Electronic Tissue Compensation Research Articles

Contralateral breast dose with electronic compensators and conventional tangential fields – A clinical dosimetric study

Dose to the contralateral breast (CLB) from radiotherapy treatment has the potential to induce secondary breast cancer. Electronic tissue compensation (eComp) for breast cancer patients is one of the alternative methods to conventional 3D-conformal radiotherapy that eliminates the use of wedges. Several studies have investigated dose to the CLB using tangential fields involving wedges, intensity-modulated radiation therapy and volumetric modulated arc radiation therapy and various other techniques via treatment planning system calculations, Monte Carlo methods and phantoms. However, there are limited data published in assessing the actual dose received by the CLB from treatment with eComp-based tangential fields.In this study, the CLB dose for patients undergoing tangential field radiotherapy with eComp and enhanced dynamic wedged (standard) tangential fields was measured and compared to assess the CLB dose between the two methods. Measurements were conducted on a randomised trial of 40 patients, 20 of them had undergone standard planning, and the remaining 20 were treated with eComp. The mean surface dose measured with TLDs at 3cm from the medial tangential border for eComp and standard techniques was 10.04±1.37% and 10.14±2.05%, respectively for a prescription dose of 2.65Gy/fraction. The estimated dose at 1cm depth in tissue, measured with the use of perspex domes placed over the TLD at the same location, was 5.12±0.87% and 6.29±2.01% for eComp and standard, respectively.The CLB dose is dependent on the proximity of the medial tangential field edge to the contralateral breast and is patient-specific. The results of this study show that at 1cm depth, eComp technique delivers significantly less dose (p<0.05) to the CLB as compared to standard tangential fields. Furthermore, the surface dose measured for both eComp and standard are comparable indicating that the eComp-based tangential field technique does not contribute any excess dose to CLB when compared to standard tangential fields. The excess relative risk (ERR) for radiation-induced cancers for eComp was found to be 0.08, compared to 0.11 for standard tangential fields.

Semi-supervised planning method for breast electronic tissue compensation treatments based on breast radius and separation.

BackgroundThe aim of the study was to develop and assess a technique for the optimization of breast electronic tissue compensation (ECOMP) treatment plans based on the breast radius and separation.Materials and methodsTen ECOMP plans for 10 breast cancer patients delivered at our institute were collected for this work. Pre-treatment CT-simulation images were anonymized and input to a framework for estimation of the breast radius and separation for each axial slice. Optimal treatment fluence was estimated based on the breast radius and separation, and a total beam fluence map for both medial and lateral fields was generated. These maps were then imported into the Eclipse Treatment Planning System and used to calculate a dose distribution. The distribution was compared to the original treatment hand-optimized by a medical dosimetrist. An additional comparison was performed by generating plans assuming a single tissue penetration depth determined by averaging the breast radius and separation over the entire treatment volume. Comparisons between treatment plans used the dose homogeneity index (HI; lower number is better).ResultsHI was non-inferior between our algorithm (HI = 12.6) and the dosimetrist plans (HI = 9.9) (p-value > 0.05), and was superior than plans obtained using a single penetration depth (HI = 17.0) (p-value < 0.05) averaged over the 10 collected plans. Our semi-supervised algorithm takes approximately 20 seconds for treatment plan generation and runs with minimal user input, which compares favorably with the dosimetrist plans that can take up to 30 minutes of attention for full optimization.ConclusionsThis work indicates the potential clinical utility of a technique for the optimization of ECOMP breast treatments.

Dosimetric comparative study of 3DCRT, IMRT, VMAT, Ecomp, and Hybrid techniques for breast radiation therapy

