Searching standard parameters for volumetric modulated arc therapy (VMAT) of prostate cancer

Background Since December 2009 a new VMAT planning system tool is available in Oncentra® MasterPlan v3.3 (Nucletron B.V.). The purpose of this study was to work out standard parameters for the optimization of prostate cancer. Methods For ten patients with localized prostate cancer plans for simultaneous integrated boost were optimized, varying systematically the number of arcs, collimator angle, the maximum delivery time, and the gantry spacing. Homogeneity in clinical target volume, minimum dose in planning target volume, median dose in the organs at risk, maximum dose in the posterior part of the rectum, and number of monitor units were evaluated using student’s test for statistical analysis. Measurements were performed with a 2D-array, taking the delivery time, and compared to the calculation by the gamma method. Results Plans with collimator 45° were superior to plans with collimator 0°. Single arc resulted in higher minimum dose in the planning target volume, but also higher dose values to the organs at risk, requiring less monitor units per fraction dose than dual arc. Single arc needs a higher value (per arc) for the maximum delivery time parameter than dual arc, but as only one arc is needed, the measured delivery time was shorter and stayed below 2.5 min versus 3 to 5 min. Balancing plan quality, dosimetric results and calculation time, a gantry spacing of 4° led to optimal results. Conclusion A set of parameters has been found which can be used as standard for volumetric modulated arc therapy planning of prostate cancer

The influence of radiotherapy techniques on the plan quality and on the risk of secondary tumors in patients with pituitary adenoma

Background This planning study compares different radiotherapy techniques for patients with pituitary adenoma, including flatness filter free mode (FFF), concerning plan quality and secondary malignancies for potentially young patients. The flatness filter has been described as main source of photon scatter. Material and methods Eleven patients with pituitary adenoma were included. An Elekta Synergy (TM) linac was used in the treatment planning system Oncentra (R) and for the measurements. 3D plans, IMRT, and VMAT plans and non-coplanar varieties were considered. The plan quality was evaluated regarding homogeneity, conformity, delivery time and dose to the organs at risk. The secondary malignancy risk was calculated from dose volume data and from measured dose to the periphery using different models for carcinoma and sarcoma risk. Results The homogeneity and conformity were nearly unchanged with and without flattening filter, neither was the delivery time found substantively different. VMAT plans were more homogenous, conformal and faster in delivery than IMRT plans. The secondary cancer risk was reduced with FFF both in the treated region and in the periphery. VMAT plans resulted in a higher secondary brain cancer risk than IMRT plans, but the risk for secondary peripheral cancer was reduced. Secondary sarcoma risk plays a minor role. No advantage was found for non-coplanar techniques. The FFF delivery times were not shortened due to additional monitor units needed and technical limitations. The risk for secondary brain cancer seems to depend on the irradiated volume. Secondary sarcoma risk is much smaller than carcinoma risk in accordance to the results of the atomic bomb survivors. The reduction of the peripheral dose and resulting secondary malignancy risk for FFF is statistically significant. However, it is negligible in comparison to the risk in the treated region. Conclusion Treatments with FFF can reduce secondary malignancy risk while retaining similar quality as with flattening filter and should be preferred. VMAT plans show the best plan quality combined with lowest peripheral secondary malignancy risk, but highest level of second brain cancer risk. Taking this into account VMAT FFF seems the most advantageous technique for the treatment of pituitary adenomas with the given equipment

Isolasi Dan Karakterisasi Bakteri Endofit Penghasil Inhibitor α-Glukosidase Dari Tanaman Pare (Momordica Charantia L)

Diabetes merupakan penyakit metabolik yang serius di Indonesia. Jumlah penderita diabetes mengalami peningkatan setiap tahunnya. Inhibitor α-glukosidase merupakan senyawa yang dapat menghambat enzim α-glukosidase sehingga bermanfaat sebagai obat antidiabetes. Tanaman Pare (Momordica charantia) diketahui memiliki kasiat sebagai anti diabetes. Senyawa aktif yang dihasilkan tanaman tersebut dapat berasal dari endofit yang hidup di dalam jaringan tanaman. Eksplorasi bakteri endofit dari tanaman pare merupakan salah satu cara untuk mendapatkan isolat bakteri penghasil inhibitor enzim α-glukosidase. Isolasi bakteri dilakukan dengan menginokulasikan sampel tanaman yang telah disterilisasi permukaan pada media agar. Isolat bakteri yang didapat selanjutnya dimurnikan dan di karakterisasi lebih lanjut baik morfologi maupun aktivitas inhibitor α-glukosidasenya. Pengujian aktivitas inhibitor α-glukosidase menggunakan metode spektrofotometer dengan nitrofenil-α-D-glukopiranosida sebagai substrat. Hasil penelitian diperoleh 5 isolat bakteri endofit penghasil inhibior α-glukosidase. Penghambatan terbesar ditunjukkan oleh isolat bakteri Ad 1 yaitu sebesar 27,4%

