Left-sided Breast Patients Research Articles

Comparison of helical and TomoDirect techniques with simultaneous integrated boost in early breast cancer patients.

The aim of the study was to perform dosimetric comparisons of helical (H) and TomoDirect (TD) plans for whole-breast irradiation (WBI) with simultaneous integrated boost (SIB) in early-stage breast cancer patients undergoing breast conserving surgery. Fifty patients, 25 with left-side and 25 with right-side tumors, were determined for a treatment planning system for a total dose of 50.4Gy in 1.8Gy per fraction to WBI, with a SIB of 2.3Gy per fraction delivered to the tumor bed. The planning target volume (PTV) doses and the conformity (CI) and homogeneity indices (HI) for PTVbreast and PTVboost, as well as organ-at-risk (OAR) doses and treatment times, were compared between the H and TD plans. All plans met the PTV coverage criteria for the H plan, except for mean V107 of PTVbreast for TD plan. The H plan yielded better homogeneity and conformity of dose distribution compared to the TD plan. The ipsilateral mean lung doses were not significantly different between the two plans. The TD plans is advantageous for mean doses to the heart, contralateral breast and lung, spinal cord, and esophagus than the H plans. In both the H and TD plans, the right-sided breast patients had lower heart dose parameters than the left-sided breast patients. The TD plan is superior to the H plan in sparing the contralateral breast and lung by decreasing low-dose volumes. While the OAR dose advantages of TD are appealing, shorter treatment times or improved dose homogeneity and conformity for target volume may be advantageous for H plan.

Automated review of patient position in DIBH breast hybrid IMRT with EPID images.

Deep Inspiration Breath Hold (DIBH) is a respiratory-gating technique adopted in radiation therapy to lower cardiac irradiation. When performing DIBH treatments, it is important to have a monitoring system to ensure the patient's breath hold level is stable and reproducible at each fraction. In this retrospective study, we developed a system capable of monitoring DIBH breast treatments by utilizing cine EPID images taken during treatment. Setup error and intrafraction motion were measured for all fractions of 20 left-sided breast patients. All patients were treated with a hybrid static-IMRT technique, with EPID images from the static fields analyzed. Ten patients had open static fields and the other ten patients had static fields partially blocked with the multileaf collimator (MLC). Three image-processing algorithms were evaluated on their ability to accurately measure the chest wall position (CWP) in EPID images. CWP measurements were recorded along a 61-pixel region of interest centered along the midline of the image. The median and standard deviation of the CWP were recorded for each image. The algorithm showing the highest agreement with manual measurements was then used to calculate intrafraction motion and setup error. To measure intrafraction motion, the median CWP of the first EPID frame was compared with that of the subsequent EPID images of the treatment. The maximum difference was recorded as the intrafraction motion. The setup error was calculated as the difference in median CWP between the MV DRR and the first EPID image of the lateral tangential field. The results showed that the most accurate image-processing algorithm can identify the chest wall within 1.2mm on both EPID and MV DRR images, and measures intrafraction motion and setup errors within 1.4mm.

Dosimetric advantages of volumetric modulated arc therapy (VMAT) with deep inspiration breath hold (DIBH) technique in Halcyon Linac for left breast cancer treatment.

To evaluate the dosimetric advantages of incorporating the deep inspiration breath hold (DIBH) technique into left breast cancer volumetric modulated arc therapy (VMAT) treatment under Halcyon Linac and to investigate the correlation between mean heart dose (MHD) and distance from the heart to target volumes in left breast cancer VMAT treatment. Fifteen Post-lumpectomy, left-sided breast patients treated between January 2017 and October 2020 were selected. Two plans were generated for each patient using Eclipse treatment planning system (TPS) with the prescription of 50.4 Gy to planning target volume (PTV) breast and 58.8 Gy to PTV boost in 28 fractions. For each patient, DIBH and free breathing (FB) VMAT treatment plans under Halcyon Linac were generated. Dosimetric parameters, monitor unit and beam-on time of both DIBH and FB groups were compared. Three-dimensional distances from heart surface to each target volume were measured on computed tomography images using the TPS contouring tool and their correlation with MHD was evaluated by Pearson's correlation coefficient (r). Comparable target coverage was shown in both groups. Mean dose to heart, left anterior descending artery, and left ventricle in Halcyon-DIBH-VMAT group were significantly reduced by 0.49 Gy, 1.19 Gy, and 0.57 Gy, respectively, compared to Halcyon-FB-VMAT (p < 0.001). A significant lung dose reduction was also achieved in Halcyon-DIBH-VMAT group. There was also a strong negative correlation between MHD and distance from heart surface to PTV boost in both FB and DIBH group (r = -0.741, p < 0.001), but not observed for distance from heart surface to PTV breast. Incorporating DIBH into left breast cancer VMAT treatment under Halcyon Linac demonstrated significant cardiac and lung dose reduction. It was also demonstrated that MHD had a strong negative correlation with distance from heart surface to PTV boost but relatively independent of distance from heart surface to PTV breast. Recognizing the distance from the heart surface to PTV boost as the main factor in affecting MHD could potentially facilitate clinical treatment planning workflow and decision.

