Rapid Arc Research Articles

THE ACCURACY OF BRAIN METASTASES CONTOURING FOR STEREOTACTIC RADIOSURGERY (SRS) BY NEURO-ONCOLOGISTS; WHAT DO THE NEURO-RADIOLOGIST AND NEURO-SURGEON ADD?

Variability exists between clinical oncologists when contouring gross tumour volume (GTV) and normal tissue organs at risk (OAR) volumes. This variability is the ‘weakest link’ in the context of the highly conformal and highly accurate treatment delivery used for SRS. In 2016-17NHS England commissioned 17 SRS centres. The service specification mandates “treatment protocols will ensure that target definition is performed by either a sub-specialised neuro-surgeon and / or neuro-oncologist (clinical oncologist) with input from a neuro-radiologist before a treatment plan is created.”. To evaluate the additional contribution by the neuro radiologist we analysed contouring conformality for all 47 patients treated in our centre between June 2017 and February 2018. GTV margins were contoured first by the clinical oncologist, and then copied and amended with input from the neuroradiologist and sometimes neurosurgeon. 1 mm margin was added to the GTV for the planning target volume (PTV). 47 patients, each with 1–4 metastases/resection cavities, resulted in treatment plans for 67 metastases/cavities. Doses used were: 15-24Gy in 1 fraction, 24Gy in 3 fractions or 25-30Gy in 5 fractions (if close to critical optic structures or brainstem). We used Eclipse TPS (v13.7) for Varian (Palo Alto, CA) Clinac iX with millennium MLC (5 mm) and Exactrac imaging system (Brainlab, Munich DE). All plans were created either using dynamic conformal arc (DCA) or VMAT RapidArc (RA) techniques with 6 MV photons and calculated using AAA (v10) on a 1 mm dose grid. Values for the final treated GTV and PTV (A) were compared with the GTV and PTV that were generated by the Clinical oncologist alone (B) will be compared using the Conformity analysis consisted of Jaccard coefficient, Dice coefficient, Geographical Miss and Discordance index as defined below. Results will be presented.

P236] Rapid Arc versus a new sectorial sliding window IMRT template in radiotherapy brain treatments: Lens sparing

The ICRP Publication 118 introduced new threshold doses for tissue reactions and other non cancer effects on lens:the new threshold doses resulted significantly lower than previous scientific evidences. Lenses are often involved in brain radiotherapy treatment volumes and the risk of cataratta becomes relevant. Our study compares the results obtained from treatment plans calculated with both Rapid Arc technique and a new SSW IMRT template, for each patient recruited in the study, in terms of lens maximum absorbed doses. 10 patients with brain tumours diagnosis (PTV medium size af about 90 cc) localized in different areas were treated with the new SSW IMRT template, that consists in five fields spreading over a The dose prescription for all patients was 60 Gy in 2 Gy daily fractions. On the same patients, Rapid Arc plans were conformed with equal optimization objectives. The target coverage was at least 97% of prescription dose to 95 % of volume in both calculated plans. All the patiens treated with the SSW IMRT technique received a lower maximum omolateral lens dose (range from 0.4 to 2.4 Gy; mean value 1.7 Gy) compared to doses obtained with Rapid Arc plans (range from 0.5 to 4.4 Gy; mean value 2.4 Gy). Relatively to contralateral dose lens, we obtained a mean value of max dose of 1.5 Gy (range 0.4–2.2 Gy) for SSW IMRT plans and 2.2 Gy (range 0.5–4.6 Gy) for Rapid Arc plans. Patients treated with the new SSW IMRT template showed a lens dose sparing of about the 28% compared to doses they would have received with Rapid Arc plans.The other OAR involved as chiasm, optical nerve and brainstem are widely lower than the corresponding constraints. The new SSW IMRT template could be applied to treat target with different size, shape and anatomical position. Furthermore, the lens maximum dose reduction could potentially reduce the risk of cataract.

