Forward Treatment Planning Research Articles

Uterine perforation during brachytherapy for cervical cancer: Complications, outcomes, and best practices for forward treatment planning and management

PurposeThe purpose of the study was to determine the incidence of uterine perforations, review the associated complications, and propose guidelines for management of perforations after brachytherapy. Methods and MaterialsA retrospective chart review was conducted for all patients with cervical cancer who received single or multiple high-dose-rate brachytherapy implants between April 2006 and May 2017 at a single academic institution. CT and MRI images were retrospectively evaluated to record incidences of uterine perforation of tandem during brachytherapy. Acute and long-term complications during and after treatment were scored using the Common Terminology Criteria for Adverse Events, Version 4.0, of the National Cancer Institute. ResultsA total of 123 patients were included in the study. Perforations were observed in 22 patients (17.9%) with 31 (6.4%) of the 482 total implants. Of the different categories of adverse events, only the rate of acute infectious complications among those with perforations (n = 3, 13.6%) versus those without perforations (n = 3, 3.0%) was significant (p = 0.040). Two of the three perforated patients with acute infections had mild urinary tract infections, and all resolved without complications or treatment delays. The remaining one patient had a frank perforation of the anterior uterine wall with a subsequent Grade 3 pyometra infection despite administration of prophylactic antibiotics and 1-week treatment delay. This case was eventually resolved with cervical dilation and evacuation of fluid. Long-term complications were not different between the two arms. ConclusionsPatients with cervical cancer with uterine perforations may be able to safely proceed with brachytherapy treatment without delay or need for prophylactic antibiotics in the acute setting. Further validating data would be able to assist in establishing a new standard of care and help prevent unnecessary and harmful breaks during treatment.

SU-F-T-608: Forward Treatment Planning Techniques On Leksell Gamma Knife for the Normalization Effect Reduction

Purpose: In the Gamma Knife forward treatment planning, we use multiple shots for large targets to cover the targets and for irregular target shapes to achieve better target conformity. However, the normalization effect can be found when multiple shots are used during treatment planning, which can cause a decrease in the coverage of high value isodose lines within targets. In this study, we aim to evaluate the performance of forward treatment planning techniques for the normalization effect reduction. Methods: We can change the shot positions and the shot weightings to reduce the normalization effect for both models of Leksell Gamma Knife with and without the new collimation system during treatment planning. The new collimation system of Leksell Gamma Knife Perfexion, which contains 8 movable sectors, can provide us another method to reduce the normalization effect by using composite shots during treatment planning. Results: We proposed different forward treatment planning techniques that can achieve the normalization effect reduction. The normalization effect reduction can increase the coverage of high value isodose lines within targets, so the mean dose to targets would increase and the high-dose regions within targets can be more uniform. Conclusion: Due to an increase in the mean dose to targets from the normalization effect reduction, we can decrease the prescribed dose or set the prescribed dose at higher isodose line, and then lower the risk of complications.

Clinical implementation of multisequence MRI‐based adaptive intracavitary brachytherapy for cervix cancer

The purpose of this study was to describe the clinical implementation of a magnetic resonance image (MRI)‐based approach for adaptive intracavitary brachytherapy (ICBT) of cervix cancer patients. Patients were implanted with titanium tandem and colpostats. MR imaging was performed on a 1.5‐T Philips scanner using T2‐weighted (T2W), proton‐density weighted (PDW), and diffusion‐weighted (DW) imaging sequences. Apparent diffusion coefficient (ADC) maps were generated from the DW images. All images were fused. T2W images were used for the definition of organs at risk (OARs) and dose points. ADC maps in conjunction with T2W images were used for target delineation. PDW images were used for applicator definition. Forward treatment planning was performed using standard source distribution rules normalized to Point A. Point doses and dose‐volume parameters for the tumor and OARs were exported to an automated dose‐tracking application. Brachytherapy doses were adapted for tumor shrinkage and OAR variations during the course of therapy. The MRI‐based ICBT approach described here has been clinically implemented and is carried out for each brachytherapy fraction. Total procedure time from patient preparation to delivery of treatment is typically 2 hrs. Implementation of our technique for structure delineation, applicator definition, dose tracking, and adaptation is demonstrated using treated patient examples. Based on published recommendations and our clinical experience in the radiation treatment of cervix cancer patients, we have refined our standard approach to ICBT by 1) incorporating a multisequence MRI technique for improved visualization of the target, OARs, and applicator, and by 2) implementing dose adaptation by use of automated dose tracking tools.PACS numbers: 87.61.‐c, 87.53.Jw, 87.19.xj

