Skin Flash Research Articles

Intensity Modulated Therapy for Patients With Breast Cancer. Practical Guidelines and Tips for an Effective Treatment Planning Strategy

PurposePractical guidelines and tips for effective and robust radiotherapy treatment planning for breast cancer patients are addressed for intensity-modulated fixed field or volumetric modulated arc therapy techniques. The concepts described here are general and valid on all the treatment planning systems. However, some details have been shown here applied to the Varian platforms used at the authors’ institutions. MethodsThe specific aspects of using C-arm or O-ring mounted linear accelerators are covered in the document, as well as tips for dealing with certain resource constraints, target cropping and skin flash aiming to reduce risks of skin toxicity and to manage (residual after breath control) respiration motion or oedema. ResultsA decision tree is presented, and practical solutions are discussed for cases where a target volume is contoured or not; where volumetric modulated arc therapy or fixed beams intensity modulation should be applied and details about the technical implementation (tangential IMRT, butterfly IMRT or VMAT, large partial VMAT arcs). Target cropping and skin flash implications are discussed in detail, and links to plan robustness are outlined. ConclusionsPractical guidelines for breast planning are presented and summarized with a decision tree and technical summaries.

Evaluation of robustness of optimization methods in breast intensity-modulated radiation therapy using TomoTherapy.

Intensity-modulated radiation therapy (IMRT) has become a popular choice for breast cancer treatment. We aimed to evaluate and compare the robustness of each optimization method used for breast IMRT using TomoTherapy. A retrospective analysis was performed on 10 patients with left breast cancer. For each optimization method (clipping, virtual bolus, and skin flash), a corresponding 50Gy/25 fr plan was created in the helical and direct TomoTherapy modes. The dose-volume histogram parameters were compared after shifting the patients anteriorly and posteriorly. In the helical mode, when the patient was not shifted, the median D1cc (minimum dose delivered to 1cc of the organ volume) of the breast skin for the clipping and virtual bolus plans was 52.2 (interquartile range: 51.9-52.6) and 50.4 (50.1-50.8) Gy, respectively. After an anterior shift, D1cc of the breast skin for the clipping and virtual bolus plans was 56.0 (55.6-56.8) and 50.9 (50.5-51.3) Gy, respectively. When the direct mode was used without shifting the patient, D1cc of the breast skin for the clipping, virtual bolus, and skin flash plans was 52.6 (51.9-53.1), 53.4 (52.6-53.9), and 52.3 (51.7-53.0) Gy, respectively. After shifting anteriorly, D1cc of the breast skin for the clipping, virtual bolus, and skin flash plans was 55.6 (54.1-56.4), 52.4 (52.0-53.0), and 53.6 (52.6-54.6) Gy, respectively. The clipping method is not sufficient for breast IMRT. The virtual bolus and skin flash methods were more robust optimization methods according to our analyses.

Effect of different CTV shrinkage and skin flash margins on skin dose for left chest wall IMRT: A dosimetric study

In postmastectomy radiation therapy (PMRT), the adequate skin surface dose remains a problem. In this study, the effect of different CTV shrinkage and Skin flash margins on skin dose was investigated, and the accuracy of skin surface dose calculated by TPS for PMRT using thermoluminescent dosimeters (TLDs) was evaluated. Eighty-eight measurement points were determined on the Alderson Rando phantom. To determine the effects of shrinkage margin on skin dose, separate CTVs were generated for 2 mm, 3 mm and 5 mm shrinkage. The prescribed dose was 50 Gy to CTV with a daily fraction dose of 2 Gy. A total of 12 plans were created using four different skin flash thicknesses for each CTV shrinkage margin. After applying 0 mm, 10 mm, 15 mm and 20 mm skin flash thicknesses for each area of the 7F-IMRT treatment plan, the plans were recalculated, and the SF-0, SF-10, SF-15 and SF-20 plans were created, respectively. The increase in skin flash thickness in IMRT plans resulted in a significant increase in skin dose. There was a significant difference between TPS and TLD doses in all chest wall areas for SF-0, SF-10, and SF-15 (p < 0.05). However, there was no significant difference in all areas of the chest wall for SF-20 (p > 0.05). The shrinkage margin thickness of the CTV was found to be inversely proportional to the skin dose for all treatment plans. In tumors near the surface, bolus or skin flash techniques can get the skin adequately dosed. However, the skin flash technique has shown superiority in the application. In PMRT, it is recommended to keep the shrinkage margin as small as possible and use the skin flash thickness of 20 mm for the skin to receive a sufficient dose.