P171] Quality control measurements for head and neck cancer patients with SHANE Phantom

Purpose To investigate irradiation techniques for simultaneous integrated boost (SIB) treatment of nasopharyngeal cancer (NPC) case in terms of organs at risk (OAR) toxicity and patient specific quality control (QC). This study is a part of an end-to-end audit programme for dose delivery using intensity modulated radiation therapy (IMRT). Methods CIRS SHANE Phantom was used to create four different treatment plans for a NPC patient. SIB schedule prescribes 54 Gy, 60 Gy and 70 Gy in 30 fractions for elective nodes (both sides), involved nodes (right side) and primary nasopharynx respectively, using 1, 2 or 3 arcs RapidArc (RA) or 7 field Sliding Window (SW) techniques. Patient specific quality control measurements were performed using EPID. Varian Portal Dosimetry was used with local gamma analysis using 2%/2 mm and 3%/3 mm criteria with 10% threshold. Results All plans met the criteria of dose to OARs: D2% of the spinal cord and the brainstem on average were 35 Gy and 35.5 Gy; mean dose of the left parotid on average was 22.9 Gy. Patient specific QC was performed without any interruption. MUs for 1, 2, 3 arcs and 7 field SW were 602, 706, 696 and 2447, respectively. Gamma analysis on EPID images gave 96.2%, 96.2%, 96.7%, 82.6% and 98,8%, 98.9%, 99.3%, 92,1% passing rate on average for 2%/ 2 mm and 3%/ 3 mm criteria, respectively. Conclusions All treatment techniques are suitable for NPC irradiation with SIB in terms of OAR toxicity although RA with 2 or 3 arcs are more preferable in terms of number of MUs.

Comparison Of Risk Organ Distribution With Target Volume Size Variations Using Rapid ARC And IMRT Techniques For Case Of Lung Cancer

This study aims to know how big the difference between dose distribution Rapid Arc and IMRT technique and gains on PTV dose 95%. This research is a descriptive qualitative research data obtained from Phantom to take three the size of the volume of the tumor is seen from the organs at risk of Medulla spinalis, heart, healthy and the lung from the results of the data processing and then analyzed the distribution of the received dose organs at risk. Data analysis is done using the Software eclipse. The result show received dose between flashes IMRT technique and Rapid arc technique on the size of the volume of cancer 250 cm3, 500 cm3, 750 cm3 on the part of the heart and the lungs, Rapid arc provides better radiation dose compared with IMRT but only the medulla spinalis get higher doses but still below the maximum dose organ and gains received on PTV dose 95% with the technique of Rapid Arc higher than IMRT technique.

A Dosimetric Comparison between RapidArc and Conventional 3D Conformal Radiotherapy in Post-Operative Irradiation of Low Grade Gliomas: Any Added Benefit?

AbstractBackground: Low-Grade Gliomas (LGG) comprise a rare group of central nervous system tumors and clinically chal-lenging cases to manage. They account for approximately 15% of all primary brain neoplasms. Radiotherapy (RT) remains an important component in the treatment of low grade gliomas and Three-Dimensional Conformal RT (3DCRT) is the current state of art for RT delivery. The main gain of modern RT technology is more likely reducing treatment related toxicity rather than an improvement in overall survival. RapidArc (RA) technology (Varian Medical Systems, Palo Alto, CA) is a novel radiation therapy technique integrating 3 important factors for treatment delivery.Aim of the Study: The aim of the study is to investigate the potential dosimetric benefit of RapidArc (RA) in compar-ison to conventional 3D-CRT for low grade gliomas of the brain regarding target coverage and doses received by organs at risk (OAR).Material and Methods: Twenty patients diagnosed with low grade glioma (WHO grade I-II) were referred to our center for postoperative irradiation using 3D-CRT. The pre-scribed dose was 54 Gy/30F/6weeks. CT scans of the 20 patients was done and delineation of the target volumes and organs at risk was performed. Two set of plans were done for each patient, one using conventional 3D-CRT and other using a RA plan. Dosimetric parameters regarding target coverage and dose received by OAR were evaluated and compared. Monitor units was also calculated.Results: Target coverage in terms of V95% was signifi-cantly better in the RA plans with a value of 98.0±1.9 versus 96.0±2.6 for the 3D-CRT plans (p-value of 0.006). The RA plans gave a better conformity with a CI95% of 1.01±0.012 compared to1.07±0.024 achieved with the 3D-CRT plans (p-value of 0.678). The Homogeneity Index (HI) was higher for the 3D-CRT plans with a value of 0.131±0.112 compared to 0.097±0.033 for the RA plans (p-value of 0.114). The OAR received less dose in RA than 3D-CRT except for both lenses which received higher doses in the RA plans with a significant p-value of 0.002 and 0.001 for the right and left lens, respec-tively. The maximum dose and D1% for the healthy brain tissue was significantly lower in the RA plans when compared to 3D-CRT (p-value of 0.001). With respect to the average MUs ±SD needed per fraction, it was found to be 257.6±16.1 for the 3D-CRT plans as opposed to 355.6±44.4 RA plans (p-value of 0.001).Conclusion: RA plans dosimetrically achieved a better PTV coverage, dose conformity, more homogenous dose distribution and better OAR sparing when compared to con-ventional 3D-CRT plans except for both lenses. The 3D-CRT plans utilized a lower number of MUs than RA.

