RapidArc Plans Research Articles

SU‐E‐T‐637: IMRT for Pancreas and Prostate Cancer Using Pulsed Low Dose Rate Delivery Techniques

Purpose: Reirradiation of patients previously treated with radiotherapy is vastly challenging. Pulsed low dose rate (PLDR) external beam radiotherapy has the potential to reduce normal tissue toxicities while still providing significant tumor control for recurrent cancers. This work investigates treatment planning techniques for IMRT‐based PLDR treatment for various sites, including pancreatic and prostate cancer cases. Methods: Treatment plans were generated with 10 gantry angles using the step‐and‐shoot delivery technique, which can be delivered in three‐minute intervals to achieve an effective low‐dose rate of 6.67cGy/min. The IMRT plans were compared with the 3DCRT plans and RapidArc plans in this study. Results: For the ten pancreas cases investigated, the mean PTV dose for each gantry angle in the IMRT plans ranged from 17.6 cGy to 22.4 cGy. The maximum doses ranged between 22.9 cGy and 34.8 cGy. The minimum doses ranged from 8.2 cGy to 17.5 cGy. For the ten prostate cases investigated, the mean PTV doses for individual gantry angles ranged from 18.8 cGy to 22.6 cGy. The maximum doses per gantry angle were between 24.0 cGy and 34.7 cGy. The minimum doses per gantry angle ranged from 4.4 cGy to 17.4 cGy. Conclusion: A significant reduction in the OAR dose was achieved with IMRT compared with 3DCRT. For most OARs, no significant differences were observed between IMRT and RapidArc. Compared with 3DCRT, IMRT could provide superior target coverage and normal tissue sparing for PLDR reirradiation of recurrent pancreatic and prostate cancers. PLDR IMRT is an effective treatment choice for recurrent cancers in most cancer centers.

SU‐E‐T‐407: Dosimetric Influence of Setup Errors On RapidArc‐Based SRS for Simultaneous Irradiation of Multiple Intracranial Targets

Purpose: To evaluate the dosimetric influence of setup errors on RapidArc‐based SRS for simultaneous irradiation of multiple intracranial targets. Methods: Eight patients previously treated with RapidArc™ technique for multiple intracranial lesions were included in this study. A RapidArc plan was designed to irradiate multiple targets simultaneously with one isocenter and 4 non‐coplanar arcs. 1 mm margin was added to generate PTVs from GTVs. BrainLAB Novalis system was used to position the targets with 6D corrections and monitor patient position during treatment. CBCT was acquired for verification before irradiation. Velocity AI was used for image registration and dose mapping for CBCT, planning CT, contours and dose matrix. The DVHs of targets and critical structures and dose distributions were compared with the planned results and dosimetric influence from setup errors was analyzed. Results: We found that the translational errors were less than 1 mm in the three directions and rotational errors were less than 0.6 degree for all the patients. The overall PTV coverage decreases of ∼10 percent on average while the overall GTV coverage slightly influenced. Although prescribed dosed still covered most of GTVs, there were still some targets with a GTV coverage drop greater than 5 percent even with a 1 mm margin. Most of influenced targets were small targets and relatively far from isocenter. Our study also showed that the dosimetric influence on critical structures was negligible. Conclusions: Although RapidArc technique can generate good plans for effectively treating multiple intracranial lesions simultaneously using stereotactic radiosurgery, this technique is more susceptible to the setup errors, especially rotational errors. 0.5 degree rotational error may Result in non‐ignorable drop in target coverage. Our study show that a 1 mm margin for PTV and 6D positioning are necessary for a successful treatment with this technique.

SU‐C‐141‐02: Evaluation of Dosimetric and Geometric Accuracy of Gated Lung SBRT with CIRS Lung Motion Phantom

