Treatment Planning Techniques Research Articles

Radiation therapy for the whole breast: Executive summary of an American Society for Radiation Oncology (ASTRO) evidence-based guideline

IntroductionThe purpose of this guideline is to offer recommendations on fractionation for whole breast irradiation (WBI) with or without a tumor bed boost and guidance on treatment planning and delivery. Methods and materialsThe American Society for Radiation Oncology (ASTRO) convened a task force to address 5 key questions focused on dose-fractionation for WBI, indications and dose-fractionation for tumor bed boost, and treatment planning techniques for WBI and tumor bed boost. Guideline recommendations were based on a systematic literature review and created using a predefined consensus-building methodology supported by ASTRO-approved tools for grading evidence quality and recommendation strength. ResultsFor women with invasive breast cancer receiving WBI with or without inclusion of the low axilla, the preferred dose-fractionation scheme is hypofractionated WBI to a dose of 4000 cGy in 15 fractions or 4250 cGy in 16 fractions. The guideline discusses factors that might or should affect fractionation decisions. Use of boost should be based on shared decision-making that considers patient, tumor, and treatment factors, and the task force delineates specific subgroups in which it recommends or suggests use or omission of boost, along with dose recommendations. When planning, the volume of breast tissue receiving >105% of the prescription dose should be minimized and the tumor bed contoured with a goal of coverage with at least 95% of the prescription dose. Dose to the heart, contralateral breast, lung, and other normal tissues should be minimized. ConclusionsWBI represents a significant portion of radiation oncology practice, and these recommendations are intended to offer the groundwork for defining evidence-based practice for this common and important modality. This guideline also seeks to promote appropriately individualized, shared decision-making regarding WBI between physicians and patients.

Treatment plan quality and delivery accuracy assessments on 3 IMRT delivery methods of stereotactic body radiotherapy for spine tumors

Stereotactic body radiotherapy (SBRT) for spine tumors has demonstrated clinical effectiveness. The treatment planning and delivery techniques have evolved from dynamic conformal arc therapy, to fixed gantry angle intensity modulated radiotherapy (IMRT), and most recently to volumetric modulated arc therapy (VMAT). A hybrid-arc (HARC) planning and delivery method combining dynamic conformal arc therapy delivery with a number of equally spaced IMRT beams is proposed. In this study we investigated plan quality, delivery accuracy, and efficiency of 3 delivery techniques: IMRT, HARC, and VMAT. Patients who underwent spine SBRT treatments were randomly selected from an Institutional Review Board-approved registry. For each patient, the prescription dose was 14 to 16 Gy in a single fraction to cover >90% of the tumor (without planning margin) while constraining V10Gy ≤ 10% of the spinal cord and the maximum point dose (MPD) of the spinal cord ≤ 14 Gy. All cases were clinically treated with fixed gantry step-shoot IMRT plans and then re-planned with VMAT using Pinnacle 9.0 and with HARC using Brainlab iPlan 4.5. Student t-test was used to compare the dosimetric end points, including V16Gy to the planning target volume, homogeneity index, MPDPTV, the conformity index, V10Gy of the spinal cord, and MPDcord. To compare the accuracy of delivery, we delivered all plans on a phantom and conducted gamma index (GI) comparisons with 3 mm/3% and 2 mm/2% criteria. All plans met our clinical requirements. Among 3 techniques, there were no differences on dose coverage to the tumor volume, maximum dose to the spinal cord, and plan homogeneity index (p > 0.05). The average V10Gy of the spinal cord was 6.66 ± 0.03%, 5.49 ± 0.03%, and 4.76 ± 0.02% for IMRT, HARC, and VMAT plans, respectively. Accordingly, the conformity indices were 1.30 ± 0.11 and 1.29 ± 0.20, 1.53 ± 0.29, respectively. VMAT plans were significantly (p < 0.05) less conformal but significantly (p < 0.05) lower V10Gy of the spinal cord than those from HARC and IMRT plans. With delivery accuracy measured by GIs, the average GIs of 3%/3 mm were 92.6 ± 1.1%, 96.5 ± 2.7%, 99.0 ± 1.1% for IMRT, HARC, and VMAT plans, respectively. The differences were significant (p < 0.05). Accordingly, the average monitor units were 9238 ± 2242, 9853 ± 2548 and 5091 ± 910. The plan quality created from the 3 planning techniques can meet the clinical requirement. Adding arc beams in delivery such as in HARC and VMAT plans improves the delivery accuracy. VMAT is the most efficient delivery method.

