Forward Planning Technique Research Articles

Is Real-Time Inverse Planning Optimizing Dose to the Normal Brain? A Prospective Comparative Trial in a Series of Brain Metastases Treated by Stereotactic Radiosurgery

Background: Radiosurgery has demonstrated good safety and efficacy in the treatment of multiple brain metastases (BMs). However, multi-target dose planning can be challenging and time-consuming. A recently developed real-time inverse treatment planning (IP) by convex optimization has been demonstrated to produce high-quality treatment plans with good conformity and selectivity in single-target plans. We intended to test the capacity of this IP to rapidly generate efficient plans while optimizing the preservation of normal tissue in multiple BM. Methods: Seventy-nine patients (mean age 62.4, age range 22–85) with a total of 272 BMs were treated by Gamma Knife Radiosurgery. All subjects were treated using a forward planning (FP) technique by an expert neurosurgeon. The new Intuitive Plan was applied and able to automatically generate an alternative plan for each patient. All planning variables were collected from the IP to be compared with the corresponding measurements obtained from the FP. A paired sample t test was applied to compare the 2 plans for the following variables: brain volumes receiving 10 Gy (V10) (primary endpoint), and 12 Gy (V12), planning indices (selectivity, coverage, gradient, and Paddick Conformity Index [PCI]), beam-on time (BOT), and integral doses. Additionally, the noninferiority margin for each item was calculated, and the 2 plans were compared for noninferiority using a paired t test. Results: The mean age of patients was 62.4 years old (age range 22–85), with a sex ratio of 1.02. The average number of lesions per patient was 3.4 (range 1–12). The mean prescription dose was 21.46 Gy (range 14–24 Gy). Noninferiority of the IP was concluded for V10, V12, prescription isodose volume, BOT, PCI, and selectivity. The V10 (and V12) was significantly lower with the IP (p < 0.001). These volumes were 8.69 cm³ ± 11.39 and 5.47 cm³ ± 7.03, respectively, for the FP and 7.57 cm³ ± 9.44 and 4.78 cm³ ± 5.86 for the IP. Only the coverage was significantly lower with the IP (−2.3%, p < 0.001), but both selectivity (+17%) and PCI (+15%) were significantly higher with the IP than FP (p < 0.001). Conclusion: This IP demonstrated its capacity to generate multi-target plans rapidly, with a dose to the brain (V10) and BOT noninferior to the one of a human expert planner. These results would benefit from confirmation in a larger prospective series.

A Novel 3D MLC-Based Forward Planning Technique for Spatial Fractionated GRID Therapy

A Novel 3D MLC-Based Forward Planning Technique for Spatial Fractionated GRID Therapy

Variation of V105% between pre- and postmerged subfields in field-in-field hypofractionated breast radiotherapy plans

Hypofractionated whole-breast irradiation has emerged as a viable alternative to conventional fractionation. In the field-in-field forward planning technique, a merged plan with 2 to 4 segmental fields is the final plan delivered to the machine. As per the ASTRO guidelines for the hypofractionation regimen, the volume of breast tissue receiving V105% of the prescription dose should be less than 200 cc. However, we have noticed substantial changes to this volume (change in V105% between −55 cc and + 47.1 cc) after merging the subfields. This study compares the V105% of 29 breast plans before and after merging the subfields.

Performance of the irregular surface compensator compared with four-field box and intensity modulated radiation therapy for gynecologic cancer

PurposeA retrospective planning study was undertaken to evaluate the dosimetric advantages of the irregular surface compensator (ISC) technique, a forward planning technique with electronic compensation algorithm available on Varian Eclipse treatment planning system. This was extensively compared to the conventional four-field box (4FB) and intensity modulated radiation therapy using 5 fields (IMRT5F) on gynecologic cancer patients. MethodsTwenty-two patients were enrolled. The prescribed dose was 50.4Gy in 28 fractions to the primary target including pelvic lymph nodes. 4FB treatment plans were generated, then fluence of anterior and posterior fields were modified to generate ISC plans. IMRT5F were inversely optimized with equally spaced five coplanar fields. Dose-volume parameters were evaluated for the comparison of three planning techniques. The MU and delivery time were also estimated. ResultsIn terms of target coverage, the conformity and homogeneity index of ISC (1.67 and 1.03, respectively) were superior to those of 4FB (2.43 and 1.06, respectively) but slightly inferior to those of IMRT5F (1.10 and 1.02, respectively). ISC also illustrated an overall improvement in normal organ saving. Compared to 4FB, the mean dose of the rectum was reduced by about 4.0–5.0Gy with ISC and IMRT5F. The volume receiving large doses was reduced for bladder with statistical significance with ISC and more with IMRT5F relative to 4FB. The mean number of MU per fraction were 200.86 (4FB), 446.09 (ISC) and 895.59 (IMRT5F). ConclusionThe ISC technique has the superior target coverage and healthy tissue sparing in comparison with conventional 4FB and comparable normal organ saving compared to IMRT5F. The ISC can be an available option for gynecologic radiotherapy.