PurposeTo assess and compare the dosimetric parameters obtained between three-dimensional conformal radiotherapy (3DCRT), three-dimensional field-in-field (3DFIF), 5-field intensity-modulated radiotherapy (IMRT MF5), tangential IMRT (tIMRT), tangential volumetric modulated arc therapy (tVMAT), electronic tissue compensation (Ecomp), and Hybrid treatment plans.Material and MethodsThirty planning computed tomography datasets obtained from patients previously treated with whole breast radiation therapy (WBRT) were utilized in this study. Treatment plans were created for 3DCRT, 3DFIF, IMRT MF5, tIMRT, tVMAT, Ecomp, and Hybrid techniques using Eclipse Treatment Planning System (version 13.6) with a prescribed dose of 42.5 Gy in 16 fractions.ResultsTechniques with tangential beams produced statistically significantly better organs-at-risk (OARs) dosimetry (p < 0.001). Planning target volume Homogeneity Index (HI) was found to be significantly different among all techniques (p < 0.001), with Ecomp resulting in better HI (1.061 ± 0.029). Ecomp was also observed to require relatively shorter planning time (p < 0.001).ConclusionsTechniques using tangential fields arrangements produced improved OARs dosimetry. Of all the treatment planning techniques employed in this study, Ecomp was found to be relatively easy to plan and produce acceptable dosimetry for WBRT in a short time.

Using flattening filter free beams in electronic tissue compensation whole breast irradiation with deep inspiration breath hold.

PurposeIn order to reduce heart dose, DIBH has become a common practice in left‐sided whole breast irradiation. This technique involves a significant strain on patients due to the breath‐hold requirements. We hereby investigate the dosimetric and delivery feasibility of using flattening filter free (FFF) energies with electronic tissue compensation (ECOMP) planning technique to reduce the required breath‐hold lengths and increase patient compatibility.MethodsFifteen left‐sided, postlumpectomy patients previously receiving DIBH whole‐breast radiotherapy (266cGy x 16fx) were retrospectively planned using ECOMP for both 6X and 6X‐FFF. A dosimetric comparison was made between the two plans for each patient using various dosimetric constraints. Delivery feasibility was analyzed by recalculating the 6X ECOMP plan with 6X‐FFF without replanning (6X‐FFF QA) and delivering both plans for a one‐to‐one comparison using Gamma analysis. Beam‐on times for the 6X and 6X‐FFF plans were measured. For all tests, Wilcoxon signed‐rank test was used with P < 0.05 as significant.ResultsNo statistical difference was observed between 6X and 6X‐FFF plans for most dosimetric endpoints except contralateral breast Dmax (P = 0.0008) and skin Dmax (p = 0.03) and Dmin (P = 0.01) for which 6X‐FFF showed favorable results when compared with 6X. 6X‐FFF significantly reduced beam‐on times for all patients by 22%–42% (average 32%). All plan QAs passed departmental gamma criteria (10% low‐dose threshold, 3%/3mm, >95% passing).ConclusionECOMP planning with FFF was found feasible for left‐sided breast patients with DIBH. Plan quality is comparable, if not better, than plans using flattened beams. FFF ECOMP could significantly reduce beam‐on time and required breath‐hold lengths thereby increasing patient compatibility for this treatment while offering satisfactory plan quality and delivery accuracy.

Correlating the depth of compensation to the 3-D shape of the breast to achieve homogeneous dose distribution using the electronic tissue compensation treatment technique

Our study aimed to correlate the overall 3-dimensional (3-D) shape of the breast to the compensation depth to produce a homogeneous dose distribution using the electronic tissue compensation (ECOMP) treatment technique. The study involved creating a number of semioval water phantoms with the diameter of the larger axis representing the breast separation and the shorter axis representing the distance from the chest wall to the apex of the breast. Multiple plans with 2 tangential fields were created for each phantom using different transmission penetration depths (TPDs) to determine the optimum TPD value based on the evaluation of dose uniformity and maximum hot spot. Optimum TPD values from the semioval water phantom plans were plotted on a graph as a function of separation and radius and were used as guidelines to choose the optimum TPD for the breast patient's cases. A total of 10 patients who had been treated with radiation therapy using ECOMP tangential fields were randomly selected. The separation and the radius of the breast were measured for 3 regions (superior, middle, and inferior) to retrospectively determine the optimum TPD from the graph for each region. These TPD values were then used to plan the breast cases. For all the patients studied, the optimized TPD technique produced a lower average homogeneity index (HI) value of 0.658 than the standard ECOMP technique of 0.856. These results showed that optimized TPD technique produced a more homogeneous dose distribution than the standard ECOMP technique. By measuring the breast size based on breast separation and the chest wall-to-apex distance at different locations along the superior-inferior axis of the breast, the optimum TPD can be determined at each location to provide a homogeneous dose distribution. A module can be created within the planning system to automatically assign the optimum TPD for both tangential fields so uniform fluence maps can be achieved throughout the whole breast volume. This method can serve as a guideline in ECOMP during the treatment planning to obtain a homogeneous dose distribution.

