3D Treatment Planning Research Articles

The use of Interactive, Real-time, Three-dimensional (3D) Volumetric Visualization for Image Guided Assistance in the Brachytherapy Needle Placement for Advanced Gynecological Malignancies

It is often difficult to predetermine needle length to target, proximity to bowel, vascularity (in relation to the needle path), and bony interference when performing a needle implant for advance gynecological malignancies. Needle placement can often require laparoscopic guidance. Three-dimensional, interactive, measurable volumetric software utilized by other subspecialties, i.e.: cardiovascular interventions is evaluated to see if it can accomplish this task. A patient with a vaginal recurrence of endometrial carcinoma status post exenteration with bowel adherent to tumor preventing the use of laparoscopic guidance was evaluated for brachytherapy needle placement utilizing interactive, 3D volumetric, image guided visualization. CTA study (computer tomographic angiography) was fused with a PET imaging study was used to define and refine target. Acquisition of the CTA data set occurred at .625 mm slices as compared to standard of care routine 2 - 5 mm acquisition, in an effort to improve 3D targeted path. Acquisition at .625 mm adds no additional dose of radiation to the patient and measurably improves 3D targeting and volume visualization. Skin to target distance, template to target distance, and ideal measured placement and trajectory of needles were predetermined prior to going to the operating room. The image-guided volume metrics were recorded on an iPad for additional insight during the intra-operative procedure. The only diagnostic imaging available in the operating room was fluoroscopy. Postoperative CT imaging verified needle placement with standard of care 3D treatment plan analysis. Needle placement was within 1 - 2mm of ideal placement. There was no boney obstruction of the needle, perforation of the bowel, or any vascular penetration of the of the needles. This was verified clinically and radiographically by postoperative imaging. Three-dimensional volumetric reconstructive software can assist the radiation oncologist in preplanning brachytherapy needle placement in advanced gynecological malignancies. In order to optimize the 3D volumetric reconstruction process the radiation oncologist needs to understand that CT data sets are routinely acquired at .625 mm slice thickness but are routinely stored at 5mm thickness on PACS or other storage devices. The technology of interactive image guided 3D volume reconstruction and visualization needs to be evaluated in a larger number of patients.

Towards accurate dose accumulation for Step-&-Shoot IMRT: Impact of weighting schemes and temporal image resolution on the estimation of dosimetric motion effects

PurposeBreathing-induced motion effects on dose distributions in radiotherapy can be analyzed using 4D CT image sequences and registration-based dose accumulation techniques. Often simplifying assumptions are made during accumulation. In this paper, we study the dosimetric impact of two aspects which may be especially critical for IMRT treatment: the weighting scheme for the dose contributions of IMRT segments at different breathing phases and the temporal resolution of 4D CT images applied for dose accumulation. MethodsBased on a continuous problem formulation a patient- and plan-specific scheme for weighting segment dose contributions at different breathing phases is derived for use in step-&-shoot IMRT dose accumulation. Using 4D CT data sets and treatment plans for 5 lung tumor patients, dosimetric motion effects as estimated by the derived scheme are compared to effects resulting from a common equal weighting approach. Effects of reducing the temporal image resolution are evaluated for the same patients and both weighting schemes. ResultsThe equal weighting approach underestimates dosimetric motion effects when considering single treatment fractions. Especially interplay effects (relative misplacement of segments due to respiratory tumor motion) for IMRT segments with only a few monitor units are insufficiently represented (local point differences >25% of the prescribed dose for larger tumor motion). The effects, however, tend to be averaged out over the entire treatment course. Regarding temporal image resolution, estimated motion effects in terms of measures of the CTV dose coverage are barely affected (in comparison to the full resolution) when using only half of the original resolution and equal weighting. In contrast, occurence and impact of interplay effects are poorly captured for some cases (large tumor motion, undersized PTV margin) for a resolution of 10/14 phases and the more accurate patient- and plan-specific dose accumulation scheme. ConclusionsRadiobiological consequences of reported single fraction local point differences >25% of the prescribed dose are widely unclear and should be subject to future investigation. Meanwhile, if aiming at accurate and reliable estimation of dosimetric motion effects, precise weighting schemes such as the presented patient- and plan-specific scheme for step-&-shoot IMRT and full available temporal 4D CT image resolution should be applied for IMRT dose accumulation.