MO‐F‐108‐04: Inverse Planning for Multi‐Stage Robotic Stereotactic Radiosurgery for Large Cerebral Arteriovenous Malformations

Purpose: A new inverse treatment planning technique was developed for multi‐staged robotic stereotactic radiosurgery of large cerebral arteriovenous malformations. Methods: Eleven patients with large (>15 cm3) cerebral arteriovenous malformations (AVMs) were selected in this study. The AVMs were contoured and divided into 3 to 8 sub‐targets with volumes of 3–7 cm3 to be treated sequentially in a staged approach at one to four week intervals. The prescription dose was 16 Gy to 20 Gy depending on the sub‐target volume and location. Inverse robotic radiosurgery treatment plans were generated for the total AVM volume and optimized to achieve 95% coverage. Staged plans for individual sub‐targets were generated from the total AVM plan usingthe weighting MUs based on beam lengths within each sub‐targets. Forward plans were created for comparison. Dose‐volume analysis was used to evaluate the PTV coverage, conformity index (CI), R50 and V12Gy values. Results: Inverse optimization outperformed forward planning for most patients for each index considered. In eight of the eleven patients the inversely optimized plans had better target coverage (96.0+/− 0.6% vs.95.8+/−1.3% for forward plan) while all of the patients had improved high dose conformality with the inversely optimized plans (1.23+/−0.16 vs. 1.44+/−0.16). Moderate dose spillage within the brain, as represented by the R50 parameter, was shown to improve in ten of the eleven patients for inversely optimized plans (3.2+/−0.7 vs. 3.9+/−0.7). Conclusion: Inverse treatment planning for staged, robotic radiosurgery of large AVMs was shown to improve target coverage, target dose conformality, and reduce normal tissue dose compared to forward treatment planning.

SU-E-T-614: An Optimization Algorithm for Beam Angle, Beam Weight and Wedge Angle in Forward Treatment Planning of External-Beam Radiotherapy Based on an Integer-Representation Adaptive Mutation Probability Genetic Algorithm

Purpose: To present the development of an optimization algorithm for beam angle, beam weight and wedge angle in forward treatment planning of external-beam radiotherapy using a genetic algorithm (GA). Methods: An adaptive mutation probability (AMP) integer-representation GA was applied for this optimization process in the MATLAB programming environment. The code allows various user-defined limits and starting points as well as comprehensive searches. We used an integer representation for all variables in the chromosomes pool for encoding the steps, because wedge angles often take discrete values (i.e. 0, 15, 30, 45 and 60 degrees). To improve performance, we designed a dynamic mutation probability assignment code in each generation so that the algorithm automatically adapts the mutation probability using the standard deviation of fitness values of the population at each generation. If the fitness diversity is great enough, a low mutation probability will be applied, and if the fitness values have low diversity, a high mutation probability will be applied. A dose calculation program using correction-based techniques and the CT images of the patient was also written within the same software. The GA code was tested using a standard test function both with AMP and with a constant mutation probability across all GA generations. Convergence of beam angle, beam weight and wedge angle was also investigated. Results: With the AMP technique, the GA maintained the population diversity in the chromosomes pool to avoid premature convergence into a local minimum. Test results showed that the algorithm with AMP (run time of 5 min for a simple standard test function) is more robust compared to the conventional method. Conclusions: This algorithm is a feasible and promising tool for optimization of treatment planning parameters with an acceptable computation time. Testing the algorithm against experienced treatment planners will be performed next.

SU-GG-T-579: A Study of Forward Treatment Planning with Integrated Multi-Prescription Dose for Patients with Nasopharyngeal Carcinoma

Purpose: To investigate the feasibility and indications of forward treatment planning with integrated multi‐prescription dose for patients with nasopharyngeal carcinoma. Methods and Materials: Six patients with nasopharyngeal carcinoma treated by IMRT technique were selected for this study. A forward IMRT treatment plan was created for each patient on Pinnacle 6.2 Treatment Planning System (TPS), which was optimized by integrating multi‐prescription dose plan according dose distribution. Six inverse IMRT plans were created and optimized on CORVUS 6.3 TPS for these six patients, dose distribution of planned treatment volume for gross tumor volume (PGTV) and clinical target volume (PCTV) and normal critical structure were compared between forward and inverse IMRT plan for each patient. Comparisons on conformity index (CI) of PCTV were made as well. Results: Based on dose constraint criterion in the RTOG0225 protocol, the dose distributions of the PTV and the normal critical structures met the goal. The dose of 95% Volume of PGTV and PCTV received was raged from 69.8Gy to 70.8 Gy and from 54 Gy to 55.6 Gy, respectively. The CI mean value of PCTV was 0.51 in forward plan, compared with 0.52 in inverse plan. It took 2 hours on average to complete a forward IMRT plan. Conclusions: The forward treatment planning with integrated multi‐prescription dose is feasible for early stage nasopharyngeal carcinoma, planning and treatment time were shortened significantly.

