RapidArc Technique Research Articles

Clinical Application of a Novel Hybrid Intensity-Modulated Radiotherapy Technique for Stage III Lung Cancer and Dosimetric Comparison With Four Other Techniques

In large stage III lung tumors, planning delivery of doses exceeding 60 Gy can be challenging and time consuming. Intensity modulated radiation therapy (IMRT) can improve target coverage but may increase volumes receiving low-dose irradiation. We clinically implemented a novel hybrid IMRT (h-IMRT) technique that allowed plans to be produced quickly, and compared these plans with 4 other techniques. h-IMRT was used to treat 14 consecutive patients with planning target volumes (PTVs) exceeding 500 cm(3) (average, 779 cm(3)) with concurrent chemo-radiation therapy to 66 Gy. h-IMRT plans consisted of 2 components: an anterior-posterior/posterior-anterior/posterior-anterior (AP-PA-PA) oblique, open-field technique delivering an average dose of 58 Gy, plus a 3-field IMRT component optimized to achieve a final homogeneous dose of 66 Gy. Total lung V(20) and contralateral lung V(5) were kept as low as possible but preferably less than 35% and less than 50%, respectively. All plans were retrospectively replanned using a 5- to 9-field 3-dimensional conformal technique, full RapidArc, 6-field full IMRT, and a hybrid RapidArc (h-RapidArc) technique similar to the h-IMRT. The h-IMRT, h-RapidArc, and full RapidArc plans could be generated in less than 2 h, with the first 2 plans achieving the lowest V(5) (36%) and V(20) (30%) values together with the smallest hot spots. Both the 3-dimensional conformal and full IMRT plans occasionally led to unacceptable hot spots outside the PTV. Full RapidArc plans were fast and achieved comparable V(20) values but led to slightly higher V(5) values. Both h-IMRT and h-RapidArc permitted delivery of 66 Gy to large stage III lung tumors, and both were superior to either full IMRT or RapidArc plans for reducing lung doses. The clinical significance of small increases in V(5) during chemo-radiation therapy delivery are unknown, but the present study suggests that h-IMRT and h-RapidArc are preferable for treatment of large tumors.

Intrafraction Verification of Gated RapidArc by Using Beam-Level Kilovoltage X-Ray Images

To verify the geometric accuracy of gated RapidArc treatment using kV images acquired during dose delivery. Twenty patients were treated using the gated RapidArc technique with a Varian TrueBeam STx linear accelerator. One to 7 metallic fiducial markers were implanted inside or near the tumor target before treatment simulation. For patient setup and treatment verification purposes, the internal target volume (ITV) was created, corresponding to each implanted marker. The gating signal was generated from the Real-time Position Management (RPM) system. At the beginning of each fraction, individualized respiratory gating amplitude thresholds were set based on fluoroscopic image guidance. During the treatment, we acquired kV images immediately before MV beam-on at every breathing cycle, using the on-board imaging system. After the treatment, all implanted markers were detected, and their 3-dimensional (3D) positions in the patient were estimated using software developed in-house. The distance from the marker to the corresponding ITV was calculated for each patient by averaging over all markers and all fractions. The average 3D distance between the markers and their ITVs was 0.8 ± 0.5 mm (range, 0-1.7 mm) and was 2.1 ± 1.2 mm at the 95th percentile (range, 0-3.8 mm). On average, a left-right margin of 0.6 mm, an anterior-posterior margin of 0.8 mm, and a superior-inferior margin of 1.5 mm is required to account for 95% of the intrafraction uncertainty in RPM-based RapidArc gating. To our knowledge, this is the first clinical report of intrafraction verification of respiration-gated RapidArc treatment in stereotactic ablative radiation therapy. For some patients, the markers deviated significantly from the ITV by more than 2 mm at the beginning of the MV beam-on. This emphasizes the need for gating techniques with beam-on/-off controlled directly by the actual position of the tumor target instead of external surrogates such as RPM.

EP-1429 MULTI-INSTITUTION INTERNAL PROCESS ANALYSIS BY PRE-TREATMENT VERIFICATION OF RAPIDARC PLANS WITH EPID

Purpose/Objective: To show a multi-institution process analysis based on the evaluation of pre-treatment quality assurance of RapidArc plans as part of internal process of risk management. Materials and Methods: Pre-treatment quality assurance data of RapidArc plans from three centres of the same hospital group with different linacs (TrueBeam, 2100-DHX, and UNIQUE from Varian) were analysed and shared as part of an internal study on treatment quality. The study was divided in two parts. i) Auto-evaluation of the internal process: one hundred plans per centre delivered according to RapidArc technique were randomly retrospectively selected and pretreatment quality assurance was performed using portal dosimetry approach in terms of? g evaluation with DD=3% and DTA=3mm scoring the Gamma Agreement Index (GAI, % of field area passing the test). ii) Multi-verification of the plans: every centre shared prospectively ten plans analyzed in the previous phase; the plans were then delivered on the other two centres with the own linacs. Mean values were compared aiming verification of internal procedures. Results: i) The results of the g analysis per institute show an average GAI >97% comfirming an optimal agreement between calculated and measured dose without considering the complexity of the plan. ii) The data of the multi-verification plan show coherence of the plan optimization and the delivered dose among the three centres with average GAI>98% in all centers.

