RapidArc Treatment Research Articles

Successful delivery of adjuvant external beam radiotherapy for ependymoma in a patient with Ondine׳s curse

Ondine׳s curse is a rare, potentially life-threatening disorder characterized by loss of automatic breathing during sleep and preserved voluntary breathing. It is seldom encountered in the radiotherapy clinic but can pose significant technical challenges and safety concerns in the delivery of a prescribed radiation course. We report a unique case of successful delivery of radiotherapy for ependymoma in a patient with Ondine׳s curse. A 53-year-old gentleman presented with vertigo when lying down. Brain magnetic resonance imaging revealed an enhancing mass in the floor of the fourth ventricle. He underwent maximal safe resection. Pathology revealed ependymoma. The patient was referred for radiotherapy. Computed tomography simulation was performed in supine position with 3-point thermoplastic mask immobilization. Sequential TomoTherapy plans were developed. At first scheduled treatment, shortly after mask placement, his arms went limp and he was unresponsive. Vitals showed oxygen saturation 83%, pulse 127, and blood pressure 172/97mmHg. He was diagnosed with Ondine׳s curse thought secondary to previous brainstem damage; the combination of lying flat and pressure from the mask was causing him to go into respiratory arrest. As supine positioning did not seem clinically advisable, he was simulated in prone position. A RapidArc plan and a back-up conformal plan were developed. Prescriptions were modified to meet conservative organs-at-risk constraints. Several strategies were used to minimize uncertainties in set-up reproducibility associated with prone positioning. He tolerated prone RapidArc treatments well. The report highlights the importance of applying practical patient safety and treatment planning/delivery strategies in the management of this challenging case.

Passive breath gating equipment for cone beam CT-guided RapidArc gastric cancer treatments

Background and purposeTo report preliminary results of passive breath gating (PBG) equipment for cone-beam CT image-guided gated RapidArc gastric cancer treatments. Material and methodsHome-developed PBG equipment integrated with the real-time position management system (RPM) for passive patient breath hold was used in CT simulation, online partial breath hold (PBH) CBCT acquisition, and breath-hold gating (BHG) RapidArc delivery. The treatment was discontinuously delivered with beam on during BH and beam off for free breathing (FB). Pretreatment verification PBH CBCT was obtained with the PBG-RPM system. Additionally, the reproducibility of the gating accuracy was evaluated. ResultsA total of 375 fractions of breath-hold gating RapidArc treatments were successfully delivered and 233 PBH CBCTs were available for analysis. The PBH CBCT images were acquired with 2–3 breath holds and 1–2 FB breaks. The imaging time was the same for PBH CBCT and conventional FB CBCT (60s). Compared to FB CBCT, the motion artifacts seen in PBH CBCT images were remarkably reduced. The average BHG RapidArc delivery time was 103s for one 270-degree arc and 269s for two full arcs. ConclusionsThe PBG-RPM based PBH CBCT verification and BHG RapidArc delivery was successfully implemented clinically. The BHG RapidArc treatment was accomplished using a conventional RapidArc machine with high delivery efficiency.

Effect of CT contrast on volumetric arc therapy planning (RapidArc and helical tomotherapy) for head and neck cancer

The objectives of the study were to evaluate the effect of intravenous contrast in the dosimetry of helical tomotherapy and RapidArc treatment for head and neck cancer and determine if it is acceptable during the computed tomography (CT) simulation to acquire only CT with contrast for treatment planning of head and neck cancer. Overall, 5 patients with head and neck cancer (4 men and 1 woman) treated on helical tomotherapy were analyzed retrospectively. For each patient, 2 consecutive CT scans were performed. The first CT set was scanned before the contrast injection and secondary study set was scanned 45 seconds after contrast. The 2 CTs were autoregistered using the same Digital Imaging and Communications in Medicine coordinates. Tomotherapy and RapidArc plans were generated on 1 CT data set and subsequently copied to the second CT set. Dose calculation was performed, and dose difference was analyzed to evaluate the influence of intravenous contrast media. The dose matrix used for comparison included mean, minimum and maximum doses of planning target volume (PTV), PTV dose coverage, and V45Gy, V30Gy, and V20Gy organ doses. Treatment planning on contrasted images generally showed a lower dose to both organs and target than plans on noncontrasted images. The doses for the points of interest placed in the organs and target rarely changed more than 2% in any patient. In conclusion, treatment planning using a contrasted image had insignificant effect on the dose to the organs and targets. In our opinion, only CT with contrast needs to be acquired during the CT simulation for head and neck cancer. Dose calculations performed on contrasted images can potentially underestimate the delivery dose slightly. However, the errors of planning on a contrasted image should not affect the result in clinically significant way.