Comparison of volumetric modulated arc therapy and intensity-modulated radiotherapy for left-sided whole-breast irradiation using automated planning

BackgroundPublished treatment technique comparisons for postoperative left-sided whole breast irradiation (WBI) with deep-inspiration breath-hold (DIBH) are scarce, small, and inconclusive. In this study, fully automated multi-criterial plan optimization, generating a single high-quality, Pareto-optimal plan per patient and treatment technique, was used to compare for a large patient cohort 1) intensity modulated radiotherapy (IMRT) with two tangential fields and 2) volumetric modulated arc therapy (VMAT) with two small tangential subarcs.Materials and methodsForty-eight randomly selected patients recently treated with DIBH and 16 × 2.66 Gy were included. The optimizer was configured for the clinical planning protocol. Comparisons between IMRT and VMAT included dosimetric plan parameters, estimated excess relative risks (ERR) for toxicities, delivery times, MUs, and deliverability accuracy at a linac.ResultsThe automatically generated IMRT and VMAT plans applied in this study were similar or higher in quality than the manually generated clinical plans. For equal PTVin V95% (98.4 ± 0.9%), VMAT had significant advantages compared to IMRT regarding breast dose homogeneity and doses in heart and ipsilateral lung, at the cost of some minor deteriorations for contralateral breast (few cases with larger deteriorations) and lung. Conformality improved from 1.38 to 1.18 (p < 0.001). With VMAT, ERR for major coronary events and ipsilateral lung tumors were reduced by 3% (range: −1–12%) and 16% (range: −3–38%), respectively. MUs and delivery times were higher for VMAT. There were no statistical differences in γ passing rates.ConclusionFor WBI in conservative therapy of left-sided breast patients treated with DIBH, VMAT with two tangential subarcs was generally dosimetrically superior to IMRT with two tangential static fields. Results need confirmation by robustness analyses.

Impact of Positioning Errors on the Dosimetry of Breath-Hold-Based Volumetric Arc Modulated and Tangential Field-in-Field Left-Sided Breast Treatments.

Heart diseases and cardiovascular events are well-known side effects in left-sided breast irradiation. Deep inspiration breath hold (BH) combined with fast delivery techniques such as volumetric modulated arc therapy (VMAT) or tangential field-in-field (TFiF) can serve as a valuable solution to reduce the dose to the heart. This study aims to compare the impact of positioning errors in VMAT and TFiF plans for BH left-sided breast treatments. Fifteen left-sided breast patients treated in BH with TFiF technique were included in this retrospective study. For each patient, a second plan with VMAT technique was optimized. Eighteen setup variations were introduced in each of these VMAT and TFiF reference plans, shifting the isocenter along six different directions by 3, 5, and 10 mm. A total of 540 perturbed plans, 270 for each technique, were recalculated and analyzed. The dose distributions on the target and organs at risk obtained in the different perturbed scenarios were compared with the reference scenarios, using as dosimetric endpoints the dose-volume histograms (DVH). The results were compared using the Wilcoxon test. Comparable plan quality was obtained for the reference VMAT and TFiF plans, except for low doses to organs at risk for which higher values (p < 0.05) were obtained for VMAT plans. For TFiF plans, perturbations of the isocenter position of 3, 5, or 10 mm produced mean deviations of the target DVH dosimetric parameters up to −0.5, −1.0, and −5.2%, respectively; VMAT plans were more sensitive to positioning errors resulting in mean deviations up to −0.5, −4.9, and −13.9%, respectively, for the same magnitude of the above mentioned perturbations. For organs at risk, only perturbations along the left, posterior, and inferior directions resulted in dose increase with a maximum deviation of +2% in the DVH dosimetric parameters. A notable exception were low doses to the left lung and heart for 10 mm isocenter shifts for which the mean differences ranged between +2.7 and +4.1%. Objective information on how external stresses affect the dosimetry of the treatment is the first step towards personalized radiotherapy.