Left-sided breast radiotherapy after conservative surgery: comparison of techniques between volumetric modulated arc therapy, forward-planning intensity-modulated radiotherapy and conventional technique

AbstractObjectiveThis study was conducted for comparison of techniques between volumetric modulated arc therapy (VMAT), forward-planning intensity-modulated radiotherapy (FIMRT) and conventional technique for left-sided breast radiotherapy after conservative surgery.MethodsIn all, 20 postoperative left breast carcinoma patients were included in this study. In all plans the planning target volume (PTV) was the breast tissue with appropriate margin as per our institutional protocol. The contouring was done on a Monaco Sim (V5.00.02) contouring workstation. All patient were planned using partial arc VMAT in Monaco treatment planning system (TPS) (V5.00.02) and treated on Elekta Synergy linear accelerator. The 3D conformal radiotherapy (3DCRT) and FIMRT planning were done in CMS XIO (V5.00.01.1) TPS. The 3DCRT planning consisted of conventional medial and tangential wedge portals with multileaf collimator field shaping conforming to the target volume. For all the plans generated the following metrics were scored: V105%, V100%, V95%, mean dose (for PTV), V5%, V20%, D2cc and mean dose (for organs at risk).ResultsThe mean PTV volume for 20 patients was 1,074·6±405·1 cc. The highest PTV dose coverage was observed in the 3DCRT technique with 94·1±1·8% of the breast PTV receiving 95% of the prescription dose (V95%). However, it was also observed that this technique resulted in 21·3±10% of the PTV receiving more than 105% of the prescription dose (V105%), which was highest among the three techniques. In contrast, VMAT yielded lowest V95% of 93·0±1·8 and 3·3±5·5% of V105%.ConclusionThis study concluded equivalent result between FIMRT and VMAT. However, VMAT was found to be the choice of radiotherapy technique as it produces lesser dose distribution to heart compared with any other technique.

Multi-staged robotic stereotactic radiosurgery for large cerebral arteriovenous malformations

To investigate a multi-staged robotic stereotactic radiosurgery (SRS) delivery technique for the treatment of large cerebral arteriovenous malformations (AVMs). The treatment planning process and strategies to optimize both individual and composite dosimetry are discussed. Eleven patients with large (30.7 ± 19.2 cm(3)) AVMs were selected for this study. A fiducial system was designed for fusion of targets between planar angiograms and simulation CT scans. AVMs were contoured based on single contrast CT, MRI and orthogonal angiogram images. AVMs were divided into 3-8 sub-target volumes (3-7 cm(3)) for sequential treatment at 1-4 week intervals to a prescription dose of 16-20 Gy. Forward and inversely developed treatment plans were optimized for 95% coverage of the total AVM volume by dose summation from each sub-volume, while minimizing dose to surrounding tissues. Dose-volume analysis was used to evaluate the PTV coverage, dose conformality (CI), and R50 and V12 Gy parameters. The treatment workflow was commissioned and able to localize within 1mm. Inverse optimization outperformed forward planning for most patients for each index considered. Dose conformality was shown comparable to staged Gamma Knife treatments. The CyberKnife system is shown to be a practical delivery platform for multi-staged treatments of large AVMs using forward or inverse planning techniques.

SU‐E‐T‐678: Normal Tissue Dose‐Volume Constrains for Inverse Planning of Acoustic Neuroma Stereotactic Radiosurgery (SRS)