Quality assurance in a phase III, multicenter, randomized trial of POstmastectomy radioThErapy in Node posiTive breast cancer with or without Internal mAmmary nodaL irradiation (POTENTIAL): a planning benchmark case

PurposeTo report the planning benchmark case results of the POTENTIAL trial—a multicenter, randomized, phase 3 trial—to evaluate the value of internal mammary nodal (IMN) irradiation for patients with high-risk breast cancer.MethodsAll participating institutions were provided the outlines of one benchmark case, and they generated radiation therapy plans per protocol. The plans were evaluated by a quality assurance team, after which the institutions resubmitted their revised plans. The information on beams arrangement, skin flash, inhomogeneity corrections, and protocol compliance was assessed in the first and final submission.ResultsThe plans from 26 institutions were analyzed. Some major deviations were found in the first submission. The protocol compliance rates of dose coverage for the planning target volume of chest wall, supraclavicular fossa plus axilla, and IMN region (PTVim) were all significantly improved in the final submission, which were 96.2% vs. 69.2%, 100% vs. 76.9%, and 88.4% vs. 53.8%, respectively. For OARs, the compliance rates of heart Dmean, left anterior descending coronary artery V40Gy, ipsilateral lung V5Gy, and stomach V5Gy were significantly improved. In the first and final submission, the mean values of PTVim V100% were 79.9% vs. 92.7%; the mean values of heart Dmean were 11.5 Gy vs. 9.7 Gy for hypofractionated radiation therapy and 11.5 Gy vs. 11.0 Gy for conventional fractionated radiation therapy, respectively.ConclusionThe major deviations were corrected and protocol compliance was significantly improved after revision, which highlighted the importance of planning benchmark case to guarantee the planning quality for multicenter trials.

Robustness of hypofractionated breast radiotherapy after breast-conserving surgery with free breathing.

This study aimed to evaluate the robustness with respect to the positional variations of five planning strategies in free-breathing breast hypofractionated radiotherapy (HFRT) for patients after breast-conserving surgery. Twenty patients who received breast HFRT with 42.72 Gy in 16 fractions were retrospectively analyzed. Five treatment planning strategies were utilized for each patient, including 1) intensity-modulated radiation therapy (IMRT) planning (IMRTpure); 2) IMRT planning with skin flash tool extending and filling the fluence outside the skin by 2cm (IMRTflash); 3) IMRT planning with planning target volume (PTV) extended outside the skin by 2cm in the computed tomography dataset (IMRTePTV); 4) hybrid planning, i.e., 2 Gy/fraction three-dimensional conformal radiation therapy combined with 0.67 Gy/fraction IMRT (IMRThybrid); and 5) hybrid planning with skin flash (IMRThybrid-flash). All plans were normalized to 95% PTV receiving 100% of the prescription dose. Six additional plans were created with different isocenter shifts for each plan, which were 1mm, 2mm, 3mm, 5mm, 7mm, and 10mm distally in the X (left-right) and Y (anterior-posterior) directions, namely, (X,Y), to assess their robustness, and the corresponding doses were recalculated. Variation of dosimetric parameters with increasing isocenter shift was evaluated. All plans were clinically acceptable. In terms of robustness to isocenter shifts, the five planning strategies followed the pattern IMRTePTV, IMRThybrid-flash, IMRTflash, IMRThybrid, and IMRTpure in descending order. V 95% of IMRTePTV maintained at 99.6% ± 0.3% with a (5,5) shift, which further reduced to 98.2% ± 2.0% with a (10,10) shift. IMRThybrid-flash yielded the robustness second to IMRTePTV with less risk from dose hotspots, and the corresponding V 95% maintained >95% up until (5,5). Considering the dosimetric distribution and robustness in breast radiotherapy, IMRTePTV performed best at maintaining high target coverage with increasing isocenter shift, while IMRThybrid-flash would be adequate with positional uncertainty<5mm.