SU‐F‐T‐499: Anatomic Features for Selection of Electronic Tissue Compensation Radiotherapy in Early‐Stage Breast Cancer Patients After Breast‐Conserving Surgery

Purpose:To explore the correlations between anatomic features and dose‐volumetric parameters in 3DCRT and eComp whole breast irradiation and identify the feasibility of anatomic parameters to predict the planning method selection.Methods:We compared the effectiveness between conventional three‐dimensional conformal radiotherapy (3DCRT) and electronic tissue compensation (eComp) for whole breast irradiation. 3DCRT and eComp planning techniques were used to generate treatment plans for 60 whole breast patients, respectively. The planning goal was to cover 95% of the planning target volume (PTV) with 95% of the prescription dose while minimizing dose to lung, heart, and skin. Statistical analyses were performed between critical organ doses and patient anatomic features, i.e., central lung distance (CLD), maximal heart distance (MHD), maximal heart length (MHL) and breast separation (BS).Results:Comparing to 3DCRT plans, on the average, eComp treatment planning process was about 7 minutes longer, but resulted in lower lung V20Gy, lower mean skin dose, with similar heart dose. The benefits were more pronounced for larger breast patients. To keep the lung V20Gy lower than 20% and mean skin dose lower than 85% of the prescription dose, eComp was the preferred method for patients with more than 2.3 cm CLD or larger than 22.5 cm BS.Conclusion:The study results may be useful in providing a handy criterion in clinical practice allowing us to easily choose between different planning techniques to satisfy the planning goal with minimal increase in complexity and cost.This study was supported by National Natural Science Foundation of China (NO. 31420103915) and Chongqing Health and Family Planning Commission Project (2015MSXM012).

A Dosimetric Comparison of Radiotherapy Techniques in the Treatment of Carcinoma of Breast

Objectives of present study are a) to compare the planning and delivery aspects of five different techniques, planned by a) forward, inverse planning and electronic tissue compensation methods; and b) to evaluate and verify the accuracy of the planning system using phantom to estimate the skin dose for target and contraletral breast from five techniques. In-vivo skin dosimetry is planned with TL detectors. Five different radiotherapy techniques for treatment of carcinoma breast were studied using archived computed tomography (CT) scans of 25 breast conserving surgery patients (leftsided whole breast), planned for 50 Gy in 25 fractions. Linear accelerator (Clinac 2300 CD) photon beams were used and thermoluminescent detectors (TLD) [LiF:Mg, Ti] estimated dose on humanoid phantom. Dose coverage (95%) (to PTV) and hot spot (105%) covering volumes did not show differences (p > 0.05) in all 5 plans; Electronic compensator plans are better than others. IP-IMRT plan showed the worst Homogeneity Index (HI) (p , contra-lateral breast (CB) and heart OARs (V20 ipsi.lung, CB, V30 Heart,) are the least with IP-IMRT. IP-IMRT and E-COMP plans resulted in significantly lower mean dose to the superficial skin (Dmean, V40skin, 45skin, 50skin) (p the least doses to the skin of PTV and contra-lateral breast and less hot spots; E-COMP showed better homogeneity, fewer MUs, and the least dose in non-target zones.

Comparison of Acute Skin Reaction between Short Course and Conventional Fractionation Radiotherapy in Breast Conserving Therapy with Skin Dose Measurement