Purpose: To evaluate the dosimetric and geometric accuracy of the gated SBRT delivery using film measurements and intra‐fractional kV images with predefined software‐markers. Methods: End‐to‐end tests of gated SBRT delivery were performed using a Varian TrueBeam™ linac and a CIRS lung motion phantom with targets of 1 and 2 cm in diameter and implanted fiducials. 4DCT images of the phantom were acquired with 1 mm slice thickness. RapidArc plans were created in Eclipse TPS with software‐markers placed on the fiducials at maximal expiration. SBRT plans were delivered to the phantom in stationary and in gating mode (2 mm and 5 mm‐gating window). Plans were also delivered with 5 mm targets shift with respect to the boney anatomy in stationary mode and 10% phase shift in 2 mm‐gating mode. To investigate the dosimetric accuracy, dose was measured by EBT3 film and compared with the TPS calculation (AcurosXB algorithm) using γ‐index criteria (3mm distance‐to‐agreement and 3% dose‐difference). The geometric accuracy was evaluated using kV intra‐fraction images of the fiducials relative to the predefined software‐markers. Results: Comparing with the stationary mode, the percentage passing γ‐index (%γ) for 1 cm target decreased significantly from 98.0% to 94.8% (2 mm‐gating window) and 84.3% (5 mm‐gating window) while for 2 cm target %y decreased from 99.5% to 99.2% (2 mm‐gating window) and 86.6% (5 mm‐gating window). The %γ for the conditions of target shift and phase shift for the 2 cm target were 89.0% and 89.9%, respectively. Geometric deviation was less than 0.05 mm, except for the phase shift condition (0.45 mm). Conclusion: Higher dosimetric impact from motion was found for the smaller target. With a proper gating window the planned dose can be accurately delivered with the use of kV intra‐fraction image and software‐maker to ensure the geometric accuracy during treatment.

SU‐E‐J‐19: Prostate Movement Evaluation During Treatment Delivery Period for Prostate Cancer

Purpose: To evaluate the intra‐fractional prostate movement during the beam delivery period using orthogonal KV image pairs. Methods: To understand the prostate internal motion range during the beam delivery period of conventional treatment, 11 conventional treatments were utilized. We followed RTOG 0815. The total dose is about 75.6 to 79.2 Gy with 1.8 Gy per fraction. The PTV margin is 5 to 10 mm. 2‐arc RapidArc plans are used for the treatment. Once the first arc was delivered, another orthogonal KV image pair was performed to setup the patient based on the prostate seeds. The shift data and the interval time between the first and second orthogonal KV image pair were recorded. Results: The relative error results of OBI QA were within 1mm. The average shift between two arc beam deliveries was 0.38cm (0.20cm ∼ 0.85cm). The interval time between two orthogonal KV image pairs was 6.71 min (4.64min ∼ 9.22 min). For conventional treatment delivery, the 2 arc beam delivery time is within 3 minutes. Hypofractionated treatment will double the beam delivery time. Accordingly, prostate movement might be larger and impair the targeting of cancer tissue. Studies about the prostate movement during longer treatment period will be carried out in the future. Real time tracking method can be employed to verify patient setup during long treatment. However, the orthogonal KV image pair can be an alternative if real time tracking method is not available. Conclusion: Hypofractionated prostate treatment or prostate SBRT need longer beam delivery time. Also the PTV margin is much less than conventional treatment. Therefore verification of patient setup during the beam delivery is critical. Real time tracking system or orthogonal KV image pairs should be used during the beam delivery period to improve treatment delivery quality.

SU-E-T-156: A Novel Patient Quality Assurance System for Both Outer and Inner Dose Verification in Volumetric Modulated Arc Therapy

Purpose: The general commercial patient specific QA systems for volumetric modulated arc therapy (VMAT) provide either O (Arccheck) or X (Delta4) shape plane measurements. The purpose of this study is to develop a cylindrical phantom with radiochromic film to concurrently verify the dose planes in outer (O shape plane) and inner (X shape plane) geometric for the VMAT treatment. Methods: A novel patient specific phantom consists of polyethylene and radiochromic film was designed. Films can be wrapped and shaped and inserted in the phantom for simultaneous measurement of the O and X dose planes. One rolled‐up and two specifically cut EBT3 films were used for the O and X dose planes measurements, respectively. A clinically approved head‐and‐neck RapidArc plan was hybrid to the phantom for patient specific QA. The calculated dose planes were extracted from treatment planning system with homemade Matlab software and compared to the measurements. The O plane was rolled out into a rectangle plane and the X geometric plane was departed into two rectangle planes for final analysis in the Film QA software. The gamma analysis with criteria [3mm, 3%] and dose profile comparison were performed. Results: A novel phantom with both O and X dose planes measurements was created. Worked with the gafchromic film, the phantom can be used for patient specific QA. For the test case, the gamma passing rates for O and two X planes were 95.5%, 98.6% and 96.0%, respectively. The dose profile analysis also showed good consistency between calculated and measurement dose planes. Conclusion: The developed phantom system provides a practical and reliable QA method for VMAT technique. It can be employed as an alternative tool for patient specific QA besides the commercial ones. This study was sponsored by grant KY0413 from Ministry of Public Health, PRC.

