma pass rates in excess of 97% relative to other tested detectors and exported TPS dose planes when a 3%, 3mm global gamma criterion was applied. Use of a gel dosimeter within a glass vial allowed comparison of measured 3D dose distributions versus EPID 3D dose and TPS calculated distributions. 3D gamma comparisons between modalities at 3%, 3mm gave pass rates in excess of 92%. Use of fluence mode was indicative of transit results under ideal conditions with slightly reduced dose definition. Conclusions: 3D EPID back projected dose distributions were validated against detectors in both 2D and 3D. Cross validation of transit dose delivered to a patient is limited due to reasons of practicality and the tests presented are recommended as a guideline for 3D EPID dosimetry commissioning; allowing direct comparison between detector, TPS, fluence and transit modes. The results indicate achievable gamma scores for a complex VMAT plan in a homogenous phantom geometry and contributes to growing experience of 3D EPID dosimetry.

Investigation of Freedom-Degrees impact on Modulation of Radiation

Introduction: Nowadays tendency to apply more degrees of freedom in high-tech radiotherapy systems, and consequent complex process to optimize dose calculation and delivery algorithms, is a challenge of radiation therapy optimization. Faster MLC speed, dose rate, Gantry angle variation, and other degrees, which have been utilized in IMRT, IMAT, VMAT, improved modulation of intensity radiation that resulted in better quality in treatment plans. In this study, we modeled a pair of multi leaf collimators(MLC) to investigate ideal dynamical features such as speed and acceleration of MLC mathematically. Then we estimate an equation of MLC's motion in dynamical sliding window algorithm to investigate impact of some factors such as initial position of MLC, speeding up MLC, delivery time and variable dose rate on optimizing dose delivery algorithms. Materials and Methods: Seven intensity maps extracted from a prostate RT plan. MATLAB environment (R2017a version) was selected to define and solve optimization problem. In one dimension a pair of MLC modeled to reach out a row of intensity matrix diagram. Because of nonconcave nature of problem, gradient descent algorithm utilized and many criteria such as different start and end point of movement of MLC, direction of MLC, time delivery and dose rate subjected to optimization process. Results: Intensity map, velocity, acceleration, and output errors were plotted. However, the increase in the time can lead to a decrease in the error value - from 91% to an optimum of 2%; the error value did not reduce by increasing over optimum time significantly. Also increasing the speed of MLCs results in a significant reduction in relative error, although the assumption of the ability to reach out the infinite velocity does not lead to a reduction in relative error rate, and the optimization process was stopped. Conclusion: Although unidirectional movement in sliding window algorithm demonstrates as a suboptimal method, in volumetric methods bidirectional movement could have been optimal. Although that seems to get better outcome by speeding up MLC, it’s not as a rule routinely and infinite speed have been result in stopping optimization prematurely. In higher speed, we don’t see the linear relationship mathematically and over speeding up may lead to more anarchy in MLC movements reality. Not only increasing time delivery dose after a certain limit did not cause to significant decrease in optimization error, but also it may lead to other errors, and trade of between time and quality should be recognized. Variable dose rate can save more photons which sacrificed in modulation with tungsten blocks.

Margin expansion for treatment field of volumetric modulated arc therapy for breast cancer

Objective We developed a method to expand margin of beam aperture for VMAT treatment planning of breast cancer and evaluated its effectiveness in clinic. Methods An expanded VMAT (E-VMAT) plan for breast cancer using Pinnacle3 9.10 planning system was made. A small tissue-equivalent bolus was added at the middle of the breast surface as part of the target and the VMAT plan was generated with beam aperture automatically expanded. Then the tissue-equivalent bolus was removed and the final dose distribution was calculated. Ten patients with breast cancer undergoing breast conserving surgery were tested. The dosimetrical metrics and delivery efficiency were compared between the E-VMAT plans and the routine VMAT plans. Results On the BEV view, it was observed that in E-VMAT plans the collimator and MLC leaf positions was extended outside the skin along the anterior-posterior direction of the thorax. There were no significant differences in conformity index and homogeneity index of target volume between the two types of plans and the planned delivery efficiency was consistent (P>0.05). Conclusions The method established in this study can automatically generate expansion of VMAT beam apertures and prevent missing of target volume due to respiratory motion and/or setup error of the patient. The method does not require programming skill and available for different treatment planning systems. Key words: Breast neoplasms/volumetric modulated arc therapy; Beam aperture

Application of real-time transperineal ultrasound in radiotherapy of prostate cancer-4D analysis of intra-fractional prostate motion