We have conducted a clinical trial to evaluate the short course whole breast irradiation to be equally effective and safe with conventional fractionation. In this study, we compared acute skin reactions in both arms with film dosimetry. The patients with stage 0 to II of breast cancer, after lumpectomy or quadrantectomy with sentinel lymph node biopsy or axillary node dissection, positive lymph nodes less than 3, and no concurrent chemotherapy were eligible for this study. Prior to the treatment, all patients were explained about the two treatment schedules and decided by the patient's free selection. The short course irradiation (SCI) consisted of 43.2Gy/16f to the whole breast with additional tumor bed boost of 8.1Gy/3f for positive or less than 5mm surgical margins. The conventional course irradiation (CCI) consisted of 50Gy/25f to the whole breast with additional tumor bed boost of 10Gy/5f for positive or less than 5mm surgical margins or 6Gy/3f in negative surgical margins which has been our standard of care. All breasts were irradiated with 4 MV photon, tangential fields using electronic tissue compensation. The acute adverse effects were observed weekly during treatment and 1 and 2 week after the completion of treatment and scored by CTCAE v3.0. Film dosimetry was performed using radiochromic film (Gafchromic EBT) at 3 settled points, point 1: 5cm away from nipple in upper-outer quadrant, point 2: 5cm away from nipple in inner-lower quadrant, point 3: just above nipple. The average doses of the points were calculated in each arm. BED was calculated using α/β ratio=10.6 in each arm (Zeman, 2007). Between 1st of April 2006 and 31st of December 2008, 767 cases were registered. Among them, 419 cases (54%) were SCI and 348 cases (46%) were CCI. The cases with tumor bed boost of 8.1Gy in SCI were 160 cases (38%), 6Gy and 10Gy were 159 cases (45%) and 189 cases (55%) in CCI, respectively. Grade 2 acute skin reactions were observed in 9 cases (2%) in SCI and 70 cases (20%) in CCI (p < 0.001). The factors affecting acute skin reactions were menopausal status (post was significantly low. p < 0.001). The average skin doses at point 1, 2, and 3 in 9 patients were 1.22Gy, 0.91Gy, 0.80Gy, and 0.87Gy in SCI and 1.09Gy and 1.18Gy in CCI, respectively. The CCI/SCI skin dose ratio at 3 points was 1.34, 1.36, and 1.35, respectively. Whole course BEDs of skin at point 1, 2 and 3 were 21.7Gy 19.1Gy, 21.0Gy in SCI and 24.8Gy, 21.5Gy, 23.6Gy in CCI, respectively. The BED differences between two arms were 3.0, 2.4, and 2.6 at each point. The short course whole breast irradiation is superior for less skin dose and less acute skin reaction.

A Novel Method of Island Blocking in Whole Abdominal Radiotherapy Using a Modified Electronic Tissue Compensation Technique

Traditionally, large fields requiring island blocking used external beam radiation therapy (EBRT) with Cerrobend blocks to limit dose to the critical structures. It is laborious to construct blocks and use them on a daily basis. We present a novel technique for island blocking using a modified electronic tissue compensation (MECOMP) technique. Five patients treated at our institution were selected for this study. The study compared two planning techniques: a novel MECOMP and a conventional EBRT technique. Conventional fields were defined using anterior-posterior and posterior-anterior (PA) fields. The kidneys were contoured and an aperture cut-out block was fitted to the OAR with a 1-cm margin (OAR CTV) and placed in the PA field. A dynamic multileaf collimation (DMLC) plan with ECOMP was developed using identical beam and blocking strategy; this tissue compensation–based fluence map was modified to deliver a “zero” dose to the CTV OAR from the PA field. There were no significant differences in the mean, maximum, and minimum doses to the right or left kidney between the two methods. The mean, maximum, and minimum doses to the peritoneal cavity were also not significantly different. The number of monitor units (MUs) required was increased using the MECOMP (273 vs. 1152, p < 0.01). The MECOMP is effectively able to deliver DMLC-based radiotherapy, even with island blocks present. This novel use of MECOMP for whole abdominal radiotherapy should substantially reduce the labor, daily treatment time, and treatment-related errors through the elimination of cerrobend blocks.

Improvement in dose homogeneity with electronic tissue compensation over IMRT and conventional RT in whole brain radiotherapy