Physician Driven Multicriteria Optimization of Advanced Lung Cancer Patients VMAT Plans

Multi-Criteria Optimization (MCO), a novel commercially available optimization method for intensity modulated and volumetric arc therapies (IMRT and VMAT) has the potential to improve treatment planning techniques and workflows. By navigating between Pareto solutions, MCO allows planners and physicians to assess in real time the impact and tradeoffs between all clinical goals and organ constraints. The purpose of our work is to investigate a universal set of objectives and constraints for lung cancer MCO VMAT plans and the impact of involving the Physician in the navigation of the generated Pareto plans. The central hypothesis is that physician-driven MCO VMAT plans will allow choice of optimal dosimetric trade-offs for a given individual patient. We randomly selected ten lung cancer patients (Stage II-IV) planned with a two arcs VMAT technique. Prescription doses ranged from 50.4Gy to 66Gy in 1.8 or 2Gy per fraction, with one case of dose painting. Target volumes were generated per clinical standard of care. The ITVs ranged from 18cc-387cc. Using the clinically delivered isocenter and beam set-up, we retrospectively generated MCO plans with a universal set of constraints and objectives that was developed by trying different combinations in a few patients. Two versions of the MCO plan scores (one navigated by the dosimetrist [MCOd] and one by the physician [MCOp]) were compared with clinical plans generated with Direct Machine Parameter Optimization (DMPO). Dosimetric and biological parameters evaluated were PTV V95%, Conformity Index (CI), PTV Dmax and the un-complicated probability (UP) representing the absence of lung and esophagus complications. The cord dose was not evaluated because almost all plans had Dmax doses of less than 45Gy, with negligible probability of complications. MCOd vs clinical comparison: the values for PTV V95 were MCOd: 99%(95-100) vs clinical plans: 98% (94-100),p-value= 0.2, the CI were similar in both cases (p-value=0.5) but the Dmax was higher for the MCO plans (average 109% vs. 107%, p =0.004), the lung-esophagus UP was similar between MCOd (Mean: 74%, range: 55-87%) and the clinical pla(Mean:75%, range: 60-89%), p= 0.1. Corresponding MCOd versus MCOp comparisons were similar for the parameters tested. However, using real time assessment of dosimetric trade-offs, in each individual plan the physician was able to actively choose a preferred combination of dose to target vs organs. When evaluating individual patients, there were five patients for which MCO plans had a clear advantage in reducing dose to lung and/or esophagus while improving/maintaining target coverage, four patients with comparable plans and one patient where MCO was worse. MCO VMAT lung plans obtained with standardized objectives and constraints generated comparable or better plans than the clinical DMPO plans while allowing physicians to make real time comparisons of dosimetric trade-offs and accept a plan optimal for an individual patient.