Really Rapid Rapid Arc using FFF for SABR Treatments and its Effect on Post-treatment Shifts

Really Rapid Rapid Arc using FFF for SABR Treatments and its Effect on Post-treatment Shifts

The Root-Ely Modified Test of Rectus Femoris Spasticity Has Reliability in Individuals with Cerebral Palsy.

Stiff-knee gait is a common gaitdeviation in individuals with cerebral palsy (CP) due to rectus femoris (RF) muscle spasticity. The Duncan-Ely test is a velocity-dependent measurement of spasticity that is recorded as positive or negative. At our institution, we use a modification of the Duncan-Ely test, a 5-point ordinal rating scale, which delineates where the catch occurs within the rapid arc of knee flexion. It has been named the Root-Ely test. We sought to determine the intra- and inter-rater reliability of the Duncan-Ely and Root-Ely tests in pediatric patients with CP. A convenience sample of 20 ambulatory subjects was recruited; mean age was 10.5 ± 4.5years, and the Gross Motor Function Classification System (GMFCS) levels were I-III. Five clinicians measured each individual's RF spasticity using the Root-Ely protocol during a single visit. Simple κ statistics with 95% confidence intervals (CI) were utilized for intra-rater reliability and weighted κ statistics with 95% CI for inter-rater reliability. The Root-Ely scale intra-rater reliability was 0.77 to 0.90 and inter-rater reliability was 0.32 to 0.87. Inter-rater reliability was good to excellent among experienced clinicians and fair to moderate in new clinicians. The Root-Ely 5-point scale has acceptable intra- and inter-rater reliability in pediatric individuals with CP among experienced clinicians. The Root-Ely test allows experienced clinicians to reliably quantify severity of RF spasticity and may give orthopaedic surgeons a clinical tool to betterpredict ideal candidates for RF transfers in individuals with CP in order to improve stiff-knee gait.

Craniospinal irradiation by rapid Arc® technique in supine position: A dosimetric and clinical analysis

Introduction: In craniospinal irradiation (CSI), prone position has been commonly used but, in some patients, especially pediatric cases where anesthesia is needed prone position may not help. In planning CSI by supine technique, beam geometry and field matching have to be considered, and immobilization is essential to ensure reproducibility of treatment. Materials and Methods: Data of four patients (3 with medulloblastoma and 1 with lymphoma) treated between March 2012 and October 2013 were included in this retrospective dosimetric study and analyzed. Patients were evaluated for dose coverage, organs at risks (OARs) sparing, number of monitor units, and daily table position shifts. Results: All patients underwent CSI by volumetric-modulated arc therapy (VMAT) technique in supine position. All four cases developed Grade 1 skin changes, and only one case developed a Grade 2 change at the end of radiotherapy; also both pediatric cases developed Grades 2 and 3 anemia and leukopenia toward their 4th week of treatment onward. The Rapid Arc®-CSI plans were able to generate dose distributions with high planning target volume (PTV) conformity and homogeneity and with sparing of OAR. The cumulative conformity index for all patients was 0.986, and homogeneity index was 0.1007. The mean PTV doses were within 108% with V110% of

RapidArc vs Conventional IMRT for Head and Neck Cancer Irradiation: Is Faster Necessary Better?