SU-E-T-709: Dosimetric Study On Volumetric Modulated Arc Therapy for Left Breast Using Four Partial Arc Technique

Purpose: To evaluate the dosimetric characteristics of Volumetric Modulated Arc Therapy (RapidArc) plan for the treatment of carcinoma of the left breast using four partial arcs. ' Methods: RapidArc (RA) plans with four partial arcs were created for five Lt.breast patients for a dose regimen of 50.4Gy in 28 fractions. Computed tomographic images of slice thickness 3 mm were acquired and used for planning. The planning was done in Eclipse Planning system, platform 8.6. Among the four arcs used, the gantry angles for first two arcs were 310 - 130 degrees (CW and CCW) and 310 - 179.9 degrees (CW and CCW) for the other two arcs. The CTV was expanded I cm beyond body artificially and assigned soft tissue HU to incorporate skin flash. Results: The mean homogeneity index for the CTV was found to be 1.18 with a standard deviation of +/− 3.02%. The mean conformity index for CTV was 0.8955 with a standard deviation of +/− 4.6%. The average maximum dose and average mean dose to the heart was 4107.3cGy and 1568.9cGy respectively. The average V20, V25 and V30 for Lt.lung were 22.8%, 8.4% and 4.77% respectively. The average maximum spinal cord dose was 7.61Gy with a standard deviation of +/−6.3%. Conclusion: It is hard to achieve high conformality and homogeneity for breast treatment using Tangential IMRT fields. But, the RA plan showed superior target coverage with good sparing of heart and Lt. Lung. This four arcs technique nicely curves the 70% isodose line away from the lung while delivering homogeneous dose to the CTV. The analysis performed in this article were physical based, an elaborate biological based evaluation studies have been initiated.

SU-D-137-04: Comparison of Treatment Planning Techniques in Treatment of Carcinoma of Left Breast: Second Cancer Risk Perspective

Purpose: To compare the secondary cancer risk (SCR) between different planning techniques for treatment of Ca. Lt.breast patients. Methods: Five treatment plans; 3DCRT tangential fields with physical wedge (PW), enhanced dynamic wedges (EDW), electronic compensator (EC), IMRT tangential fields (ITF) and Rapid-Arc (RA) plan (partial arcs) with 6 MV photon beams were generated for a carcinoma of Lt.breast patient of age 40 to a prescription dose of 50.4Gy in 28 fractions. The SCR was estimated using the organ equivalent dose (OED) concept with a linear exponential, a plateau, and a linear dose response model for OARs. Also, the low dose bath volume (5Gy) was calculated for all the plans. Results: For contralateral breast the SCR relative to PW were (linear, plateau, linear-exponential) (−25.89%, −99.985%, −85.96%) for RA, (−50.12%,−41.94%,−44.57%) for ITF, (−47.78%, −38.43%,−42.05%) for EC and (−32.70%,−26%,−28.31%) for EDW respectively. The relative SCR for heart and Lt-lung were (−89.99% & −89.38%) for RA, (−0.05% & 5.69%) for ITF, (−0.16% & 0.04%) for EC and ( −0.04% & 0.01%)for EDW. In contrast, for skin the relative SCR were 77.68%, −7.71%, −11.11% and −9.04% for RA, ITF, EC and EDW respectively. Also, the 5Gy low dose volume relative to PW for RA was 201.45%, whereas the same for ITF, EC and EDW were −8.41%, −7.33% and −4.2%. Conclusion: Compared to all plans, RA plan showed high conformity for CTV and superior heart, contralateral breast and left lung sparing. But SCR for skin and the low dose volume were significantly high in RA. ITF plan showed relatively better sparing for contralateral breast and heart at the same time has the least low dose bath volume. EC plan shows moderately good sparing for OARs while scoring least SCR value for skin. EDW and PW plans were similar but later had high SCR for contralateral breast.