4D CBCT image guidance in liver SBRT

To analyze 4D CBCT image guided accuracy and dose volume histograms in SBRT for liver tumors. The treatment with SBRT in hepatic cancer using 4D image guidance is analyzed in this work. Patients are inmovilized employing an arm support, knee fix and a dampening system. Respiration correlated 4D CT and diagnostic CT performed using IV contrast media are used to delineate gross tumor volume (GTV). GTVs in eight 4DCT sets and two contrast sets are combined to create an internal target volume (ITV). Comparing center of mass of GTV in every respiratory phase a dampening device is selected and a set of CT images is chosen as reference for planning and simulation. In this reference CT organs at risk are contoured and it is selected to match in the daily image guided radiotherapy (IGRT). IGRT using anatomy fiducials respiration correlated 4DCBCT with automatic registration of the planning reference CT is used to setup patient in every treatment session. Results were compared for three registration techniques: 3D CBCT using mean ITV and soft tissue registration, 4dCBCT clipbox and bone anatomy registration (4D bCBCT), and 4D soft tissue registration using a 0.5 cm mask from ITV (4D mCBCT). Significant differences in ITV localization were observed between 4D mCBCT and the other modalities, up to 16.0 mm ± 6.0 mm (3D vector). The differences between 4D bCBCT and 4D mCBCT are closer than 4DbCBCT and 3D CBCT. These differences are larger when respiratory amplitude increase. Mean respiratory amplitude was 21.1 mm ± 7.0 mm when measured in simulation CT, in agreement with 20.0 ± 7.8 mm when measured in 4D CBCT. Visual comparison of reference respiratory curve and treatment daily respiratory curve makes possible to asses reproducibility of patients and tumor position reproducibility. Interobserver variability was reduced using 4D mCBCT and soft tissue automatic registration. With this protocol we can assert that interpatient variability in dose volume histograms is due mainly to treatment planning technique and tumor volume definition, and not directly correlated with motion amplitude. Respiration correlated 4D CBCT with soft tissue registration improves accuracy of IGRT because of the more precise target localization in the presence of respiratory motion, allowing the comparison of reference respiratory curve with treatment respiratory curve. Moreover, this method enables the realization of 4D CBCT without external surrogates with good correlation with reference 4D CT using external sensors.

MRI-based treatment planning and dose delivery verification for intraocular melanoma brachytherapy

PurposeEpiscleral plaque brachytherapy (EPB) planning is conventionally based on approximations of the implant geometry with no volumetric imaging following plaque implantation. We have developed an MRI-based technique for EPB treatment planning and dose delivery verification based on the actual patient-specific geometry. Methods and MaterialsMR images of 6 patients, prescribed 85 Gy over 96 hours from Collaborative Ocular Melanoma Study–based EPB, were acquired before and after implantation. Preimplant and postimplant scans were used to generate “preplans” and “postplans”, respectively. In the preplans, a digital plaque model was positioned relative to the tumor, sclera, and nerve. In the postplans, the same plaque model was positioned based on the imaged plaque. Plaque position, point doses, percentage of tumor volume receiving 85 Gy (V100), and dose to 100% of tumor volume (Dmin) were compared between preplans and postplans. All isodose plans were computed using TG-43 formalism with no heterogeneity corrections. ResultsShifts and tilts of the plaque ranged from 1.4 to 8.6 mm and 1.0 to 3.8 mm, respectively. V100 was ≥97% for 4 patients. Dmin for preplans and postplans ranged from 83 to 118 Gy and 45 to 110 Gy, respectively. Point doses for tumor apex and base were all found to decrease from the preimplant to the postimplant plan, with mean differences of 16.7 ± 8.6% and 30.5 ± 11.3%, respectively. ConclusionsBy implementing MRI for EPB, we eliminate reliance on approximations of the eye and tumor shape and the assumption of idealized plaque placement. With MRI, one can perform preimplant as well as postimplant imaging, facilitating EPB treatment planning based on the actual patient-specific geometry and dose-delivery verification based on the imaged plaque position.

Cone Beam Computed Tomographic imaging in orthodontics.

Over the last 15 years, cone beam computed tomographic (CBCT) imaging has emerged as an important supplemental radiographic technique for orthodontic diagnosis and treatment planning, especially insituations which require an understanding of the complex anatomic relationships and surrounding structures of the maxillofacial skeleton. CBCT imaging provides unique features and advantages to enhance orthodontic practice over conventional extraoral radiographic imaging. While it is the responsibility of each practitioner to make a decision, in tandem with the patient/family, consensus-derived, evidence-based clinical guidelines are available to assist the clinician in the decision-making process. Specific recommendations provide selection guidance based on variables such as phase of treatment, clinically-assessed treatment difficulty, the presence of dental and/or skeletal modifying conditions, and pathology. CBCT imaging in orthodontics should always be considered wisely as children have conservatively, on average, a three to five times greater radiation risk compared with adults for the same exposure. The purpose of this paper is to provide an understanding of the operation of CBCT equipment as it relates to image quality and dose, highlight the benefits of the technique in orthodontic practice, and provide guidance on appropriate clinical use with respect to radiation dose and relative risk, particularly for the paediatric patient.