Purpose:The aim of this study was to dosimetrically evaluate and compare double arc RapidArc (RA) with conventional IMRT (7 fields) plans for irradiation of locally advanced head and neck cancers (LAHNC), focusing on target coverage and doses received by organs at risk (OAR).Methods:Computed tomography scans of 20 patients with LAHNC were obtained. Contouring of the target volumes and OAR was done. Two plans were made for each patient, one using IMRT and the other double arc RA, and calculated doses to planning target volume (PTV) and OAR were compared. Monitor units for each technique were also calculated.Results:PTV coverage was similar with both techniques. The homogeneity index (HI) was higher for the IMRT plans with a value of 0.108 ± 0.021 compared to 0.0975 ± 0.017 for double arc RA plans (p-value of 0.540). The double arc RA plans achieved a better conformity with a CI95%= 1.01 ± 0.021 compared to 1.05 ± 0.057 achieved with the IMRT plans (p-value of 0.036). The average monitor units (MU) ±SD were 930.5 ± 142.42 for the IMRT plans as opposed to 484.25 ± 69.47 for the double arc RA plans (P-value of 0.002). Double arc plans provided better OAR sparing with a significant p-value of 0.002 and 0.004 for the right and left parotid glands, respectively.Conclusions:RA is a rapid and accurate technique that uses lower MUs than conventional IMRT. Double arc plans provide better dose conformity, OAR sparing and a more homogeneous target coverage compared to IMRT.

Dosimetric evaluation of modern radiation therapy techniques for left breast in deep-inspiration breath-hold

PurposeThe dosimetric differences between four radiation therapy techniques for left sided whole breast irradiation were evaluated side by side in the same patient population. MethodsRadiotherapy treatment plans were retrospectively created with Accuray TomoDirect (TD), Elekta Volumetric Modulated Arc Therapy (E-VMAT), Varian RapidArc (RA) and Field-in-field (FinF) technique for 20 patients, who had received left breast irradiation during deep-inspiration breath-hold. Dose characteristics of planning target volume and organs at risk were compared. ResultsThe E-VMAT, TD and RA treatment plans had higher target coverage (V95%) than FinF plans (97.7–98.3% vs. 96.6%). The low-dose spillage to contralateral breast and lung was smaller with FinF and TD (mean 0.1 and 0.3 Gy) compared to E-VMAT and RA (mean 0.6 and 0.9 Gy). E-VMAT, RA and TD techniques were more effective than FinF in sparing left anterior descending artery (mean 4.0, 4.2 and 4.7 Gy vs. 6.1 Gy, respectively). ConclusionsIn whole breast irradiation TD, E-VMAT and RA plans generated in this study achieved higher dose coverage and sparing of organs from the high dose in the vicinity of the PTV. The advantage of calculated FinF plans is the lowest dose on contralateral organs. The choice of the technique used should be weighted by each institution taking into account the dose characteristics of each technique and its fit with patient anatomy bearing in mind the increased workload of using modulated techniques and the increased beam on time.

29. Implementing stereotactic RapidArc treatments into clinical routine: From algorithm configuration to treatment validation

Introduction This work aims to aid the medical physicist with the safe implementation of RapidArc (RA) (Varian Medical Systems, Palo Alto, CA) stereotactic radiotherapy treatments (SRS/SBRT) into clinical routine, from treatment planning system (TPS) configuration to patient plan verification. Implementation procedures are applicable to different Varian linear accelerators, either equipped with a standard Millennium 120MLC or a high-definition HDMLC, but always with on-board imaging. Methods A systematic approach was used to assure proper control of the different aspects of the implementation. First, an extensive series of detectors (all from PTW, Freiburg, Germany) – from numerous point dose detectors to the 1000SRS/Octavius4D 3D dose measurement system - were carefully benchmarked to assess their dosimetric characteristics, their precision and their practical usefulness. This benchmarking was performed independently of the TPS. Second, the necessary measurements were performed to include small field data in the Analytical Anisotropoic Algorithm (AAA) and Acuros (AXB) algorithm configuration. Third, validation of the Eclipse small field dose calculation was performed for both algorithms, starting off with static gantry (small) MLC fields and ending with RA SRS/SBRT test plans. Finally, pre-treatment QA procedures were implemented, executed and analyzed on all patient treatments. Results While one can do a substantial part of the basic validation with a single, high resolution, directionally independent point dose detector, a water phantom and a small solid water phantom to hold this detector, a point dose measurement is insufficient to assess the geometric precision of the dose-fall off during arc delivery. Given the safety requirements for stereotactic treatments, it is therefore highly recommended to invest in a detector system that can provide 2D and 3D dose information as well. The 1000SRS was found to provide very reliable planar dose measurements and, in combination with the Octavius4D system, measurement-based 3D dose reconstructions. It is also the most efficient method, especially when multiple lesions are concerned. From the battery of validation measurements, it was found that, although the algorithm configuration as well as the MLC modeling within the Eclipse TPS could benefit from further improvements, the currently obtained results are within clinical acceptance for the specific requirements of stereotactic treatment plans. Conclusions Target localization remains the key aspect of successful stereotactic radiotherapy and should be carefully addressed according to the treatment site. However, from a dosimetric point of view, when the appropriate measurement equipment is available, safe implementation of stereotactic RA treatments should be within reach of all radiotherapy departments outfitted with an up to date Clinac (or TrueBeam) and state-of-the-art on-board imaging.