Volumetric-modulated arc therapy and intensity-modulated radiation therapy treatment planning for prostate cancer with flattened beam and flattening filter free linear accelerators

This study on patients with localized prostate cancer was set up to investigate valuable differences using flattened beam (FB) and flattening filter free (FFF) mode in the application of intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT). For ten patients, four different plans were calculated with Oncentra planning system of Elekta, using Synergy machines: IMRT and VMAT, with and without flattening filter. Homogeneity and conformity indexes, dose to the organs at risk, and measurements of peripheral dose and dosimetric plan verification including record of the delivery times were analyzed and statistically evaluated. The indexes for homogeneity and conformity (CTV and PTV) are either advantageous or not significantly different for FFF compared to FB with one minor exception. Regarding the doses to the organs at risk and the measured peripheral dose, equivalent or lower doses were delivered for FFF than with FB. Furthermore, the delivery times were significantly shorter for FFF. VMAT compared to IMRT reveals benefits or at least equivalent values. VMAT-FFF combines the most advantageous plan quality parameters with the shortest delivery times and reduced peripheral dose and is therefore recommended for the given equipment and cancer localization

Volumetric Modulated Arc Therapy (VMAT) Treatment Planning for Prostate - A Comparison of Flatness Filter Free (FFF) and Flat Beam Plans

Introduction Linear accelerators (Linacs) with Flatness Filter Free (FFF) mode obtain a much higher dose rate by omitting the flatness filter. The resulting inhomogeneous dose distribution is compensated by fluence modulating techniques like IMRT or VMAT. This planning study compares VMAT plans for patients with prostate carcinoma. Optimizations were performed using both modes: flattened beam (FB) and FFF. The aim of this study is to evaluate the plan quality and the number of monitor units (MU). Material and Methods Data sets of 10 patients with localized prostate cancer and reliable dose volume objectives were used for this retrospective planning study. A simultaneous integrated boost radiation therapy aims at a minimum dose of 71.0Gy and maximum of 74.2Gy in the CTV and a minimum dose of 59.4Gy in the PTV in 33 fractions. The posterior rectum wall is limited to 50.0Gy. The median values of rectum and urinary bladder are set to 50.0Gy. Additionally the maximum dose to the rectum is set to 74.2Gy. The VMAT parameters in the treatment planning system (TPS) Oncentra® External Beam v4.5 are set to: Single Arc rotation (182°-178°), collimator 45°, maximum delivery time 110s, gantry spacing 4°, and collapsed cone algorithm. The linac Synergy Agility offers a dose rate of 550MU/min (FB) and 1700MU/min (FFF). The leaves have a width of 5mm projected to the isocenter. The following parameters are evaluated: average dose DAv and homogeneity H = (D5–D95)/DAv in the CTV, minimum dose in the PTV represented by the D98PTV-CTV of the difference volume of PTV and CTV, maximum dose in the posterior rectum wall represented by the D2Rpost, median dose to rectum D50R and urinary bladder D50B, and the number of MU. Results Generally the dose volume statistics are very close for both modes. Taking the average dose in the CTV as normalization value, the maximum does not exceed 107%. The minimum dose in the PTV has been reached in one plan of each group only. The objectives for the median values in rectum and urinary bladder as well as maximum dose to the posterior rectum wall have been achieved in all cases. The only statistically significant difference for both groups is the number of MU which is about 10% lower for the FB plans. Discussion The plans for both modes show a good homogeneity in the CTV. The minimum dose to the PTV and the maximum dose to the posterior rectum wall are counterworking objectives which resulted in favour for the rectum for the given weights of the objectives. The high dose rate of the FFF mode aims at shorter treatment times which would reduce intrafractional organ motion. Measurements of the delivery times will be performed and discussed in the presentation

EP-1615: Second cancer risk after radiation of localized prostate cancer with and without flattening filter