Comparison of treatment planning techniques in treatment of carcinoma of left breast: Second cancer perspective

AimTo compare the secondary cancer risk (SCR) between different planning techniques for treatment of Ca. Left-Breast patient. Materials and methodsFive treatment plans; 3DCRT tangential fields with physical wedge (PW), enhanced dynamic wedges (EDW), electronic compensator (EC), IMRT tangential fields (ITF) and Volumetric modulated arc (VMAT) plan (partial arcs) with 6MV photon beams were generated for a carcinoma of Left breast patient of age 40 to a prescription dose of 50Gy in 25 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. ResultsFor contra lateral breast the SCR relative to PW were (linear, plateau, linear-exponential) (−26.0%, −35.0%, −39.0%) for VMAT, (−50.0%,−50.0%,−51.0%) for ITF, (−48.0%, −49.0%,−49.0%) for EC and (−33.0%, −24% , −25.0%) for EDW respectively. The relative SCR (plateau) for heart and left lung were (−66.0% & −73.0%) for VMAT, (−20.0% & −6.0%) for ITF, (−24.0% & −18.0%) for EC and ( −17.0% & −14.0%)for EDW. In contrast, for skin the relative SCR (linear - exponential) were 78.0%, −8.0%, −13.0% and −10.0% for VMAT, ITF, EC and EDW respectively. The 5Gy low dose volume relative to PW for VMAT was 201.45%, whereas the same for ITF, EC and EDW were 17.0%, −7.33% and −4.3%. ConclusionCompared to all plans, VMAT plan showed high conformity for CTV and superior heart and left lung sparing. But SCR for skin and the low dose bath volume were significantly high in VMAT. ITF plan showed relatively better sparing for contra lateral breast and heart. EC plan shows moderately good sparing for OARs while scoring least SCR value for skin next to EDW. EDW and PW plans were similar but later had high SCR for contra lateral-breast. Planning techniques like ITF and VMAT can be strongly considered for left breast, provided better skin sparing techniques and less dose spillage can be achieved.

Development of a model web-based system to support a statewide quality consortium in radiation oncology

PurposeA database in which patient data are compiled allows analytic opportunities for continuous improvements in treatment quality and comparative effectiveness research. We describe the development of a novel, web-based system that supports the collection of complex radiation treatment planning information from centers that use diverse techniques, software, and hardware for radiation oncology care in a statewide quality collaborative, the Michigan Radiation Oncology Quality Consortium (MROQC). Methods and materialsThe MROQC database seeks to enable assessment of physician- and patient-reported outcomes and quality improvement as a function of treatment planning and delivery techniques for breast and lung cancer patients. We created tools to collect anonymized data based on all plans. ResultsThe MROQC system representing 24 institutions has been successfully deployed in the state of Michigan. Since 2012, dose-volume histogram and Digital Imaging and Communications in Medicine-radiation therapy plan data and information on simulation, planning, and delivery techniques have been collected. Audits indicated >90% accurate data submission and spurred refinements to data collection methodology. ConclusionsThis model web-based system captures detailed, high-quality radiation therapy dosimetry data along with patient- and physician-reported outcomes and clinical data for a radiation therapy collaborative quality initiative. The collaborative nature of the project has been integral to its success. Our methodology can be applied to setting up analogous consortiums and databases.