Purpose: Stereotacic radiosurgery (SRS) of acoustic neuroma was traditionally planned using forward planning techniques, either with Elekta GammaKnife ball‐packing technique, or with multiple conformal dynamic arcs technique using micro‐MLC and Linac (BrainLAB Novalis). As the recent development of Volumetric Modulated Arc Therapy (VMAT), inverse planning using multiple‐arcs VMAT technique for SRS becomes commercially available, and it has the advantage of faster delivery with comparable dosimetry. However, planners need proper dose volume constrains to drive the optimizer to achieve the dosimetric goals, both clinically acceptable and technically achievable. This study is investigating how to set up the proper dose volume constraints for SRS plans of acoustic neuroma. Methods: Twenty cases were selected with their volumes cover the general range of acoustic neuroma SRS (0.1 cc to 5cc). Each case was planned using Gammaknife Perfexion with sector optimization. Prescription is 12Gy to 50% isodose, with 100% target coverage. The total tissue volumes that receive greater than 12, 8, and 6 Gy (V12, V8, and V6) were recorded. The relationship between the target volumes (Vtarget) and V12, V8, and V6 were plotted and linear regressions were fitted for each parameter. Results: A set of linear relationships between the target volume and the volumes that receive greater than 12, 8, and 6Gy was constructed as the following: V12 = 1.476Vtarget (R2 = 0.995), V8 = 3.04Vtarget +0.16(R2 = 0.990), and V6 = 4.64 Vtarget + 0.35 (R2 = 0.982). Conclusions: Traditional plan quality indices such as conformity index, selectivity, etc. are good for evaluating forward plans, but cannot be used to drive the inverse planning engine to optimize inverse plans. The normal tissue dose volume constraints obtained in this study, combined with clinical constraints for brainstem and cochlea, can provide inverse planner with objectives to obtain an inverse plan for acoustic neuroma SRS.

18P - Radiation Treatment Planning in Postmastectomy Patients - Comparison of 3D Versus 2D Plans

Objective: To compare the quality of 3D versus 2D planning in postmastectomy patients in terms of target volume coverage and sparing of organs at risk. Patients and methods: 27 postmastectomy patients, 16 with left and 11 with right sided breast cancer. PTV1a consisted of chest wall, up to skin surface and PTV1b of supraclavicular fossa +/- axilla plus 1 cm margin; distance from skin surface was 5 mm. Delineated OAR were both lungs, spinal cord and heart for left sided breast cancer. Total dose was 50 Gy in 25 fractions. For each patient a 3D and 2D plan were made. For the 3D plan the forward IMRT planning technique was used. Tangential beams were used for PTV1a and AP-PA opposed fields for PTV1b, all with 6MV photons. 2D plan was made using direct electron field (9-12 MeV) on PTV1a and combination of direct electron (18 Mev) and direct photon field (6 MV) on PTV1b. For PTV1a 5 mm bolus was used. For 3D plans required PTV coverage with 95-107% of prescribed dose was at least 85%. Dose constraints for OAR were V20Gy< 35% for lung, Dmax <45 Gy for spinal cord and V20Gy< 10% and V40Gy< 5% for heart. For planning XIO 4.3.1 and 4.6.4 was used. Electron field was calculated with pencil beam algorithm. The CT slice thickness and calculation resolution of 2 mm was used. Statistical method: student t-test. Results: See table 18P below. Conclusion: 3D planning provided significantly better PTV coverage and lower maximal doses, but without significant influence on doses on OAR (lungs and spinal cord) when compared with 2D planning. Nevertheless, higher doses on the heart were observed with 3D planning, but within dose constraints.Tabled 1Coverage PTV1a (%)Coverage PTV1b (%)Dmax (Gy)Lung L V20Gy (%)Lung L MD (Gy)Lung R V20Gy (%)Lung R MD (Gy)Heart V20Gy (%)Heart V40Gy (%)Heart MD (Gy)Spinal cord Dmax (Gy)Left sided3D88.8 (3.5)*90.4 (3.9)53.5 (0.2)31.9 (6.3)16.2 (2.7)0.35 (0.88)0.67 (0.49)7.6 (1.9)3.5 (1.1)5.0 (1.2)36.5 (9.6)2D83.1 (7.2)61.2 (16.2)73.5 (3.3)31.0 (13.3)15.2 (5.4)0.85 (1.39)1.98 (0.98)5.3 (3.5)0.4 (0.5)5.6 (1.9)33.2 (6.2)p-value<0.01<10-6<10-6NS**NSNS<10-4<0.03<10-6NSNSRight sided3D91.2 (3.2)89.5 (2.0)53.6 (0.2)0.06 (0.1)0.4 (0.1)34.2 (2.0)17.0 (1.3)39.7 (5.8)2D82.4 (6.4)51.7 (19.3)74.4 (2.2)0.25 (0.4)2.2 (0.8)28.6 (9.6)14.8 (4.2)34.1 (4.6)p-value<0.01<10-5<10-6<10-6NSNSNS<0,03* median and standard deviation, ** not significant Open table in a new tab * median and standard deviation, ** not significant Disclosure: All authors have declared no conflicts of interest.