Quality Assurance in a Phase III, Multicenter, Randomized Trial of POstmastectomy radioThErapy in Node posiTive Breast Cancer with or without Internal mAmmary nodaL Irradiation (POTENTIAL): A Planning Dummy Run

To report the planning dummy run results of the POstmastectomy radioThErapy in Node posiTive breast cancer with or without Internal mAmmary nodaL irradiation (POTENTIAL) trial-a multicenter, randomized, phase 3 trial-to evaluate postmastectomy radiotherapy, with or without internal mammary nodal irradiation, for patients with high-risk breast cancer. All participating institutions were provided the contours of the dummy run case, and they generated radiotherapy (RT) plans per protocol guidelines. The plans were reviewed and feedback were provided by the quality assurance team, after which the institutions resubmitted revised plans. The information on beams arrangement, skin flash, inhomogeneity corrections, and protocol compliance was assessed both in the primary and final submission. Theplans from 26 institutions were included in the analysis. A number of major deviations were found in the primary submission, such as less strict constraint on organs at risk (OARs) V5Gy, and no application of chest wall skin flash. The protocol compliance rates of the dose coverage for the planning target volume of the chest wall (PTVcw), PTV of supra/infraclavicular fossa plus axilla levels I, II, III (PTVsc+ax), and PTV of the IMN region (PTVim) were all significantly improved in the final submission compared with those in the primary submission, which were 96.2% vs. 69.2%, 100% vs. 76.9%, and 88.4% vs. 53.8, respectively. For OARs, the protocol compliance rates of heart Dmean, left anterior descending coronary artery V40Gy, ipsilateral lung V5Gy, and stomach V5Gy were significantly improved. All major deviations were corrected and protocol compliance was significantly improved and of high level in the final submission. Moreover, the variations were reduced. Therefore, a planning dummy run was essential to guarantee good RT plan quality and inter-institutional consistency for multicenter trials.

Optimal Combination of Pitch, Modulation Factor and Dosimetric Considerations in Treatment Planning for Total Body Irradiation Using Helical Tomotherapy.

The aim of this study is to makethe standard total body irradiation (TBI) protocol for Helical tomotherapy© (HT) and to analyze the optimal pitch and modulation factor (MF) with respect to dose homogeneity index (HI), target dose coverage, target overdose, beam on time (BOT) and mean lung dose. Ten patients who underwent high-dose TBI were taken for this study. For each patient, 35 dose plans were created by different combination of pitch and MF. The optimal pitch and MF were deduced using scatter plot and regression methodology based on target coverage, HI, target volume receiving 103%(V103%), 105%(V105%) and 107% (V107%) of the prescription dose and BOT. Using these optimal pitch and MF, the final dose plan was made and the planning aim and achieved dose was compared using two tailed student's t-test. Radiochromic films and ionization chambers were used to measure the delivered dose using anthropomorphic phantom on various points for the head and pelvis regions to verify the skin flash margin and its effect on skin dose. The optimal pitch and MF value were 0.287 and 2.4 respectively. Based on optimal pitch and MF, the mean BOT was 1692 seconds with optimal inhomogeneity (7.4%). For target, D95 and D98 were 97.09% (range:94.7-99.6%, p=0.002) and 93.9% (range:91.5-94.4%,p=0.007) respectively, and mean D2 was within 107% with SD of ±1.22% (p=0.04). The mean of PTV receiving V103, V105 and V107 was 24.48% (range=7.7-36.6%, p=0.03), 5.76% (range=1.4-12.1%, SD=±3.3%), 1.93% (range=0.1-4.6%, p=0.008) respectively. Our measurements show that the flash margin did not increase the skin dose. In our study, the optimal combination of pitch value of 0.287 and MF value of 2.4 provided acceptable plans for all patients planned for TBI in HT. The flash margin can provide adequate coverage during patient position uncertainty without increasing the skin dose.