Dosimetric study of RapidArc plans with flattened beam (FB) and flattening filter-free (FFF) beam for localized prostate cancer based on physical indices

Purpose: To identify the continual diversity between flattening photon beam (FB) and Flattening Filter Free (FFF) photon beams for localized prostate cancer; and to determine potential benefits and drawbacks of using unflattened beam for this type of treatment. Methods : Eight prostate cases including seminal vesicles selected for this study. The primary planning target volume (PTV P ) and boost planning target volume (PTV B ) were contoured. The total prescription dose was 78 Gy (56 Gy to PTV P and an additional 22 Gy to PTVB). For all cases, treatment plans using 6MV with FB and FFF beams with identical dose-volume constraints, arc angles and number of arcs were developed. The dose volume histograms for both techniques were compared for primary target volume and critical structures. Results: A low Sigma index (FFF: 1.65 + 0.361; FB: 1.725 + 0.39) indicating improved dose homogeneity in FFF beam. Conformity index (FFF: 0.994 + 0.01; FB: 0.993 + 0.01) is comparable for both techniques. Minimal difference of Organ at risk mean dose was observed. Normal tissue integral dose in FB plan resulted 1.5% lower than FFF plan. All the plans displayed significant increase (1.18 times for PTV P and 1.11 for PTB B ) in the average number of necessary MU with FFF beam. Conclusion : Diversity between FB and FFF beam plans were found. FFF beam accelerator has been utilized to develop clinically acceptable Rapid Arc treatment plans for prostate cancer with 6 MV. --------------------------------- Cite this article as : Rout BK, Muralidhar KR, Ali M, Shekar MC, Kumar A. Dosimetric study of RapidArc plans with flattened beam (FB) and flattening filter-free (FFF) beam for localized prostate cancer based on physical indices. Int J Cancer Ther Oncol 2014; 2 (4):02046. DOI : 10.14319/ijcto.0204.6

The Dosimetric Consequences of a Rotational Positioning Correction in IGRT Prostate RapidArc Treatment Using a 6DOF Robotic Couch

The Dosimetric Consequences of a Rotational Positioning Correction in IGRT Prostate RapidArc Treatment Using a 6DOF Robotic Couch

Poster — Thur Eve — 31: Dosimetric Effect of Respiratory Motion on RapidArc Lung SBRT Treatment Delivered by TrueBeam Linear Accelerator

Volumetric modulated arc therapy (VMAT) allows fast delivery of stereotactic radiotherapy. However, the discrepancies between the calculated and delivered dose distributions due to respiratory motion and dynamic multileaf collimators (MLCs) interplay are not avoidable. The purpose of this study is to investigate RapidArc lung SBRT treatment delivered by the flattening filter‐free (FFF) beam and flattened beam with Varian TrueBeam machine. CIRS Dynamic Thorax Phantom with in‐house made lung tumor insertion was CT scanned both in free breathing and 4DCT. 4DCT was used to determine the internal target volume. The free breathing CT scan was used for treatment planning. A 5 mm margin was given to ITV to generate a planning target volume. Varian Eclipse treatment planning was used to generate RapidArc plans based on the 6 MV flattened beam and 6MV FFF beam. The prescription dose was 48 Gy in 4 fractions. At least 95% of PTV was covered by the prescribed dose. The RapidArc plans with 6 MV flattened beam and 6MV FFF beam were delivered with Varian TrueBeam machine. The dosimetric measurements were performed with Gafchromic XR‐RV3 film, which was placed in the lung tumor insertion. The interplay between the dynamic MLC‐based delivery of VMAT and the respiratory motion of the tumor degraded target coverage and created undesired hot or cold dose spots inside the lung tumor. Lung SBRT RapidArc treatments delivered by the FFF beam of TrueBeam linear accelerator is superior to the flattened beam. Further investigation will be performed by Monte Carlo simulation.