Automated planning of whole breast irradiation using hybrid IMRT improves efficiency and quality.

PurposeTo develop an automated workflow for whole breast irradiation treatment planning using hybrid intensity modulated radiation therapy (IMRT) approach and to demonstrate that this workflow can improve planning quality and efficiency when compared to manual planning.MethodsThe auto planning framework was built based on scripting with MIM and Pinnacle systems. MIM workflows were developed to automatically segment normal structures and targets, identify landmarks for beam placement, select beam energies, and set beam configurations. Pinnacle scripts were generated from the MIM workflow to create hybrid IMRT plans automatically. Each hybrid IMRT plan included two prescriptions: a three‐dimensional (3D) prescription consisted of two open tangent beams, and an IMRT prescription consisted of two step‐and‐shoot IMRT beams. The 3D prescription delivered a full prescription dose to the maximum dose point, and the IMRT prescription was optimized to deliver a uniform dose to the entire breast while sparing dose to the normal structures. For 30 patients, the auto plans were compared with clinically accepted manual plans using the paired sample t‐test.ResultsThe auto planning process took approximately 8 min to complete. The mean dice coefficients between auto‐segmentation and manual contours were 0.98, 0.94 and 0.88 for the lungs, heart, and PTVeval_Breast, respectively. The MUs of the auto plans was on average 13% higher than that of the manual plans. Auto planning improved plan quality significantly: percentage volume receiving 95% of the prescription dose (V95%) of the PTVeval_Breast increased from 91.5% to 93.2% (P = 0.001), V105% of the PTVeval_Breast decreased from 7.2% to 1.2% (P = 0.013), V20Gy of the ipsilateral lung decreased from 13.1% to 10.4% (P = 0.001) and mean heart dose for left‐sided breast patients decreased from 1.2 Gy to 0.9 Gy (P < 0.001).ConclusionAn automated treatment planning process can make the planning process efficient with improved plan quality.

Setup uncertainties and the optimal imaging schedule in the prone position whole breast radiotherapy

BackgroundTo investigate the setup uncertainties and to establish an optimal imaging schedule for the prone-positioned whole breast radiotherapy.MethodsTwenty prone-positioned breast patients treated with tangential fields from 2015 to 2017 were retrospectively enrolled in this study. The prescription dose for the whole breast treatment was 266 cGy × 16 for all of the patients and the treatments were delivered with the SSD setup technique. At every fraction of treatment, patient was firstly set up based on the body localization tattoos. MV portal imaging was then taken to confirm the setup; if discrepancy (> 3 mm) was found between the portal images and corresponding plan images, the patient positioning was adjusted accordingly with couch movement. Based on the information acquired from the daily tattoo and portal imaging setup, three sets of data, named as weekly imaging guidance (WIG), no daily imaging guidance (NIG), and initial 3 days then weekly imaging guidance (3 + WIG) were sampled, constructed, and analyzed in reference to the benchmark of the daily imaging guidance (DIG). We compared the setup uncertainties, target coverage (D95, Dmax), V5 of the ipsilateral lung, the mean dose of heart, the mean and max dose of the left-anterior-descending coronary artery (LAD) among the 4 imaging guidance (IG) schedules.ResultsRelative to the daily imaging guidance (IG) benchmark, the NIG schedule led to the largest residual setup uncertainties; the uncertainties were similar for the WIG and 3 + WIG schedules. Little variations were observed for D95 of the target among NIG, DIG and WIG. The target Dmax also exhibited little changes among all the IG schedules. While V5 of the ipsilateral lung changed very little among all 4 schedules, the percent change of the mean heart dose was more pronounced; but its absolute values were still within the tolerance. However, for the left-sided breast patients, the LAD dose could be significantly impacted by the imaging schedules and could potentially exceed its tolerance criteria in some patients if NIG, WIG and 3 + WIG schedules were used.ConclusionsFor left-side whole breast treatment in the prone position using the SSD treatment technique, the daily imaging guidance can ensure dosimetric coverage of the target as well as preventing critical organs, especially LAD, from receiving unacceptable levels of dose. For right-sided whole breast treatment in the prone position, the weekly imaging setup guidance appears to be the optimal choice.