EP-1557 RADIOTHERAPY OF SOFT-TISSUE SARCOMA OF LOWER EXTREMITY WITH HIGH BONE SPARING WITH RAPIDARC AND PROTONS

Purpose/Objective: To investigate the advanced radiotherapy treatments of soft-tissue sarcoma with adequate target coverage and bone high sparing with volumetric modulated arc therapy (RapidArc) and proton beams. Materials and Methods: Ten patients presenting soft tissue sarcoma of the leg, and treated with RapidArc in author’s institutions were collected for the study. Dose was prescribed to 66.5 Gy in 25 fractions to mean planning target volume (PTV), and significant maximum dose to the bone was limited to 50 Gy. Plans were prepared using RapidArc with flattened 6 MV (6X) and unflattened 10 MV (10FFF) photon beams from a Varian TrueBeam facility, and using proton beams up to 250 MeV. RapidArc photon plans were computed with AAA and Acuros XB in the two options of dose to medium and dose to water. Proton plans were prepared using intensity modulated spot scanned proton beams. Plan evaluation was assessed by dose volume histogram analysis, comparing different dose distributions and different dose calculation algorithms (and dose to medium or to water option). Results: All plans acceptably met the criteria of target coverage (V95%>90-95%) and bone sparing (D1cm3<50 Gy). Better coverage was shown for proton plans with respect to 6X RapidArc photon plans, at 95% of the prescription dose (V95% about 5% higher for protons, p<0.05). Dose was more homogeneously distributed in the proton cases: Standard Deviation 2.3Gy for protons, 3.0-3.3Gy for photons, p<0.05. A small difference tending to be significant was found between 6X and 10FFF plans, in favor of using flattened beams. Bone significant maximum dose objective of 50Gy was met in all cases, photon RapidArc and protons, with no significant differences. The largest difference between proton and photon plans in Bone tissue is reflected in the medium/low doses. Similar results were found for surrounding normal tissue. For Healthy Tissue, the low dose bath is minimized with protons, where the Dose Integral is about halved with respect to all photon plans. Interesting result is the significant (p<<0.01) lower Dose Integral when FFF photon beams are used in place of more conventional flattened beams. Dose to water calculations resulted in bone doses of about 5% higher than for dose to medium calculations. A deep understanding of the two calculation options would lead the user to properly choose between the two modalities of dose to water, or the dose to medium (that better reflects the physical dose to the specific tissue). Conclusions: A substantial equivalence between RapidArc technique for photon beams and proton plans for the management of soft-tissue sarcoma of the lower extremity was here presented, yielding good target coverage to 66.5 Gy prescription, while keeping the maximum significant dose to the bone below the 50 Gy minimizing the risk of bone fractures.

Comparative dosimetric and radiobiological assessment among a nonstandard RapidArc, standard RapidArc, classical intensity-modulated radiotherapy, and 3D brachytherapy for the treatment of the vaginal vault in patients affected by gynecologic cancer

To evaluate a nonstandard RapidArc (RA) modality as alternative to high-dose-rate brachytherapy (HDR-BRT) or IMRT treatments of the vaginal vault in patients with gynecological cancer (GC). Nonstandard (with vaginal applicator) and standard (without vaginal applicator) RapidArc plans for 27 women with GC were developed to compare with HDR-BRT and IMRT. Dosimetric and radiobiological comparison were performed by means of dose-volume histogram and equivalent uniform dose (EUD) for planning target volume (PTV) and organs at risk (OARs). In addition, the integral dose and the overall treatment times were evaluated. RA, as well as IMRT, results in a high uniform dose on PTV compared with HDR-BRT. However, the average of EUD for HDR-BRT was significantly higher than those with RA and IMRT. With respect to the OARs, standard RA was equivalent of IMRT but inferior to HDR-BRT. Furthermore, nonstandard RA was comparable with IMRT for bladder and sigmoid and better than HDR-BRT for the rectum because of a significant reduction of d2cc, d1cc, and dmax (p < 0.01). Integral doses were always higher than HDR-BRT, although the values were very low. Delivery times were about the same and more than double for HDR-BRT compared with IMRT and RA, respectively. In conclusion, the boost of dose on vaginal vault in patients affected by GC delivered by a nonstandard RA technique was a reasonable alternative to the conventional HDR-BRT because of a reduction of delivery time and rectal dose at substantial comparable doses for the bladder and sigmoid. However HDR-BRT provides better performance in terms of PTV coverage as evidenced by a greater EUD.