Poster — Thur Eve — 33: The Influence of a Modeled Treatment Couch on Dose Distributions During IMRT and RapidArc Treatment Delivery

Treatment couches have been known to perturb dose delivery in patients. This effect is most pronounced in techniques such as IMRT and RapidArc. Although modern treatment planning systems (TPS) include data for a “default” treatment couch, actual couches are not manufactured identically. Thus, variations in their Hounsfield Unit (HU) values may exist. This study demonstrates a practical and simple method of acquiring reliable HU data for any treatment couch. We also investigate the effects of both the default and modeled treatment couches on absorbed dose. Experimental verifications show that by neglecting to incorporate the treatment couch in the TPS, dose differences of up to 9.5% and 7.3% were present for 4 MV and 10 MV photon beams, respectively. Furthermore, a clinical study based on a cohort of 20 RapidArc and IMRT (brain, pelvis and abdominal) cases is performed. 2D dose distributions show that without the couch in the planning phase, differences ≤ 4.6% and 5.9% for RapidArc and IMRT cases are present for the same cases that the default couch was added to. Additionally, in comparison to the default couch, employing the modeled couch in the calculation process influences dose distributions by ≤ 2.7% and 8% for RapidArc and IMRT cases, respectively. This result was found to be site specific; where an accurate couch proves to be preferable for IMRT brain plans. As such, adding the couch during dose calculation decreases dose calculation errors, and a precisely modeled treatment couch offers higher dose delivery accuracy for brain treatment using IMRT.

Poster — Thur Eve — 13: Inter‐Fraction Target Movement in Image‐Guided Radiation Therapy of Prostate Cancer

We investigated the setup variations over the treatment courses of 113 patients with intact prostate treated with 78Gy/39fx. Institutional standard bladder and bowel preparation and image guidance protocols were used in CT simulation and treatment. The RapidArc treatment plans were optimized in Varian Eclipse treatment planning system and delivered on Varian 2100X Clinacs equipped with On‐Board Imager to localize the target before beam‐on. The setup variations were calculated in terms of mean and standard deviation of couch shifts. No correlation was observed between the mean shift and standard deviation over the treatment course and patient age, initial prostate volume and rectum size. The mean shifts in the first and last 5 fractions are highly correlated (P < 10−10) while the correlation of the standard deviations cannot be determined. The Mann‐Kendall tests indicate trends of the mean daily Ant‐Post and Sup‐Inf shifts of the group. The target is inferior by ∼1mm to the planned position when the treatment starts and moves superiorly, approaching the planned position at 10th fraction, and then gradually moves back inferiorly by ∼1mm in the remain fractions. In the Ant‐Post direction, the prostate gradually moves posteriorly during the treatment course from a mean shift of ∼2.5mm in the first fraction to ∼1mm in the last fraction. It may be related to a systematic rectum size change in the progress of treatment. The biased mean shifts in Ant‐Post and Sup‐Inf direction of most patients suggest systematically larger rectum and smaller bladder during the treatment than at CT simulation.

SU-E-T-212: Influence of the Modulation Index On Daily Quality Assurance in Rapid Arc Treatments

Purpose: At our Institute some measured parameters for daily quality assurance (DQA) of dynamic arc therapy plans showed an unexpected behavior, therefore an investigation of the influence of the magnitude of modulation was conducted. Methods: In our clinical practice all DQAs of dynamic arc therapy plans are measured and analyzed prior to treatments using commercial software. For this study these plans were additionally exported to our in-house software written in MATLAB. The developed software extracted the leaf position, gantry angle, cumulative meterset weight of each control point (CP) and the total number of Monitor Units (MU) of each arc. Based on this information we calculated the leaf travel distance, irradiated segment area, number of MUs and dose rate for each CP. These data allowed us to calculate the modulation indexes (MI) of the plans, applying five different definitions of MI. The results were then correlated to the results of our DQA measurements. To validate the software, additional plans of known MIs were created and analyzed. For confirmation, the calculated parameters were compared to the segmented treatment table (STT) coming from the treatment planning system. Results: All calculated CP-parameters matched the STT by 99% or better. For linac 1, the comparison of the MI evaluation and the DQA results showed a slight tendency: 91.3% failed DQA plans had a MI lower than the average value. For this definition we consider that the lower the MI the higher the modulation. The results of the linac 2 present no significant relevance due to the low sample sizes for each DQA software. Conclusion: Available data and given definitions of the modulation index do not bring conclusive results; one cannot find a clear and distinct correlation with the failure of the DQA. The ongoing analysis with an increased sample size might lead to another conclusion.