Reducing the Potential for Catastrophic Radiation Error by Using Historical Treatment Data

The increasing complexity of IMRT treatment plans requires carefully checking the correctness and consistency of an increasingly large number of treatment parameters between planning and each delivery session. A new level of safety can be added in the planning and delivery process by exploiting the similarities that exist among treatment parameters of a large pool of plans for the same disease using the same technique. The goal of this study is to develop the proof of concept for a software program that analyzes machine parameter distributions from historical treatment data for a given disease site and alerts the user of any deviation. The distribution of treatment parameters for a population of 60 patients treated with whole brain irradiation using a forward planning technique with parallel opposed beams was analyzed. A total of 15 treatment parameters were considered, including the number of beams, beam energy, gantry, collimator and couch angles, SSD, field size, number of monitor units, number of monitor units (MU) per Gy at isocenter and beam weight. For each parameter, a range of acceptable values was extracted from the population distribution. A new plan was considered consistent with historical data if each of its parameter values was compatible with 60% of the population. In order to test the software, errors such as a wrong number of beams, beam energy, CT dataset or absence of heterogeneity correction were manually introduced in new plans. As expected, the population of whole brain plans is very homogeneous. The SSD and number of MU per Gy exhibited a narrow Gaussian distribution. The field size, beam weight and number of MU show 2 Gaussian peaks corresponding to the open field and field-in-field, respectively. All other parameters had a single value. These narrow distributions made deviations easy to detect. The plans with the wrong number of beams or beam energy were obvious. The plan using the wrong CT dataset led to an SSD that was outside the historical range and was detected. Interestingly, the plan calculated without homogeneity correction was not detected. However, since such corrections are not of great importance for whole brain radiation, the machine parameters were not affected and such a treatment would not have led to a radiation error. We developed a software program to compare each new treatment plan to historical treatment parameters for the same disease. We successfully tested it on a population of whole brain treatment plans. The use of such a program can detect potential errors that were accidentally introduced during data transfer and recording, such as those reported in the New York Times. In addition, it will ultimately demonstrate that by using more standardized treatment approaches for a given disease, the risk for errors can be reduced.

Radiobiological evaluation of forward and inverse IMRT using different fractionations for head and neck tumours

PurposeTo quantify the radiobiological advantages obtained by an Improved Forward Planning technique (IFP) and two IMRT techniques using different fractionation schemes for the irradiation of head and neck tumours. The conventional radiation therapy technique (CONVT) was used here as a benchmark.MethodsSeven patients with head and neck tumours were selected for this retrospective planning study. The PTV1 included the primary tumour, PTV2 the high risk lymph nodes and PTV3 the low risk lymph nodes. Except for the conventional technique where a maximum dose of 64.8 Gy was prescribed to the PTV1, 70.2 Gy, 59.4 Gy and 50.4 Gy were prescribed respectively to PTV1, PTV2 and PTV3. Except for IMRT2, all techniques were delivered by three sequential phases. The IFP technique used five to seven directions with a total of 15 to 21 beams. The IMRT techniques used five to nine directions and around 80 segments. The first, IMRT1, was prescribed with the conventional fractionation scheme of 1.8 Gy per fraction delivered in 39 fractions by three treatment phases. The second, IMRT2, simultaneously irradiated the PTV2 and PTV3 with 59.4 Gy and 50.4 Gy in 28 fractions, respectively, while the PTV1 was boosted with six subsequent fractions of 1.8 Gy. Tissue response was calculated using the relative seriality model and the Poisson Linear-Quadratic-Time model to simulate repopulation in the primary tumour.ResultsThe average probability of total tumour control increased from 38% with CONVT to 80% with IFP, to 85% with IMRT1 and 89% with IMRT2. The shorter treatment time and larger dose per fraction obtained with IMRT2 resulted in an 11% increase in the probability of control in the PTV1 with respect to IFP and 7% relatively to IMRT1 (p < 0.05). The average probability of total patient complications was reduced from 80% with CONVT to 61% with IFP and 31% with IMRT. The corresponding probability of complications in the ipsilateral parotid was 63%, 42% and 20%; in the contralateral parotid it was 50%, 20% and 9%; in the oral cavity it was 2%, 15% and 4% and in the mandible it was 1%, 5% and 3%, respectively.ConclusionsA significant improvement in treatment outcome was obtained with IMRT compared to conventional radiation therapy. The practical and biological advantages of IMRT2, employing a shorter treatment time, may outweigh the small differences obtained in the organs at risk between the two IMRT techniques. This technique is therefore presently being used in the clinic for selected patients with head and neck tumours. A significant improvement in the quality of the dose distribution was obtained with IFP compared to CONVT. Thus, this beam arrangement is used in the clinical routine as an alternative to IMRT.