MO-A-204B-02: Efficient Outcomes-Driven IMRT Treatment Planning Using Commercial Treatment Planning Systems

The goal of radiation therapy is to deliver a therapeutic dose of radiation to target tissues while minimizing the risks of normal tissue complications. Until recently, the quality of a radiation treatment plan was routinely judged by physical quantities only, i.e., dose and dose-volume parameters, thought to correlate with biological response rather than by estimates of the biological outcome itself. Developments in our understanding of advantages and limitations of existing dose-response models are enabling the incorporation of biological concepts, or at least objective functions with biological relevance, into the routine treatment planning process. Outcomes-driven treatment planning aims to design dose distributions which find a balance between tumor cure and normal tissue damage. Such a multidimensional problem is most appropriately addressed in the framework of constrained treatment planning presently employed for the optimization of IMRT plans. The feedback may be either passive/automated in the case of inverse treatment planning, or with active participation from the planner in the case of forward treatment planning. To address many issues in this emerging topic, AAPM has established a task group (TG166) (1) to review the dose-response models likely to be used in treatment planning process, (2) to discuss strategies, limitations, conditions and cautions for using these models and parameters in clinical treatment planning, (3) to point out dosimetric differences between biologically based and physically based treatment plan optimization and evaluation, and (4) to provide general guidelines and methodology for the acceptance testing, commissioning and routine QA of biologically-based models in treatment planning process. Three of the speakers will discuss the use of commercial systems to do outcomes-driven treatment planning efficiently and effectively, including: the Philips/Pinnacle, CMS/Monaco, and Varian/Eclipse systems. The presenters will share their knowledge and findings concerning the most efficient and effective ways to use these systems such that planning is driven in a direction that is believed to improve outcomes, even though proof that the result is optimal is always lacking. Both radiobiological and dosimetric objective functions will be discussed, especially in the framework of constrained optimization. Multiple datasets and sites will be discussed for each planning system. The presentation is intended to provide familiarity with the tools available to users and also a practical clinical perspective on the magnitude of improvements that one may reasonably expect to be able to achieve. It is becoming increasingly clear that with the right constrained optimization approaches and outcomes-relevant objective functions, IMRT optimization can become much more efficient in terms of user time reductions, while at the same time achieving results that can be judged to push in the direction of improved patient outcomes. Research partially sponsored by Elekta Corporation (MA), and NIH grant CA85181 (JOD)

Determination of critical dosimetric parameters for breast radiation using forward-planned segmented fields for intensity modulation

The purpose of this study was to determine factors associated with acute skin toxicity from breast radiation for optimizing forward-planned intensity modulation. Treatment plans in 100 patients who received breast radiation using three-dimensional treatment planning were analyzed. Fifty-two patients were treated with tangent fields using wedges (nonsegmented), and 48 patients were treated with forward-planned fields segmented by a multileaf collimator to modulate intensity. Clinical and dosimetric variables were recorded. Acute skin toxicity was prospectively documented using a standard scale. Body weight, breast target volume, maximum body dose (encompassing 10 mL), and volume of body receiving >50 Gy and 55 Gy (V 50Gy, and V 55Gy) were associated with acute toxicity. Patients treated with segmented plans had significantly larger breast targets and were treated to lower prescription isodoses, confounding comparison with nonsegmented plans. Consequently, datasets from patients treated with segmented plans were used to design new nonsegmented plans for paired comparison. Segmented plans were superior with respect to dosimetric endpoints predictive of toxicity in this paired comparison. Limitations of 55 Gy for maximum body dose and 1100 mL for V 50Gy appeared to be appropriate values to guide forward treatment planning of segmented fields.