SU‐E‐T‐221: Evaluation of Quality Assurance for Rapid Arc Treatments Using EPIQA Software

Purpose: To evaluate the patient specific quality assurance of Rapid Arc treatments using EPID and EpiQA software. Methods: Eclipse TPS is used for the creation and calculation of patient and verification plans. The treatments were delivered on aS1000 EPID attached to the Varian Clinac iX Linear Accelerator. EpiQA software supplied by the EPIdos is used for the analysis of calculated and measured dose maps. In this retrospective study 75 Rapidarc treatment plans consisting of 150 arc fields were considered from three different sites of 25 plans each namely head & neck, pelvis and brain. All plans were treated with 6 MV photons with two arcs and QA measurements acquired with Portal Vision aS1000 and analyzed by EpiQA software. To evaluate the QA results, we used Gamma agreement Index (GAI). GAI represents the percentage of the field area with gamma value greater than 1.0 to the gamma criteria of 3mm DTA and 3% Dose Difference. Results: Calculated mean values and standard deviations are 1.95 ± 1.25, 2.44 ± 1.35 and 2.69 ± 1.13 for Brain, Pelvis and Head & Neck respectively. It is noted that all the results were well within 95% of pass criteria of gamma agreement index. We found that the mean GAI values for head & neck and pelvis plans are greater than that of brain plans. This deviation may be attributed due to the variations in the geometry of the field, volume of irradiation, depth of penetration and complexity of planning objectives (more critical organs) etc. However further data of measurements is needed for further evaluation. Conclusion: Since all the plans were passed the GAI and the results are comparable with phantom studies, we conclude that the portal dosimetry can be used conveniently to carryout patient specific QA measurements of Rapidarc plans.

WE-G-108-09: Modulation Severity as a Predictor for Patient-Specific IMRT QA Delivery Failure

Purpose: The goal of this work was to determine if highly modulated fields contribute to decreased passing rates for patient-specific IMRT delivery QA. Methods: Data for 10 Varian Eclipse-planned patients in each of 3 categories were collected: IMRT, carriage shift, and RapidArc. Total plan modulation was calculated as the ratio of total MU to dose per fraction. Applied modulation, in cGy, was determined for each field as the ratio of total MU per field to total plan modulation. The difference between applied modulation and dose from the planning system on a per beam basis was calculated and the mean values found for each patient and each category. Limits were applied based on the category mean plus 3 standard deviations for 2 beams as well as maximum limits for a single beam. Data were evaluated with respect to these limits for 889 patients. The individual results were compared with the IMRT delivery QA data collected with the IBA Matrixx using absolute 3% dose and 3mm DTA acceptance criteria. Results: Modulation limits were exceeded for IMRT plans in 64%, 44% and 22% of cases and for RapidArc plans in 43%, 22% and 2% of cases for delivery QA passing rates of 92%, 95% and 98%, respectively. The mean passing rate for delivery QA was approximately 97% (range 90.4–100%). Conclusion: There is a definite trend indicating lower delivery QA passing rates with severe modulation for both modalities. However, given an arbitrary acceptable passing rate of 95% with the modulation test failing 44% and 22% of the time for IMRT and RapidArc, respectively, modulation may not be a strong predictor of delivery QA acceptability. The cause(s) of severe modulation should be evaluated on a case-by-case basis with appropriate time and attention allotted for all phases of the QA process.

SU‐C‐108‐05: A Novel Technique to Evaluate 4D Dose Delivery to a Moving Tumor

Purpose: Delivering highly modulated radiation beams accurately to a moving tumor is a difficult task; it is crucial to have tools to evaluate the efficacy of treatment delivery in such cases. We are reporting a novel technique to evaluate 4D dose delivery to moving tumors. We are also presenting an evaluation of RapidArc treatment delivery using this method. 4D position dependant dose is crucial because the peripheral regions of the tumor may not get adequate dose due to moving out of the MLC aperture. In our procedure we accomplish the position dependant dose evaluation by creating the effects of tumor motion as follows: instead of moving the tumor, we simulate to move the active MLCs in the direction opposite to tumor motion by the corresponding motion amplitude calculated at the time of delivery. Methods: Ten RapidArc plans were created, delivered at a Varian Trilogy unit and corresponding log files were recorded. A simulation, written in MATLAB, reads in the dynalog files, and calculates average time per each control point delivery with respect to beam initiation. A sinusoidal respiratory motion signal with a given maximum amplitude and period was implemented to obtain the motion amplitude at the time of delivery of each control point. A modified DICOM file was created where the active MLCs were moved to simulate the effects of tumor motion. This DICOM plan was reimported to Eclipse treatment planning system, and 4D dose was recalculated. To verify the accuracy of our simulation, a sample plan with 2.5cm motion amplitude was compared with delivery. Results: Simulation agrees well with the dose measurement (3% /3mm gamma acceptance of 98%). GTV under‐dosing is observed for large motion amplitudes, and small tumor volumes. Conclusion: A novel technique is developed to obtain delivered 4D dose distributions for moving tumors using machine log files.