Application of a spacer gel to optimize three-dimensional conformal and intensity modulated radiotherapy for prostate cancer

Background and purposeThe aim was to evaluate the impact of a spacer gel on the dose distribution, applying three-dimensional conformal (3D CRT) and intensity modulated radiotherapy (IMRT) planning techniques. Material and methodsThe injection of a spacer gel (10ml SpaceOAR™) was performed between the prostate and rectum under transrectal ultrasound guidance in 18 patients with prostate cancer. 3D CRT and IMRT treatment plans were compared based on CT before and after injection (78Gy prescription dose). ResultsIn contrast to the PTV and bladder, significant advantages (p<0.01) resulted in respect of all analysed rectal dose values comparing pre spacer with post spacer plans for both techniques. Rectal NTCP (normal tissue complication probability) reached the lowest percentage after spacer injection irrespective of the technique, with a mean reduction of >50% for both IMRT and 3D CRT. Significantly (p<0.01) higher Dmean, and V78 for the PTV were reached with IMRT vs. 3D CRT plans, with a smaller rectum V76 but larger rectum V50. ConclusionsThe injection of a spacer gel between the prostate and anterior rectal wall is associated with considerably lower doses to the rectum and consequentially lower NTCP values irrespective of the radiotherapy technique.

4D analysis of influence of patient movement and anatomy alteration on the quality of 3D U/S‐based prostate HDR brachytherapy treatment delivery

Modern HDR brachytherapy treatment for prostate cancer based on the 3D ultrasound (U/S) plays increasingly important role. The purpose of this study is to investigate possible patient movement and anatomy alteration between the clinical image set acquisition, made after the needle implantation, and the patient irradiation and their influence on the quality of treatment. The authors used 3D U/S image sets and the corresponding treatment plans based on a 4D-treatment planning procedure: plans of 25 patients are obtained right after the needle implantation (clinical plan is based on this 3D image set) and just before and after the treatment delivery. The authors notice the slight decrease of treatment quality with increase of time gap between the clinical image set acquisition and the patient irradiation. 4D analysis of dose-volume-histograms (DVHs) for prostate: CTV1 = PTV, and urethra, rectum, and bladder as organs at risk (OARs) and conformity index (COIN) is presented, demonstrating the effect of prostate, OARs, and needles displacement. The authors show that in the case that the patient body movement/anatomy alteration takes place, this results in modification of DVHs and radiobiological parameters, hence the plan quality. The observed average displacement of needles (1 mm) and of prostate (0.57 mm) is quite small as compared with the average displacement noted in several other reports [A. A. Martinez et al., Int. J. Radiat. Oncol., Biol., Phys. 49(1), 61-69 (2001); S. J. Damore et al., Int. J. Radiat. Oncol., Biol., Phys. 46(5), 1205-1211 (2000); P. J. Hoskin et al., Radiotherm. Oncol. 68(3), 285-288 (2003); E. Mullokandov et al., Int. J. Radiat. Oncol., Biol., Phys. 58(4), 1063-1071 (2004)] in the literature. Although the decrease of quality of dosimetric and radiobiological parameters occurs, this does not cause clinically unacceptable changes to the 3D dose distribution, according to our clinical protocol.

Three‐dimensional conformal versus non‐graphic radiation treatment planning for apocrine gland adenocarcinoma of the anal sac in 18 dogs (2002–2007)

Differences in dose homogeneity and irradiated volumes of target and surrounding normal tissues between 3D conformal radiation treatment planning and simulated non-graphic manual treatment planning were evaluated in 18 dogs with apocrine gland adenocarcinoma of the anal sac. Overall, 3D conformal treatment planning resulted in more homogenous dose distribution to target tissues with lower hot spots and dose ranges. Dose homogeneity and guarantee of not under-dosing target tissues with 3D conformal planning came at the cost, however, of delivering greater mean doses of radiation and of irradiating greater volumes of surrounding normal tissue structures.

