Multi-field Optimization Research Articles

Three‐dimensional gamma criterion for patient‐specific quality assurance of spot scanning proton beams

The purpose of this study was to evaluate the effectiveness of full three‐dimensional (3D) gamma algorithm for spot scanning proton fields, also referred to as pencil beam scanning (PBS) fields. The difference between the full 3D gamma algorithm and a simplified two‐dimensional (2D) version was presented. Both 3D and 2D gamma algorithms are used for dose evaluations of clinical proton PBS fields. The 3D gamma algorithm was implemented in an in‐house software program without resorting to 2D interpolations perpendicular to the proton beams at the depths of measurement. Comparison between calculated and measured dose points was carried out directly using Euclidian distance in 3D space and the dose difference as a fourth dimension. Note that this 3D algorithm faithfully implemented the original concept proposed by Low et al. (1998) who described gamma criterion using 3D Euclidian distance and dose difference. Patient‐specific proton PBS plans are separated into two categories, depending on their optimization method: single‐field optimization (SFO) or multifield optimized (MFO). A total of 195 measurements were performed for 58 SFO proton fields. A MFO proton plan with four fields was also calculated and measured, although not used for treatment. Typically three different depths were selected from each field for measurements. Each measurement was analyzed by both 3D and 2D gamma algorithms. The resultant 3D and 2D gamma passing rates are then compared and analyzed. Comparison between 3D and 2D gamma passing rates of SFO fields showed that 3D algorithm does show higher passing rates than its 2D counterpart toward the distal end, while little difference is observed at depths away from the distal end. Similar phenomenon in the lateral penumbra was well documented in photon radiation therapy, and in fact brought about the concept of gamma criterion. Although 2D gamma algorithm has been shown to suffice in addressing dose comparisons in lateral penumbra for photon intensity‐modulation radiation therapy (IMRT) plans, results here showed that a full 3D algorithm is required for proton dose comparisons due to the existence of Bragg peaks and distal penumbra. A MFO proton plan with four fields was also measured and analyzed. Sharp dose gradients exist in MFO proton fields, both in the middle of the modulation and toward the most distal layers. Decreased 2D gamma passing rates at locations of high dose gradient are again observed as in the SFO fields. Results confirmed that a full 3D algorithm for gamma criterion is needed for proton PBS plan's dose comparisons. The 3D gamma algorithm is implemented by an in‐house software program. Patient‐specific proton PBS plans are measured and analyzed using both 3D and 2D gamma algorithms. For measurements performed at depths with large dose gradients along the beam direction, gamma comparison passing rates using 2D algorithm is lower than those obtained with the full 3D algorithm.PACS number: 87.53.Bn, 87.53.Jw, 87.55.de, 87.55.kd, 87.55.ne, 87.55.Qr

Comparative Proton and Photon Treatment Planning in Pediatric Patients with Various Diagnoses

Abstract Purpose: Radiation therapy with protons, owing to its physical properties, can be advantageous for the treatment of children. This study was conducted in order to quantify the advantages of proton therapy from a treatment planning point of view in a consecutive, realistic, and mixed pediatric/adolescent population with varying diagnoses and target locations. Patients and Methods: Forty-five patients treated with conventional 3-dimensional conformal radiation therapy photon radiation therapy were retrospectively re-planned with scanned proton beams. Treatment sites represented were the central nervous system, head and neck, thorax, and abdomen. Median age was 8 years (range, 2-18 years). All plans were optimized with intensity-modulated proton therapy (multi-field optimization). We analyzed a number of dose-volume descriptors for planned target volumes (PTVs). Organ-specific mean doses and relevant DV -values were derived for organs at risk. In addition, homogeneity index, conformity index, treate...

SU‐E‐T‐127: Application of TG‐119 for Evaluation of Proton Spot Scanning Based Planning and Treatment Delivery