Dosimetric comparison of two dose expansion methods in intensity modulated radiotherapy for breast cancer

BackgroundTo explore the dosimetric difference between IMRT-VB plan based on the establishment of external expansion structure and virtual bolus (VB) and IMRT-SF based on the skin flash (SF) tool of the Eclipse treatment planning system in postoperative chest wall target intensity modulation radiotherapy plan of breast cancer.MethodsTwenty patients with breast cancer were randomly selected as subjects to develop IMRT-VB plan based on virtual bolus and IMRT-SF plan based on skin flash tool of Eclipse treatment planning system. The planning target volume, monitor unit (MU) of every single treatment and the dosimetric parameters of organ at risk (OARs) were recorded. Paired t-test was used for normal distribution data while nonparametric paired Wilcoxon rank sum test was used for non-normal distribution data.ResultsBoth IMRT-VB and IMRT-SF plan can expand outward to the chest wall skin and meet the dose requirements of clinical prescription. The conformal index, the homogeneity index, D2%, D98% and D50% were significantly better in IMRT-SF plan than those in IMRT-VB plan (P < 0.05). The average MU of the IMRT-SF plan was much higher than that of the IMRT-VB plan (866.0 ± 68.1 MU vs. 760.9 ± 50.4 MU, P < 0.05). In terms of organ at risk protection, IMRT-SF plan had more advantages in the protection of ipsilateral lung and spinal cord than IMRT-VB plan (P < 0.05).ConclusionOur study indicated that IMRT-SF plan displayed clinical application superiority compared to IMRT-VB plan, and the operation steps of which are simpler and faster. Besides, IMRT-SF plan took advantages in achieve effective external expansion of skin dose intensity and OARs protection.

Impact of Respiratory Motion on the Skin Dose for Breast Cancer in Tomotherapy: A Study in the In-house Moving Phantom.

Purpose: The dose expansion methods as the skin flash and virtual bolus were used to solve intrafraction movement for breast planning due to breathing motion. We investigated the skin dose in each planning method by using optically stimulated luminescence on an in-house moving phantom for breast cancer treatment in tomotherapy. The impact of respiratory motion on skin dose between static and dynamic phantom's conditions was evaluated. Methods: A phantom was developed with movement controlled by the respirator for generating the respiratory waveforms to simulate respiratory motion. Five optically stimulated luminescence dosimeters were placed on the phantom surface to investigate the skin dose for the TomoDirect and TomoHelical under static and dynamic conditions. Eight treatment plans were generated with and without skin flash or virtual bolus by varying the thickness. The difference in skin dose between the two phantom conditions for each plan was explored. Results: All plans demonstrated a skin dose of more than 87% of the prescription dose under static conditions. However, the skin dose was reduced to 84.1% (TomoDirect) and 78.9% (TomoHelical) for dynamic conditions. The treatment plans without skin flash or virtual bolus showed significant skin dose differences under static and dynamic conditions by 4.83% (TomoDirect) and 9.43% (TomoHelical), whereas the skin flash with two leaves (TomoDirect 2L) or virtual bolus of at least 1.0 cm thickness (VB1.0) application compensated the skin dose in case of intrafraction movements by presenting a skin dose difference of less than 2% between the static and dynamic conditions. Conclusion: The skin dose was reduced under dynamic conditions due to breathing motion. The skin flash method with TomoDirect 2L or virtual bolus application with 1.0 cm thickness was useful for maintaining skin dose following the prescription by compensating for intrafraction movement due to respiratory motion for breast cancer in tomotherapy.

Prospective Clinical Integration of AI Based Treatment Planning Tool for Whole Breast Radiation Therapy (WBRT): A Single Institution's Three-Year Experience