SU‐GG‐T‐166: Patient Characteristics That Predict the Need for Breast IMRT

Purpose: Dose inhomogeneities in RT of the breast have been associated with increased acute and late toxicity. IMRT can reduce dose inhomogeneities, but is associated with increased costs, requires additional department resources and not all patients require IMRT. This work seeks patient variables that predict the need for IMRT to achieve dose homogeneity. Method and Materials: 100 patients were planned with an algorithmic forward planning technique. Subfields were added to initial open fields to reduce dose inhomogeneity. Characteristics, including separation, size, breast volume and maximum open field dose and number of subfields, were recorded. Receiver operator characteristic analysis evaluated the ability of binary classifiers of patient characteristics to predict the number of subfields. Results: Variable values were (median [min‐max]) will be presented. One third of patients required seven or more subfields to achieve the planning method's dose homogeneity goal. No single variable predicted the number of subfields with a zero rate of false positives or false negatives. A composite index, created from separation, size and volume, selected roughly 2/3 of these patients but with only a 5% false positive rate. Conclusion: The majority of tangent breast cases did not require IMRT to attain the desired dosimetric outcome. Neither geometric measures nor composite measures could select all patients requiring a large number of fields without including a greater number of patients that require fewer fields. Dosimetric evaluation of the patient at the time of simulation offers the highest specificity with a sensitivity of 1 for a large number of fields. Dose cutoff of 120% predicts necessity for 8 or more subfields with high specificity and selectivity. Including relatively simple dosimetric calculations in the simulation process may be in the effort to optimize use of department resources.

Crew Resource Management and Shared Mental Models: A Proposal

Crew Resource Management (CRM) training focuses on situation awareness, communication skills, teamwork, task allocation, and decision making. More recently, an interest in cognitive skill is beginning to appear in relation to CRM. One aspect of cognitive skill that has been examined in a variety of team domains is the notion of overlapping or mental models among teammates. While a growing amount of evidence on the relationship between shared mental models and team performance exists, only limited research has focused on the role that shared mental models have-in crew resource management. The purpose of this paper is to provide researchers and practitioners an understanding of the shared mental model construct and the role of shared mental models in team performance, as well as to encourage additional research on this topic within the aviation domain. Crew Resource Management and Shared Mental Models Human error is a major factor in aviation accidents. As a result, pilot training has shifted fiom an emphasis on purely technical skills, to a combination of both technical and teamwork skills (Reynolds & Rhoades, 2004). These training programs have a variety of names, but the most common is Crew Resource Management (CRM). is currently required by all 185 International Civil Aviation Orgauization members, is incorporated into each of the US military branches, and is gaining steady support outside aviation in industries as diverse as nuclear power producers and medical practitioners (American Psychological Association, 2005; Flin, Meams, & O ' C o ~ o r , 2002). Typically, three main skill clusters are targeted: communication, team building and workload management. Within these broad categories, however, content may vary to include: adaptability, assertiveness, communication, leadership, mission analysis, situational awareness, forward planning, risk assessment, group dynamics, stress and coping techniques, and how to monitor automated equipment (Naval Education and Training Command, 2003). The Federal Aviation Administration (FAA) (2004) suggests that CRM training focuses on situation awareness, communication skills, teamwork, task allocation, and decision making within a comprehensive m e w o r k of standard operating procedures (SOP) @. l). Under the topic of team building, the FAA notes that 'This topic includes interpersonal relationships and practices. Effective leadership/followership and interpersonal relationships are key concepts to be stressed. Cunicula can also include recognizing and dealing with diverse personalities and operating styles (p. l2). One area not emphasized is team cognition. The goal of this paper is to foster an understanding of the impact of team cognition in promoting effective team work, and to suggest the addition of team cognition, particularly shared mental models, as a focus of CRM. To accomplish this, we begin by discussing the evolution of CRM. Next, we discuss one aspect of team cognition, shared mental models, and how both implicit communication and team performance can be linked to shared mental models. This discussion includes a review of current research on shared mental models, as well as methods of measuring and training such models. We conclude by suggesting that future research and training incorporate shared mental models. Evolution of Kern (200 1) suggested that the roots of can be found in a 1951 U.S. Air Force Inspector General's report which analyzed data fiom 7518 major accidents between 1948 and 195 1, and found that poor teamwork and