P260] Evaluation of cardiac dose after breast irradiation

Purpose The importance of minimizing heart dose during breast irradiation has attracted increased interest in recent years stating that major coronary events are avoided if threshold of 3 Gy is kept for the mean heart dose and are increased linearly with the mean dose to heart by 7.4% per Gy and 4% increase in risk of heart disease. Current constraints for long term cardiac morbidity state that the volume of heart receiving more than 40 Gy needs to be kept lower than 5% ( V 40 5 % ) and the volume receiving more than 20 Gy be kept under 10% ( V 20 10 % ) . Treatment planning techniques used to reduce dose to heart during irradiation are discussed. Methods A sample of 100 patients from our centre (50% right breast and 50% left breast), were treated with 6MV 3D-conformal radiotherapy planning with two tangential fields. Angles were chosen to avoid OAR (lungs and heart) from receiving unnecessary dose and not compromising target coverage or increasing contra-lateral breast dose. After evaluating the OAR doses, a simple planning technique was used by blocking heart with the use of MLCs (MbT) on the medial tangential field. It was applied for patients with left sided breast cancer who had mean heart dose ranging from 4.2–8 Gy. Results For left sided breast patients the mean heart dose resulted in an average value of 3.54 Gy. 60% of the left sided breast patients in our sample had a mean heart dose greater than 3 Gy. 70% of the left breast patients were large sized. 32% of the left sided breast sample patients violated the V 40 constraint and 10% of them violated the V 20 . After applying the MbT, dose to the heart was reduced with a max reduce on MHD of 3 Gy and the criteria of V 20 and V 40 were achieved. Conclusion The necessity of minimising irradiated heart amount especially for young left sided-large breast patients and planning techniques to achieve this, were discussed in detail above. Although the ideal technique is the Active Breathing Coordinator, providing non-invasive, internal immobilization of anatomies affected by respiratory motion, considering the economic situation of our country, the alternative Mbt is suggested instead.

Normal tissue sparing potential of scanned proton beams with and without respiratory gating for the treatment of internal mammary nodes in breast cancer radiotherapy

Proton therapy has shown potential for reducing doses to normal tissues in breast cancer radiotherapy. However data on the impact of protons when including internal mammary nodes (IMN) in the target for breast radiotherapy is comparatively scarce. This study aimed to evaluate normal tissue doses when including the IMN in regional RT with scanned proton beams, with and without respiratory gating. The study cohort was composed of ten left-sided breast patients CT-scanned during enhanced inspiration gating (EIG) and free-breathing (FB). Proton plans were designed for the target including or excluding the IMN. Targets and organs-at-risk were delineated according to RTOG guidelines. Comparison was performed between dosimetric parameters characterizing target coverage and OAR radiation burden. Statistical significance of differences was tested using a paired, two-tailed Student’s t-test. Inclusion of the IMN in the target volume led to a small increase of the cardiopulmonary burden. The largest differences were seen for the ipsilateral lung where the mean dose increased from 6.1 to 6.6 Gy (RBE) (P < 0.0001) in FB plans and from 6.9 to 7.4 Gy (RBE) (P = 0.003) in EIG plans. Target coverage parameters were very little affected by the inclusion of IMN into the treatment target. Radiotherapy with scanned proton beams has the potential of maintaining low cardiovascular burden when including the IMN into the target, irrespective of whether respiratory gating is used or not.