Volumetric modulated arctherapy (VMAT) compared with sliding window intensity-modulated radiotherapy (IMRT) for whole pelvis irradiation (WPI) of locally advanced prostate cancer (LAPC).

171 Background: Concurrent radiotherapy to the pelvis plus a prostate boost with long term androgen deprivation is a standard of care for LAPC. IMRT has the ability to deliver highly conformal dose to the target while lowering the irradiation of critical organs around the prostate. However, delivery time is signicantly prolonged with static gantry IMRT. VMAT is able to reduce treatment time but results concerning organ sparing are controversial when compared to static gantry IMRT. Methods: 10 patients with locally advanced prostate cancer were included in this dosimetric study. The planning target volumes (PTV) 1 was defined as the pelvic lymph nodes, the prostate and the seminal vesicles plus set up margins. The PTV 2 consisted of the prostate with set up margins. The aimed dose to PTV1 was 54 Gy in 37 fractions and to PTV2, 74 Gy in 37 fractions, in a single plan using the integrated boost method, by means of a 7 coplanar static split fields IMRT, a one arc (RA1) and a two arc (RA2) Rapidarc planification. Results: All three techniques allow a very good coverage of both PTVs with an acceptable homogeneity. Static IMRT enables a better homogeneity for PTV 2 than Rapidarc techniques. Sliding-window IMRT and VMAT permitted to maintain doses to OAR within acceptable levels with a low risk of side-effects for each organ. Nevertheless, VMAT plans result in clinically and statistically significant reduction in doses to bladder (IMRT Vs RA2: Mean dose: 50.1 ± 4.6 Vs 47.1 ± 3.9 Gy, p = 0.037), rectum (Mean dose: 44 ± 4.5 Vs 41.6 ± 5.5 Gy, p = 0.006) and small bowel (V30: 76,47 ± 14,91% Vs. 47,49 ± 16,91%, p = 0.002). Conclusions: VMAT allows for better OAR sparing as compared to sliding-window IMRT while maintining PTV coverage into acceptable levels for WPI of LAPC.

Can volumetric modulated arc therapy with flattening filter free beams play a role in stereotactic body radiotherapy for liver lesions? A volume-based analysis

To compare volumetric modulated arc therapy with flattening filter free (FFF) and flattening filter (FF) beams in patients with hepatic metastases subject to hypofractionated radiotherapy (RT). A planning study on 13 virtual lesions of increasing volume was performed. Two single arc plans were optimized with the RapidArc technique using either FFF or FF beams. A second planning study was performed on ten patients treated for liver metastases to validate conclusions. In all cases, a dose of 75 Gy in 3 fractions was prescribed to the planning target volume (PTV) and plans were evaluated in terms of coverage, homogeneity, conformity, mean dose to healthy liver and to healthy tissue. For each parameter, results were expressed in relative terms as the percentage ratio between FFF and FF data. In terms of PTV coverage, conformity index favored FFF for targets of intermediate size while FF resulted more suitable for small (<100 cm(3)) and large (>300 cm(3)) targets. Plans optimized with FFF beams resulted in increased sparing of healthy tissue in ≈85% of cases. Despite the qualitative results, no statistically significant differences were found between FFF and FF results. Plans optimized with un-flattened beams resulted in higher average MU∕Gy than plans with FF beams. A remarkable and significant difference was observed in the beam-on time (BOT) needed to deliver plans. The BOT for FF plans was 8.2 ± 1.0 min; for FFF plans BOT was 2.2 ± 0.2 min. RapidArc plans optimized using FFF were dosimetrically equivalent to those optimized using FF beams, showing the feasibility of SBRT treatments with FFF beams. Some improvement in healthy tissue sparing was observed when using the FFF modality due to the different beam's profile. The main advantage was a considerable reduction of beam-on time, relevant for SBRT techniques.

Stereotactic body radiation therapy for liver tumours using flattening filter free beam: dosimetric and technical considerations