Magnetic resonance temperature imaging validation of a bioheat transfer model for laser‐induced thermal therapy

Purpose: Magnetic resonance‐guided laser‐induced thermal therapy (MRgLITT) is currently undergoing initial safety and feasibility clinical studies for the treatment of intracranial lesions in humans. As studies progress towards evaluation of treatment efficacy, predictive computational models may play an important role for prospective 3D treatment planning. The current work critically evaluates a computational model of laser induced bioheat transfer against retrospective multiplanar MR thermal imaging (MRTI) in a canine model of the MRgLITT procedure in the brain.Methods: A 3D finite element model of the bioheat transfer that couples Pennes equation to a diffusion theory approximation of light transport in tissue is used. The laser source is modelled conformal with the applicator geometry. Dirichlet boundary conditions are used to model the temperature of the actively cooled catheter. The MRgLITT procedure was performed on n = 4 canines using a 1‐cm diffusing tip 15‐W diode laser (980 nm). A weighted norm is used as the metric of comparison between the spatiotemporal MR‐derived temperature estimates and model prediction.Results: The normalised error history between the computational models and MRTI was within 1–4 standard deviations of MRTI noise. Active cooling models indicate that the applicator temperature has a strong effect on the maximum temperature reached, but does not significantly decrease the tissue temperature away from the active tip.Conclusions: Results demonstrate the computational model of the bioheat transfer may provide a reasonable approximation of the laser–tissue interaction, which could be useful for treatment planning, but cannot readily replace MR temperature imaging in a complex environment such as the brain.

Dosimetric Comparison of 3D Tangential Radiotherapy of Post-Lumpectomy Breast at Two Different Energies

Introduction: Radiation therapy following breast conserving surgery is one of the most common procedures performed in any radiation oncology department. A tangential parallel-opposed pair is almost always the technique of choice for this purpose. This technique is often performed based on 3D treatment planning. The aim of this study was to compare 3D treatment planning for two different energies (Cobalt 60 versus 6 MV photon beams) in tangential irradiation of breast conserving radiotherapy. In this comparison, homogeneity of isodoses within the breast volume and dose received by lungs were considered. Materials and Methods: In this study, twenty patients with breast cancer treated with conservative surgery were included. A CT scan was performed on selected patients. Three-dimensional treatment planning with 6 MV photon beams was carried out for patients on the Eclipse 3D treatment planning system (TPS). The volumes receiving lower than 95% (Vol 105) (hot areas) of the reference dose, and the volume of lung receiving ≥30Gy (Vol≥30Gy) were derived from dose volume histograms (DVHs). Dose homogeneity index was calculated as: DHI = 100 – (Vol>105 + Vol<95). In the second stage, each patient was replanned with Cobalt 60 and the quantities of interest were obtained from the DVHs. Results: Comparing 3D treatment planning by 6 MV and Cobalt 60 photons, cold areas were reduced (p<0.001), hot areas were decreased (p<0.7), DHI was improved (P<0.001) and Vol≥30Gy was reduced (P<0.017) with 6 MV photons. Discussion and Conclusion: Our results indicate that treatment planning with Cobalt 60 causes more cold areas in the treated volume as compared with 6 MV photons. Cold areas within the target volume of the breast result in reduced tumor control probability. The plan can be optimized to limit dose to lung volume by using 6 MV photons. So lung fibrosis is more likely to occur with Cobalt 60. In addition, DHI was improved with 6 MV photon beams. Improvement of dose homogeneity can lead to higher tumor control probability and cosmetic results, and less skin and lung side effects. Hence, 3D treatment planning with 6 MV photon beams is a more suitable option for patients with breast cancer treated with conserving surgery

SU‐E‐T‐865: Biologically Optimized 4D Dose Distributions for the Treatment of Incurable Glioblastoma