Reducing the dosimetric impact of positional errors in field junctions for craniospinal irradiation using VMAT

AimTo improve treatment plan robustness with respect to small shifts in patient position during the VMAT treatment by ensuring a linear ramp-like dose profile in treatment field overlap regions. BackgroundCraniospinal irradiation (CSI) is considered technically challenging because the target size exceeds the maximal field size, which necessitates using abutted or overlapping treatment fields. Volumetric modulated arc therapy (VMAT) is increasingly being examined for CSI, as it offers both better dose homogeneity and better dose conformance while also offering a possibility to create field junctions which are more robust towards small shifts in patient position during the treatment. Materials and methodsA VMAT treatment plan with three isocenters was made for a test case patient. Three groups of overlapping arc field pairs were used; one for the cranial and two for the spinal part. In order to assure a ramp-like dose profile in the field overlap region, the upper spinal part was optimised first, with dose prescription explicitly enforcing a ramp-like dose profile. The cranial and lower spinal part were done afterwards, taking into account the dose contribution of the upper spinal fields. ResultsUsing simple geometrical reasoning, we demonstrated that hot- and cold spots which arise from small displacement of one treatment field relative to the other treatment field can be reduced by taking two precautions: (a) widening the field overlap region, and (b) reducing the field gradient across the overlap region. The function with the smallest maximal gradient is a linear ramp. We present a treatment planning technique which yields the desired dose profile of the two contributing fields, and minimises dosimetric dependence on minor positional errors in patient set-up.

Optimization of dental implant treatment

Aim ― Modern dentistry cannot exist without dental implantation. The lifetime of the installed implants depends on condition of the bone and on the quality of the treatment planning and surgery technique. Usually, complications during the implant treatment are related to the inability to accurately predict the condition and location of intraosseous structure that entails the selection of the wrong type of implant and installation position. Methods ― This work is devoted to the bone-implant system investigation aiming on the optimization of dental prostheses installation. The objective of this study was to develop the implant treatment planning technique. Modern non-invasive methods such as computer tomography (CT) and 3D-scanning as well as numerical calculations and 3D-prototyping allow optimizing all of dental prosthetics stages. Results ― In this work, complex methodology of dental prosthesis installation is presented. Patient-specific dental templates developed in this work are easy to create and very accurate. Conclusion ― CT processing method, numerical modeling and 3D prototyping techniques allowed us to develop a methodology of dental prosthesis installation. An integrated approach to the planning of implant surgery can significantly reduce the risk of complications in the first few days after treatment, and throughout the period of operation of the prosthesis.

Treatment Plan Technique and Quality for Single Isocenter Stereotactic Ablative Radiation Therapy of Multiple Lung Lesions With Volumetric Modulated Arc Therapy or Intensity Modulated Radiosurgery

Treatment Plan Technique and Quality for Single Isocenter Stereotactic Ablative Radiation Therapy of Multiple Lung Lesions With Volumetric Modulated Arc Therapy or Intensity Modulated Radiosurgery

Treatment Plan Technique and Quality for Single-Isocenter Stereotactic Ablative Radiotherapy of Multiple Lung Lesions with Volumetric-Modulated Arc Therapy or Intensity-Modulated Radiosurgery.

The aim of this study is to provide a practical approach to the planning technique and evaluation of plan quality for the multi-lesion, single-isocenter stereotactic ablative radiotherapy (SABR) of the lung. Eleven patients with two or more lung lesions underwent single-isocenter volumetric-modulated arc therapy (VMAT) radiosurgery or IMRS. All plans were normalized to the target maximum dose. For each plan, all targets were treated to the same dose. Plan conformity and dose gradient were maximized with dose-control tuning structures surrounding targets. For comparison, multi-isocenter plans were retrospectively created for four patients. Conformity index (CI), homogeneity index (HI), gradient index (GI), and gradient distance (GD) were calculated for each plan. V5, V10, and V20 of the lung and organs at risk (OARs) were collected. Treatment time and total monitor units (MUs) were also recorded. One patient had four lesions and the remainder had two lesions. Six patients received VMAT and five patients received intensity-modulated radiosurgery (IMRS). For those treated with VMAT, two patients received 3-arc VMAT and four received 2-arc VMAT. For those treated with IMRS, two patients were treated with 10 and 11 beams, respectively, and the rest received 12 beams. Prescription doses ranged from 30 to 54 Gy in three to five fractions. The median prescribed isodose line was 84% (range: 80–86%). The median maximum dose was 57.1 Gy (range: 35.7–65.1 Gy). The mean combined PTV was 49.57 cm3 (range: 14.90–87.38 cm3). For single-isocenter plans, the median CI was 1.15 (range: 0.97–1.53). The median HI was 1.19 (range: 1.16–1.28). The median GI was 4.60 (range: 4.16–7.37). The median maximum radiation dose (Dmax) to total lung was 55.6 Gy (range: 35.7–62.0 Gy). The median mean radiation dose to the lung (Dmean) was 4.2 Gy (range: 1.1–9.3 Gy). The median lung V5 was 18.7% (range: 3.8–41.3%). There was no significant difference in CI, HI, GI, GD, V5, V10, and V20 (lung, heart, trachea, esophagus, and spinal cord) between single-isocenter and multi-isocenter plans. This multi-lesion, single-isocenter lung SABR planning technique demonstrated excellent plan quality and clinical efficiency and is recommended for radiosurgical treatment of two or more lung targets for well-suited patients.