PurposeTo report the initial institute experience in terms of dosimetric and technical aspects in stereotactic body radiation therapy (SBRT) delivered using flattening filter free (FFF) beam in patients with liver lesions.Methods and MaterialsFrom October 2010 to September 2011, 55 consecutive patients with 73 primary or metastatic hepatic lesions were treated with SBRT on TrueBeam using FFF beam and RapidArc technique. Clinical target volume (CTV) was defined on multi-phase CT scans, PET/CT, MRI, and 4D-CT. Dose prescription was 75 Gy in 3 fractions to planning target volume (PTV). Constraints for organs at risk were: 700 cc of liver free from the 15 Gy isodose, Dmax < 21 Gy for stomach and duodenum, Dmax < 30 Gy for heart, D0.1 cc < 18 Gy for spinal cord, V15 Gy < 35% for kidneys. The dose was downscaled in cases of not full achievement of dose constraints. Daily cone beam CT (CBCT) was performed.ResultsForty-three patients with a single lesion, nine with two lesions and three with three lesions were treated with this protocol. Target and organs at risk objectives were met for all patients. Mean delivery time was 2.8 ± 1.0 min. Pre-treatment plan verification resulted in a Gamma Agreement Index of 98.6 ± 0.8%. Mean on-line co-registration shift of the daily CBCT to the simulation CT were: -0.08, 0.05 and -0.02 cm with standard deviations of 0.33, 0.39 and 0.55 cm in, vertical, longitudinal and lateral directions respectively.ConclusionsSBRT for liver targets delivered by means of FFF resulted to be feasible with short beam on time.

Anatomy driven optimization strategy for total marrow irradiation with a volumetric modulated arc therapy technique

The purpose of this study was to evaluate the possibility of dose distribution optimization for total marrow irradiation (TMI) employing volumetric‐modulated arc therapy (VMAT) with RapidArc (RA) technology setting isocenter's positions and jaw's apertures according to patient's anatomical features. Plans for five patients were generated with the RA engine (PROIII): eight arcs were distributed along four isocenters and simultaneously optimized with collimator set to 90°. Two models were investigated for geometrical settings of arcs: (1) in the “symmetric” model, isocenters were equispaced and field apertures were set the same for all arcs to uniformly cover the entire target length; (2) in the “anatomy driven” model, both field sizes and isocenter positions were optimized in order to minimize the target volume near the field edges (i.e., to maximize the freedom of motion of MLC leaves inside the field aperture (for example, avoiding arcs with ribs and iliac wings in the same BEV)). All body bones from the cranium to mid of the femurs were defined as PTV; the maximum length achieved in this study was 130 cm. Twelve (12) Gy in 2 Gy/fractions were prescribed in order to obtain the covering of 85% of the PTV by 100% of the prescribed dose. For all organs at risk (including brain, optical structures, oral and neck structures, lungs, heart, liver, kidneys, spleen, bowels, bladder, rectum, genitals), planning strategy aimed to maximize sparing according to ALARA principles, looking to reach a mean dose lower than 6 Gy (i.e., 50% of the prescribed dose). Mean MU/fraction resulted 3184±354 and 2939±264 for the two strategies, corresponding to a reduction of 7% (range −2% to 13%) for (1) and (2). Target homogeneity, defined as D2%−D98% was 18% better for (2). Mean dose to the healthy tissue, defined as body minus PTV, had 10% better reduction with (2). The isocenter's position and the jaw's apertures are significant parameters in the optimization of the TMI with RA technique, giving the medical physicist a crucial role in driving the optimization and thus obtaining the best plan. A clinical protocol started in our department in October 2010.PACS numbers: 87.55.de, 87.55.dk, 87.56.nk, 87.57.uq

Prospective phase II trial of cetuximab plus VMAT-SIB in locally advanced head and neck squamous cell carcinoma

Cetuximab plus radiotherapy (RT) may be an effective alternative to chemoradiation in locally advanced head and neck squamous cell carcinoma (LASCCHN) patients. We analyzed a group of patients treated at our institute with cetuximab plus volumetric modulation arc therapy (VMAT) with the RapidArc technique in a simultaneous integrated boost (SIB) regime. The primary end point was the assessment of acute toxicity and the feasibility of the combined approach. Between December 2008 and March 2010, 22patients were submitted to IMRT-SIB plus cetuximab for radical intent in case of LASCCHN. None of the patients was suitable for chemotherapy because of important comorbidities (the majority suffered of heart chronic diseases). All patients underwent planning CT (additional image modalities were acquired for contouring purposes in the same treatment position: MRI in 12 and FDG-PET in 4out of 22patients). VMAT, by means of RapidArc, and SIB with two dose levels of 54.45Gy and 69.96Gy in 33fractions were adopted. All patients included in the analysis were concomitantly treated with cetuximab: administration of the drug was initiated 1week before RT at a loading dose of 400mg/m(2) body surface area over a period of 120min, follow by a weekly 60min infusion of 250 mg/m(2) for the duration of RT. Patients were assessed for toxicities according to the Radiation Therapy Oncology Group (RTOG) criteria. All but 2patients completed treatment and achieved the minimum follow-up of 12months after the end of the treatment. Of the 22patients, 18% (4patients) showed grade1, 36% (8patients) grade2, and 36% (8patients) showed grade3 dermatitis, while 9% (2patients) had grade1, 36% (8patients) grade2, and 45% (10patients) had grade3 mucositis/stomatitis. No grade4 toxicities were recorded. Considering blood parameters, 3cases of grade1 anemia and 1case of grade2 thrombocytopenia were observed. Nobody required feeding tube placement during treatment. The here reported toxicity data are promising and encouraging in regard to the adoption of moderate hypofractionation with VMAT-SIB techniques, when cetuximab is concomitantly administered.