AAA and AXB algorithms for the treatment of nasopharyngeal carcinoma using IMRT and RapidArc techniques

The aim of this study is to evaluate the impact of anisotropic analytical algorithm (AAA) and 2 reporting systems (AXB-Dm and AXB-Dw) of Acuros XB algorithm (AXB) on clinical plans of nasopharyngeal patients using intensity-modulated radiotherapy (IMRT) and RapidArc (RA) techniques. Six plans of different algorithm-technique combinations are performed for 10 patients to calculate dose-volume histogram (DVH) physical parameters for planning target volumes (PTVs) and organs at risk (OARs). The number of monitor units (MUs) and calculation time are also determined. Good coverage is reported for all algorithm-technique combination plans without exceeding the tolerance for OARs. Regardless of the algorithm, RA plans persistently reported higher D2% values for PTV-70. All IMRT plans reported higher number of MUs (especially with AXB) than did RA plans. AAA-IMRT produced the minimum calculation time of all plans. Major differences between the investigated algorithm-technique combinations are reported only for the number of MUs and calculation time parameters. In terms of these 2 parameters, it is recommended to employ AXB in calculating RA plans and AAA in calculating IMRT plans to achieve minimum calculation times at reduced number of MUs.

Coupled magmatism–erosion in continental arcs: Reconstructing the history of the Cretaceous Peninsular Ranges batholith, southern California through detrital hornblende barometry in forearc sediments

Continental magmatic arcs are characterized by voluminous flare-ups accompanied by rapid arc unroofing and sedimentation in the forearc basin. Such magmatism and erosion may be dynamically linked and influence the long-term evolution of crustal thickness. To evaluate these effects, we conducted a case study in the Peninsular Ranges batholith (PRB) in southern California, where mid-Late Cretaceous (125–75 Ma) emplacement of felsic plutons coincided with a major pulse of arc-derived sediments into the adjacent forearc basin. We compiled zircon U–Pb ages in the PRB plutons and estimated magmatic addition rates from exposed areas of plutons with different ages. To obtain erosion rates, sandstone samples of known depositional age from the PRB forearc basin were investigated. Major element compositions of detrital hornblendes were determined by electron probe microanalysis and used to calculate emplacement depths of eroded plutons using Al-in-hornblende barometry. These results were combined with laser ablation ICPMS based U–Pb ages of accompanying detrital zircons to estimate the integrated erosion rate by dividing the detrital hornblende emplacement depth by the lag time between peak detrital zircon age and depositional age. Both magmatic addition and erosion rates are between 0.1–2 km/Myr. Magmatic addition peaked at 100–90 Ma, followed by a long, protracted period of erosion between 90–50 Ma. Mass balance and isostatic modeling suggests that due to high magmatic influx, more than 30 km integrated crustal growth and 5 km elevation increase was achieved shortly after peak magmatism. The data and models suggest that erosion was driven by magma-induced crustal thickening and subsequent surface uplift, with an erosional response time of 3–6 Myr. Prolonged erosion after the cessation of magmatism resulted in gradual smoothing of the topography and significant removal of the excess crustal thickness by late Eocene time. The short erosional response times inferred from this study suggest that erosion and magmatism are intimately linked, begging the question of whether the thermal state, metamorphism and rheology of crust in continental arcs is controlled in part by the interplay between erosion and magmatism. We speculate that syn-magmatic erosion, through its effects on the thermal structure of the crust, may also play a role in modulating the depth of pluton emplacement.