3D-Segmentation of the 18F-choline PET Signal for Target Volume Definition in Radiation Therapy of the Prostate

Volumetric assessment of PET signals becomes increasingly relevant for radiotherapy (RT) planning. Here, we investigate the utility of 18F-choline PET signals to serve as a structure for semi-automatic segmentation for forward treatment planning of prostate cancer. 18F-choline PET and CT scans of ten patients with histologically proven prostate cancer without extracapsular growth were acquired using a combined PET/CT scanner. Target volumes were manually delineated on CT images using standard software. Volumes were also obtained from 18F-choline PET images using an asymmetrical segmentation algorithm. PTVs were derived from CT 18F-choline PET based clinical target volumes (CTVs) by automatic expansion and comparative planning was performed. As a read-out for dose given to non-target structures, dose to the rectal wall was assessed. Planning target volumes (PTVs) derived from CT and 18F-choline PET yielded comparable results. Optimal matching of CT and 18F-choline PET derived volumes in the lateral and cranial-caudal directions was obtained using a background-subtracted signal thresholds of 23.0+/-2.6%. In antero-posterior direction, where adaptation compensating for rectal signal overflow was required, optimal matching was achieved with a threshold of 49.5+/-4.6%. 3D-conformal planning with CT or 18F-choline PET resulted in comparable doses to the rectal wall. Choline PET signals of the prostate provide adequate spatial information amendable to standardized asymmetrical region growing algorithms for PET-based target volume definition for external beam RT.

Three-dimensional conformal radiotherapy for locally advanced (Stage II and worse) head-and-neck cancer: Dosimetric and clinical evaluation

To evaluate the dosimetric parameters of three-dimensional conformal radiotherapy (3D-CRT) in locally advanced head-and-neck tumors (Stage II and above) and the effects on xerostomia. A total of 49 patients with histologically proven squamous cell cancer of the head and neck were consecutively treated with 3D-CRT using a one-point setup technique; 17 had larynx cancer, 12 oropharynx, 12 oral cavity, and 6 nasopharynx cancer; 2 had other sites of cancer. Of the 49 patients, 41 received postoperative RT and 8 definitive treatment. Also, 13 were treated with cisplatin-based chemotherapy before and during RT; in 6 cases, 5-fluorouracil was added. The follow-up time was 484-567 days (median, 530 days). One-point setup can deliver 96% of the prescribed dose to the isocenter, to the whole planning target volume, including all node levels of the neck and without overdosages. The mean dose to the primary planning target volume was 49.54 +/- 4.82 Gy (51.53 +/- 5.47 Gy for larynx cases). The average dose to the contralateral parotid gland was approximately 38 Gy (30 Gy for larynx cases). The maximal dose to the spinal cord was 46 Gy. A Grade 0 Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer xerostomia score corresponded to a mean dose of 30 Gy to one parotid gland. A lower xerostomia score with a lower mean parotid dose and longer follow-up seemed to give rise to a sort of functional recovery phenomenon. Three dimensional-CRT in head-and-neck cancers permits good coverage of the planning target volume with about 10-11 segments and one isocenter. With a mean dose of approximately 30 Gy to the contralateral parotid, we observed no or mild xerostomia.

SU‐FF‐T‐175: Dose Rate Optimization for Intensity‐Modulated Arc Therapy

Purpose: We use multiple dynamic arcs with different MLC shapes at different gantry angles for Intensity‐modulated arc therapy (IMAT). This study is to develop a fast and simple algorithm to optimize the dose rate as a function of gantry angle for IMAT for linear accelerators with dose rate variation capability for a dynamic arc. Method and Materials: The dose rate as a function of gantry angle for a dynamic arc is expressed by an analytical expression that favors beam directions with lower dose deposited to critical structures and higher dose deposited to the target volume. Three parameters are included in the analytical expression for further optimization of the dose rate base on an objective function. The optimized plan is transferred to a forward treatment planning system for final dose calculation. The method is applied to a phantom and a few clinical cases using 6 MV and 18 MV beams for a Varian linear accelerator. Results: The method has been demonstrated with a test phantom and a few clinical radiotherapy cases. We have showed that dose distributions and dose volume histograms have been improved with the dose rate optimization for IMAT. It gives more uniform dose to the target volume and lower dose to the critical structure. Conclusions: We have developed a fast and simple technique to optimize the dose rate as a function of gantry angle for intensity‐modulated arc therapy, while retaining its advantages of an intuitive treatment planning process and efficient radiation delivery.

Inverse Plan Optimization Incorporating Random Setup Uncertainties Using Monte Carlo Based Fluence Convolution

Purpose/Objective: Recent investigations in forward treatment planning have invoked the reciprocity between the patient and incident beam fluence (under the assumption of rigid body motion) to show how fluence convolution may be used as an alternative to direct simulation in accounting for random setup uncertainties. Here we focus on the inverse problem. In inverse planning, highly conformal dose distributions optimized from a static instance of the patient geometry are likely to be more sensitive to the effects of motion.