Dosimetry comparison between volumetric modulated arc therapy with RapidArc and fixed field dynamic IMRT for local-regionally advanced nasopharyngeal carcinoma

A dosimetric study was performed to evaluate the performance of volumetric modulated arc radiotherapy with RapidArc on locally advanced nasopharyngeal carcinoma (NPC). The CT scan data sets of 20 patients of locally advanced NPC were selected randomly. The plans were managed using volumetric modulated arc with RapidArc and fixed nine-field coplanar dynamic intensity-modulated radiotherapy (IMRT) for these patients. The dosimetry of the planning target volumes (PTV), the organs at risk (OARs) and the healthy tissue were evaluated. The dose prescription was set to 70 Gy to the primary tumor and 60 Gy to the clinical target volumes (CTV) in 33 fractions. Each fraction applied daily, five fractions per week. The monitor unit (MU) values and the delivery time were scored to evaluate the expected treatment efficiency. Both techniques had reached clinical treatment's requirement. The mean dose (Dmean), maximum dose (Dmax) and minimum dose (Dmin) in RapidArc and fixed field IMRT for PTV were 68.4±0.6 Gy, 74.8±0.9 Gy and 56.8±1.1 Gy; and 67.6±0.6 Gy, 73.8±0.4 Gy and 57.5±0.6 Gy (P<0.05), respectively. Homogeneity index was 78.85±1.29 in RapidArc and 80.34±0.54 (P<0.05) in IMRT. The conformity index (CI: 95%) was 0.78±0.01 for both techniques (P>0.05). Compared to IMRT, RapidArc allowed a reduction of Dmean to the brain stem, mandible and optic nerves of 14.1% (P<0.05), 5.6% (P<0.05) and 12.2% (P<0.05), respectively. For the healthy tissue and the whole absorbed dose, Dmean of RapidArc was reduced by 3.6% (P<0.05), and 3.7% (P<0.05), respectively. The Dmean to the parotids, the spinal cord and the lens had no statistical difference among them. The mean MU values of RapidArc and IMRT were 550 and 1,379. The mean treatment time of RapidArc and IMRT was 165 s and 447 s. Compared to IMRT, the delivery time and the MU values of RapidArc were reduced by 63% and 60%, respectively. For locally advanced NPC, both RapidArc and IMRT reached the clinic requirement. The target volume coverage was similar for the different techniques. The RapidArc technique showed some improvements in OARs and other tissue sparing while using reduced MUs and delivery time.

The clinical impact of the couch top and rails on IMRT and arc therapy

The clinical impact of the Varian Exact Couch on dose, volume coverage to targets and critical structures, and tumor control probability (TCP) has not been described. Thus, we examined their effects on IMRT and arc therapy. Five clinical prostate patients were planned with both 6 MV eight-field IMRT and 6 MV two-arc RapidArc techniques using the Eclipse treatment planning system. These plans neglected treatment couch attenuation, as is a common clinical practice. Dose distributions were then recalculated in Eclipse with the inclusion of the Varian Exact Couch (imaging couch top) and the rails in varying configurations. The changes in dose and coverage were evaluated using the dose-volume histograms from each plan iteration. We used a TCP model to calculate losses in tumor control resulting from not accounting for the couch top and rails. We also verified dose measurements in a phantom. Failure to account for the treatment couch and rails resulted in clinically unacceptable dose and volume coverage losses to the targets for both IMRT and RapidArc. The couch caused average prescription dose losses (relative to plans that ignored the couch) to the prostate of 4.2% and 2.0% for IMRT with the rails out and in, respectively, and 3.2% and 2.9% for RapidArc with the rails out and in, respectively. On average, the percentage of the target covered by the prescribed dose dropped to 35% and 84% for IMRT (rails out and in, respectively) and to 18% and 17% for RapidArc (rails out and in, respectively). The TCP was also reduced by as much as 10.5% (6.3% on average). Dose and volume coverage losses for IMRT plans were primarily due to the rails, while the imaging couch top contributed most to losses for RapidArc. Both the couch top and rails contribute to dose and coverage losses that can render plans clinically unacceptable. A follow-up study we performed found that the less attenuating unipanel mesh couch top available with the Varian Exact couch does not cause a clinically impactful loss of dose or coverage for IMRT but still causes an unacceptable loss for RapidArc. Therefore, both the imaging or mesh couch top and the rails should be accounted for in arc therapy. The imaging couch top should be accounted for in IMRT treatment planning or the mesh top can be used, which would not need to be accounted for, and the rails should be moved to avoid the beams during treatment.