Purpose: A patient‐specific method to optimize IMRT treatment of incurable disease by maximizing tumor cell death and minimizing dose to normal tissue is proposed. Methods: A multiobjective evolutionary algorithm was used to optimize IMRT dose distributions on an example patient throughout treatment using a published patient‐specific 4D mathematical model of glioblastoma proliferation and invasion [Rockne 2010] to calculate the distribution of diffusely invaded tumor cells, hypoxia, and radiosensitivity and recalculate distributions after each week of treatment. Each optimized IMRT plan was designed to maximize EUD for tumor cells while holding constant the EUD for normal tissue. Dose distributions were scaled such that the EUD delivered to the normal tissue for each fraction was equal to the EUD delivered from one fraction using the current clinical protocol of 1.8 Gy to the frank tumor with a 2.5 cm margin. Results: The mathematical model predicted that the total volume of tumor was reduced by 41.0% after one week and 72.5% after two weeks of treatment using the proposed protocol. The current clinical protocol was shown to reduce volume by only 5.5% after one week and 11.2% after two weeks for the same EUD delivered to normal tissue. After 7 weeks of treatment using the clinical protocol and 250% higher normal tissue EUD, the tumor burden was only reduced by 40.4%. Conclusions: A patient‐specific mathematical model showed that a 4D treatment plan that maximizes tumor cell killing while sparing normal tissue reduces the tumor volume more in one week than in seven weeks using current clinical protocol for the same EUD delivered to normal tissue. This approach has the potential to optimize and tailor IMRT treatment planning to individual patientˈs disease through an iterative dialog between a mathematical model for disease and response to therapy with objective‐based treatment optimization.

TU-A-BRB-11: 4D Optimization for Respiratory Phase-Dependent IMRT Treatment Planning

Purpose: To develop 4D optimization for respiratory phase‐dependent IMRTtreatment planning with dynamic MLC motion tracking, including MLC leaf motion constraints, which takes respiration‐induced anatomic motion into account and is robust to the variations of fractional time spent in respiratory phases within a 4D CT planning scan. Method and Materials: A tool for 4D treatment‐planning optimization that integrates a commercially available treatment‐planning system and a general‐purpose optimization system was developed and applied to the 4D CT planning scans of two lungcancer patients. The optimization variables were MLC leaf positions as a function of monitor units and respiratory phase. The objective function was the deformable dose‐summed 4D treatment plan score. MLC leaf motion was constrained by the maximum leaf velocity between control points in terms of monitor units and between phases and between leaves for tumor motion parallel and perpendicular to the leaf travel direction, respectively, in terms of phases. Without loss of generality, due to the computational burden, 4D optimization was performed with two phases, end inhale and exhale. For comparison and a starting point for the 4D optimization, 3D optimization was performed on each of the phases. Results: 4D treatment plan score improved during 4D optimization by 34% for Patient 1 and 50% for Patient 2, indicating 4D optimization generated a better 4D plan than the sum of individually optimized phase plans. The DVHs for each phase remained similar, indicating robustness of the 4D plan to respiratory variations expected during treatment delivery. Conclusions: 4D optimization for respiratory phase‐dependent treatment planning with dynamic MLC motion tracking improved the 4D plan score by 42% on average compared with 3D optimization. 4D treatment plans generated changed from phase to phase to account for anatomic motion, but showed similar dose distributions in each phase. Research supported by NIH/NCI R01‐93626 and Philips Healthcare.

SU-E-T-596: High Dose Brachytherapy Planning of a Left Breast Cancer Patient with in Situ Pacemaker:

Purpose: To investigate the benefits of multilumen partial breast Brachytherapy device, SAVI, in reducing dose to in situ pacemakers in patients with cancer of the left breast. Methods: A left breast cancer patient with an in situ pacemaker underwent breast conservative surgery and was referred for Partial Breast Irradiation (PBI) using Ir‐192 High Dose Rate Brachytherapy. The preliminary estimation of the pacemaker dose from a pre‐insertion CT study was about 8 % of the prescribed dose which exceeded the generally accepted dose of 2Gy. The challenge was to use a suitable applicator to treat the tumor bed and 1 cm margin without exceeding the 2Gy limit to the pacemaker and the leads. A seven catheter SAVI device was selected and implanted in the left breast in an optimal direction and a 3D treatment plan was generated following a post insertion CT scan, using the Oncentra Brachy treatment planning system. Several optimization tools available in the planning system namely inverse, graphical, and dose point optimization were utilized to selectively load the catheters and reduce the dose to pacemaker and leads. A set of calibrated TLD chips were used to determine the surface dose on the pacemaker, which was then compared to the calculated surface dose. The pacemaker parameters were monitored before and after the 10 fraction (bid 5days) HDR brachytherapy, by a vendor representative and were found to functioning properly. Results: Using the seven catheter SAVI device it was possible to limit the pacemaker/ leads dose to less than 2 Gy, with an overall satisfactory dose to the target volume. Conclusions: By combining the optimization tools of today's Brachytherapy planning system and a multilumen SAVI applicator, HDR partial breast irradiation can be successfully delivered for left breast cancer patients with in situ pacemaker, with out the concern of interrupting pacemaker functionality

SU-E-T-890: Comparison of SBRT Lung Treatments Using 3D Conformal, Conformal Arcs and VMAT

Purpose: Stereotactic Body Radiotherapy(SBRT)treatments for lungtumors were originally delivered using multiple (>10) non‐coplanar 3D conformal beams. This technique produces very conformal dose distributions that minimize the amount of normal lung irradiated. The disadvantage of this treatment technique is the extended treatment delivery time, usually between 30 to 45 minutes, due to the numerous beams and couch angles. These prolonged treatments times can be prohibitive in busy departments where machine time is limited, or where certain patients, especially elderly patients, have a hard time remaining still for extended periods of time. The aim of this study is to show that lungSBRTtreatment plans created using VMAT and conformal arc treatment plans are dosimetrically equivalent to 3D conformal plans. Methods: This is a retrospective study of 5 patients treated in our clinic. All plans will be created using Pinnacle version 9.0 (Phillips Radiation Oncology Systems, Fitchburg, WI) and delivered using and Elekta Synergy S linear accelerator (Elekta, Inc., Peachtree, GA). All patients were treated to to 50 Gy in 5 fractions, and all plans used the conformality criteria from RTOG 0236 as goals. Results: 3D conformal treatment plans were planned with 10 beams, including 6 couch angles, while VMAT and conformal arc plans were used 2 arcs. All plans easily meet the R100 criteria, while no planning method is able to meet the strict R50 criteria. However, the R50 was lower for the 3D conformal plan. Additionally, the V20 volumes were satisfactory for all plans. Treatment delivery times were reduced by a factor of 5 for VMAT plans and a factor of 3–4 for conformal arc plans. Conclusions: All SBRTtreatments are treated using VMAT because the advantage of significantly reduced treatment times outweighs any slight dosimetric disadvantages. Funding provided by Elekta, Inc.

TH-E-220-06: Selection of External Surrogate for 4DCT Sorting: Does It Impact Target Delineation?

Purpose: To evaluate differences observed between two different external surrogate acquisition systems: Varianˈs Real-Time Position Management (RPM) and Philips Medical Systems pneumatic bellows, in the context of 4DCT sorting and tumor delineation. Methods: Eight patient displacement curves from RPM data were inputted into the motion platform with a variety of amplitudes (0.5 to 3 cm). Simultaneous 4DCT acquisition was performed with both bellows and RPM block placed on the platform. The bellows signal was used for on-line retrospective phase-based sorting, while raw 4DCT data was reconstructed off-line using RPM signal on a research version of the Extended Brilliance Workspace (Philips Healthcare). Curves were resampled, normalized, and analyzed to determine the association between different external surrogates, amplitude differences, and latency between systems. 4DCT data was imported into Eclipse, and a lung window/level was used for all contouring. The volumes and centroids were compared among techniques. Results: Pearson r correlations between the RPM and bellows-acquired breathing traces were 0.987– 0.999. Slight discrepancies were observed with low amplitude displacement, where bellows were not as sensitive as RPM to slight variations in motion platform position. Target volumes were 200.27 +/− 12 cc and 199.96 +/− 13.3 cc for RPM and bellows targets, respectively, which was not significantly different (t(7) = 0.33, p = 0.75). Small centroid variations were observed between bellows and RPM contoured MIP targets: 0.025 +/− 0.05 mm, 0.013 +/− 0.04 mm, and 0.25 +/− 0.32 mm in lateral, anterior-posterior, and superior- inferior directions, respectively. Largest volume difference was observed for an RPM target 2.5 cc (1%) less than bellows target, which showed the largest difference in centroid displacement (0.9 mm). Overall, RPM data lagged behind the bellows data ∼126 ms. Conclusions: We have demonstrated comparable results between Philips bellows and Varianˈs RPM system, particularly in the management of 4D treatment planning. Acknowledgment: This work is supported in part by Philips Healthcare Conflict of interest: Henry Ford Health Systems holds a research agreement with Philips Healthcare.