Comparison of Rapid Arc and Intensity-modulated Radiotherapy Plans Using Unified Dosimetry Index and the Impact of Conformity Index on Unified Dosimetry Index Evaluation.

The aim of this study was to evaluate the impact of conformity index in the unified dosimetry index (UDI) score for two different planning techniques namely intensity-modulated radiotherapy (IMRT) and Rapid Arc. Rapid Arc and IMRT plans of 57 patients were evaluated and compared using UDI score which incorporates four indices. To determine the impact of conformity index on the IMRT and Rapid Arc plans, UDI at conformity index one of all plan (UDIunit_CI) score was calculated by assuming conformity index is equal to one. Mean and standard deviations of all indices were calculated. Rapid Arc technique plans of different treatment sites of all patients scored lesser UDI than IMRT plans, and the conformity index of Rapid Arc plan was significantly better than IMRT plan. The average dose gradient, homogeneity, coverage, and conformity index of all sites with Rapid Arc plans were 0.212 ± 0.05, 1.123 ± 0.03, 0.959 ± 0.03, and 1.056 ± 0.09; with IMRT plans were 0.190 ± 0.05, 1.113 ± 0.04, 0.950 ± 0.04, and 1.172 ± 0.16, respectively. UDI score value with actual conformity index of Rapid Arc and IMRT plans differed significantly (P < 0.001). However, UDIunit_CI score values with assumed conformity index equal to one did not differ significantly (P = 0.528). In the comparison of IMRT and Rapid Arc plans using the UDI score, the impact of conformity index was significant.

Treatment Planning With Unflattened as Compared to Flattened Beams for Bilateral Carcinoma of the Breast

Aim:To evaluate the plan quality of 6MV unflattened (UFB) and flattened beam (FB) photon energy using AAA dose calculation algorithms for volumetric arc therapy.Materials and Methods:Plans were generated for bilateral carcinoma of breast and the dose prescribed was 50.4Gy in 28 fractions. Two different plans were made for each patient using 6MV FB and 6MV UFB. Dose calculations were performed on an AAA dose calculation algorithm. Plans were generated on Eclipse TPS and were capable of being delivered with a true beam STx linear accelerator. The homogeneity index (HI), conformity index (CI), normal tissue integral dose (NTID), and effect of low dose volume on normal tissue and monitor units (MU) were noted.Results:All the plans were clinically acceptable. The HI and CI of 6MV UF rapid arc (RA) plans were higher than with the 6MV FB plan (1.16±0.05 and 0.12±0.00 respectively). There was no appreciable difference observed in Organ at risk (OAR) doses. The mean NTID and low dose volume were significantly low with 6MV RA UFB as compared to FB. 6MV RA UFB required a 35% higher MU than with the 6MV RA plan (p<0.05).Conclusion:RA plans generated with UFB on Eclipse TPS achieved target volume coverage and preserved OAR’s essentially similar to 6MV RA FB plans. However RA plans generated in Varian Eclipse of UFB were superior with respect to mean NTID and low dose volumes in normal tissue.

Outcome of high grade gliomas–An institutional experience

Objective: In this study we evaluated the prognostic factors, dosimetry and survival outcome of high grade gliomas receiving radiotherapy with concurrent temozolomide and with or without adjuvant temozolomide. Materials and Methods: Eighty patients with high grade gliomas were treated with concurrent chemoradiation post operatively. 27 patients received 3D Conformal Radiotherapy, 25 received Intensity Modulated Radiotherapy and 28 were treated with Rapid arc. Temozolomide 75mg/m2/d seven days a week was given concurrently with radiation (60Gy in 30 fractions) followed by 6 cycles of adjuvant Temozolomide with a dose of 150mg/m2/d for 5 days in every 28 days. Primary end point was overall survival and secondary end point was effect of radiation technique on overall survival and dose to organs at risk. Results: All patients completed concurrent chemoradiation but only 52 patients completed 6 months course of adjuvant chemotherapy. Median age was 52.5 years; The prognostic factors important for overall survival are at least 6 cycles of adjuvant temozolomide (p

Radiotherapy of Prostate Cancer Using Rapid Arc: Dosimetric Study of Military Teaching Hospital Mohamed V, Morocco