A Dosimetric Study of Inhomogeneous Dose Delivery: A Novel Approach to Dose Escalation

Materials/Methods: The study included volumetric modulated arc plans obtained with an Eclipse planning system from 11 localized prostatecancer cases. The clinical targetvolume (CTV) was the prostategland. The planningtargetvolume (PTV) was an expansion of CTV by 3 mm posteriorly and 4 mm in other directions. The prescribed dose (PD) to the PTV was 40 Gy (100%) to be delivered in 5 fractions with a RapidArc technique, similar to an ongoing SBRT protocol in our department. The intent in this exercise was to perform dose escalation within the PTV by increasing mean doses, rather than the minimum or peripheral doses. To create PTV dose inhomogeneity, a PTV sub-volume was defined to receive a higher dose. This high-dose volume (HDV) was created by shrinking the CTV by 5 mm and subtracting the urethral volume with a margin of 3 mm. The HDV was intended to receive at least 150% of the PD with no maximal dose limit. The mean PTV was 90 cc (range 54 to 127 cc). The HDV represented an average of 24% of the prostate PTV volume (range 15 to 38%). Rectal and bladder constraints were the same at: 50%\40 Gy, 20%\32 Gy, 12%\36 Gy, and 8%\40 Gy. Results: The profiles of the PTV dosevolume histograms resemble those achieved with high dose rate brachytherapy of the prostate. With respect to the target areas, the average PTV dose was 132% of the PD (range 110 to 140%). The HDV received an average of 155% of the PD (range 120 to 183%). The average of the HDV maximal doses was 195% of the PD (range 128.3 to 236.3%). Critical structure constraints were met in all cases. Overall, the mean rectal volume receiving 36 Gy was\5% (range 3 to 11%); the mean bladder volume receiving 36 Gy was\3% (range 1 to 12%) The urethral mean dose was 106% of the PD (range 91 to 128%). Conclusions:In this study, allowing dose inhomogeneity within the prostategland resulted in large dose escalation without compromiseofcriticalnormaltissues.Brachytherapytargetdose/volumeprofilescanbesafelyachievedwiththisnovelexternalbeam technique. Author Disclosure: N.G. Nickols: None. N. Agazaryan: None. C. King: None. P. Lee: None. M. Steinberg: None. P. Kupelian: None.

Influence Of Weight Loss On The Dose Distribution In Gynecological Patients Receiving Radiation Treatment With The RapidArc Technique

Influence Of Weight Loss On The Dose Distribution In Gynecological Patients Receiving Radiation Treatment With The RapidArc Technique

Volumetric modulated arc radiotherapy for esophageal cancer

A treatment planning study was performed to evaluate the performance of volumetric arc modulation with RapidArc (RA) against 3D conformal radiation therapy (3D-CRT) and conventional intensity-modulated radiation therapy (IMRT) techniques for esophageal cancer. Computed tomgraphy scans of 10 patients were included in the study. 3D-CRT, 4-field IMRT, and single-arc and double-arc RA plans were generated with the aim to spare organs at risk (OAR) and healthy tissue while enforcing highly conformal target coverage. The planning objective was to deliver 54 Gy to the planning target volume (PTV) in 30 fractions. Plans were evaluated based on target conformity and dose-volume histograms of organs at risk (lung, spinal cord, and heart). The monitor unit (MU) and treatment delivery time were also evaluated to measure the treatment efficiency. The IMRT plan improves target conformity and spares OAR when compared with 3D-CRT. Target conformity improved with RA plans compared with IMRT. The mean lung dose was similar in all techniques. However, RA plans showed a reduction in the volume of the lung irradiated at V20Gy and V30Gy dose levels (range, 4.62–17.98%) compared with IMRT plans. The mean dose and D35% of heart for the RA plans were better than the IMRT by 0.5–5.8%. Mean V10Gy and integral dose to healthy tissue were almost similar in all techniques. But RA plans resulted in a reduced low-level dose bath (15–20 Gy) in the range of 14–16% compared with IMRT plans. The average MU needed to deliver the prescribed dose by RA technique was reduced by 20–25% compared with IMRT technique. The preliminary study on RA for esophageal cancers showed improvements in sparing OAR and healthy tissue with reduced beam-on time, whereas only double-arc RA offered improved target coverage compared with IMRT and 3D-CRT plans.