TU‐E‐BRC‐06: Rapid MRI for Personalized 4D Image‐Guided Lung Cancer Radiotherapy

Purpose: Respiratory motion causes thoracic anatomy to change continuously in all four dimensions (4D = 3D+time). However, current image‐guidance tools (e.g., 4DCT) provide only a reconstituted, single‐cycle snapshot of motion, thereby ignoring complex cycle‐to‐cycle spatial and temporal effects. In this work, we investigate the use of rapid MRI as a truly 4D, non‐invasive monitoring tool for lung SBRT Methods: Under an IRB‐approved protocol, two lung cancer patients were imaged under free breathing conditions, without extrinsic contrast, on a 1.5T MRI scanner using a 4‐channel cardiac coil. A balanced SSFP sequence (TE/TR: 1.68/3.16 ms; FOV: 240×240 mm2; half‐Fourier acquisition; voxel: 2.4×3x5 mm3) was used to acquire 2D+t and 4D (8 slices, parallel acceleration=4) time series for 20s and 60s respectively. For each 2D+t series, the tumor centroid, the diaphragm and ∼15 points on the tumor boundary were manually contoured on one image frame. An optical fluid‐flow‐based deformable image registration algorithm was applied to the time series to map the motion trajectory of each point on each contour. A temporal smoothness constraint was imposed so as to avoid non‐physical registration. Results: Acquisition times of ∼0.15s/frame and ∼1.5s/volume were achieved for 2D+t and 4D acquisition, respectively. In each case, image quality was adequate to clearly delineate and monitor the motion of the tumor, the diaphragm and the cardiac wall. Both patients showed significant cycle‐to‐cycle variation in tumor position. One of the patients with a left mid‐lobe lesion showed significant tumor deformation and rotation (&gt;4 degrees) due to the combined influence of cardiac and diaphragmatic motion. Conclusions: Rapid 2D+t and 4D MRI offers a highly attractive, non‐invasive tool for characterizing respiratory motion from a truly 4D perspective. Such image‐guidance will lay the groundwork for personalized motion management based on patient‐specific, long‐term monitoring, personalized 4D treatment planning and, if necessary, inter‐ and intra‐fraction treatment adaptations.

Large breast size as a risk factor for late adverse effects of breast radiotherapy: Is residual dose inhomogeneity, despite 3D treatment planning and delivery, the main explanation?

Background and PurposeLarge breast size is associated with an increased risk of late adverse effects after breast conservation surgery and radiotherapy, even when 3D dosimetry is used. The purpose of this study is to test the hypothesis that residual dose inhomogeneity is sufficient to explain the association. MethodsPatients previously treated after breast conservation surgery with whole breast radiotherapy using 3D dosimetry and followed up in the UK FAST hypofractionation trial were selected for this analysis. The residual level of dose inhomogeneity across the whole breast treatment volume was used to test for association between residual dosimetry and post-treatment change in breast appearance at 2years post-radiotherapy. ResultsAt 2years, 201/279 (72%) of women had no change in photographic breast appearance, 61 (22%) had mild change and 17 (6%) had marked change. Breast size and dosimetry were both significantly associated with late effects in univariate analyses, but only breast size remained an independent significant risk factor for change in breast appearance when included in a multiple regression model together with other prognostic factors (p=0.006 for trend). ConclusionLarge-breasted women are more likely to suffer change in breast size and shape after whole breast radiotherapy delivered using 3D dosimetry, but residual dose inhomogeneity is insufficient to explain the association.