Purpose:The clinical test cases presented in AAPM TG‐119 are used to evaluate the accuracy of treatment planning and delivery through spot scanning proton beams.Methods:An IBA spot scanning delivery system has been commissioned to be used with the RayStation treatment planning system. Various test cases provided in TG‐119 were used for planning and delivery verification. The CT dataset and structures as provided by TG‐119 were imported into a mock patient. The plans were optimized using the multi field optimization (MFO) to achieve the desired goals. The planner was given the flexibility to achieve the given dose‐volume goals by creating appropriate objectives and constraints. Beams were delivered to a phantom and measurements were performed at multiple depths using the MatrixxPT detector array. The analyses were performed on beam by beam basis and quantified using the gamma index. A tolerance of 3%/3 mm in 2D was used for gamma index analysis along with dose threshold of 10%.Results:The clinical goals for targets and critical structures were met or improved for all cases except the C‐Shape target with difficult constraints. The minimum gamma index using the 3%/3mm as a criterion is 93.3% for one of the planes measured for C‐Shape target. Using 2%/2mm as a criterion, the minimum gamma index drops to 70%. Only Prostate target has all the planes above >90% pass using the 2%/2mm criterion.Conclusion:The overall accuracy of the treatment planning and delivery is deemed clinically acceptable. The test cases with highly modulated beams can have steep gradients in the dose profiles that can reduce the gamma index pass rate. Gamma analysis based on 3D data may be needed for routine use of 2%/2mm criterion. In addition, improvements in modelling of spot profiles in dose engine may be required for further improving the gamma index pass rate.

SU‐E‐T‐640: Proton Modulated Arc Therapy Using Scanned Pencil Beams

Purpose:Rotational proton radiotherapy would be an interesting treatment modality if it proves to produce dose distributions that conform to the target as well or better than currently available treatment modalities, while reducing the dose to the surrounding organs at risk. A treatment planning study is presented, showing how this objective can be achieved using a single or small number of scanned mono‐energetic pencil beams delivered while the proton gantry rotates at the same time that they may deliver faster and more biologically effective treatments than current proton modalities.Methods Proton treatment using single‐ (SFO) and multi‐field optimized (MFO) PBS plans are compared with PMAT plans in phantoms of different shape and uniformity as well as on a brain case. The method followed in ECLIPSE to produce PMAT plans is presented and the feasibility is discussed. Results Table 1 shows that the conformity and uniformity of the PMAT plans is of similar order than those of the SFO and MFO plans. However, in the brain case, the DVHs shown in Figure 1 indicate a significant reduction of the dose to the OARs when PMAT is used. Similarly, the use of PMAT increases the LET in the treatment area, which could translate into a more biologically effective treatment.Conclusions PMAT could provide dose distributions as conformal as current PBS plans but could also offer faster beam delivery and more biologically effective proton plans.

Robust optimization in intensity-modulated proton therapy to account for anatomy changes in lung cancer patients

Background and purposeRobust optimization for IMPT takes setup and range uncertainties into account during plan optimization. However, anatomical changes were not prospectively included. The purpose of this study was to examine robustness and dose variation due to setup uncertainty and anatomical change in IMPT of lung cancer. Material and methodsPlans were generated with multi-field optimization based on planning target volume (MFO-PTV) and worst-case robust optimization (MFO-RO) on simulation computed tomography scans (CT0) for nine patients. Robustness was evaluated on the CT0 by computing the standard deviation of DVH (SD-DVH). Dose variations calculated on weekly CTs were compared with SD-DVH. Equivalent uniform dose (EUD) change from the original plan on weekly dose was also calculated for both plans. ResultsSD-DVH and dose variation on weekly CTs were both significantly lower in the MFO-RO plans than in the MFO-PTV plans for targets, lungs, and the esophagus (p<0.05). When comparing EUD for ITV between weekly and planned dose distributions, three patients and 28% of repeated CTs for MFO-RO plans, and six patients and 44% of repeated CTs for MFO-PTV plans, respectively, showed an EUD change of >5%. ConclusionsRO in IMPT reduces the dose variation due to setup uncertainty and anatomy changes during treatment compared with PTV-based planning. However, dose variation could still be substantial; repeated imaging and adaptive planning as needed are highly recommended for IMPT of lung tumors.

SU-E-T-214: Intensity Modulated Proton Therapy (IMPT) Based On Passively Scattered Protons and Multi-Leaf Collimation: Prototype TPS and Dosimetry Study