Purpose: Radiotherapy is a standard treatment modality with curative intent for localized prostate cancer. Prostate cancer is a disease of elderly men. Nevertheless these patients have a remaining life span of ten years or more. Radiotherapy compared to surgery may increase the risk for second cancer. Minimizing this risk can be one criterion in deciding for a specific technique. Therefore we compared the organ equivalent dose (OED) and excess absolute risk (EAR) for second cancer for different treatment techniques. Material and methods: For ten patients four different plans were calculated, using a seven field intensity modulated radiotherapy (IMRT) and a single arc volumetric modulated arc therapy (VMAT) with and without flattening filter. The optimization was performed as simultaneous integrated boost in 33 fractions, aiming for 59.4 Gy minimum dose to the PTV and 71.0 Gy minimum dose and 74.2 Gy maximum dose to the CTV. The OED was computed for the urinary bladder and the rectum from dose volume histograms for the linear-exponential and the plateau dose-response model. The EAR can be derived from the OED, taking age modifying parameters into account. The statistical analysis was performed using the Wilcoxon test in IBM® SPSS® Statistics 23 (IBM Corporation). Results: Within one technique (IMRT or VMAT) the average value of the OED is lower for the flattening filter free (FFF) mode compared to flat beams (FB) in both organs and for both dose-response models with one exception: In the urinary bladder it is the other way round for IMRT and the linear-exponential model. These results are statistically significant (level of significance 5%). The results for VMAT are statistically significant for the rectum only in both models. Comparing IMRT and VMAT the results are ambiguous: For the linear-exponential model the OED is lower with IMRT for both FB and FFF, for the plateau model lower OEDs are achieved with VMAT. All results are significant, except of one (lin-exp. model, FFF, urinary bladder, p = 7.4%). Conclusion: Some statistically significant differences have been found for the different treatment techniques and modes. However, they depend on the dose-response model. For the plateau model the lowest EAR is found for VMAT FFF in both organs at risk, for the linear-exponential model IMRT FB shows the minimum values. Plan quality and efficiency should additionally be regarded before the decision for a specific technique and mode

Simultaneous integrated boost therapy of carcinoma of the hypopharynx/larynx with and without flattening filter - a treatment planning and dosimetry study

Background: The aim of this study was to investigate if the flattening filter free (FFF) irradiation mode of a linear accelerator (linac) is advantageous as compared to the flat beam (FF) irradiation mode in intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) for carcinoma of the hypopharynx/larynx. Methods: Four treatment plans were created for each of 10 patients for an Elekta Synergy linac with Agility collimating device, a dual arc VMAT and a nine field step and shoot IMRT each with and without flattening filter. Plan quality was compared considering target coverage and dose to the organs at risk. All plans were verified by a 2D-ionization-chamber-array and delivery times were compared. Peripheral point doses were determined as a measure of second cancer risk. The Wilcoxon test was used for statistical analysis with a significance level of 0.05. Results: Plan quality was similar for all four treatment plans without statistically significant differences of clinical relevance. The clinical goals were met in all plans for the PTV-SIB (V-95% > 95%), the spinal cord (D1ccm < 45 Gy) and the brain stem (D-1ccm < 48 Gy). For the parotids, the goal of D-50% < 30 Gy was met in 70% and 60% of the plans for the left and right parotid respectively, and the V-95% of the SIB reached an average of 94%. Delivery times were similar for FF and FFF and significantly decreased by around 70% for VMAT as compared to IMRT. Peripheral doses were significantly reduced by 18% in FFF mode as compared to FF and by 26% for VMAT as compared to IMRT. Lowest peripheral doses were found for VMAT FFF, followed by VMAT FF. Conclusions: The FFF mode of a linear accelerator is advantageous for the treatment of hypopharynx/ larynx carcinoma only with respect to reduction of second cancer induction in peripheral organs for the combination of Elekta Synergy linacs and Oncentra (R) External Beam v4.5 treatment planning system. This might be of interest in a therapy with curative intent

Simultaneous integrated boost (SIB) radiation therapy of right sided breast cancer with and without flattening filter - A treatment planning study