Quality assurance of rapidarc treatments with FFF

Introduction With a maximum dose rate of 1400 MU/min X6FFF (Flattening Filter Free) is a major device for the development of hypofractionated stereotactic treatments. But the use of such a dose rate requires specific quality controls. The purpose of this study is to evaluate the feasibility of these controls and the validation of X6FFF RapidArc treatment delivery. Material and methods First of all, simple fields (square, rectangular and MLC) were analyzed. Absolute dose measures at the isocenter were performed with a 0.125 cc ionization chamber and a cylindrical water equivalent phantom. Planar dose distribution at the isocenter was verified with portal imager (aS1000) and EpiQA software (Epidos, Brastislavia). In this case, the analysis was performed using GAI (3%–3 mm) and smoothing detector response to adjust the resolution to the TPS dose calculation (2.5 mm/pixel). Then, 20 patients (10 prostates, 5 livers and 5 lungs), previously treated in X6 RapidArc, were replanned in X6FFF with Eclipse TPS (PRO v10 and AAA v10). They were checked on TrueBeam Novalis linear accelerator using the same devices as for simple fields. Results The variation of the correction factor for recombination between 1400 and 600 MU/min is less than 0.5%. For simple fields, GAI is 95.45%. The difference in absolute dose for 20 RapidArc plans is 1.7 ± 2.51% (mean ± 1 SD). This value is 1.23 ± 1.29% for prostate, 1.95 ± 2.59% for liver, 2.15 ± 3.74% for lung. As regards the comparison of dose distribution the overall GAI is 99.26 ± 0.75% (99.12 ± 0.76% for prostate, 99.27 ± 0.69% for liver et 99.46 ± 0.83% for lung). Conclusion RapidArc treatment delivery in X6FFF is dosimetrically acceptable and comparable to those obtained in X6. With a maximum dose rate of 1400 MU/min X6FFF (Flattening Filter Free) is a major device for the development of hypofractionated stereotactic treatments. But the use of such a dose rate requires specific quality controls. The purpose of this study is to evaluate the feasibility of these controls and the validation of X6FFF RapidArc treatment delivery. First of all, simple fields (square, rectangular and MLC) were analyzed. Absolute dose measures at the isocenter were performed with a 0.125 cc ionization chamber and a cylindrical water equivalent phantom. Planar dose distribution at the isocenter was verified with portal imager (aS1000) and EpiQA software (Epidos, Brastislavia). In this case, the analysis was performed using GAI (3%–3 mm) and smoothing detector response to adjust the resolution to the TPS dose calculation (2.5 mm/pixel). Then, 20 patients (10 prostates, 5 livers and 5 lungs), previously treated in X6 RapidArc, were replanned in X6FFF with Eclipse TPS (PRO v10 and AAA v10). They were checked on TrueBeam Novalis linear accelerator using the same devices as for simple fields. The variation of the correction factor for recombination between 1400 and 600 MU/min is less than 0.5%. For simple fields, GAI is 95.45%. The difference in absolute dose for 20 RapidArc plans is 1.7 ± 2.51% (mean ± 1 SD). This value is 1.23 ± 1.29% for prostate, 1.95 ± 2.59% for liver, 2.15 ± 3.74% for lung. As regards the comparison of dose distribution the overall GAI is 99.26 ± 0.75% (99.12 ± 0.76% for prostate, 99.27 ± 0.69% for liver et 99.46 ± 0.83% for lung). RapidArc treatment delivery in X6FFF is dosimetrically acceptable and comparable to those obtained in X6.