Purpose. Intensity-modulated proton therapy is usually implemented with multi-field optimization of pencil-beam scanning (PBS) proton fields. However, at the view of the experience with photon-IMRT, proton facilities equipped with double-scattering (DS) delivery and multi-leaf collimation (MLC) could produce highly conformal dose distributions (and possibly eliminate the need for patient-specific compensators) with a clever use of their MLC field shaping, provided that an optimal inverse TPS is developed. Methods. A prototype TPS was developed in MATLAB. The dose calculation process was based on a fluence-dose algorithm on an adaptive divergent grid. A database of dose kernels was precalculated in order to allow for fast variations of the field range and modulation during optimization. The inverse planning process was based on the adaptive simulated annealing approach, with direct aperture optimization of the MLC leaves. A dosimetry study was performed on a phantom formed by three concentrical semicylinders separated by 5 mm, of which the inner-most and outer-most were regarded as organs at risk (OARs), and the middle one as the PTV. We chose a concave target (which is not treatable with conventional DS fields) to show the potential of our technique. The optimizer was configured to minimize the mean dose to the OARs while keeping a good coverage of the target. Results. The plan produced by the prototype TPS achieved a conformity index of 1.34, with the mean doses to the OARs below 78% of the prescribed dose. This Result is hardly achievable with traditional conformal DS technique with compensators, and it compares to what can be obtained with PBS. Conclusion. It is certainly feasible to produce IMPT fields with MLC passive scattering fields. With a fully developed treatment planning system, the produced plans can be superior to traditional DS plans in terms of plan conformity and dose to organs at risk.

Multifield Optimization Intensity Modulated Proton Therapy for Head and Neck Tumors: A Translation to Practice

We report the first clinical experience and toxicity of multifield optimization (MFO) intensity modulated proton therapy (IMPT) for patients with head and neck tumors. Fifteen consecutive patients with head and neck cancer underwent MFO-IMPT with active scanning beam proton therapy. Patients with squamous cell carcinoma (SCC) had comprehensive treatment extending from the base of the skull to the clavicle. The doses for chemoradiation therapy and radiation therapy alone were 70 Gy and 66 Gy, respectively. The robustness of each treatment plan was also analyzed to evaluate sensitivity to uncertainties associated with variations in patient setup and the effect of uncertainties with proton beam range in patients. Proton beam energies during treatment ranged from 72.5 to 221.8 MeV. Spot sizes varied depending on the beam energy and depth of the target, and the scanning nozzle delivered the spot scanning treatment "spot by spot" and "layer by layer." Ten patients presented with SCC and 5 with adenoid cystic carcinoma. All 15 patients were able to complete treatment with MFO-IMPT, with no need for treatment breaks and no hospitalizations. There were no treatment-related deaths, and with a median follow-up time of 28 months (range, 20-35 months), the overall clinical complete response rate was 93.3% (95% confidence interval, 68.1%-99.8%). Xerostomia occurred in all 15 patients as follows: grade 1 in 10 patients, grade 2 in 4 patients, and grade 3 in 1 patient. Mucositis within the planning target volumes was seen during the treatment of all patients: grade 1 in 1 patient, grade 2 in 8 patients, and grade 3 in 6 patients. No patient experienced grade 2 or higher anterior oral mucositis. To our knowledge, this is the first clinical report of MFO-IMPT for head and neck tumors. Early clinical outcomes are encouraging and warrant further investigation of proton therapy in prospective clinical trials.

A dosimetric comparison of intensity‐modulated proton therapy optimization techniques for pediatric craniopharyngiomas: A clinical case study

To evaluate the dosimetric characteristics of intensity-modulated proton therapy (IMPT) optimization techniques and pencil-beam scanning (PBS) nozzle designs on pediatric craniopharyngiomas. We compared a double-scatter (DS) plan with IMPT plans using single-field uniform dose (SFUD) optimization or multi-field optimization (MFO) and different PBS nozzles. The clinical impacts of SFUD versus MFO, range shifters, and two different PBS nozzles were compared. For target coverage assessment, the conformity index and inhomogeneity coefficient were evaluated. Although both proton therapy techniques achieved adequate target coverage, IMPT achieved a better conformity index of 0.78 versus 0.60 for DS. For the inhomogeneity coefficient, IMPT with MFO performed better than using SFUD or DS. MFO with the dedicated nozzle (MFO-DN) achieved the best result of 0.023, as compared to values of 0.03 or higher for the other plans. IMPT achieved lower doses to the normal tissues, as compared to DS; MFO-DN had the best results. The DN provided the best beam-spot characteristics and the sharpest lateral penumbra. MFO reduced the need for range shifters. As compared to DS proton therapy for pediatric craniopharyngiomas, IMPT achieved significantly better target coverage and dose sparing of normal tissue. Nozzle designs that provided small beam spots and sharp lateral penumbra allowed for better target coverage and reduced dose to normal tissue. In the case of shallow targets, MFO, in contrast to SFUD, required minimal use of range shifters, which preserved the penumbra and the dosimetric advantage. MFO-DN proved to be the optimal technique for IMPT.