Objective To apply real-time transperineal ultrasound (TPUS) to monitor the intra-fractional prostate motion, collect and analyze the data of the prostate motion, aiming to provide evidence for the optimization of the target area and plan of radiotherapy for prostate cancer. Methods TPUS is a non-invasive monitoring technique that utilizes an automatic scanning ultrasound probe to dynamically monitor and correct the motion of organs during radiotherapy. In this study, TPUS was utilized to collect 1588 intra-fractional data of 70 patients with prostate cancer. Prior to each cycle of radiotherapy, CBCT was adopted to correct the errors between intra-factional data by using VMAT. During radiotherapy, real-time (once per second) ultrasound images were acquired to monitor the 3D motion of the prostate on the x (left+ , right-), y (cranial+ , caudal-), and z (abdominal+ , dorsal-) axes, emphasizing the analysis of 4D motion of the prostate. Results All patients successfully completed the treatment and data collection. The median time of effective monitoring per faction was 179 seconds (132-286 seconds). During 95% of the monitoring time, the distance of prostate motion was 2.22 mm in the left direction, 2.17 mm in the right, 2.08 mm in the cranial, 1.98 mm in the caudal, 2.44 mm in the abdominal and 2.97 mm in the dorsal direction, respectively. In the x, y and z axes, the percentage of time in which the distance of prostate motion less than 1 mm among the total time was 83.07%, 85.46% and 78.27%, respectively, whereas 97.70%, 97.87% and 96.45% for<3 mm, respectively. Conclusions TPUS is a non-invasive real-time monitoring technique, which can detect the 4D motion of the prostate during radiotherapy. By using VMAT, the range of prostate motion is relatively small, and the motion range is less than 3 mm in each direction within 95% of the time. Key words: Prostate neoplasms; Transperineal ultrasound; Intra-fractional motion; Real-time monitoring

Effect of statistical uncertainty on Monaco Monte-Carlo dose calculation

Purpose: The aim of this study is to evaluate influence of statistical uncertainty on Monte-Carlo dose calculation of Monaco 5.11 treatment planning system (TPS). Methods: Phantom with contoured C-Shape structure set was downloaded from AAPM website provided with TG119 report. VMAT plan was created for C-Shape test case using Monaco TPS for 6 MV Elekta Versa-HD linear-accelerator. Dose prescription and constraints were as per TG119. After optimizations, C-Shape plan was calculated with different statistical-uncertainty (i) 0.5%, 1.0%, 3.0% and 5.0% per control point and (ii) 0.5%, 1.0%, 3.0% and 5.0% per calculation. Base plan was calculated with 0.5% per control point. Results: Variations in PTV doses for different statistical-uncertainties with respect to 0.5% per control point were within PTV-D95: 82 cGy(1.64%); PTV-D10: 14.8 cGy(0.28%); Core-D10: 3.7 cGy(0.15%). MU required to deliver a plan (920 MU) were observed same with different statistical-uncertainty. Calculation time increases with decrease in statistical-uncertainty due to more number of histories. 2D-Gamma pass rate was ranging from 98.1% to 98.9% for analyzed statistical-uncertainties. Statistical-uncertainty 0.5% per control point showed higher Gamma pass-rate (98.9%). Conclusion: Minor variation (<1.64%) in dose volume parameters was observed with different statistical-uncertainties, whereas Monitor unit remain same. 3.0% per control point and 0.5% per calculation resulted in almost similar results and found optimal with reasonable calculation time in terms of plan quality and delivery accuracy (gamma pass-rate).

Comparison of dosimetric characteristics between flattening-filter-free and flattening filter mode VMAT plans in nasopharyngeal carcinoma

Objective To compare the dosimetric characteristics of the VMAT plans between the flattening-filter-free (FFF) and flattening filter (FF) modes for nasopharyngeal carcinoma and analyze the feasibility of VMAT plans in the FFF model applied in clinical practice. Methods Ten patients diagnosed with stage Ⅱ nasopharyngeal carcinoma between 2016 and 2017 were recruited in this investigation. For the CT image and clinical target volume (CTV) of the identical patient, FFF-and FF-mode VMAT plans were established with the identical prescription dose of 6 975 cGy and the identical modified parameters on the RayStation platform (6 MV X-ray). The dosimetric characteristics, the number of machine hops and the time of beam were recorded and statistically compared between the FFF and FF modes. Results The minimum dose D98% target, target coverage, conformal index (CI) did not significantly differ between the FF and FFF plans (P=0.262-0.975), whereas the maximum dose of D2%, the average dose of Dmean and target homogeneity index (HI) of the FF plans were slightly advantageous to those of the FFF plan (P=0.004-0.038). The acceptable dose of bilateral lenses, the volume of the left parotid gland with an acceptable dose of> 30 Gy and the average dose of the left temporal lobe in the FFF mode were declined compared with those in the FF mode (P=0.002-0.025). The volume of normal tissues (Body) within the dose range of 2-30 Gy in the FFF mode was less than that in the FF mode (P=0.000-0.003). In the FFF mode, the mean number of machine hops was 1.188 times (P=0.000) and the average time of beam was 91.2% of the FF plan (P=0.024). Conclusions Both the FF and FFF plans qualify the dosimetric requirements in clinical settings. FF plan is advantageous in terms of the dose distribution in the target area, whereas FFF plan yields better OAR protection and low-dose irradiation. In spite of the increasing quantity of machine hops, the time of beam is declined in the FFF plan. Consequently, FFF mode probably contributes to enhance the clinical efficacy. Key words: Nasopharyngeal neoplasm/volumetric modulated arc therapy; Flattening-filter-free; Dosimetry

EP-1885: Evaluation of Pinnacle automated VMAT planning for complex pelvic treatments