<h3>Purpose/Objective(s)</h3> Artificial intelligence (AI) has shown promising results of treatment planning in well-controlled retrospective environment. However, its clinical acceptability and long-term robustness has not been widely investigated. We report the prospective clinical results of AI-based whole breast/chest wall radiation therapy (WBRT) planning tool. We evaluated the 3-year overall performance and the progression of AI tool's acceptance among human planners. <h3>Materials/Methods</h3> In-house AI based WBRT treatment planning tool using random forest was commissioned for clinic since 2019. A total of 1151 patients have been planned with AI tool by Dec 2021, and all were included in this study. The AI tool is seamlessly integrated with clinical planning workflow and treatment planning system (TPS) – AI automatically generates fluence maps, which are used for final dose calculation in TPS (AI plan). The planner evaluates the plan quality and attempts to improve by manually modifying fluence if deemed necessary before physician's approval (final plan). The manual modification value (MMV) of each beamlet is the difference between fluence maps in AI and final plans. The manually modified beamlets were located and correlated to the dosimetry quality enhancement of the final plan over AI plan. In the longitudinal dimension, MMV also tracks the adaptation of human planner towards AI tools over 3 years. A regression model captures planner's frequency of editing AI plans over time. If the planner becomes more acceptive of the AI over time, the regression trend line will be significantly different from zero. <h3>Results</h3> Table 1 shows the dosimetric endpoints, as well as mean MMV of the entire patient population. No statistical significance was observed between the AI and final plans in PTV coverage and OAR sparing (Mood's median test), except V105% (reduced in final plan by 18.4 cc, <i>p</i>< 0.001). Spatially, irradiated lung region received most frequent editing, while skin flash region received minimum editing. Among all 12 planners, the number of cases planned ranged from 13 to 150. The max mean absolute MMV of a single planner was 5.0% (planned 131 cases) and minimum was 0.8% (planned 38 cases). Ten out of 12 planners showed a significantly decreasing editing AI plans with yearly mean MMV of 4.0%, 2.3% and 0.8% for 2019, 2020 and 2021 respectively, indicating improving acceptability/trust over time (<i>p</i><0.001). <h3>Conclusion</h3> This 3-year study demonstrated robustness of AI planning and steady improvement in acceptability by planners over time. It also revealed key areas towards human planner's preference that can be adopted in future AI tools.

116P Robustness evaluation of VMAT by robust optimization and manual flash approach for breast cancer radiotherapy

The importance of including skin flash in planning strategies for volumetric modulated arc therapy (VMAT) of breast cancer has been proposed by various researchers in the past few years. Recently, the robust planning concept from proton therapy had also incorporated in photon radiotherapy. This may provide a wider scope to deal with uncertainties. This study aimed to compare the conventional manual skin flash (MF) approach with the novel robust optimization (RO) approach in terms of robustness in VMAT for breast cancer.

Comparing the robustness of different skin flash approaches using wide tangents, manual flash VMAT, and simulated organ motion robust optimization VMAT in breast and nodal radiotherapy.

Compare the robustness of wide tangents (WT) and volumetric modulated arc therapy (VMAT) using different skin flash approaches in breast and nodal radiotherapy. Ten patients treated with WT using 2-cm flash were replanned with VMAT using no flash (NF), manual 2-cm flash (MF), and robust optimization (RO). Plan robustness was assessed for target coverage and organs at risk (OAR) by recalculating on 5 deformed CT scans (SOM1-5), daily cone beam (CBCT), and by shifting the isocenter 5 mm. VMAT NF gave poor coverage of CTVp with its smallest change of -3.2% for V38Gy on CBCT. VMAT RO plans showed the least variations in target coverage loss compared to WT and VMAT MF which dropped as anatomical swelling increased. CTVp D0.5cc decreased on CBCT and increased most for VMAT MF plans (case max increase +3.3 Gy), whereas VMAT RO plans were relatively stable (case max increase +1.2 Gy). OAR dose changed little with anatomical changes (isocenter shifts more important with medial, posterior, and inferior increasing dose). Nodal coverage was superior for VMAT which led to the WT being less robust for coverage toward both geometric and anatomical uncertainties. All techniques except NF plans gave high levels of coverage under minor uncertainties. VMAT RO was highly robust for target coverage for anatomical changes. Manually editing control points on VMAT plans was time-consuming and less predictable. CBCT anatomical changes were modest resulting in small delivered dose changes. OAR dose changes were small with no significant differences between techniques.