SU‐E‐T‐803: Dosimetric Evaluation for Pulsed Low Dose Rate Radiation Therapy Using RapidArc Delivery Techniques

Purpose: There has been no consensus standard of care to treat recurrent cancer patients who have previously been irradiated. Pulsed low dose rate (PLDR) radiotherapy has potential to reduce normal tissue toxicities while still providing significant tumor control for recurrent cancers. This work investigates the dosimetry feasibility of PLDR radiotherapy using the RapidArc delivery technique for a dose escalation trial. Methods: Five body sites were investigated including breast, pancreas, prostate, head and neck, and lung. RapidArc plans were generated using the Varian Eclipse system with 6, 10 and 15MV beams. Each plan consisted of two arcs and the plan was delivered 5 times to achieve a daily dose of 2Gy. The dosimetry requirement was to deliver 20cGy/arc with a 3min interval to achieve an effective dose rate of 6.7cGy/min. Monte Carlo simulations were performed to calculate the actual dose delivered to the planning target volume (PTV) considering beam attenuation/scattering and intensity modulation. The maximum, minimum and mean doses to the PTV were analyzed together with the dose volume histograms and isodose distributions. Results: Two full arcs were necessary to achieve superior dose distributions for complex recurrent cancers to spare critical structures effectively. For 9 patients, the mean PTV dose for each arc ranged 18.9–22.6cGy/arc. For breast the minimal and the maximal PTV dose was 8.56 and 31.2cGy/arc, respectively. The RapidArc dose varied between 12.9 and 27.5cGy/arc for pancreas, 12.6 and 28.3cGy/arc for prostate, 12.1 and 30.4cGy/arc for H&amp;N, and 16.2 and 27.6cGy/arc for lung, respectively. Good agreement was achieved between the planned doses and Matrix measurements with 95–98% passing rates Conclusions: Advanced image‐guided radiotherapy can provide superior target coverage and normal tissue sparing for PLDR reirradiation of recurrent cancers, which can be delivered using the RapidArc technique with 10 full arcs and an effective dose rate of 3–10cGy/min.

SU‐E‐T‐459: Measurement of Gated Rapidarc Accuracy

Purpose: Recently, Kyung Hee university hospital at Gangdong installed the Varian 21iX linac which has the volumetric imrt (RapidArc) option and a real‐time position management (RPM) system. One of advantage of rapidarc is a short treatment time comparing with other treatments. Thus, the rapidarc treatment with the RPM system for the lung and liver cases, can reduce the treatment time comparing with the intensity modulation radiotherapy (IMRT) and 3 dimensional radiotherapy (3DRT) with gating system. Therefore, we estimate the accuracy of the gated rapidarc treatment. Methods: 10 patients data are used for this study. Each patient was planned by rapidarc technique using varian ECLISPE v8.6 planning machine. For the patient Quality Assurence (QA), a MATRIXX detector and IˈM RT software are used. At bottom and top of MATRIXX detector, 5×30×30cm̂3 of solid water phantoms are install for build up. A MATRIXX detector is fixed but the infrared reflecting box is periodically moved to provide the gating signal to the RPM system. Each patients dosimetric distribution is measured and the treatment summary which is provided by linac operating system is recoded to estimate the accuracy of the gated rapidarc treatment. Results: The dosimetric comparison between the measurement and the treatment plan is matched well for the 10 patients. With 3% of delta dose and 3mm of delta distance, more than 98% of area gives the gamma value as less than 1. Conclusions: We found that the patient dose measurement is matched well with the RTP planˈs dose distribution for the gated rapidarc treatment cases in the mechanical point of view. This study shows the gated rapidarcˈs dose reproducibility during the patient QA but this result has a limitation for the dose confirming for the real patients which has more soft and flexible body than the solid phantom.

SU‐C‐BRC‐02: Plan Quality and Delivery Efficiency with Varian TrueBeam FFF Mode at High Dose Rate

Purpose: The maximum dose rate at the regular filter mode of a Varian Linac is 600 MU/min. In comparison, the dose rate for flattering filter free (FFF) mode of Varian TrueBeam linac is up to 1400 MU/min at 6MV. The purpose of this study is to investigate the clinical use of IMRT treatment in FFF mode at high dose rate. Method: Ten prostate patientsˈ plans were generated using regular and FFF mode at 6 MV using Eclipse treatment planning system. PTV varies from 122–233 cc. Four types of plans were generated for each patient: multifield IMRT using regular filter mode, multifield IMRT using FFF mode, RapidArc(RA) using filter mode, RA using FFF mode. To facilitate comparison, same constraint table was used for each patient to optimize the fluence. Continuous high definition MLC sequences were generated at maximum dose rate of each mode. Results: With same optimization parameters, the plan quality is comparable for each plan. The maximum doses to target and organs are slightly higher for FFF mode with the same IMRT technique. Total MU for FFF mode and multifield IMRT technique is much higher than their counterparts. Nonetheless the beam‐on time is substantially lower for FFF mode due to higher dose rate. Conclusion: IMRT plans for the two filter modes are comparable. Although the dose rate for FFF mode is much higher than filter mode, FFF mode requires much more MUs to deliver the same amount of dose. Many MUs are used to move MLC leaves to compensate sloping region of beam profile in FFF mode. This reduces MU efficiency when irradiating large targets with irregular shapes. High dose rate treatment in FFF mode is more efficient to SRS treatment for small target. RapidArc technique may help reduce the delivery time for treatment of large target.