Background: The aim of the study was to compare the two irradiation modes with (FF) and without flattening filter (FFF) for three different treatment techniques for simultaneous integrated boost radiation therapy of patients with right sided breast cancer. Methods: An Elekta Synergy linac with Agility collimating device is used to simulate the treatment of 10 patients. Six plans were generated in Monaco 5.0 for each patient treating the whole breast and a simultaneous integrated boost (SIB) volume: intensity modulated radiation therapy (IMRT), volumetric modulated arc therapy (VMAT) and a tangential arc VMAT (tVMAT), each with and without flattening filter. Plan quality was assessed considering target coverage, sparing of the contralateral breast, the lungs, the heart and the normal tissue. All plans were verified by a 2D-ionisation-chamber-array and delivery times were measured and compared. The Wilcoxon test was used for statistical analysis with a significance level of 0.05. Results: Significantly best target coverage and homogeneity was achieved using VMAT FFF with V95% = (98.7 +/- 0.8) % and HI = (8.2 +/- 0.9) % for the SIB and V95% = (98.3 +/- 0.7) % for the PTV, whereas tVMAT showed significantly lowest doses to the contralateral organs at risk with a D-mean of (0.7 +/- 0.1) Gy for the contralateral lung, (1.0 +/- 0.2) Gy for the contralateral breast and (1.4 +/- 0.2) Gy for the heart. All plans passed the gamma evaluation with a mean passing rate of (99.2 +/- 0.8) %. Delivery times were significantly reduced for VMAT and tVMAT but increased for IMRT, when FFF was used. Lowest delivery times were observed for tVMAT FFF with (1:20 +/- 0:07) min. Conclusion: Balancing target coverage, OAR sparing and delivery time, VMAT FFF and tVMAT FFF are considered the preferable of the investigated treatment options in simultaneous integrated boost irradiation of right sided breast cancer for the combination of an Elekta Synergy linac with Agility and the treatment planning system Monaco 5.0

Second cancer risk after radiation therapy of ependymoma using the flattening filter free irradiation mode of a linear accelerator

Pediatric patients suffering from ependymoma are usually treated with cranial or craniospinal three-dimensional (3D) conformal radiotherapy (3DCRT). Intensity-modulated techniques spare dose to the surrounding tissue, but the risk for second malignancies may be increased due to the increase in low-dose volume. The aim of this study is to investigate if the flattening filter free (FFF) mode allows reducing the risk for second malignancies compared to the mode with flattening filter (FF) for intensity-modulated techniques and to 3DCRT. A reduction of the risk would be advantageous for treating pediatric ependymoma. 3DCRT was compared to intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) with and without flattening filter. Dose volume histograms (DVHs) were compared to evaluate the plan quality and used to calculate the excess absolute risk (EAR) to develop second cancer in the brain. Dose verification was performed with a two-dimensional (2D) ionization chamber array and the out-of-field dose was measured with an ionization chamber to determine the EAR in peripheral organs. Delivery times were measured. Both VMAT and IMRT achieved similar plan quality in terms of dose sparing in the OAR and higher PTV coverage as compared to 3DCRT. Peripheral dose in low-dose region, which is proportional to the EAR in organs located in this region, for example, gonads, bladder, or bowel, could be significantly reduced using FFF. The lowest peripheral EAR and lowest delivery times were hereby achieved with VMAT(FFF). The EAR calculated based on DVH in the brain could not be reduced using FFF mode. VMAT(FFF) improved the target coverage and homogeneity and kept the dose in the OAR similar compared to 3DCRT. In addition, delivery times were significantly reduced using VMAT(FFF). Therefore, for radiotherapy of ependymoma patients, VMAT(FFF) may be considered advantageous for the combination of Elekta Synergy linac and Oncentra External Beam planning system used in this study

[P278] The use of flattening filter free irradiation mode in normo-fractionated treatments

Purpose The aim of this study was to identify general advantages and disadvantages of the flattening filter free irradiation mode in normo-fractionated intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT). Methods Various studies have been performed at our department to identify specific advantages and disadvantages of the use of the flattening filter free irradiation mode for the normo-fractionated treatment of different tumor sites. Volumetric modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT) plans were created with and without flattening filter for at least 10 patients for each tumor site. All treatment plans were verified by a 2D-ionization-chamber-array and delivery times were measured from first beam on to last beam off. Peripheral doses were determined with an ionization chamber as a measure of radiation induced second cancer risk. Differences were evaluated in terms of plan quality, irradiation time, and radiation induced second cancer risk. The results of these studies were reviewed to assess general advantages or disadvantages independent on the specific tumor entity or treatment technique. Results Differences in plan quality and irradiation time were dependent on the tumor entity and treatment technique. The peripheral dose as a measure of radiation induced second cancer risk, however, was significantly reduced in the flattening filter free mode for all tumor sites and treatment techniques. The reduction ranged from 17% to 33%. Conclusion The only general advantage of the flattening filter free irradiation mode observed for all tumor sites and treatment techniques was a reduction in dose to peripheral organs corresponding to a reduction in radiation induced second cancer risk in these organs. No general advantage or disadvantage could be observed in terms of plan quality or treatment time