Background and purpose To perform a dosimetric analysis of whole brain radiotherapy using electronic tissue compensation (ECOMP) with dynamic multileaf collimation (dMLC) and its comparisons with inverse-planned intensity modulated radiation therapy (IMRT) with optimization constraints and conventional whole brain radiotherapy (WBRT). Materials and methods Ten patients (6 adult, 4 pediatric) who were treated at our institution were selected for this study. WBRT fields were defined using opposed lateral fields directed at the intracranial contents and MLC leaves were used to block the critical normal structures. A two-field inverse-planned IMRT plan was then developed using sliding window technique and two optimization constraints. Finally, a dMLC plan with electronic tissue compensation (ECOMP) was developed using identical beam and collimator angles and blocking strategy; the fluence map was generated based on tissue compensation and no additional constraints were given for optimization purposes. This tissue compensation based fluence map was applied to deliver a homogenous dose to the intracranial contents. Radiation dose was identically prescribed to the isocenter (30.0 Gy in 10 fractions) for all the cases. A dosimetric comparison was then performed for each method in our patient population. Results ECOMP significantly reduced the mean maximum dose ( D max) to the intracranial contents as compared to both WBRT (103.9% vs. 112.4%, p < 0.0001) and IMRT (106.1%, p = 0.02). ECOMP also reduced the intracranial volume receiving greater than 103% of the prescribed dose (2.6% vs. 54.9%, p < 0.0001) and the intracranial volume receiving greater than 105% of the prescribed dose (0% vs. 26%, p < 0.0001) as compared to WBRT; there was no statistical difference in these two parameters between ECOMP and IMRT. The mean number of monitor units was increased, however, using both ECOMP and IMRT as compared to WBRT (870 and 860 vs. 318, p < 0.0001). Conclusions Dynamic multileaf collimation with electronic tissue compensation (ECOMP) leads to improved dose homogeneity with less ‘hot spots’ as compared to conventional and inverse-planned intensity modulated whole brain radiotherapy. At our institution, ECOMP is being used in all pediatric patients or select adult patients with a long life expectancy requiring cranial radiotherapy.

A Dosimetric Comparison of Electronic Compensation, Conventional Intensity Modulated Radiotherapy, and Tomotherapy in Patients With Early-Stage Carcinoma of the Left Breast

Intensity modulated radiation therapy (IMRT) has been shown to significantly reduce dose to normal tissue while maintaining coverage of the clinical target volume (CTV) in patients with intact breast cancer. We compared delivery of whole breast irradiation utilizing three techniques: electronic tissue compensation (ECOMP), inverse-planned dynamic multileaf collimation IMRT (DMLC), and tomotherapy (TOMO). Ten patients with early stage, left-sided breast cancer were selected for planning. CTV was defined as breast encompassed in a standard tangent field minus the superficial 5 mm from the skin edge. Normal tissue contours included the heart, lungs, and contralateral breast. Plans included delivery of 45 Gy in 25 fractions and were normalized to ensure > or =95% coverage of the CTV. Isodose distributions and dose-volume histograms for CTV and normal tissue were compared between plans. The time it took to plan each patient excluding contouring, as well as number of monitor units (MUs) required to execute each plan were additionally tabulated. The TOMO plans resulted in significantly greater heterogeneity (CTV V(115)) versus ECOMP (p = 0.0029). The ECOMP plans resulted in significantly lower doses to heart, lung, and contralateral breast when compared with TOMO plans. The ECOMP plans were generated in the shortest time (12 min) and resulted in the lowest number of MUs when compared with DMLC (p = 0.002, p < 0.0001) and TOMO (p = 0.0015, p < 0.0001). The ECOMP plans produced superior dose distributions in both the CTV and normal tissue when compared with TOMO or DMLC plans. In addition, ECOMP plans resulted in the lowest number of MUs and labor cost.

SU‐FF‐T‐199: Electronic Tissue Compensation Achieved with Both Dynamic and Static Multileaf Collimator in Eclipse Treatment Planning System for Clinac 6EX and 2100CD Varian Linear Accelerators: Feasibility and Dosimetric Study

Purpose: Dynamic multileaf collimator (DMLC) and static multileaf collimator (SMLC) along with three dimensional treatment planning system (3DTPS) opens the possibility of tissue compensation. A method using electronic tissue compensator (ETC) has been implemented in Eclipse 3DTPS at our centre. The ETC was tested for head and neck conformal RT planning. The purpose of this study was to verify the feasibility of DMLC and SMLC in head and neck field irradiation, simultaneously delivering homogeneous dose at depth. In addition, the emphasis was given on the dosimetric aspects in commissioning ETC in Eclipse. Methods and Materials: A Head and Neck Phantom (The Phantom Laboratory, USA) was used for the dosimetric verification. Planning was carried out for both DMLC and SMLC ETC plans. The point dose calculated at central axis by Eclipse with DMLC and SMLC was noted. This was compared with the measured dose on machine with ion chamber and TLD. The calculated idsodoses and profiles were also compared with the measured one. The line dose profiles from Eclipse were also compared with the profile obtained from Amorphous Silicon (AS500) Electronic portal imaging device (EPID) on Clinac 6EX machine. Results: In uniform dose regions, measured dose values resulted in agreements with the calculated doses within 3%. Distance to agreement between calculated and measured isodoses in dose gradient zone was within 3 mm. Both the comparison of isodoses and the profile were in good agreement and acceptable. The measured and the calculated line dose profiles were flat for both DMLC and SMLC. Conclusion: The dosimetric verification of ETC for both the linacs demonstrated the feasibility and the accuracy of the ETC treatment modality for achieving uniform dose distributions. Therefore ETC can be used as a new tool in head and neck treatment planning optimization for improved dose uniformity.