Chung-Ang University (CAU) protocol for orthognathic surgery: 3-dimensional treatment planning, navigation and key-hole technique for correcting facial asymmetry

Chung-Ang University (CAU) protocol for orthognathic surgery: 3-dimensional treatment planning, navigation and key-hole technique for correcting facial asymmetry

Brachytherapy: state‐of‐the‐art radiotherapy in prostate cancer

Brachytherapy: state‐of‐the‐art radiotherapy in prostate cancer

A forward planned treatment planning technique for non-small-cell lung cancer stereotactic ablative body radiotherapy based on a systematic review of literature

AbstractPurpose and MethodA systematic literature review of six computerised databases was undertaken in order to review and summarise a forward planned lung stereotactic ablative body radiotherapy (SABR) treatment planning (TP) technique as a starting point for clinical implementation in the author’s department based on current empirical research. The data were abstracted and content analysed to synthesise the findings based upon a SIGN quality checklist tool.FindingsA four-dimensional computed tomography scan should be performed upon which the internal target volume and organs at risk (OAR) are drawn. A set-up margin of 5 mm is applied to account for inter-fraction motion. The field arrangement consists of a combination of 7–13 coplanar and non-coplanar beams all evenly spaced. Beam modifiers are used to assist in the homogeneity of the beam, although a 20% planning target volume dose homogeneity is acceptable. The recommended fractionations by the UK SABR Consortium are 54 Gy in 3 fractions (standard), 55–60 Gy in 5 fractions (conservative) and 50–60 Gy in 8–10 fractions (very conservative). Conformity indices for both the target volume and OAR will be used to assess the planned distribution.ConclusionAn overview of a clinically acceptable forward planned lung SABR TP technique based on current literature as a starting point, with a view to inverse planning with support from the UK SABR Consortium mentoring scheme.

The concept and evolution of involved site radiation therapy for lymphoma

We describe the development of radiation therapy for lymphoma from extended field radiotherapy of the past to modern conformal treatment with involved site radiation therapy based on advanced imaging, three-dimensional treatment planning and advanced treatment delivery techniques. Today, radiation therapy is part of the multimodality treatment of lymphoma, and the irradiated tissue volume is much smaller than before, leading to highly significant reductions in the risks of long-term complications.

WE-A-304-01: Strategies and Technologies for Cranial Radiosurgery Planning: MLC-Based Linac

The high fractional doses, stringent requirements for accuracy and precision, and surgical perspective characteristic of intracranial radiosurgery create considerations for treatment planning which are distinct from most other radiotherapy procedures. This session will introduce treatment planning techniques specific to two popular intracranial SRS modalities: Gamma Knife and MLC-based Linac. The basic treatment delivery characteristics of each device will be reviewed with a focus on how those characteristics determine the paradigm used for treatment planning. Basic techniques for treatment planning will be discussed, including considerations such as isodose selection, target and organ-at-risk definition, quality indices, and protection of critical structures. Future directions for SRS treatment planning will also be discussed. Learning Objectives: 1. Introduce the basic physical principles of intracranial radiosurgery and how they are realized in the treatment planning paradigms for Gamma Knife and Linac radiosurgery. 2. Demonstrate basic treatment planning techniques. 3. Discuss metrics for evaluating SRS treatment plan quality. 4. Discuss recent and future advances in SRS treatment planning. D. Schlesinger receives research support from Elekta, AB