Comparison of cardiac and lung doses for breast cancer patients with free breathing and deep inspiration breath hold technique in 3 dimensional conformal radiotherapy - a dosimetric study

Abstract Purpose: To investigate the cardio-pulmonary doses between Deep Inspiration Breath Hold (DIBH) and Free Breathing (FB) technique in left sided breast irradiation. Materials &amp; Methods: DIBH CT and FB CT were acquired for 10 left sided breast patients who underwent whole breast irradiation with or without nodal irradiation. Three fields single isocenter technique were used for patients with node positive patients along with two tangential conformal fields whereas only two tangential fields were used in node negative patients. All the critical structures like lungs, heart, esophagus, thyroid, etc., were delineated in both DIBH and FB scan. Both DIBH and FB scans were fused with the Dicom origin as they were acquired with the same Dicom coordinates. Plans were created in the DIBH scan for a dose range between 50 Gy in 25 fractions. Critical structures doses were recorded from the Dose Volume Histogram for both the DIBH and FB data set for evaluation. Results: The average mean heart dose in DIBH vs FB was 13.18 Gy vs 6.97 Gy, (p = 0.0063) significantly with DIBH as compared to FB technique. The relative reduction in average mean heart dose was 47.12%. The relative V5 reduced by 14.70% (i.e. 34.42% vs 19.72%, p = 0.0080), V10 reduced by 13.83% (i.e. 27.79 % vs 13.96%, p = 0.0073). V20 reduced by 13.19% (i.e. 24.54 % vs 11.35%, p = 0.0069), V30 reduced by 12.38% (i.e. 22.27 % vs 9.89 %, p = 0.0073) significantly with DIBH as compared to FB. The average mean left lung dose reduced marginally by 1.43 Gy (13.73 Gy vs 12.30 Gy, p = 0.4599) but insignificantly with DIBH as compared to FB. Other left lung parameters (V5, V10, V20 and V30) shows marginal decreases in DIBH plans compare to FB plans. Conclusion: DIBH shows a substantial reduction of cardiac doses but slight and insignificant reduction of pulmonary doses as compared with FB technique. Using the simple DIBH technique, we can effectively reduce the cardiac morbidity and at the same time radiation induced lung pneumonitis is unlikely to increase.

EP-1630: The impact of DIBH on dose to the junction in loco-regionally treated left-sided breast patients

EP-1630: The impact of DIBH on dose to the junction in loco-regionally treated left-sided breast patients

A novel method for radiotherapy patient identification using surface imaging.

Performing a procedure on the wrong patient or site is one of the greatest errors that can occur in medicine. The addition of automation has been shown to reduce errors in many processes. In this work we explore the use of an automated patient identification process using optical surface imaging for radiotherapy treatments. Surface imaging uses visible light to align the patient to a reference surface in the treatment room. It is possible to evaluate the similarity between a daily set‐up surface image and the reference image using distance to agreement between the points on the two surfaces. The higher the percentage overlapping points within a defined distance, the more similar the surfaces. This similarity metric was used to intercompare 16 left‐sided breast patients. The reference surface for each patient was compared to 10 daily treatment surfaces for the same patient, and 10 surfaces from each of the other 15 patients (for a total of 160 comparisons per patient), looking at the percent of points overlapping. For each patient, the minimum same‐patient similarity score was higher than the maximum different‐patient score. For the group as a whole a threshold was able to classify correct and incorrect patients with high levels of accuracy. A 10‐fold cross‐validation using linear discriminant analysis gave cross‐validation loss of 0.0074. An automated process using surface imaging is a feasible option to provide nonharmful daily patient identification verification using currently available technology.PACS number(s): 87.53.Jw, 87.55.N‐, 87.55.Qr, 87.57.N‐, 87.63.L‐

SU‐E‐T‐317: The Development of a DIBH Technique for Left Sided Breast Patients Undergoing Radiation Therapy Utilizing Varians RPM System in a Community Hospital