SU‐GG‐T‐479: Dosimetric Comparison of Whole Breast Irradiation Using Helical Tomographic Technique and Static Multileaf Collimated Field‐In‐Field Technique

Purpose: To review the dosimetry results of whole breast irradiation using a helical Tomotherapy Hi‐Art device and discuss the feasibility of such treatment technique by comparing the data with linear accelerator based Eclipse field‐in‐field (FIF) technique. Method and Materials: Twenty breast plans were generated using a Tomotherapy Hi‐Art planning system. Among them, 11 were left breast cases and 9 were right breast cases. Treatment planning techniques such as contour delineation and optimization strategy/parameters were described. Key dosimetric results including target dose coverage and organs‐at‐risk (OAR) dose statistics were compiled and presented. Radio‐biological consequences to the OARs were studied using the normal tissue complication probability (NTCP) models. A retrospective study using the forward FIF planning technique was also performed for those 20 patients as comparison benchmark. Results: On the ipsilateral side, the Tomotherapy plans performed slightly better than the forward FIF plans in target coverage and dose uniformity (p=0.0018), and significantly better in OAR high dose statistics such as V20 in lung (p=0.0001) and V30 in heart (p=0.0003). Meanwhile, the Tomotherapy plans delivered slightly higher average dose to both ipsilateral and contralateral OAR, including the heart, the lung, the breast, the esophagus, and the spinal cord. However, the differences in NTCPs between the two techniques for the total lung (p=0.298) and the heart (p=0.268) were statistically insignificant, whereas the NTCPs for the esophagus were too low to compare. Conclusion: The Tomotherapy technique can provide better target coverage for breast cancer treatment. The differences in NTCPs associated with slightly higher mean doses to the OAR were insignificant comparing with the forward FIF technique.

Accelerated Hypofractionated Intensity Modulated Radiotherapy With Concurrent and Adjuvant Temozolomide for Patients With Glioblastoma Multiforme: A Safety and Efficacy Analysis

Despite multimodality treatments, the outcome of patients with glioblastoma multiforme (GBM) remains poor. In an attempt to improve results, we have begun a program of accelerated hypofractionated IMRT with concomitant and adjuvant temozolomide. We report our initial experience with this novel approach. Between March 2004 and June 2006, 35 unselected patients (median age: 63 years), with histologically proven GBM, were treated. A total of 26 patients (74.3%) had RTOG RPA class 5 or 6. Nine patients underwent biopsies only, while 26 patients had partial or complete resections. The methylation status of the MGMT promoter was known in the pathological specimens of 30 patients. Of these, 20 patients had a methylated-MGMT promoter while the other 10 had an unmethylated pattern. IMRT was delivered either by a forward or inverse planning technique. Gross Tumor Volume (GTV) consisted of the contrast-enhanced area and surgical cavity on the post-operative CT/MRI images. Planning target volume (PTV) was the GTV +15 mm. Patients received 60 Gy in 20 fractions (3 Gy per fraction), over 4 weeks, prescribed to the edge of the GTV, while 40 Gy was delivered to the periphery of the PTV. Temozolomide was administered according to the Stupp regimen. The median follow-up was 12.6 months (range: 3.2–26.5). Twenty-nine patients (82.8%) completed the combined modality treatment, and 25 of them (71.4%) received adjuvant temozolomide, with a median number of 4 cycles. Median survival was 14.2 months and median disease-free survival was 6.1 months. Median survival differed significantly between patients who underwent a biopsy versus a partial or total resection, (8.6 vs. 16.8 months, p < 0.01). Median survival was also significantly different between patients with methylated versus unmethylated MGMT promoters (17.23 vs. 7.083 months, p < 0.049). The pattern of failure was mainly central, within the initial GTV. Grade III-IV toxicity was limited to one patient with nausea and emesis during adjuvant temozolomide administration. Seven patients who relapsed received further treatment: five received temozolomide and procarbazine second-line chemotherapy, three underwent further debulking surgery, one patient underwent stereotactic radiosurgery and one patient started metronomic temozolomide. Accelerated hypofractionated IMRT with concomitant and adjuvant temozolomide is well tolerated with a useful two-week shortening of radiotherapy. Despite a high number of patients with poor prognostic features (74.3% RPA class 5–6), median survival was comparable to standard radiotherapy fractionation schedules plus temozolomide.