SU‐E‐T‐505: CT‐Based Independent Dose Verification for RapidArc Plan as a Secondary Check

Purpose:To design and develop a CT‐based independent dose verification for the RapidArc plan and also to show the effectiveness of inhomogeneous correction in the secondary check for the plan.Methods:To compute the radiological path from the body surface to the reference point and equivalent field sizes from the multiple MLC aperture shapes in the RapidArc MLC sequences independently, DICOM files of CT image, structure and RapidArc plan were imported to our in‐house software. The radiological path was computed using a three‐dimensional CT arrays for each segment. The multiple MLC aperture shapes were used to compute tissue maximum ratio and phantom scatter factor using the Clarkson‐method. In this study, two RapidArc plans for oropharynx cancer were used to compare the doses in CT‐based calculation and water‐equivalent phantom calculation using the contoured body structure to the dose in a treatment planning system (TPS).Results:The comparison in the one plan shows good agreement in both of the calculation (within 1%). However, in the other case, the CT‐based calculation shows better agreement compared to the water‐equivalent phantom calculation (CT‐based: ‐2.8% vs. Water‐based: ‐3.8%). Because there were multiple structures along the multiple beam paths and the radiological path length in the CT‐based calculation and the path in the water‐homogenous phantom calculation were comparatively different.Conclusion:RapidArc treatments are performed in any sites (from head, chest, abdomen to pelvis), which includes inhomogeneous media. Therefore, a more reliable CT‐based calculation may be used as a secondary check for the independent verification.

Quasi real time in vivo dosimetry for VMAT.

Results about the feasibility of a method for quasi real time in vivo dosimetry (IVD) at the isocenter point for volumetric modulated arc therapy (VMAT) are here reported. The method is based on correlations between the EPID signal and the dose on the beam central axis. Moreover, the γ-analysis of EPID images was adopted to verify off-axis reproducibility of fractionated plan delivery. An algorithm to reconstruct in vivo the isocenter dose, D(iso), for RapidArc treatments has been developed. 20 VMAT plans, optimized with two opposite arcs, for prostate, pancreas, and head treatments have been delivered by a Varian linac both to a conic PMMA phantom with elliptical section and to patients. The ratios R between reconstructed D(iso) and the planned doses were determined for phantom and patient irradiations adopting an acceptance criterion of ±5%. In total, 40 phantom checks and 400 patient checks were analyzed. Moreover, 3% and 3 mm criteria were adopted for portal image γ-analysis to assess patient irradiation reproducibility. The average ratio R, between reconstructed and planned doses for the PMMA phantom irradiations was equal to 1.007 ± 0.024. When the IVD method was applied to the 20 patients, the average R ratio was equal to 1.003 ± 0.017 and 96% of the tests were within the acceptance criteria. The portal image γ-analysis supplied 88% of the tests within the pass rates γ(mean) ≤ 0.4 and P(γ<1) ≥ 98%. All the warnings were understood comparing the CT and the cone beam CT images and in one case a patient's setup error was detected and corrected for the successive fractions. This preliminary experience suggests that the method is able to detect dosimetric errors in quasi real time at the end of the therapy session. The authors intend to extend this procedure to other pathologies with the integration of in-room imaging verification by cone beam CT.