Outcomes of chemoradiotherapy with a high irradiation dose using a 3D radiation treatment planning system for esophageal cancer.

89 Background: The standard irradiation dose of chemoradiotherapy (CRT) for esophageal cancer is 50.4 Gy, however, the trials in which this standard dose was originated were based on 2D radiation treatment planning. In this study we assessed the survival and toxicities of CRT with a dose of 60-66 Gy using a 3D radiation treatment planning system (3DRTPS) for esophageal cancer. Methods: One hundred and two eligible patients with esophageal cancer treated by definitive CRT between 2000 and 2006 were assessed. Median age was 67 years old. There were stage I in 22 patients, stage II-III (without T4) in 27 and T4/M1Lymph legions in 53. There were 100 patients with squamous cell carcinoma histology and 2 with small cell carcinoma. Main tumor sites were cervical/upper/middle/lower thoracic in 15/19/43/25 patients. Treatment planning of irradiation was performed using a CT based 3DRTPS. Total irradiation dose of our protocol was 60-66 Gy. Accomplishment rate of planned irradiation was 93%. All patients received chemotherapy concurrently with radiotherapy. Fluorouracil based chemotherapy was performed in 96 patients (94%). Results: The data was updated in August 2010. The median follow-up was 67 months. Cause-specific survival rates at 5 years for stage I, II-III (without T4) and T4/M1lymph were 100%, 49% and 17%, respectively and overall survival rates were 66%, 35% and 13%, respectively. Complete response (CR) rates were 100%, 79% and 35%, respectively and failure rates of CR cases were 5%, 43% and 42%, respectively. Late adverse effects (≥ grade 3) were observed in 11 patients (10%); pneumonitis in 4 (4%), pleural effusion in 4 (4%) and pericardial effusion in 5 (5%). Treatment related deaths were observed in 2 cases (pneumonitis developed during treatment in 1 and debility due to treatment in 1). Conclusions: Toxicities of CRT with a high irradiation dose using 3DRTPS for esophageal cancer were acceptable and survival was promising. Dose intensification study of 50.4 Gy versus ≥ 60 Gy in CRT using a 3D-conformal radiation therapy technique for esophageal cancer should be considered. No significant financial relationships to disclose.

Verification of monitor unit calculations for non‐IMRT clinical radiotherapy: Report of AAPM Task Group 114

The requirement of an independent verification of the monitor units (MU) or time calculated to deliver the prescribed dose to a patient has been a mainstay of radiation oncology quality assurance. The need for and value of such a verification was obvious when calculations were performed by hand using look-up tables, and the verification was achieved by a second person independently repeating the calculation. However, in a modern clinic using CT/MR/PET simulation, computerized 3D treatment planning, heterogeneity corrections, and complex calculation algorithms such as convolution/superposition and Monte Carlo, the purpose of and methodology for the MU verification have come into question. In addition, since the verification is often performed using a simpler geometrical model and calculation algorithm than the primary calculation, exact or almost exact agreement between the two can no longer be expected. Guidelines are needed to help the physicist set clinically reasonable action levels for agreement. This report addresses the following charges of the task group: (1) To re-evaluate the purpose and methods of the "independent second check" for monitor unit calculations for non-IMRT radiation treatment in light of the complexities of modern-day treatment planning. (2) To present recommendations on how to perform verification of monitor unit calculations in a modern clinic. (3) To provide recommendations on establishing action levels for agreement between primary calculations and verification, and to provide guidance in addressing discrepancies outside the action levels. These recommendations are to be used as guidelines only and shall not be interpreted as requirements.