Purpose:To develop and implement a Deep Inhalation Breath Hold program (DIBH) for treatment of patients with Left‐sided breast cancer in a community hospital.Methods:All patients with left sided breast cancer underwent a screening free breathing CT. Evaluation of the conventional tangent treatment fields and the heart was conducted. If the heart would not be excluded using tangents, the patient then received DIBH breathe coaching. The patients returned for a 4D CT simulation. The patients breathing cycle was monitored using the Varian Real‐Time position ManagementTM (RPM) system to assess duration of DIBH, amplitude, phase and recovery time to normal breathing. Then a DIBH CT was obtained at the desired amplitude. Duplicate plans were developed for both free breathing and DIBH on the Eclipse planning system and comparison DVH's were created. The plan that provided the prescribed treatment coverage and the least doses to the OAR (heart, Lt. Lung) was determined. Those patients selected to receive treatment with DIBH were set up for treatment, and breathing was monitored using the RPM system. Practice trials were used to confirm that the amplitude, phase and recovery were consistent with findings from simulation.Results:10 patients have been treated using the DIBH procedure in our clinic. The DIBH patients had an average increase of 80% lung volume on DIBH, decreased lung volume receiving 50% of the dose, and decreases in the V20 dose. Significant reduction in the maximum and mean dose to the heart, as well as the dose to 1CC of the volume for the DIBH plans.Conclusion:Using the RPM system already available in the clinic, staff training, and patient coaching a simple DIBH program was setup. The use of DIBH has shown promise in reducing doses to the critical organs while maintaining PTV coverage for left sided breast treatments.

Comparison of different breast planning techniques and algorithms for radiation therapy treatment

This work aims at investigating the impact of treating breast cancer using different radiation therapy (RT) techniques – forwardly-planned intensity-modulated, f-IMRT, inversely-planned IMRT and dynamic conformal arc (DCART) RT – and their effects on the whole-breast irradiation and in the undesirable irradiation of the surrounding healthy tissues. Two algorithms of iPlan BrainLAB treatment planning system were compared: Pencil Beam Convolution (PBC) and commercial Monte Carlo (iMC).Seven left-sided breast patients submitted to breast-conserving surgery were enrolled in the study. For each patient, four RT techniques – f-IMRT, IMRT using 2-fields and 5-fields (IMRT2 and IMRT5, respectively) and DCART – were applied. The dose distributions in the planned target volume (PTV) and the dose to the organs at risk (OAR) were compared analyzing dose–volume histograms; further statistical analysis was performed using IBM SPSS v20 software.For PBC, all techniques provided adequate coverage of the PTV. However, statistically significant dose differences were observed between the techniques, in the PTV, OAR and also in the pattern of dose distribution spreading into normal tissues. IMRT5 and DCART spread low doses into greater volumes of normal tissue, right breast, right lung and heart than tangential techniques. However, IMRT5 plans improved distributions for the PTV, exhibiting better conformity and homogeneity in target and reduced high dose percentages in ipsilateral OAR. DCART did not present advantages over any of the techniques investigated. Differences were also found comparing the calculation algorithms: PBC estimated higher doses for the PTV, ipsilateral lung and heart than the iMC algorithm predicted.

MO‐F‐WAB‐01: A Comparison of 20 Free Breathing Versus AlignRT Based DIBH Breast Treatments

Purpose: Deep inspiration breath hold (DIBH) for treatment of left breast cancer is a technique that is rapidly gaining acceptance due to the possibility of reducing heart dose, particularly dose to the left anterior descending coronary artery. We report on the treatment of twenty patients using AlignRT (VisionRT, London, UK) to monitor breath hold. Methods: Patients were simulated with a breath hold and free breathing CT scan. A treatment plan was created on each scan in the XiO treatment planning system (Elekta AB, Stockholm, Sweden). Plans consisted of two parent tangent fields and 1–2 reduced fields per side. The maximum point dose and volume receiving 30 Gy (V30) to the heart from each plan is compared. Patients were set‐up using an AlignRT reference surface generated from the breath hold scan with a 3 mm / 3 degree tolerance. Patient position was evaluated by comparing boney landmarks, breast tissue, and heart position on port images prior to the first treatment, then once per week. We examine the number of port images retaken as compared to free breathing set‐ups. Results: For DIBH plans the maximum heart dose was reduced by an average of 39% and the V30 was reduced by an average of 78%. For 16 patients that had completed treatment at this time the number of retaken port images was 9.6%, which is in line with 8.5% of retaken port images previously reported for our free breathing patients. Conclusion: Patients were generally able to complete each of the 4–6 fields in one breath hold per field. The number of port images was comparable to free breathing treatments. Treatment of left sided breast patients using DIBH is an effective way to reduce heart dose without impactful change in treatment time.