Background: RapidArc®, the Varian solution of Volumetric-modulated arc therapy (VMAT) is currently used in the curative treatment of localized prostate cancer. The aim of this study was to evaluate the dosimetric parameters (effectiveness and efficiency) of the arc dynamic therapy at the Teaching Hospital Mohamed V. Materials and methods: Thirty two patients were treated with curative intent, between June 2013 and December 2014, for localized prostate cancer with RapidArc. Computed tomography (CT) based treatment planning was performed in the supine position with immobilization devices. The patients were instructed to have a comfortably full bladder and an empty rectum at CT acquisition and before each treatment. Delineation of target volume and organs at risk (OARs) was based on the consensus recommendations of the RTOG. The dose prescription was performed with simultaneous integrated boost (SIB) method. Data was collected from dose-volume histograms (DVH) either for planning target volumes (PTV2) or OARs. We calculated the homogeneity index (HI) and the conformity index (CI). We also reported acute and late toxicity related to radiation therapy. Results: The mean age was 66.63 ±7.24 years old. Of the 32 patients, 24(75%) defined as high-risk. All PTV received dose ranging from 95% to 107% of the prescribed dose. The homogeneity and conformity index was very close to 1 of all treatment plans. The dose limits were respected in all OARs as recommended in QUANTEC reviews 2010. Respectively, the analysis of the HDV in the rectum and the bladder found a V70 at 7.15 ± 5.63% and 16.88 ± 8.62% and a V60 at 16.32 ± 7.97% and 27.68 ± 10 32%. The V50 in the femoral heads was 0.39 ± 0.57% on the right and 0.71 ± 1.35% on the left. The V50, V40 and V30 in the bowel bag were 38.76 ± 39.73 cc, 155.38 ± 85,60 cc and 320.09 ± 180.41 cc, respectively. The mean MU was 555.94 ± 86.34 and delivery treatment time (min) was 1.99 ± 0.47. After three months of radiation therapy, no grade 3 or 4 toxicity was reported. The median control PSA was very low at 0,052 [0.012, 0.417] ng/ml. Conclusion: This present study demonstrated that RapidArc showed optimal PTV coverage and the best OARs sparing with less number of MUs and short treatment time. Acute GI and GU toxicities were very low. Further studies are needed to evaluate late toxicities and tumor control.

Dosimetric influence of filtered and flattening filter free photon beam on rapid arc (RA) radiotherapy planning in case of cervix carcinoma

AimTo investigate the dosimetric influence of filtered and flattening filter free (FFF) photon beam of 6 and 10MV energies on cervix RA radiotherapy planning and to find possibilities to develop the clinically acceptable RA plans with FFFB photon beam and explore their potential benefits to cervix cancer patients. BackgroundFFF photon beams enhances the treatment delivery by increased dose rate which results in shorter treatment time, this shorter treatment time reduces intrafraction motion and enhance comfort to the patients. Materials and methodsRA plans were generated for filtered and flattening filter free photon beams of 6 and 10MV energies using same dose–volumes constraints. RA plans were generated to deliver a dose of 50.4Gy in 28 fractions, for a cohort of eleven patients reported with cervix carcinoma. RA plans were evaluated in terms of PTV coverage, dose to OAR's, CI, HI, total no. of monitor units (MUs) and NTID and low dose volume of normal tissues. ResultsClinically acceptable and similar plans were generated for filtered and flattening filter free photon beams. FFFB delivered slightly higher mean target dose (52.28Gy vs. 52.0Gy, p=0.000 for 6MV and 52.42Gy vs. 52.0Gy, p=0.000 for 10MV) less homogeneous (1.062 vs. 1.052, p=0.000 for 6MV and 1.066 vs. 1.051, p=0.000 for 10MV) and less conformal (1.007 vs. 1.004, p=0.104 for 6MV and 1.012 vs. 1.003, p=0.010 for 10MV) RA plans compared to FB. FFFB delivered more doses to the bladder and rectum, also required more numbers of MUs in comparison to FB. ConclusionsThis study concludes that FB is more beneficial for cervix RA planning in comparison to FFFB, as FB generates more conformal and homogenous rapid arc plans and offers better OAR's sparing.