TH-A-137-08: On the Validity of Target Density Overrides for RapidArc Lung SBRT Treatment Planning

Purpose: It is common practice to calculate lung SBRT plans on free breathing CT scans. Recently, literature has suggested using time average scans or ITV density overridden scans to more accurately calculate dose in lung. We evaluate each of these techniques. Methods: A free breathing (FB) and 4D-CT were acquired for a Quasar Motion Phantom with lung insert and 3 cm spherical target (Modus Medical Devices Inc, Canada). Target motion was set to ± 1cm parallel to CT table travel at 16 cycles per minute. An ITV was defined on the 4D-CT with a PTV defined as a 5 mm expansion. RapidArc plans giving 1000 cGy to 96–97% of the PTV in two arcs were created on four image sets: the time average, FB, FB with the ITV set to tissue density, and FB with the PTV set to tissue density. Plans were delivered on a Varian TrueBeam STx (Varian Medical Systems, Palo Alto, CA) and measured on EBT3 film placed in the phantom target. Reference dose distributions that accounted for film motion were created for each plan by shifting the dose in 2 mm steps over the range of motion and convolving these shifted doses. The film was analyzed in with a gamma metric of 1mm/1%. Results: The passing gamma percentages were 77.9%, 83.6%, 89.1%, and 92.7% for the FB, time average, ITV, and PTV plans, respectively. Profiles along the direction of travel showed hot spots of 5-10% above the predicted dose just outside the target for the FB and average plans. The ITV plan showed similar hot spots ∼2% above predicted dose. The PTV profile was in good agreement with predicted dose. Conclusion: Though this study is a greatly simplified case, it shows that planning to a tissue density target in lung may produce the most accurate dose predictions.

Volumetric modulated arc therapy with flattening filter free (FFF) beams for stereotactic body radiation therapy (SBRT) in patients with medically inoperable early stage non small cell lung cancer (NSCLC)

PurposeTo assess the impact of volumetric modulated arc therapy (VMAT) with flattening filter free (FFF) beams for stereotactic body radiotherapy (SBRT) in inoperable stage I NSCLC. Current data were compared against a cohort of patients previously treated with advanced conformal techniques (3DCRT) based on conformal arcs. Methods and materialsFrom July 2006 to December 2011 132 patients underwent SBRT, 86 by 3DCRT with flattened beams (FF), while the last 46 with VMAT RapidArc and unflattened beams (FFF). All patients were treated with 48Gy in four fractions of 12Gy each. Patients underwent follow-up. Clinical outcome was evaluated with thoracic and abdominal CT scan and 18FDG-CTPET before and after treatment. ResultsBoth techniques achieved adequate dose conformity to the target but with a statistically significant reduction of ipsilateral lung doses in RapidArc plans and also of Beam-on-Time (BOT) with FFF mode. The median follow up was 16months (range 2–24months). At 1year, local control rate was 100% with FFF beams compared with 92.5% with FF beams (p=0.03). ConclusionsSBRT with FFF beams permitted us a safe delivery of high dose per fraction in a short treatment time and resulted in an earlier radiological response compared with FF beams.

Radiobiological evaluation of dose calculation algorithms in RapidArc planning of esophageal cancer treatment plans

Normal 0 false false false EN-US X-NONE X-NONE Purpose: The purpose of current study is to investigate the impact of tissue heterogeneity corrections in Acuros XB algorithm (AXB) and Anisotropic Analytical Algorithm (AAA) on RapidArc esophageal cancer treatment plans using equivalent uniform dose (EUD) calculations and tumor control probability (TCP). Methods: Ten esophageal cancer cases were selected for the current study. All cases were planned using RapidArc technique in Eclipse treatment planning system (10.0.28). The treatment plans were inversely optimized using progressive resolution optimizer and each optimized plan was calculated using AAA with tissue heterogeneity correction. The AAA plans were then normalized such that prescription dose covered 95% of the planning target volume (PTV). The AXB plans were generated by recalculating the normalized AAA plans using AXB with tissue heterogeneity correction for identical monitor units and beam parameters as in the corresponding AAA plans. The EUD and TCP calculations were then performed on the AAA and AXB plans. Results: For PTV, the EUD values in AXB plans were always lower than in AAA plans with an average difference of 1.3%. Similarly, AXB calculations produced smaller magnitude of EUD for the organs at risk (OARs) compared to AAA calculations. On average, in AXB plans, the lung EUD was lower by 3.5%, the liver EUD was lower by 2.3%, the heart EUD was lower by 2.8%, and the spinal cord EUD was lower by 1.8%. The TCP of AXB plans was lower by average difference of 7.1% compared to that of AAA plans. Conclusion: In comparison to AAA calculations, the preliminary results presented in the current study showed that AXB calculations produced lower EUD and TCP for the PTV as well as lower EUD for OARs in the esophageal cancer treatment plans created by RapidArc planning technique.