The robustness of VMAT radiotherapy for breast cancer with tissue deformations

To investigate the near-surface doses and target coverage in modulated arc radiotherapy (RT) of the breast or chest wall in two treatment planning systems (TPS) in the presence of soft tissue deformations. This retrospective study consisted of 10 breast cancer patients with axillary lymph node inclusion. For each case, five RT plans were created: (1) tangential 3D conformal field-in-field (FinF) technique; (2) 200° to 240° arcs with optimization bolus (OB) in Eclipse (EB); (3) 243° to 250° arcs with an 8-mm OB in Monaco (MB); (4) 243° to 250° arcs with automatic skin flash tool (ASF) in Monaco TPS (MA); (5) 243° to 250° arcs with both ASF and OB in Monaco (MAB). Soft tissue deformation was simulated by editing CT-images with 4-, 8-, and 12-mm swelling and recalculating the dose. The increasing swelling from 0 to 12 mm caused the coverage (V95%) in clinical target volume to decrease from 96% ± 2% to 90% ± 6% for the FinF plans. For volumetric-modulated arc therapy (VMAT), the coverage decreased from 99% ± 1% to 92% ± 4% in the EB plans, and from 97% ± 1% to 68% ± 8%, 85% ± 6%, and 86% ± 5% for MA, MB, and MAB, respectively. The mean dose in the surface extending from 0 to 3 mm from the skin decreased on average 5%, 17%, 20%, 15%, and 8% in FinF, EB, MA, MB, and MAB, respectively. In the Monaco plans, the use of an OB(+ASF) provided better target coverage and lower dose maxima despite of tissue swelling than the ASF alone. With modulated arc therapy, we recommend the use of an OB instead of or in addition to the ASF. The use of 8 mm OB with VMAT plans is robust to account deformations extending outside up to 8mm. If soft tissue deformation is larger than 8 mm, the need for replanning should be evaluated.

Using Robust Optimization for Skin Flashing in Intensity Modulated Radiation Therapy for Breast Cancer Treatment: A Feasibility Study

PurposeTo study the feasibility and the effectiveness of a novel implementation of robust optimization on 2 sets of computed tomography (CT) data simultaneously for skin flashing in intensity modulated radiation therapy for breast cancer. Method and MaterialsFive patients who received treatment to the breast and regional lymphatics were selected for this study. For each patient, 3 plans were generated using 3 different skin-flashing methods, including (1) a manual flash plan with optimization on the nominal planning target volume (PTV) not extending beyond the skin that required manually postplanning the opening of the multi-leaf collimator and jaw to obtain flash; (2) an expanded PTV plan with optimization on an expanded PTV that included the target in the air beyond the skin; and (3) a robust-optimized (RO) plan using robust optimization that simultaneously optimizes on the nominal CT data set and a simulated geometry error CT data set. The feasibility and the effectiveness of the robust optimization approach was investigated by comparing it with the 2 other methods. The robustness of the plan against target position variations was studied by simulating 0-, 5-, 10-, and 15-mm geometry errors. ResultsThe RO plans were the only ones able to meet acceptable criteria for all patients in both the nominal and simulated geometry error scenarios. The expanded PTV plans developed major deviation on the maximum dose to the PTV for 1 patient. For the manual flash plans, every patient developed major deviation either on 95% of the dose to the PTV or the maximum dose to the PTV in the simulated geometry error scenarios. The RO plan demonstrated the best robustness against the target position variation among the 3 methods of skin flashing. The doses to the lung and heart were comparable for all 3 planning techniques. ConclusionUsing robust optimization for skin flash in breast intensity modulated radiation therapy planning is feasible. Further investigation is warranted to confirm the clinical effectiveness of this novel approach.

Dosimetric comparison of VMAT with integrated skin flash to 3D field-in-field tangents for left breast irradiation.