SU‐FF‐T‐118: Can the Use of Respiratory Gating Reduce Radiation Dose to Heart in Whole Left Breast Irradiation Treatment? — A Preliminary Study

Purpose: To investigate the potential benefit of using respiratory gating technique to reduce radiation doses to patient's heart in whole left breast irradiation treatment. Method and Materials: Conventional helical CT scan and retrospective 4D CT scans were acquired for 5 left sided breast patients. The 4DCT scans were sorted into 10 phases per respiratory cycle. Treatment plans, which consisted of two wedged tangential fields, were designed based on the helical CT scan. The PTV coverage, heart and lung doses in this plan were used as references for comparison. 10 separate optimal plans were generated from the 10 different phases obtained from the 4DCT images. All beam parameters, except for beam energy and wedges, were adjusted so that the PTV coverage in these plans was similar to or better than that in the corresponding reference plan. The heart and lung doses were then computed from these plans and compared to the corresponding doses in the reference plan. Results: The present results show that one patient would benefit from gated treatment at any given phase in terms of heart dose reduction. For four other patients respiratory gating would reduce dose to the heart. Gating at a given phase would reduce mean dose to the heart by 24%, 17%, 8% for 3 patients; for another patient a 17% reduction in maximum dose to the heart was found while the impact to the mean dose was insignificant. Conclusion: The use of respiratory gating in the irradiation of whole left breast treatment has the potential to reduce dose to the heart.

TU‐E‐T‐6C‐01: Intensity Modulated Radiation Therapy for the Treatment of Breast Cancer

Intensity modulated radiation therapy for the treatment of Stage 0, I and II breast cancer has been in clinical use at William Beaumont Hospital since March 1999. The goals of IMRT for breast cancer delivered through static, multileaf collimator segments include optimizing dose homogeneity, avoiding unnecessary normal tissue irradiation and standardizing target volume coverage without significantly increasing the time required to plan and treat patients. The IMRT process can be divided into four different phases, simulation, treatment planning, treatment delivery and quality assurance. During the initial simulation procedure an immobilization device is constructed, level marks are tattooed and the treatment borders are defined. A CT is done in the treatment position in order to define the treatment area as well as delineate normal tissues. In addition to the CT scan the use of MR is becoming a useful tool to define nodal regions of interest. The treatment plan is generated to deliver a homogeneous dose throughout the breast volume and minimize dose to the lungs and in the case of left sided breast patients the heart. The beam arrangement of two tangential fields is adjusted for depth, gantry angle and collimator angle in order to provide full coverage to the breast and lumpectomy cavity with sufficient margin and avoid unnecessary irradiation of normal tissue. The IMRT segments are created based on 5% increments of isodose surfaces; these forward planned segments are then optimized in order to deliver a homogeneous dose throughout the breast volume. The plan is evaluated with respect to percent of breast volume receiving doses in excess of 105% and 110% of the prescribed dose. The treatment process includes patient positioning and setup, electronic portal imaging and treatment delivery. This is accomplished in a conventional treatment time slot of 12 minutes. As part of the overall patient quality assurance patients are imaged everyday for every port during their treatment. On weekly review the physicians have ten images, five medial and five lateral, with which to make clinical treatment decisions as to patient setup and treatment port placement. In addition to patient quality assurance plan quality assurance is assessed by completion of an independent calculation check as well as analysis of treatment delivered to the MapCheck device as compared to the planned treatment. Both the fluence and absolute dose measurements can be analyzed with this system. Using intensity modulated radiation therapy to deliver whole breast irradiation has proven to be an efficient method to deliver uniform dose throughout the entire breast volume which can be seen to reduce the acute and chronic toxicity's associated with radiation therapy for the treatment of breast cancer. Research supported by Philips Medical Systems and Elekta Corporation.Educational Objectives:1. To understand the goals and use of IMRT in the treatment of breast cancer.2. To understand the IMRT process for simulation, planning, treatment and quality assurance in the treatment of breast cancer.