Electronic tissue compensation achieved with both dynamic and static multileaf collimator in eclipse treatment planning system for Clinac 6 EX and 2100 CD Varian linear accelerators: Feasibility and dosimetric study

Dynamic multileaf collimator (DMLC) and static multileaf collimator (SMLC), along with three-dimensional treatment planning system (3-D TPS), open the possibility of tissue compensation. A method using electronic tissue compensator (ETC) has been implemented in Eclipse 3-D TPS (V 7.3, Varian Medical Systems, Palo Alto, USA) at our center. The ETC was tested for head and neck conformal radiotherapy planning. The purpose of this study was to verify the feasibility of DMLC and SMLC in head and neck field irradiation for delivering homogeneous dose in the midplane at a pre-defined depth. In addition, emphasis was given to the dosimetric aspects in commissioning ETC in Eclipse. A Head and Neck Phantom (The Phantom Laboratory, USA) was used for the dosimetric verification. Planning was carried out for both DMLC and SMLC ETC plans. The dose calculated at central axis by eclipse with DMLC and SMLC was noted. This was compared with the doses measured on machine with ion chamber and thermoluminescence dosimetry (TLD). The calculated isodose curves and profiles were compared with the measured ones. The dose profiles along the two major axes from Eclipse were also compared with the profiles obtained from Amorphous Silicon (AS500) Electronic portal imaging device (EPID) on Clinac 6 EX machine. In uniform dose regions, measured dose values agreed with the calculated doses within 3%. Agreement between calculated and measured isodoses in the dose gradient zone was within 3 mm. The isodose curves and the profiles were found to be in good agreement with the measured curves and profiles. The measured and the calculated dose profiles along the two major axes were flat for both DMLC and SMLC. The dosimetric verification of ETC for both the linacs demonstrated the feasibility and the accuracy of the ETC treatment modality for achieving uniform dose distributions. Therefore, ETC can be used as a tool in head and neck treatment planning optimization for improved dose uniformity.

Mantle fields in the era of dynamic multileaf collimation: Field shaping and electronic tissue compensation

Mantle field radiotherapy for Hodgkin’s disease is complicated by significant dose gradient (up to 10–20%) across the large fields required. Many different strategies of tissue compensation have been investigated, including custom physical compensators to provide better dose distributions. We present a method using dynamic multileaf collimator (dMLC) fluence modulation to simultaneously shape the treatment field and give homogeneous dose at depth throughout the classic mantle field. Five patients were treated for early-stage Hodgkin’s disease with a conventional anterior-posterior–posterior-anterior (AP-PA) mantle field. The patients were planned using the Varian Eclipse treatment planning system, version 6.1.3, and treated on a Varian 2300CD. An AP-PA dynamic MLC beam-shaped and dose-compensated plan was created for each, and compared with the conventional blocked plan. Nine dose points were calculated at midplane in each plan. Chamber measurements were taken to confirm accurate dMLC delivery of the planned doses. The mean dose per fraction, relative to a central axis dose of 1.8 Gy, was increased in the conventional plans compared with the dMLC plans in the right (R) neck, left (L) neck, R supraclavicular, L supraclavicular, and L axillary points. The mediastinum tended to be underdosed relative to central axis, with the mid-mediastinal and lower mediastinal points showing improved coverage with the dMLC plans. Measurements showed excellent agreement between planned doses and delivered doses, with less than 2% in-field variation. Dynamic MLC fluence modulation was used to effectively deliver a mantle field that is both shape- and electronically-dose-compensated with sliding window MLC. Homogeneity was significantly improved throughout the treatment field, and measurements confirmed accurate dose delivery using this technique.