OC-0401: Validation of Gated RapidArc treatments delivery using the Electronic Portal Imaging Device

OC-0401: Validation of Gated RapidArc treatments delivery using the Electronic Portal Imaging Device

Evaluation of Acuros XB algorithm based on RTOG 0813 dosimetric criteria for SBRT lung treatment with RapidArc

The Radiation Therapy Oncology Group (RTOG) 0813 protocol requires the use of dose calculation algorithms with tissue heterogeneity corrections to compute dose on stereotactic body radiation therapy (SBRT) non‐small cell lung cancer (NSCLC) plans. A new photon dose calculation algorithm called Acuros XB (AXB) has recently been implemented in the Eclipse treatment planning system (TPS). The main purpose of this study was to compare the dosimetric results of AXB with that of anisotropic analytical algorithm (AAA) for RTOG 0813 parameters. Additionally, phantom study was done to evaluate the dose prediction accuracy of AXB and AAA beyond low‐density medium of different thicknesses by comparing the calculated results with the measurements. For the RTOG dosimetric study, 14 clinically approved SBRT NSCLC cases were included. The planning target volume (PTV) ranged from 3.2‐43.0 cc. RapidArc treatment plans were generated in the Eclipse TPS following RTOG 0813 dosimetric criteria, and treatment plans were calculated using AAA with heterogeneity correction (AAA plans). All the AAA plans were then recalculated using AXB with heterogeneity correction (AXB plans) for identical beam parameters and same number of monitor units. The AAA and AXB plans were compared for following RTOG 0813 parameters: ratio of prescription isodose volume to PTV (R100%), ratio of 50% prescription isodose volume to PTV (R50%), maximal dose 2 cm from the PTV in any direction as a percentage of prescription dose (D2cm), and the percentage of ipsilateral lung receiving dose equal to or larger than 20 Gy (V20). The phantom study showed that the results of AXB had better agreement with the measurements, and the difference ranged from −1.7% to 2.8%. The AAA results showed larger disagreement with the measurements, with differences from 4.1% to 12.5% for field size 5×5 cm2 and from 1.4% to 6.8% for field size 10×10 cm2. The results from the RTOG SBRT lung cases showed that, on average, the AXB plans produced lower values for R100%, R50%, and D2cm by 4.96%, 1.15%, and 1.60%, respectively, but higher V20 of ipsilateral lung by 1.09% when compared with AAA plans. In the set of AAA plans, minor deviation was seen for R100% (six cases), R50% (nine cases), D2cm (four cases), and V20 (one case). Similarly, the AXB plans also showed minor deviation for R100% (one case), R50% (eight cases), D2cm (three cases), and V20 (one case). The dosimetric results presented in the current study show that both the AXB and AAA can meet the RTOG 0813 dosimetric criteria.PACS number: 87.55.D‐, 87.55.dk, 87.55.kd, 87.55.km

Sensitivity of volumetric modulated arc therapy patient specific QA results to multileaf collimator errors and correlation to dose volume histogram based metrics

This study investigates the impact of systematic multileaf collimator (MLC) positional errors on gamma analysis results used for quality assurance (QA) of Rapidarc treatments. In addition, this study evaluates the relationship of these gamma analysis results and clinical dose volume histogram metrics (DVH) for Rapidarc treatment plans. Five prostate plans were modified by the introduction of systematic MLC errors. The MLC shifts to each individual active leaf introduced were 0.25, 0.5, 0.75, and 1 mm. All QA verification plans were delivered and estimated 3D patient dose or high density phantom dose were obtained based on the ArcCHECK measurement files. QA gamma analysis of 3%/3 mm and 2%/2 mm were implemented and relationships to dose differences in DVH metrics encountered due to MLC errors were determined. Tolerances of 3% and 5% for DVH metric were implemented to determine the sensitivity of gamma analysis to MLC errors. A calculation of sensitivity was determined from the number of incidences of false negative and false positive cases in gamma analysis results. The sensitivity of global gamma analysis for criteria of 3%/3 mm was 0.78 and for 2%/2 mm was 0.82. A number of instances occurred for an acceptable VMAT QA gamma index which did not indicate a DVH metric dose error greater than 5%. The correlation between global gamma analysis using criteria 3%/3 mm and DVH metric dose error were all <0.8 indicating less than a strong correlation. There is a greater sensitivity for detection of dosimetric errors occurring in a Rapidarc plan using gamma criteria of 2%/2 mm than 3%/3 mm. However, there is lack of consistently strong correlation between global gamma indexes and clinical DVH metrics for PTV and bladder and rectum for Rapidarc plans. It is recommended that the sole use of gamma index for Rapidarc QA plan evaluation could be insufficient and a methodology for evaluation of delivered dose to patient is required.