Volumetric modulated arc therapy (VMAT) has been implemented for left breast irradiation to reduce prescription dose to the heart and improve dose homogeneity across the targeted breast. Our in‐house method requires application of a bolus during the optimization process with a target outside of the body, then removing the bolus during the final calculation in order to incorporate skin flash in VMAT plans. To quantify the dosimetric trade‐offs between traditional 3D field‐in‐field tangents and VMAT with integrated skin flash for these patients, we compared nine consecutive patients who recently received radiation to their entire left breast but not their regional lymphatics. Tangent plans used non‐divergent tangents of mixed energies and VMAT plans utilized four 6 MV arcs of roughly 260°. Mean dose to the heart, contralateral lung, and contralateral breast and their volume receiving 5%, 10%, and 20% of the prescription dose were higher in all nine VMAT plans than in the static tangential beam plans. For all critical structures, the mean VMAT DVH was higher in the low‐dose region and crossed the 3D field‐in‐field DVH between 23.13% and 34.18% of the prescription dose (984.75‐1454.70 cGy). However, the volume of the contralateral breast and heart receiving the prescription dose was slightly lower in the VMAT plans, but not statistically significant. VMAT provided superior homogeneity, with a mean homogeneity index of 9.41 ± 1.64 compared to 11.05 ± 1.82 for 3D tangents. Results indicate that VMAT spares the heart, contralateral lung, and contralateral breast from prescription dose at the cost of increasing their mean and low‐dose volume and delivers a more homogenous dose distribution to the breast. For these reasons, VMAT is selectively applied at the request of the physician for left breast radiation without respiratory gating to spare the heart from prescription dose in cases of poor anatomical geometry.

A Fatal Case of Accidental High-Voltage Electrocution

High voltage electrical injuries are relatively uncommon but exhibit a high rate of mortality. A body of a 39-yearold electrician who had died while working on high tension cables was brought for post-mortem examination. The autopsy revealed first and second-degree burns, exfoliated skin and crocodile flash burns around the neck. There was a penetrating skull fracture with exposed brain and surrounding charring. Microscopic examination revealed evidence of electrocution in the skin and myocardium. Cause of death was stated as multiple injuries following high voltage electrocution. Detailed history, scene visit and proper postmortem examination with histological and toxicological analysis are recommended prior to concluding the cause of death as electrocution.

Optimal selection of optimization bolus thickness in planning of VMAT breast radiotherapy treatments

The aim of this study was to find an optimal optimization skin flash thickness in volumetric modulated arc radiotherapy of the breast in consideration of soft tissue deformations during the treatment course. Ten breast radiotherapy patients with axillary lymph node inclusion were retrospectively planned with volumetric modulated arc radiotherapy technique. The plans were optimized with the planning target volume (PTV) extending outside the skin contour by 0, 5, 7, and 10 mm; and with optimization boluses of 3 or 5 mm on the extended PTV. The final dose was calculated without the bolus. The plans were compared in terms of PTV homogeneity and conformity, and dose minima and maxima. The doses to organs at risk were also evaluated. The doses were recalculated in real patient geometries based on cone beam computed tomography (CBCT) images captured 3 to 6 times during each patient's treatment course. The optimization to the PTV without the PTV extension resulted in the best CTV coverage in the original plans (V95% = 98.0% ± 1.2%). However, when these plans were studied in real CBCT-based patient geometries, the CTV V95% was compromised (94.6% ± 8.3%). In addition, for the surface (4 mm slap inside the PTV 4 mm below the body contour) dose V95% was reduced from the planned 74.7% ± 7.5% to the recalculated 65.5% ± 11.5%. Optimization with an 8-mm bolus to a PTV with 5-mm extension was the most robust choice to ensure the CTV and surface dose coverage (recalculated V95% was 95.2% ± 6.4% and 74.6% ± 8.4%, respectively). In cases with the largest observed deformations, even a 10-mm PTV extension did not suffice to cover the target. Optimization with a 5-mm PTV extension and an 8-mm optimization bolus improved the surface dose and slightly improved the CTV dose when compared to no extension plans. For deformations over 1 cm, no benefit was seen in PTV extensions and replanning is recommended. Frequent tangential and CBCT imaging should be used during treatment course to detect potential large anatomical changes.

Dosimetric effects of anatomical deformations and positioning errors in VMAT breast radiotherapy.