Preliminary evaluation of multifield and single-field optimization for the treatment planning of spot-scanning proton therapy of head and neck cancer

Spot-scanning proton therapy (SSPT) using multifield optimization (MFO) can generate highly conformal dose distributions, but it is more sensitive to setup and range uncertainties than SSPT using single-field optimization (SFO). The authors compared the two optimization methods for the treatment of head and neck cancer with bilateral targets and determined the superior method on the basis of both the plan quality and the plan robustness in the face of setup and range uncertainties. Four patients with head and neck cancer with bilateral targets who received SSPT treatment in the authors' institution were studied. The patients had each been treated with a MFO plan using three fields. A three-field SFO plan (3F-SFO) and a two-field SFO plan (2F-SFO) with the use of a range shifter in the beam line were retrospectively generated for each patient. The authors compared the plan quality and robustness to uncertainties of the SFO plans with the MFO plans. Robustness analysis of each plan was performed to generate the two dose distributions consisting of the highest and the lowest possible doses (worst-case doses) from the spatial and range perturbations at every voxel. Dosimetric indices from the nominal and worst-case plans were compared. The 3F-SFO plans generally yielded D95 and D5 values in the targets that were similar to those of the MFO plans. 3F-SFO resulted in a lower dose to the oral cavity than MFO in all four patients by an average of 9.9 Gy, but the dose to the two parotids was on average 6.7 Gy higher for 3F-SFO than for MFO. 3F-SFO plans reduced the variations of dosimetric indices under uncertainties in the targets by 22.8% compared to the MFO plans. Variations of dosimetric indices under uncertainties in the organs at risk (OARs) varied between organs and between patients, although they were on average 9.2% less for the 3F-SFO plans than for the MFO plans. Compared with the MFO plans, the 2F-SFO plans showed a reduced dose to the parotids for both the nominal dose and in the worst-case scenario, but the plan robustness in the target of the 2F-SFO plans was not notably greater than that of the MFO plans. Compared with MFO, 3F-SFO improves plan robustness in the targets but degrades dose sparing in the parotids in both the nominal and worst-case scenarios. Although 2F-SFO improves parotid sparing compared with MFO, it produces little improvement in plan robustness. Therefore, considering its tolerable target coverage and sparing of OARs in worst-case scenarios, the authors recommend MFO as the planning method for the treatment of head and neck cancer with bilateral targets.

Multifield optimization intensity-modulated proton therapy (MFO-IMPT) for prostate cancer: Robustness analysis through simulation of rotational and translational alignment errors

To evaluate the dosimetric consequences of rotational and translational alignment errors in patients receiving intensity-modulated proton therapy with multifield optimization (MFO-IMPT) for prostate cancer. Ten control patients with localized prostate cancer underwent treatment planning for MFO-IMPT. Rotational and translation errors were simulated along each of 3 axes: anterior-posterior (A-P), superior-inferior (S-I), and left-right. Clinical target-volume (CTV) coverage remained high with all alignment errors simulated. Rotational errors did not result in significant rectum or bladder dose perturbations. Translational errors resulted in larger dose perturbations to the bladder and rectum. Perturbations in rectum and bladder doses were minimal for rotational errors and larger for translational errors. Rectum V45 and V70 increased most with A-P misalignment, whereas bladder V45 and V70 changed most with S-I misalignment. The bladder and rectum V45 and V70 remained acceptable even with extreme alignment errors. Even with S-I and A-P translational errors of up to 5mm, the dosimetric profile of MFO-IMPT remained favorable. MFO-IMPT for localized prostate cancer results in robust coverage of the CTV without clinically meaningful dose perturbations to normal tissue despite extreme rotational and translational alignment errors.