Dosimetric analysis of patient setup and mechanical uncertainties in RapidArc prostate treatments

Over the course of a full radiotherapy treatment, patient setup errors result in differences between the calculated, optimised dose distribution and the delivered distribution. In addition, there are mechanical tolerances associated with the linac components, treatment table, and positioning lasers together with allowed dosimetric variations in the radiation beams over the timeframe of weeks in which a treatment course is completed. The aim of this study is to investigate the geometric and dosimetric variations that result from such uncertainties and which will have an impact on the dose distribution to the target volume and organs at risk. To do this, the Rando anthropomorphic phantom was treated as a standard prostate patient undergoing a course of radiotherapy. A full RapidArc treatment was designed for a typical structure set delineated on a CT scan of the phantom. EBT3 gafchromic film was placed between two axial slices of Rando for each fraction, which was then placed in the treatment position and irradiated. The dose actually delivered to the film could then be evaluated for that fraction and compared to the optimised distribution that was originally prescribed. From this, the institutional baseline uncertainty in the distribution due to patient setup, mechanical, and dosimetric uncertainties for each individual fraction over the course of a patient's treatment could be determined as well as the cumulative impact that these variations can have on the dose distribution actually delivered to the patient. This will aid in defining appropriate treatment margins.

Octavius 4D characterization for flattened and flattening filter free rotational deliveries

In this study the Octavius detector 729 ionization chamber (IC) array with the Octavius 4D phantom was characterized for flattening filter (FF) and flattening filter free (FFF) static and rotational beams. The device was assessed for verification with FF and FFF RapidArc treatment plans. The response of the detectors to field size, dose linearity, and dose rate were assessed for 6 MV FF beams and also 6 and 10 MV FFF beams. Dosimetric and mechanical accuracy of the detector array within the Octavius 4D rotational phantom was evaluated against measurements made using semiflex and pinpoint ionization chambers, and radiochromic film. Verification FF and FFF RapidArc plans were assessed using a gamma function with 3%∕3 mm tolerances and 2%∕2 mm tolerances and further analysis of these plans was undertaken using film and a second detector array with higher spatial resolution. A warm-up dose of >6 Gy was required for detector stability. Dose-rate measurements were stable across a range from 0.26 to 15 Gy∕min and dose response was linear, although the device overestimated small doses compared with pinpoint ionization chamber measurements. Output factors agreed with ionization chamber measurements to within 0.6% for square fields of side between 3 and 25 cm and within 1.2% for 2 × 2 cm(2) fields. The Octavius 4D phantom was found to be consistent with measurements made with radiochromic film, where the gantry angle was found to be within 0.4° of that expected during rotational deliveries. RapidArc FF and FFF beams were found to have an accuracy of >97.9% and >90% of pixels passing 3%∕3 mm and 2%∕2 mm, respectively. Detector spatial resolution was observed to be a factor in determining the accurate delivery of each plan, particularly at steep dose gradients. This was confirmed using data from a second detector array with higher spatial resolution and with radiochromic film. The Octavius 4D phantom with associated Octavius detector 729 ionization chamber array is a dosimetrically and mechanically stable device for pretreatment verification of FF and FFF RapidArc treatments. Further improvements may be possible through use of a detector array with higher spatial resolution (detector size and∕or detector spacing).