SU-E-T-476: Volumetric Modulated Arc Therapy (VMAT) Plan Validation Using MatriXX Measurements and Monte Carlo Calculation

Purpose: To establish confidence in VMAT plan delivery for recently launched VMAT with Varianˈs RapidArc technique at our clinic, a sophisticated plan validation has been performed by comparison of ion- chamber measurements, planning system calculations, and independent Monte Carlo calculations. Methods: Although MatriXX has been used as a reliable device for validations of intensity modulate radiation therapy (IMRT) treatment plans, it was challenging to use it for VMAT plan validations because of its angle-dependent dose response. A new version of MatriXX Evolution with a gantry angle sensor is able to correct the angle dependency and promises accurate measurements while the gantry rotates. To evaluate the performance of MatriXX for RapidArc plan validations, Monte Carlo calculations using XVMC was used as an independent method to our IMRT validation program. DICOM plans and CT images from Eclipse planning system were translated by an in-house code for XVMC input. Measured dose planes were compared with XVMC dose planes as well as Eclipse dose planes for 12 pelvis plans, 19 prostate plans, and 5 head and neck (H&N) plans. Construction of a scatterplot by taking differences of calculations from measurements displayed a positive correlation between them. Results: Eclipse calculations were off from measurements by 2.64%, 1.89%, and 1.84% in quadratic mean for pelvis, prostate, and H&N plans, respectively. XVMC calculations were off from the measurement by 2.18%, 1.73%, and 2.30% in quadric mean for pelvis, prostate, and HN plans, respectively. Passing percent of Gamma test for Eclipse calculations was over 97.0% and that for XVMC calculations was about 95.7% due to inherent statistical uncertainty of Monte Carlo calculation. Eclipse and XVMC calculations agreed to each other within 4 % Conclusions: The present study shows that Eclipse calculations and measurements using MatriXX evolution can be used for validation of VMAT plans using Rapid Arc delivery technique.

SU‐E‐T‐885: A Planning Comparison of Dynamic Conformal Arc (DCA), Static Non‐ Coplanar Intensity Modulated Radiotherapy (NCP‐IMRT), Volumetric Modulated Arc Therapy (RapidArc), Robotic Radiosurgery (Cyberknife), and Helical Tomotherapy (HI‐ART TomoTherapy) for SRS

Purpose: This work compares all linac‐based SRS treatment techniques currently available for single lesion cranial SRS. This study includes the planning comparison of dynamic conformal arc (DCA), static non‐coplanar intensity modulated radiotherapy (NCP‐IMRT), volumetric modulated arc therapy (RapidArc), robotic radiosurgery (Cyberknife), and helical tomotherapy (HI‐ART TomoTherapy) for cranial SRS. Methods: Thirteen target volumes with range 0.23 to 20.76 cc were retrospectively selected and transferred to a CT scan of a phantom designed for end‐to‐end SRS QA (Lucy phantom, Standard Imaging). Plans were developed using, iPlan TPS (v4.1, BrainLAB) for DCA (4 arcs) and NCP‐IMRT (16 beams), meanwhile the Eclipse TPS (v8.6, Varian Medical Systems) was used for the RapidArc (4 arcs) technique. Multiplan TPS (v3.5, Accuray) and TomoTherapy HI‐ART TPS (v3.1.4.23) was used for Cyberknife and TomoTherapy respectively. All plans were evaluated using four criteria, (1) Paddickˈs Conformity Index (CI), (2) Paddickˈs Gradient Index (GI), (3) Homogeneity Index and (4) Wagnerˈs Conformity/Gradient Index (CGI). Results: The average Paddick conformity index, CI was 0.64, 0.72, 0.76, 0.78, and 0.65 for the DCA, NCP‐IMRT, RapidArc, Cyberknife and Tomotherapy techniques respectively.The average Paddick gradient index, GI was 3.3, 3.6, 4.2, 4.4, and 4.9 for the DCA, NCP‐IMRT, RapidArc, Cyberknife and Tomotherapy techniques respectively. The average Wagnerˈs CGI was 71.6, 74.5, 72.2, 71.37, and 62.18 for the DCA, NCP‐IMRT, RapidArc, Cyberknife and Tomotherapy techniques respectively. IMRT‐based techniques and robotic radiosurgery showed better CI and CGI, whereas DCA showed the best dose fall off followed by NCP‐IMRT Conclusions: All methods were able to produce comparable plans for most of the targets tested. More importantly, it is suggested that for future planning studies the plan criteria must be explicit in their goals. In particular, the gradient index should be specified along with the desired dose prescription and conformality.