Monitor unit optimization in RapidArc plans for prostate cancer

Intensity‐modulated radiation therapy (IMRT) has become a standard treatment for prostate cancer based on the superior sparing of the bladder, rectum, and other surrounding normal tissues compared to three‐dimensional conformal radiotherapy, despite the longer delivery time and the increased number of monitor units (MU). The novel RapidArc technique represents a further step forward because of the lower number of MUs per fraction and the shorter delivery time, compared to IMRT. This paper refers to MU optimization in RA plans for prostate cancer, using a tool incorporated in Varian TPS Eclipse. The goal was to get the lowest MU RA plan for each patient, keeping a well‐defined level of PTV coverage and OAR sparing. Seven prostate RA plans (RA MU‐Optimized) were retrospectively generated using the MU optimization tool in Varian Eclipse TPS. Dosimetric outcome and nontarget tissue sparing were compared to those of RA clinical plans (RA Clinical) used to treat patients. Compared to RA Clinical, RA MU‐Optimized plans resulted in an about 28% (p=0.018) reduction in MU. The total integral dose (ID) to each nontarget tissue (but not the penile bulb) showed a consistent average relative reduction, statistically significant only for the femoral heads. Within the intermediate dose region (40–60 Gy), ID reductions (4%−17% p<0.05) were found for the rectum, while a slight but significant (0.4%−0.9%,p<0.05) higher ID was found for the whole body. Among the remaining data, the mean dose to the bladder was also reduced (−12%,p=0.028). Plans using MU optimization are clinically applicable and more MU efficient, ameliorating the exposure of the rectum and the bladder to intermediate doses.PACS number: 87

Volumetric modulated arc therapy for prostate cancer patients with hip prosthesis

AimTo study the use of RapidArc techniques in the treatment of prostate cancer patients with hip prosthesis. BackgroundAn important aspect of treatment planning is to achieve dose homogeneity inside the planning target volume (PTV). Especially for those patients presenting with hip prosthesis, it becomes a challenging task to achieve dose uniformity inside the PTV. Materials and methodsFive prostate patients presenting with hip prosthesis who had undergone radical radiotherapy were selected for this study. Depending on the composition of prosthesis, a predefined set of Hounsfield values were assigned to each study set. RapidArc plans were generated on an Eclipse treatment planning system. Two arcs that include clockwise and counter-clockwise arcs were used in all these cases. To avoid beams passing through the prosthesis, a simple structure was defined around it with 1cm margin and a strict dose constraint applied to the block during VMAT optimization. ResultsThe mean D2/D98 ratio of PTV for all the patients was 1.06±0.01. The mean percentage rectum volume receiving 50Gy, 60Gy, 70Gy and 75Gy for all the patients were 33.1±5.9, 21.7±5.5, 13.8±4.4 and 9.5±3.0, respectively. ConclusionsThis study shows that using a double arc RapidArc technique is a simple and effective treatment method of treating prostate cancer in patients presenting with a hip prosthesis. The definition of a beam avoidance structure encompassing the prosthesis and applying strict dose constraints to it reduces the beam contribution to the prosthesis

VMAT monthly QA using two techniques: 2D ion chamber array with an isocentric gantry mount and an in vivo dosimetric device attached to gantry