The impacts of dental filling materials on RapidArc treatment planning and dose delivery: Challenges and solution

The presence of high-density material in the oral cavity creates dose perturbation in both downstream and upstream directions at the surfaces of dental filling materials (DFM). In this study, the authors have investigated the effect of DFM on head and neck RapidArc treatment plans and delivery. Solutions are proposed to address (1) the issue of downstream dose perturbation, which might cause target under dosage, and (2) to reduce the upstream dose from DFM which may be the primary source of mucositis. In addition, an investigation of the clinical role of a custom-made plastic dental mold∕gutter (PDM) in sparing the oral mucosa and tongue reaction is outlined. The influence of the dental filling artifacts on dose distribution was investigated using a geometrically well-defined head and neck intensity modulated radiation therapy (IMRT) verification phantom (PTW, Freiberg, Germany) with DFM inserts called amalgam, which contained 50% mercury, 25% silver, 14% tin, 8% copper, and 3% other trace metals. Three RapidArc plans were generated in the Varian Eclipse System to treat the oral cavity using the same computer tomography (CT) dataset, including (1) a raw CT image, (2) a streaking artifacts region, which was replaced with a mask of 10 HU, and (3) a 2 cm-thick 6000 HU virtual filter [a volume created in treatment planning system to compensate for beam attenuation, where the thickness of this virtual filter is based on the measured percent depth dose (PDD) data and Eclipse calculation]. The dose delivery for the three plans was verified using Gafchromic-EBT2 film measurements. The custom-made PDM technique to reduce backscatter dose was clinically tested on four head and neck cancer patients (T3, N1, M0) with DFM, two patients with PDM and the other two patients without PDM. The thickness calculation of the PDM toward the mucosa and tongue was purely based on the measured upstream dose. Patients' with oral mucosal reaction was clinically examined initially and weekly during the course of radiotherapy. For a RapidArc treatment technique, the backscatter dose from the DFM insert was measured to be 9.25±2.17 in the IMRT-verification-phantom. The measured backscatter upstream dose from DFM for a single-field was 22% higher than without the DFM, whereas the downstream dose was lower by 14%. The values of homogeneity index for the plans with and without the application of mask were 0.09 and 0.14, respectively. The calculated mean treatment planning volume (PTV) dose differed from the delivered dose by 13% and was reduced to 2% when using the mask and virtual filter together. A grade 3 mucosa reaction was observed in the control group after 22-24 fractions (44-48 Gy). In contrast, no grade 3 mucositis was observed in the patients wearing the PDM after 25-26 fractions (50-52 Gy). The backscatter from the DFM for a single, parallel-opposed fields, and RapidArc treatment technique was found significant. The application of mask in replacing streaking artifacts can be useful in improving dose homogeneity in the PTV. The use of a virtual filter around the teeth during the planning phase reduces the target underdosage issue in the phantom. Furthermore, a reduction in mucositis is observed in the head and neck patients with the use of PDM.

Investigating the reproducibility of a complex multifocal radiosurgery treatment

Stereotactic radiosurgery has become a widely used technique to treat solid tumors and secondary metastases of the brain. Multiple targets can be simultaneously treated with a single isocenter in order to reduce the set-up time to improve patient comfort and workflow. In this study, a 5-arc multifocal RapidArc treatment was delivered to multiple PRESAGE® dosimeters in order to explore the repeatability of the treatment. The three delivery measurements agreed well with each other, with less than 3% standard deviation of dose in the target. The deliveries also agreed well with the treatment plan, with gamma passing rates greater than 90% (5% dose-difference, and 2 mm distance-to-agreement criteria). The optical-CT PRESAGE® system provided a reproducible measurement for treatment verification, provided measurements were made immediately following treatment.

Quality assurance of Rapid Arc treatments: Performances and pre-clinical verifications of a planar detector (MapCHECK2)

The purpose of this study is to evaluate the use of MapCHECK2 in a patient-specific quality assurance (QA) procedure for Rapid Arc (RA) radiotherapy and to obtain reference values of gamma index (γ) for different irradiation geometries. Dose distributions of 386 patients, optimized with Eclipse treatment planning system for RA on Varian Clinac 2300IX were exported and measured with MapCHECK2 detector array inserted in a MapPHAN dedicated phantom. Gamma index analysis was used to evaluate differences between calculated and delivered doses; collected data were analysed on the basis of complexity of plans and type of disease. Angular dependence and dose drift of detectors were estimated. The overall mean passing rate (percentage of points with γ < 1) was equal to 97.0% ± 3.1%; plan-specific evaluation of %γ < 1 showed significant differences among different treatment protocols (pancreas 98.6% ± 1.5%, prostate 96.6% ± 2.8% and rectum 92.8% ± 5.7%). MapCHECK2 demonstrated a strong angular dependence over a restricted range of angles (90° ± 5° and 270° ± 5°); this condition affected the result of pre-treatment QA only for plans with intense lateral fluence. The drift of diode array response due to the accumulated dose was found to be comparable with the manufacturer's declaration (0.5% per 1000 Gy). MapCHECK2 proved to be a useful and accurate tool in the process of patient-specific QA for RA treatment. Excluding the irradiation geometries with a high contribution of lateral fluence, the mean percentage of cases with γ-index > 95% equal to 90.3% was obtained instead of 81.7% including all plans.