SU‐E‐T‐403: Intensity Modulated Proton Therapy Plans with Multiple Fields for Prostate Cancer

Purpose: To investigate the possible improvements in the dose conformity in intensity modulated proton therapy (IMPT) plans with multiple fields as compared to widely used single field optimized (SFO) plans with two lateral fields for spot scanned proton therapy (SSPT) and to verify the accuracy of the delivered dose using the Radiological Physics Center Proton Prostate Phantom (RPCPPP). Methods: The CT images of RPCPPP were used to design multiple IMPT plans using both SFO and multi field optimization (MFO) methods in the Varian Eclipse treatment planning system (TPS). The standard SFO clinical plan used two lateral fields going through the femoral heads. Non‐standard plans were generated using three or more oblique fields based on the SFO and MFO options of the TPS. The angles were carefully chosen to avoid bladder and rectum as much as possible. The RPC phantom containing films and TLDs was irradiated using the standard clinical SFO plan and the four field MFO plan to compare the planned and delivered dose. Results: Based on the DVHs, MFO plan with multiple oblique fields is found to have superior target conformity with reduced dose to organs at risk (OAR) and normal tissue, especially in the high dose regions, as compared to SFO plans. The point doses measured by TLDs and 2‐D dose distribution measured by GafChromic films in the RPCPPP irradiation passed the commonly used RPC acceptance criteria, namely +/− 7% agreement in point does and more than 85% of the voxels meeting the gamma index criteria of 7% dose or 4 mm distance agreement. Conclusion: The MFO SSPT plans for prostatic targets with multiple fields lead to better target conformity with lower doses to OARs as compared to SFO plans. The results of irradiations of the RPCPPP show that these plans can be delivered with acceptable accuracy

SU‐E‐T‐665: Investigation of Uniform Planning Margin for Intensity Modulated Proton Therapy of Pediatric Brain Tumors

Purpose: Determine if a uniform planning target volume (PTV) margin can be used for intensity modulated proton therapy (IMPT) of centrally located pediatric brain tumors and determine the most appropriate value. Methods: Treatment planning data from three pediatric patients with centrally located brain tumors were used in this study. For each patient, two IMPT plan types, a 3 field multi‐field‐optimized (MFO) and a 3 field single‐field‐optimized (SFO), and a 5 field IMRT plan were created for 7 uniform PTV margins that ranged from 0 to 10mm. The IMPT plans did not use robust optimization. For all plan types, the target coverage was held constant (98% of CTV received 54Gy and 95% of PTV received &gt;53Gy) and normal tissue doses were minimized. Four error types, each with numerous variations, were simulated and their effect were recorded. The four error types were: systematic plan position error, systematic field position error, systematic range error, and random position error. Results: Regarding normal tissues, there was no notable difference between MFO and SFO, both were substantially better than IMRT, e.g. mean cochlea dose was 14Gy for IMRT with 3mm margin and 5Gy for the IMPT plans. In general, smaller margins gave better normal tissue sparring. For both IMPT plan types and IMRT, PTV margins less than 3mm lead to target coverage deficits under the various errors. For position errors, the IMPT and IMRT plans gave similar results as a function of margin size. For density and systematic field errors, the SFO plans maintained target coverage better than MFO. Conclusions: A uniform PTV margin is not suitable for MFO planning. However, a uniform PTV margin of 3mm is appropriate for SFO planning when considering the above uncertainties (excluding large errors). At 3mm, which is also required for IMRT, the SFO plans had superior normal tissue sparing. Varian Medical Systems

TU-A-108-05: Quantification and Prediction of Dose Variation in Scanning Beam Proton Therapy From Setup and Anatomical Change for Single-Field, Multi-Field, and Robustly Optimized Plans

Purpose: The purpose of this study is two-fold: 1) to study proton dose variation due to weekly patient setup and anatomy change; and 2) to evaluate the effectiveness of robustness optimization and robustness evaluation techniques. Methods: For a given patient, single-field optimized (SFO), multi-field optimized (MFO) and multi-field optimized with robustness constrains (MFO-Robust) plans were generated on a simulation CT (CT0). The robustness of the plans was evaluated on CT0 with a statistical technique to compute standard deviation of the dose-volume histogram (SD-DVH) of the target volumes and critical structures for 600 combinations of setup and range uncertainties. The original plans were recalculated on subsequent weekly CTs (CTn), and the dose distributions on weekly CTs were deformed onto CT0 using the Velocity (Velocity Medical Solutions) software. The DVHs of weekly doses, as well as the accumulated dose were compared on CT0 with the anticipated SD-DVH variations predicted by the statistical plan robustness evaluation system. Results: The mean standard deviation of weekly doses for voxels within the GTV is <2%, for all techniques, the standard deviation of dose difference between the accumulated dose and the planned dose is <1% in GTV for all techniques. The DVH deviations of weekly and accumulated doses were within the 2SD-DVH confidence interval. Conclusion: This study quantifies the weekly variation of the patient dose, and the accumulated dose variation due to setup uncertainty and anatomy change. The SD-DVH, which is calculated at the time of planning, could be a good predictor of dose variation over the course of treatment.