TH-D-M100E-06: Unified Dosimetry Index (UDI): A New Paradigm for Ranking Treatment Plans

Purpose: A new index for scoring treatment plans that unifies the four dosimetry indices of coverage, conformity, homogeneity and dose gradient, into one simple equation, is introduced. We present results of actual clinical cases evaluated with new scoring index, validating its effectiveness. Methods and Materials: We formulated a unified dosimetry index (UDI) that computes for any given treatment plan its deviations in terms of dose coverage, conformity, homogeneity, and dose gradient vis‐a‐vis an ideal plan. We define an ideal plan as one with perfect dose coverage, conformity, homogeneity, and a step‐wise fall‐off to zero dose outside the planning target. To demonstrate effectiveness of the scoring system, a retrospective evaluation of 21 stereotactic radiosurgery cases was conducted. The cases presented were planned on BrainSCAN (by BrainLAB Inc) utilizing 5–8 single‐isocenter non‐coplanar fixed beams collimated with micro multi‐leaf collimator (MMLC). This index is designed to be utilized also for scoring of radiotherapy treatment plans obtained using various other forward and inverse planning techniques including IMRT, and multiple‐isocenters noncoplanar arcs. Results: For most of the cases evaluated, conformity and dose gradient were the two dominant components. The contribution from dose homogeneity was significant only in a few cases. All plans received very close to full dose coverage, and as a result the contribution from dose coverage component to the overall score was negligible. However, for inverse planning the contributions from dose coverage and homogeneity components to the overall score are expected to be quite more significant and variable. Conclusion: The unified dosimetry index is demonstrated as an effective tool for scoring treatment plans. Utilizing the mean and standard deviation of UDI scores from a pool of treatment plans of similar modality and planning technique, we suggest a general guide for ranking treatment plans as “excellent”, “good”, “average”, or “poor”.

SU‐FF‐T‐399: Study the Difference Between IMRT and Forward Planning in Designing the Flash Required in Breast Treatemnet

Purpose: Study the difference between IMRT and forward planning in designing the flash required in breast treatment Method and Materials: Using the Pinnacle3 radiation treatment planning system to deliver a uniform dose to the Planning Target Volume (PTV) by using both forward planning techniques and inverse planning techniques (IMRT). The most important issue when it comes to IMRT breast treatment planning is to control the flash opening between the breast and the MLC in order to consider the breathing parameter. In forward planning 80% of the dose is delivered by open segmentation, and similarly, in IMRT the percentage of open segmentation can be controlled by drawing a flash target volume by extension of the PTV by 2.5 cm to 3.0 cm depending on the amount of flash desired. This flash target volume is included in the objective list of the IMRT parameters as “Uniform Dose” assigned to a minimum of 80% of the total prescribed dose and a minimal weight contribution such as 1E‐15. In comparing IMRT and forward planning techniques, IMRT not only allows a percentage of flash similar to the forward plan but it also achieves a more uniform dose coverage of the breast both at superior and inferior borders with reduced dose to the surrounding structures such as heart and lung. Results: Using a flash target volume with minimal weighting as a objective parameters allows a higher percentage of each beam to be treated open in the modulated segmentation. Conclusion: For IMRT breast treatment planning, a flash target volume can be used as an objective parameter during optimization to help increase the percentage of segmentation to be treated as open.

SU‐FF‐T‐166: Different Method of IMRT Planning for Breast Treatment

Purpose: To compare three different methods of IMRT planning for breast treatment. Method and Material: Breast IMRT plans are conducted for several Patients using Pinnacle PHILIPS system. Three IMRT methods have been utilized; the first is Forward Planning (FP) technique using segment weight optimization for selected set of objectives such as GTV, PTV, lung, heart, etc. The second method is Inverse planning (IP) technique using Direct Machine Parameters Optimization (DMPO) with same objectives used in FP plus an extra segment to account for flash. The third is IP technique using DMPO with same objectives used in FP plus an extra objective called “Flash Planning Target (FPT)” defined by expanding the PTV by 2.5–3.0 cm in the interior direction of the breast depending on the required amount of flash. The “FTP” objective is defined as a uniform dose with 80% or higher of the prescribed dose with an extremely minimum dose in the order of 1E‐15. “FPT” objective is included in the DMPO to generate sufficient flash (due to breathing parameter) which could not have happen without including this objective in the IP optimization. Comparing all methods, IP technique using the two DMPO methods will allow having a Flash for most of the treatment without defining segments and they will give better coverage of the breast from the superior and inferior direction with better controlling the dose to the surrounding organs. Results: Using the “FPT” objective along with DMPO techniques provide the open segment higher percentages for each beam with some other segments generated by Pinnacle not by the planner are superior over FP method. Conclusion: Inverse planning techniques using DMPO technique mentioned above will give a better coverage of the breast from the superior and inferior direction with better controlling the dose to the surrounding healthy tissues.