Validation of the delivered dose for gated rapidarc treatments using the electronic portal imaging device

Purpose Validate the dose for Gated RapidArc (RA) treatment technique using portal imaging dosimetry aSi1000. Methods and materials 5 cases of liver stereotactic gated treatments were selected. RA plans were optimized using the Eclipse TPS (v.10) and the PRO3 (v.) algorithm. Verification of treatment plans was performed using an Electronic Portal Imaging Dose (EPID). Portal Dose Prediction algorithm was used to predict the dose at the isocenter. Gated RA treatments were performed using a Varian Novalis TrueBeam linear accelerator. The portal dose images were acquired with a portal imager aSi1000. A respiratory gating signal was generated using a phantom using infrared reflective markers providing a periodic movement. The measurements were performed with respiratory gating in the same conditions of treatment and compared with portal images acquired without gating and both were then compared to images of dose predicted by the TPS. Quantitative analysis of the consistency of dose distributions was performed using the gamma index. Criteria 2 mm in distance (DTA Distance To Agreement) and 2% in dose difference (DDmax) and 3 mm/3% were selected for the evaluation. Results The average gamma index <1 obtained for plans with Gated RA compared with images dose predicted by the TPS is 97.25% (±2.32) for 2 mm DTA criteria and 2% DD and 98.95% (±1.10) for 3 mm DTA criteria and 3% in DD. The average index for gamma RA plans without gating compared to images of dose predicted by the TPS is 97.16% (±2.46) for 2 mm DTA and DD 2% and 98.92% (±1.13) for 3 mm/ 3%.Comparison of images dose acquired with and without gating is 100% (±0) for 2 mm in DTA and 2% in DD as well as 3 mm/3%. Conclusion The dose for RA treatment technique with and without respiratory gating shows a very good agreement. The portal imager aSi1000 can be used as a tool for verification of Gated RA treatment plans. Validate the dose for Gated RapidArc (RA) treatment technique using portal imaging dosimetry aSi1000. 5 cases of liver stereotactic gated treatments were selected. RA plans were optimized using the Eclipse TPS (v.10) and the PRO3 (v.) algorithm. Verification of treatment plans was performed using an Electronic Portal Imaging Dose (EPID). Portal Dose Prediction algorithm was used to predict the dose at the isocenter. Gated RA treatments were performed using a Varian Novalis TrueBeam linear accelerator. The portal dose images were acquired with a portal imager aSi1000. A respiratory gating signal was generated using a phantom using infrared reflective markers providing a periodic movement. The measurements were performed with respiratory gating in the same conditions of treatment and compared with portal images acquired without gating and both were then compared to images of dose predicted by the TPS. Quantitative analysis of the consistency of dose distributions was performed using the gamma index. Criteria 2 mm in distance (DTA Distance To Agreement) and 2% in dose difference (DDmax) and 3 mm/3% were selected for the evaluation. The average gamma index <1 obtained for plans with Gated RA compared with images dose predicted by the TPS is 97.25% (±2.32) for 2 mm DTA criteria and 2% DD and 98.95% (±1.10) for 3 mm DTA criteria and 3% in DD. The average index for gamma RA plans without gating compared to images of dose predicted by the TPS is 97.16% (±2.46) for 2 mm DTA and DD 2% and 98.92% (±1.13) for 3 mm/ 3%.Comparison of images dose acquired with and without gating is 100% (±0) for 2 mm in DTA and 2% in DD as well as 3 mm/3%. The dose for RA treatment technique with and without respiratory gating shows a very good agreement. The portal imager aSi1000 can be used as a tool for verification of Gated RA treatment plans.