WE-G-BRCD-03: Improvement in Robustness and Delivery Efficiency of Intensity-Modulated Proton Therapy Using Single-Field Optimization with Energy Absorber.

Intensity-modulated proton therapy (IMPT) using multi-field optimization (MFO) could generate highly conformal dose distributions but it is more sensitive to setup and proton range uncertainties than IMPT using single-field optimization (SFO). This work evaluates the effectiveness of SFO treatment plans with the use of energy absorbers (EAs) to improve the robustness and delivery efficiency of IMPT for head and neck cancers. IMPT treatment plans were generated using 2-field SFO with an EA in each field (EA-SFO) for four patients with head and neck cancers. We compared the plan quality, robustness, and delivery efficiency of the EA- SFO plan with a 3-field MFO plan that was used to treat the patient. Robustness analysis of each plan was performed to generate two dose distributions, consisting of the highest and the lowest possible doses from spatial and range perturbations at every voxel. Dosimetric indices and the numbers of energy layers required in the EA-SFO and MFO plans were compared. All the nominal EA-SFO plans are clinically acceptable. They achieved similar levels of target coverage compared to the MFO plans; the differences in D95 of the GTV and CTVs between the two plans were within 3.5%. Although some of the OARs received higher dose in the EA- SFO plan, they were all within tolerance. The EA-SFO plans yielded an average of 38.5% reduction of plan sensitivity to uncertainties in the targets and 18.5% overall. The EA-SFO plans used an average of 79 (46%) fewer energy layers than the MFO plans, which corresponds to nearly 3 minutes shorter delivery time. The use of energy absorber greatly facilitated the design of clinically acceptable SFO treatment plans. Compared to MFO, EA-SFO not only improved the robustness to setup and range uncertainties, but also reduced the time required for delivery and patient QA.

SU-E-T-506: Dosimetric Study for Shallow-Seated Tumor Using Passive/active Scanning Proton Beam.

To investigate the possibility of using a single spot scanning proton beam to treat superficial lesions. A cylindrical phantom with a simulated superficial target (it seated 0.5-4cm depth from the surface, volume: 270cm3 ) was created in Eclipse treatment planning system. Three proton plans were generated: (a) a single AP uniform scanning beam with aperture and range compensator; (b) a single AP spot scanning beam with a pre-absorber. The location and thickness of the pre-absorber were calculated using Geant4 to Monte Carlo code to make use of the available spot scanning beams to get a conformal plan. (c) a five-beam spot scanning beam plan using multi-field optimization. The prescription is 54 cobalt grey equivalent (CGE) which covers 95% of the target. The target coverage, lateral penumbra at 2 and 4cm depth in water, the doses to normal tissue (phantom-target) and skin (2mm from the surface) were evaluated and compared for three plans. The mean doses to the target are comparable within 2.4% for all three plans. The conformity indices (at 95%) are 1.36, 1.04 and 0.98 for plan (a), (b) and (c) respectively. The lateral penumbra (80% to 20%) for plan (a), (b) are both 0.73 cm, while it is 3.75 cm for plan (c). The skin dose which received more than 40 (CGE) from plan (a) is 10% higher than that of other two plans. Plan (c) has 70% higher mean doses to normal tissue than that of plan (a) and (b). Each plan provides good coverage of target. And in this study, it showed that, with a properly designed pre-absorber, it is possible to use a single spot scanning beam to treat superficial lesion. The plan provides good target coverage and maintains normal tissue sparing in the mean time.

MO-E-BRCD-01: Proton Treatment Planning Issues.

1. Understand the issues associated with proton treatment planning and the effects of range uncertainty, LET variations, and setup uncertainties. 2. Understand the differences of photon and proton treatment planning issues. 3. Understand the methods developed to reduce errors in proton treatment planning and delivery at three different centers.