AbstractPurposeVarian RapidArc is a volumetric modulated arc therapy (VMAT) that obtains a conformal dose around the desired structure by employing variable gantry speed, dose rate and dynamic multileaf collimator (DMLC) speed as the gantry rotates about machine isocenter. This study is meant to build upon previous research by Ling et al. by completing the tests with an in vivo dosimetric device attached to the linac gantry and a 2D ionisation chamber array with an isocentric gantry mount.Materials and methodsTwo PTW detectors, seven29 array with gantry mount and DAVID, were attached to the linear accelerator gantry, allowing each device to remain perpendicular to the beam at all gantry angles. Three tests for RapidArc evaluation were performed on these devices including: dose rate and gantry speed variation, DMLC speed and dose rate variation and DMLC position accuracy. The reproducibility of the arc data was also reported.ResultsA picket fence plan varying dose rates (111 to 600 MU/minute) and gantry speeds (5·5 to 4·3°/second) was delivered consisting of seven sections of different combinations. These measurements were compared with static gantry, open field measurements and found to be within 2·39% for the DAVID device and 0·84% for the seven29. A four-section picket fence of varying DMLC speeds (0·46, 0·92, 1·84 and 2·76 cm/second) was similarly evaluated and found to be within 1·99% and 3·66% for the DAVID and seven29, respectively. For DMLC position accuracy, a picket fence arc plan was compared with a static picket fence and found to agree within 0.38% and 2.91%. Reproducibility for these three RapidArc plans was found to be within 0·30% and 2·70% for the DAVID and seven29.ConclusionThe DAVID and seven29 detectors were able to perform the RapidArc quality assurance tests efficiently and accurately and the results were reproducible. Periodic verification of DMLC movement, dose rate variation and gantry speed variation relating to RapidArc delivery can be completed in a timelier manner using this equipment.

Dosimetric Impact of Intrafraction Motion During RapidArc Stereotactic Vertebral Radiation Therapy Using Flattened and Flattening Filter-Free Beams

To study the dosimetric impact of relatively short-duration intrafraction shifts during a single fraction of RapidArc delivery for vertebral stereotactic body radiation therapy (SBRT) using flattened (FF) and flattening filter-free (FFF) beams. The RapidArc plans, each with 2 to 3 arcs, were generated for 9 patients using 6-MV FF and 10-MV FFF beams with maximum dose rates of 1000 and 2400 MU/min, respectively. A total of 1272 plans were created to estimate the dosimetric consequences in target and spinal cord volumes caused by intrafraction shifts during one of the arcs. Shifts of 1, 2, and 3 mm for periods of 5, 10, and 30 seconds, and 5 mm for 5 and 10 seconds, were modelled during a part of the arc associated with high doses and steep dose gradients. For FFF plans, shifts of 2 mm over 10 seconds and 30 seconds could increase spinal cord Dmax by up to 6.5% and 13%, respectively. Dosimetric deviations in FFF plans were approximately 2-fold greater than in FF plans. Reduction in target coverage was <1% for 83% and 96% of the FFF and FF plans, respectively. Even short-duration intrafraction shifts can cause significant dosimetric deviations during vertebral SBRT delivery, especially when using very high dose rate FFF beams and when the shift occurs in that part of the arc delivering high doses and steep gradients. The impact is greatest on the spinal cord and its planning-at-risk volume. Accurate and stable patient positioning is therefore required for vertebral SBRT.

EP-1179: What the gamma? The correlation between QA and clinical risk estimates for prostate RapidArc plans

EP-1179: What the gamma? The correlation between QA and clinical risk estimates for prostate RapidArc plans

Investigating VMAT planning technique to reduce rectal and bladder dose in prostate cancer treatment plans

Background: RapidArc is a volumetric modulated arc therapy (VMAT) technique that can deliver conformal dose distribution to the target while minimizing dose to critical structures. The main purpose of this study was to compare dosimetric quality of full double arc (full DA), full single arc (full SA), and partial double arc (partial DA) techniques in RapidArc planning of prostate cancer. Materials and Methods: Twelve cases of prostate cancer involving seminal vesicles were selected for this retrospective study. For each case, RapidArc plans were created using full DA (two full arcs), full SA (one full arc), and partial DA (two partial arcs with anterior and posterior avoidance sectors) techniques. For planning target volume (PTV), the maximum and mean doses, conformity, and inhomogeneity indices were evaluated. For bladder and rectum, volumes that received 70, 50, 40, and 20 Gy (V 70Gy , V 50Gy , V 40Gy and V 20Gy , respectively), and mean dose were compared. For femoral heads, V 40Gy , V 20Gy , and mean dose were evaluated. Additionally, an integral dose and monitor units (MUs) were compared for each treatment plan. Results: In comparison to full DA and full SA techniques, the partial DA technique was better in sparing of rectum and bladder but delivered higher femoral head dose, which was nonetheless within the planning criteria. No clear dosimetric differences were found between full DA and partial DA plans for dose conformity and target homogeneity. The number of MUs and integral dose were largest with the partial DA technique and lowest with the full SA technique. Conclusion: The partial DA technique provides an alternative RapidArc planning approach for low risk prostate cancer.