Technical Advances of Radiation Therapy for Thymic Malignancies

Radiation therapy often plays a critical role in the treatment of thymic malignancies. However, because of the location of these tumors, historically patients have been at a significant risk for radiation-related toxicity such as pericardial effusions, radiation pneumonitis, long-term pulmonary fibrosis, and occasional long-term esophageal stricture, particularly for unresectable thymoma. Recent advancements in technology have provided the treating radiation oncologist with the ability to more accurately target the region at risk while sparing normal structures. In this review, we provide an overview of key advances in radiation techniques for thymoma over the past two decades. These techniques include 3D conformal therapy, intensity-modulated radiation therapy, 4D treatment planning, adaptive radiation therapy, and proton therapy. Each advancement has brought with it unique advantages in maintaining long-term disease control while improving quality of life in this manageable disease.

Fast 4D Modeling for Real-time Motion Management in Radiation Therapy

Fast 4D Modeling for Real-time Motion Management in Radiation Therapy

THE COMPARISON 2D AND 3D TREATMENT PLANNING IN BREAST CANCER RADIOTHERAPY WITH EMPHASIS ON DOSE HOMOGENEITY AND LUNG DOSE

Introduction: Breast conserving radiotherapy is one of the most common procedures performed in any radiation oncology department. A tangential parallel-opposed pair is usually used for this purpose. This technique is performed using 2D or 3D treatment planning systems. The aim of this study was to compare 2D treatment planning with 3D treatment planning in tangential irradiation in breast conserving radiotherapy. In this comparison, homogeneity of isodoses in the breast volume and lung dose were considered. Material and Methods: Twenty patients with breast cancer treated with conservative surgery were included in this study. The patients were CT scanned. Two-dimensional treatment planning with the Alfard 2D TPS was performed for each patient using a single central CT slice. The data used on the Alfard 2D TPS was imported into the Eclipse 3D TPS, on which 3D treatment planning was performed. Cobalt-60 beams were used in all plans. Results: Comparing 2D and 3D treatment planning, homogeneity of isodoses was improved in 3D treatment planning (p 30Gy was increased in 3D treatment planning (p< 0.01). Discussion and Conclusion: 3D treatment planning is a more suitable option for patients with breast cancer treated with conservative surgery because of improved dose homogeneity in 3D treatment planning. The results of the treatment can be improved with reduced recurrence probability and skin problems.

An investigation of intensity-modulated radiation therapy versus conventional two-dimensional and 3D-conformal radiation therapy for early stage larynx cancer

IntroductionIntensity modulated radiation therapy (IMRT) has been incorporated at several institutions for early stage laryngeal cancer (T1/T2N0M0), but its utility is controversial.MethodsIn three representative patients, multiple plans were generated: 1) Conventional 2D planning, with the posterior border placed at either the anterior aspect ("tight" plan) or the mid-vertebral body ("loose" plan), 2) 3D planning, utilizing both 1.0 and 0.5 cm margins for the planning target volume (PTV), and 3) IMRT planning, utilizing the same margins as the 3D plans. A dosimetric comparison was performed for the target volume, spinal cord, arytenoids, and carotid arteries. The prescription dose was 6300 cGy (225 cGy fractions), and the 3D and IMRT plans were normalized to this dose.ResultsFor PTV margins of 1.0 cm and 0.5 cm, the D95 of the 2D tight/loose plans were 3781/5437 cGy and 5372/5869 cGy, respectively (IMRT/3D plans both 6300 cGy). With a PTV margin of 1.0 cm, the mean carotid artery dose was 2483/5671/5777/4049 cGy in the 2D tight, 2D loose, 3D, and IMRT plans, respectively. When the PTV was reduced to 0.5 cm, the the mean carotid artery dose was 2483/5671/6466/2577 cGy to the above four plans, respectively. The arytenoid doses were similar between the four plans, and spinal cord doses were well below tolerance.ConclusionsIMRT provides a more ideal dose distribution compared to 2D treatment and 3D planning in regards to mean carotid dose. We therefore recommend IMRT in select cases when the treating physician is confident with the GTV.