SU-FF-T-59: A Comparison of Forward and Inverse Planned IMRT Treatment of Breast Cancer

Purpose: To compare a forward planning technique with a commercial inverse planning module for breast IMRT treatments. Method and Materials: Currently, our clinic uses the Pinnacle IMRT InvPlan module for left breast IMRT treatment planning. Before the planning, the treatment volume (TV), the heart and the lungs are contoured on the patient CT scans. The isocenter and two tangential fields are defined in our treatment planning system (TPS), and an IMRT treatment plan was then generated using the inverse planning module. For the purpose of this study, we created forward planned IMRT breast plans with the same isocenter and tangential beams. Beam intensities in the forward plan were modulated by adding “control points” (CP), a special functionality provided by Pinnacle TPS. CP combines multiple tangential beams into a step-and-shoot IMRT field with multiple segments. A tangential beam in a forward IMRT breast plan typically consists of one open segment and 4 MLC segments blocking hot spots. A typical inverse IMRT breast plan has 6 to 7 segments in each beam. Isodose distributions and DVH's were compared between the breast IMRT plans generated using the forward planning technique and the inverse planning module. The statistical results were examined for the TV volumes receiving 95%, 100% and 105% of the prescription dose, the lung volume receiving more than 20 Gy and the heart volume receiving more than 30 Gy. Results: Five left breast cases were studied. The DVH's generated from both methods were comparable. It was found that the forward planned breast IMRT plans used fewer segments. The average values for V95, V100 and V105 between forward and inverse planed IMRT breast plans were within 2%. Conclusion: The forward planning technique can generate comparable breast IMRT plans and these plans met the clinical constraints used in our IMRT breast protocol.

Forward planning using multileaf collimation as a replacement for patient tissue compensation

In treatment planning, a dosimetrist may encounter a technique that would best be treated by including some type of compensation to correct for tissue or depth variations throughout the field, allowing for a more homogeneous dose distribution. Recent innovations, such as intensity-modulated radiotherapy (IMRT), have been introduced in an effort to address these issues. In many institutions, however, the treatment planning capabilities available may not accommodate consideration of such new technologies. The treatment planner is therefore left to determine how to incorporate these concepts with the current technologies available. While compensation may be an option, this may not always be possible due to the position of the beam or to actual mechanical restraints. Some institutions may also lack the ability and equipment to consider compensation at all. The answer is forward planning IMRT. This concept combines current forward planning techniques with multiple asymmetrically blocked treatment fields, varying the intensity of the beam from a given orientation to produce the desired treatment plan.

Three Dimensional Planning Significantly Improves Dose Homogeneity of Pelvic Sidewall Boost Plans Following Intracavitary Brachytherapy in Management of Cervical Carcinoma

Purpose: We propose that the current practice of prescribing the parametrial boost with the pt B estimation can be made significantly more uniform aby utilizing 3D treatment planning to produce a homogenous dose profile at the reference volume and that this practice can be simply performed using an in-house forward planned IMRT. This would have several clinical ramifications including improved clinical outcome in terms of enhanced tumor control while minimizing treatment related complications. Materials and Methods: At UTMB, women with IIB-IIIB cervical carcinoma are treated with brachytherapy implants. A CT scan is performed after placement of the tandem and ovoid. The CT data sets of 20 patients and their respective 3D brachytherapy dosimetry have been analyzed. Our analysis selected the entire region within the parametrial boost that would be treated to the 95% isodose line of this field and assessed for dose homogeneity when the brachytherapy contributions were added. Custom pelvic sidewall boost plans were designed based on the brachytherapy dosimetry. This was performed using a simple and efficient method of viewing isodose clouds in 5% gradations and iteratively shielding the hot areas thereby creating uniform dose distribution. These customized plans were then contrasted to the original plans visually with comparison of the coronal, sagittal and transverse isodose clouds. DVH profiles were compared. Results and Conclusions: The forward planning IMRT successfully created a homogenous dose distribution when analyzed with 3d isodose clouds and with our forward planning technique. The distribution of dose was significantly changed based on 3d treatment planning with increased number of fractions by maintaining a 180 cGy fraction size prescribe to the 100% isodose line which corresponded to the lateral aspect of the radiation field.