Dosimetric comparison of flattened and unflattened beams for stereotactic body radiation therapy: Impact of the size of the PTV on dynamic conformal arc and volumetric modulated arc therapy

PurposeFlattening filter free (FFF) beams are frequently used for stereotactic body radiation therapy with various treatment modalities: conventional static fields, dynamic conformal arc (DCA) or Rapid Arc (RA). The goal of this study was to obtain some criteria to enable a conscious choice of the employment of FFF beams and of the DCA or RA technique, depending on the PTV size. Methods and materials24 PTVs from 1.52cm3 to 445.24cm3 were studied in various sites: virtual phantom, lung and liver. For each PTV, DCA and RA plans were prepared using two flattened (FF) and two unflattened photon beams. Parameters such as conformity index, gradient index, healthy-tissue and organs at risk mean doses, number of monitor units (MU), beam on time (BOT) were used to quantify obtained dose distributions. Friedman tests and Spearman’s rank correlation coefficients were also performed. ResultsNo significant differences were found between FF and FFF beams for RA regarding conformity and gradient indices. For DCA, 10FFF is less suitable and forward planning becomes more challenging as PTV volume increases. FFF beams provided a better sparing of healthy-tissues except for 10FFF used with DCA. 6FFF was slightly better than 10FFF in terms of healthy-tissue mean doses. FFF beams generated significantly reduced BOTs and increased MUs. These effects were more pronounced for larger volumes and especially for RA plans. ConclusionsFFF showed better results than FF beams for the considered plans. 10FFF used with DCA should be used with caution for medium and large volumes.

Acute high-intensity noise induces rapid Arc protein expression but fails to rapidly change GAD expression in amygdala and hippocampus of rats: Effects of treatment with D-cycloserine

Tinnitus is a devastating auditory disorder impacting a growing number of people each year. The aims of the current experiment were to assess neuronal mechanisms involved in the initial plasticity after traumatic noise exposure that could contribute to the emergence of tinnitus and to test a potential pharmacological treatment to alter this early neural plasticity. Specifically, this study addressed rapid effects of acute noise trauma on amygdalo-hippocampal circuitry, characterizing biomarkers of both excitation and inhibition in these limbic regions, and compared them to expression of these same markers in primary auditory cortex shortly after acute noise trauma. To assess excitatory plasticity, activity-regulated cytoskeleton-associated (Arc) protein expression was evaluated in male rats 45 min after bilateral exposure to acute high-intensity noise (16 kHz, 115 dB SPL, for 1 h), sufficient to cause acute cochlear trauma, a common cause of tinnitus in humans and previously shown sufficient to induce tinnitus in rat models of this auditory neuropathology. Western blot analyses confirmed that up-regulation of amygdalo-hippocampal Arc expression occurred rapidly post-noise trauma, corroborating several lines of evidence from our own and other laboratories indicating that limbic brain structures, i.e. outside of the classical auditory pathways, exhibit plasticity early in the initiation of tinnitus. Western blot analyses revealed no noise-induced changes in amygdalo-hippocampal expression of glutamate decarboxylase (GAD), the biosynthetic enzyme required for GABAergic inhibition. No changes in either Arc or GAD protein expression were observed in primary auditory cortex in this immediate post-noise exposure period, confirming other reports that auditory cortical plasticity may not occur until later in the development of tinnitus. As a further control, our experiments compared Arc protein expression between groups exposed to the quiet background of a sound-proof chamber to those exposed not only to the traumatic noise described above, but also to an intermediate, non-traumatic noise level (70 dB SPL) for the same duration in each of these three brain regions. We found that non-traumatic noise did not up-regulate Arc protein expression in these brain regions. To see if changes in Arc expression due to acute traumatic noise exposure were stress-related, we compared circulating serum corticosterone in controls and rats exposed to traumatic noise at the time when changes in Arc were observed, and found no significant differences in this stress hormone in our experimental conditions. Finally, the ability of D-cycloserine (DCS; an NMDA-receptor NR1 partial agonist) to reduce or prevent the noise trauma-related plastic changes in the biomarker, Arc, was tested. D-cycloserine prevented traumatic noise-induced up-regulation of Arc protein expression in amygdala but not in hippocampus, suggesting that DCS alone is not fully effective in eliminating regionally-specific early plastic changes after traumatic noise exposure.