EP-1885: Evaluation of Pinnacle automated VMAT planning for complex pelvic treatments

OC-0613: The ACDS IMRT and VMAT audits: results from a two level approach

OC-0613: The ACDS IMRT and VMAT audits: results from a two level approach

EP-1753: Sensing ability of EPID-based in vivo dosimetry for VMAT

EP-1753: Sensing ability of EPID-based in vivo dosimetry for VMAT

EP-1922: Standardisation of VMAT frameless SRS/SRT planning using ensemble mapped knowledge based planning

EP-1922: Standardisation of VMAT frameless SRS/SRT planning using ensemble mapped knowledge based planning

Study on patient movements features during radiotherapy

Objective To study the patient movements features during radiotherapy. Methods Randomly selected 120 patients treated in our hospital from February to July on 2016, including 60 thorax treatment and 60 abdomen treatment. The movement data of patient treatment location during radiotherapy treatment was real time monitored by using Sentinel system, movement features of patient′s location during radiotherapy was analyzed. Paired t-test difference. Results During radiotherapy, patient′s treatment location movement types and proportion were motionless type 14.0%, Moving stable type 64.0%, Jumping type 8.7%, increasing type 13.3%.Patients with thoracic and abdominal radiotherapy, the maximum deviation of IMRT and VMAT treatment were (6.55±2.34) mm and (4.97±1.24) mm (P=0.002), (3.97±1.80) mm and (2.69±1.42) mm (P=0.004). In single treatment, the deviation value of the patient′s treatment location increased gradually with the treatment time increasing and the deviant of thoracic is greater than abdominal at the same time after the treatment beginning. Conclusions Patient′s treatment location movement during radiotherapy is commonly exist, using the technology of VMAT treatment can effectively reduce the treatment site movement of the patient during the treatment and ensure the accuracy of dose. Key words: Radiotherapy planning, computer-assisted; Laser Scanning; Maximum deviation

Effect of angle correction factors of MatriXX on VMAT dose verification

Objective To investigate the effect of the angle correction factors of ionization chamber array Matrixx on the dosimetric verification of volumetric modulated arc therapy plan. Methods The Matrixx (IBA) was put in the middle of the MultiCube Phantom. Computed tomography scan was performed and the results were sent to the Raystation treatment planning system (TPS). All data calculated from TPS and actually measured using MatriXX were gained under the following conditions: 6 MV, 100 MU, 28 cm×28 cm radiation field. And the directions of beam were from 0°to 180°with an interval of 5°(except an interval of 1° from 85° to 95°). The angle correction factors (CF)(θ) cor of MatriXX were calculated by the calculated dose values from TPS and the measured values using MatriXX and then mirrored to the opposite side. CF (θ) cor values were compared with CF (θ) def values that were given by manufacturer. The comparison was made by paired t-test. Results CF (θ) cor and CF (θ) def were different, and the difference was significant between 85° and 95°, with a maximum of 7.5%(P<0.05). The CF (θ) cor correction method had a higher gamma pass rate than the CF (θ) def correction method, with a maximum of 17%(P<0.05). Conclusions The ionization chamber array MatriXX has an angular dependence and the angle correction should be performed. The angle correction factors have the individual characteristics and are different in every unit ionization chamber of the MatriXX. Therefore, it is necessary to do angle correction for every unit ionization chamber of the MatriXX and the possible errors caused by various factors should be considered in order to improve the accuracy rate and gamma pass rate of the plan verification. Key words: Ionization chamber matrix; Angle correction factor; Volumetric modulated arc radiotherapy; Plan verification

Application of detector array in treatment planning system modeling adjustment

Objective To investigate the feasibility of detector array in Monaco modeling for MLC parameters adjustment. Methods One parameter was fixed, and then the other parameter was changed. The γ pass rates of the test beams, namely 3ABUT, 7SegA, and FOUR L, were assessed to determine the values of leaf transmission and leaf offset. A total of 12 tumor cases from different anatomical sites were randomly selected. Two-dimensional dose verification (rack angle zero) of Step& Shot and dMLC plans as well as three-dimensional dose validation of VMAT plan were performed using Octavius 4D system. The γ pass rates were analyzed at a standard of 3%/3 mm. Meanwhile, the point dose verification for these three plans was analyzed to obtain the dose deviations. Results The values of leaf transmission and leaf offset were 0.0105 and-0.08 mm, respectively. The average γ pass rates (%) of Step& Shot, dMLC, and VMAT plans were 88.59±2.94, 87.81±3.28, and 87.45±2.24 before adjustment and 98.45±1.23, 98.9±1.01, and 96.03±1.66 after adjustment. In addition, the average dose deviations (%) according to the point dose verification were 0.85±0.75, 0.95±0.39, and 0.98±0.40 before adjustment and 0.97±0.57, 1.08±0.76, and 0.86±0.45 after adjustment. Conclusions Octavius detector 729 ionization chamber array is a feasible and reliable device in Monaco modeling for MLC parameters adjustment. Key words: Post modeling adjustment; Detector array; γpass rates; Leaf transmission; Leaf offset