AimTraditional radiotherapy treatment techniques of the breast are insensitive for deformations and swelling of the soft tissue. The purpose of this study was to evaluate the dose changes seen with tissue deformations using different image matching methods when VMAT technique was used, and compare these with tangential technique.MethodsThe study included 24 patients with breast or chest wall irradiations, nine of whom were bilateral. In addition to planar kV setup imaging, patients underwent weekly cone‐beam computed tomography (CBCT) imaging to evaluate soft tissue deformations. The effect of the deformations was evaluated on VMAT plans optimized with 5‐mm virtual bolus to create skin flash, and compared to standard tangential plans with 2.5 cm skin flash. Isocenter positioning using 2D imaging and CBCT were compared.ResultsWith postural changes and soft tissue deformations, the target coverage decreased more in the VMAT plans than in the tangential plans. The planned V90% coverage was 98.3% and 99.0% in the tangential and VMAT plans, respectively. When tattoo‐based setup and online 2D match were used, the coverage decreased to 97.9% in tangential and 96.5% in VMAT plans (P < 0.001). With automatic CBCT‐based image match the respective coverages were 98.3% and 98.8%. In the cases of large soft tissue deformations, the replanning was needed for the VMAT plan, whereas the tangential plan still covered the whole target volume.ConclusionsThe skin flash created using an optimization bolus for VMAT plans was in most cases enough to take into account the soft tissue deformations seen in breast VMAT treatments. However, in some cases larger skin flash or replanning were needed. The use of 2D match decreased the target coverage for VMAT plans but not for FinF plans when compared to 3D match. The use of CBCT match is recommended when treating breast/chest wall patients with VMAT technique.

(P03) Impact of Breast Board Position on Skin Dose in Patients Receiving Prone Breast Radiotherapy

Prone positioning on a breast board is a simple and effective way for improving dosimetry in patients receiving breast radiotherapy. This technique has been demonstrated to reduce the degree of moist desquamation in patients with pendulous breasts and has also been shown to significantly reduce dose to heart and lungs. We recently observed a case of unanticipated severe moist desquamation in the inframammary fold of a patient treated with prone positioning. Review of pre-treatment port-films demonstrated that the inferior edge of the board aperture was closer to the inframammary fold during treatment than planned. We conducted a dosimetric and phantom study to investigate possible causative factors. We hypothesized that 1) proximity of the breast to the support structure at time of treatment and 2) the method of optimizing beam fluence during segment weighting both contribute to increased skin dose. A breast phantom was constructed using silicone breast prostheses affixed to a RANDO thorax and abdomen phantom. This was placed on a prone breast board and scanned in different positions: Breast centered vs Breast touching medial and inferior board edge. Plans were generated in the Treatment Planning System (TPS) using AAA. A forward planned, segment weighted photon plan was generated on the control scan (breast centered). The fluence from these plans was then deposited onto the shifted scan and dose was recalculated. The plans were then delivered onto the phantom and surface doses in the inframammary region were recorded using MOSFETs. To evaluate the impact of planning technique, the same process was also performed using a separate plan in which the inferior flash (fluence in air) was not segmented out. Surface dose in the inframammary region significantly increased with proximity to the breast board edge. With the breast centered using fully segmented plan, the calculated (TPS) and measured (MOSFET) surface doses were 83-87% and 81-84% of prescription (Rx) respectively. With the breast touching the inferior board edge, these doses increased to 105% and 101-103% of Rx. Segmentation of skin flash had minimal impact on calculated skin doses in the TPS. In contrast, lack of segmentation increased measured doses in the inframammary fold by 6-10%. Proximity of the breast to support structures at the time of treatment can significantly increase surface doses to the inframammary fold. This problem is magnified when inferior skin flash is not segmented out or blocked during the process of segment weighting. Taken together, these variables can result in increased surface doses of up to 30% over predicted and may significantly contribute to severed dermatitis. Care should be taken to ensure maximum separation of breast tissue from immobilization devices both at time of simulation and during treatment. Additionally, when optimizing plans for homogeneity with segment weighting, additional blocking should be used in areas of skin flash. While these changes in beam fluence may not significantly alter the observed dose distribution in the TPS, they can result in significant changes in surface dose during actual treatment.

EP-1896: Is robust optimization better than virtual bolus method to achieve skin flash in breast VMAT plans?

EP-1896: Is robust optimization better than virtual bolus method to achieve skin flash in breast VMAT plans?