WE-A-304-00: Stereotactic Radiosurgery

The high fractional doses, stringent requirements for accuracy and precision, and surgical perspective characteristic of intracranial radiosurgery create considerations for treatment planning which are distinct from most other radiotherapy procedures. This session will introduce treatment planning techniques specific to two popular intracranial SRS modalities: Gamma Knife and MLC-based Linac. The basic treatment delivery characteristics of each device will be reviewed with a focus on how those characteristics determine the paradigm used for treatment planning. Basic techniques for treatment planning will be discussed, including considerations such as isodose selection, target and organ-at-risk definition, quality indices, and protection of critical structures. Future directions for SRS treatment planning will also be discussed. Learning Objectives: 1. Introduce the basic physical principles of intracranial radiosurgery and how they are realized in the treatment planning paradigms for Gamma Knife and Linac radiosurgery. 2. Demonstrate basic treatment planning techniques. 3. Discuss metrics for evaluating SRS treatment plan quality. 4. Discuss recent and future advances in SRS treatment planning. D. Schlesinger receives research support from Elekta, AB

WE-A-304-02: Strategies and Technologies for Cranial Radiosurgery Planning: Gamma Knife

The high fractional doses, stringent requirements for accuracy and precision, and surgical perspective characteristic of intracranial radiosurgery create considerations for treatment planning which are distinct from most other radiotherapy procedures. This session will introduce treatment planning techniques specific to two popular intracranial SRS modalities: Gamma Knife and MLC-based Linac. The basic treatment delivery characteristics of each device will be reviewed with a focus on how those characteristics determine the paradigm used for treatment planning. Basic techniques for treatment planning will be discussed, including considerations such as isodose selection, target and organ-at-risk definition, quality indices, and protection of critical structures. Future directions for SRS treatment planning will also be discussed. Learning Objectives: 1. Introduce the basic physical principles of intracranial radiosurgery and how they are realized in the treatment planning paradigms for Gamma Knife and Linac radiosurgery. 2. Demonstrate basic treatment planning techniques. 3. Discuss metrics for evaluating SRS treatment plan quality. 4. Discuss recent and future advances in SRS treatment planning. D. Schlesinger receives research support from Elekta, AB

SU‐C‐213‐04: Application of Depth Sensing and 3D‐Printing Technique for Total Body Irradiation (TBI) Patient Measurement and Treatment Planning

Purpose:To develop and validate an innovative method of using depth sensing cameras and 3D printing techniques for Total Body Irradiation (TBI) treatment planning and compensator fabrication.Methods:A tablet with motion tracking cameras and integrated depth sensing was used to scan a RANDOTM phantom arranged in a TBI treatment booth to detect and store the 3D surface in a point cloud (PC) format. The accuracy of the detected surface was evaluated by comparison to extracted measurements from CT scan images. The thickness, source to surface distance and off‐axis distance of the phantom at different body section was measured for TBI treatment planning. A 2D map containing a detailed compensator design was calculated to achieve uniform dose distribution throughout the phantom. The compensator was fabricated using a 3D printer, silicone molding and tungsten powder. In vivo dosimetry measurements were performed using optically stimulated luminescent detectors (OSLDs).Results:The whole scan of the anthropomorphic phantom took approximately 30 seconds. The mean error for thickness measurements at each section of phantom compare to CT was 0.44 ± 0.268 cm. These errors resulted in approximately 2% dose error calculation and 0.4 mm tungsten thickness deviation for the compensator design. The accuracy of 3D compensator printing was within 0.2 mm. In vivo measurements for an end‐to‐end test showed the overall dose difference was within 3%.Conclusion:Motion cameras and depth sensing techniques proved to be an accurate and efficient tool for TBI patient measurement and treatment planning. 3D printing technique improved the efficiency and accuracy of the compensator production and ensured a more accurate treatment delivery.