Utilizing A Multifield Optimization Intensity Modulated Proton Technique (MFO-IMPT) To Deliver A Simultaneous Integrated Boost (SIB) To The Dominant Intraprostatic Lesion For Localized Prostate Cancer

Utilizing A Multifield Optimization Intensity Modulated Proton Technique (MFO-IMPT) To Deliver A Simultaneous Integrated Boost (SIB) To The Dominant Intraprostatic Lesion For Localized Prostate Cancer

Fast multifield optimization of the biological effect in ion therapy

In this paper, we present a new technique for simultaneous multifield optimization of the biological effect (i.e. relative biological effectiveness times dose) for intensity modulated radiotherapy with ion beams. It offers complete inverse treatment planning by taking into account planning constraints for the target volume as well as for organs at risk. The approach is based on the mixed irradiation formalism of the linear-quadratic model from radiobiology. We employ a novel objective function to directly optimize the biological effect rather than the physical dose. The required biological input data are reduced to a minimum and are completely independent from the optimization itself. They can be derived from any radiobiological model or even from directly measured data. The new optimization method was fully integrated into our inverse treatment planning tool KonRad. Comparisons with the TRiP98 treatment planning code were done for simple spread-out Bragg peaks as well as for three-dimensional treatment plans, where all fields were optimized separately. While the agreement between both planning systems was very good, the calculation time was substantially reduced in KonRad. By enabling the multifield optimization, the quality of the treatment plans and the sparing of healthy tissues can be clearly improved.

TU‐C‐224A‐01: Fast Multifield Optimization of the Biological Effect in IMRT with Ion Beams

Purpose: To investigate a new technique for multifield optimization of the biological effect (relative biological effectiveness times dose) for intensity modulated radiotherapy with scanned ion beams and to compare this method to an existing planning system for ions. Method and Materials: Our approach is based on the mixed irradiation formalism of the linear‐quadratic model using dose averaged mean values of alpha and sqrt(beta). We employ a novel objective function to directly optimize the biological effect rather than the physical dose. It is based on constraints in biologically effective dose for targets and organs at risk in close analogy to inverse planning for photons. The required biological input data are reduced to a minimum and are completely independent from the optimization itself. They can be derived from any radiobiological model or even from directly measured data. The new optimization method is fully integrated into the inverse treatment planning tool KonRad. Results: Comparisons with the TRiP98 treatment planning code are shown for spread‐out Bragg peaks as well as for three‐dimensional treatment plans for carbon ions, where all fields are optimized separately. While the agreement between both planning systems is very good, the calculation time is substantially reduced in KonRad. By enabling the multifield optimization in KonRad, the quality of the treatment plans and the sparing of healthy tissues can be clearly improved, which is demonstrated on several examples. Depending on the number of beam spots used, typical optimization times are between 10 and 60 minutes. Conclusion: The proposed system offers complete and fast inverse treatment planning for ions. Simultaneous multifield optimization of the biological effect can considerably enhance the resulting plans since it makes the best use of all possible degrees of freedom. Conflict of Interest: Research sponsored by Siemens Medical Solutions corporation.

Optimization of radiobiological effects in intensity modulated proton therapy

Today, inverse treatment planning for intensity modulated proton therapy (IMPT) usually employs a constant relative biological effectiveness (RBE). In this paper, the potential clinical relevance of RBE variations for scanning techniques in IMPT is investigated, and a new strategy to include the RBE into the inverse planning process is presented. Three-dimensional RBE distributions are calculated based on a phenomenological model that describes the RBE as a function of dose, linear energy transfer (LET) and tissue type in the framework of the linear-quadratic model. This RBE model is integrated into the optimization loop of inverse planning by using a modified version of the standard quadratic objective function, where the physical dose is replaced by the biological effect. This system for "biological optimization" was implemented into a research version of the inverse planning software KonRad and allows the direct optimization of the product of RBE and physical dose. Several treatment plans for a prostate case are presented, which compare the biological with the conventional physical dose optimization for IMPT scanning techniques, in particular distal edge tracking (DET) and the full three-dimensional (3D) modulation of beam spots. Mainly due to their different LET distributions, the RBE effects for these two techniques are quite different: while the RBE distribution was more or less homogeneous in the planning target volume (PTV) for 3D modulation, considerable RBE variations within the PTV were observed for DET. These unfavorable effects could be compensated for by employing the new biological objective function, which led to a more homogeneous distribution of the product of RBE and physical dose in the PTV. The computation time increased by a factor of 2 compared to the optimization of the physical dose. In conclusion, the proposed method allows the simultaneous multifield optimization of the biological effect in a reasonable time, and is therefore well suited for studying the influence of a variable RBE in IMPT as well as for minimizing potentially adverse effects.