Breast Treatment Plans Research Articles

Dosimetric evaluation of VMAT automated breast treatment plans: Towards the establishment of an institutional plan acceptability criteria

Abstract Introduction: To evaluate the clinical suitability of the current facility-based treatment plan protocol in establishing acceptability criteria. Material and methods: Automated Volumetric Arc Therapy (VMAT) treatment plans were retrospectively evaluated for intact breast and chest-wall cancer patients from January 2021 to January 2023. Results: A total of 94 patients were planned and treated using automated contouring and VMAT planning technique. The number of patients planned and treated for intact breast and chest-wall were 41 (43.6%) and 53 (56.4%), respectively. The mean intact breast volumes for optimization (Brst_opt) receiving 95% and 105% of the prescribed doses were 92.80% ± 1.11 and 1.54% ± 1.02, respectively. Their corresponding mean chest-wall volumes for optimization (Chst_opt) were 90.65% ± 3.19 and 2.28% ± 2.99, respectively. For left-sided cases, the mean heart dose received was 4.61 Gy ± 1.76 and 5.18 Gy ± 1.55 for intact breast plans and that for chest-wall plans, respectively. The mean ipsilateral lung volume receiving 20 Gy of the prescribed dose was 12.22% ± 3.86 and 13.19% ± 3.74 for intact breast plans and chest-wall plans, respectively. For the Brst_opt and Chst_opt dose metrics were calculated; the mean homogeneity index (HI) was 0.14 ± 0.03 and 0.15 ± 0.04, mean uniformity index (UI) was 1.09 ± 0.03 and 1.11 ± 0.03, and mean conformity index (CI) were 0.92 ± 0.04 and 0.91 ± 0.04, respectively. Conclusions: The dosimetric evaluation shows a good dose distribution in the target volumes with minimal doses to the organs at risk (OAR). Assessment of the current data affirms the clinical usefulness of the facility-adopted protocol in achieving quality treatment plans for intact breast and chest-wall irradiations. The establishment of plan acceptability criteria will help achieve improved overall treatment outcomes.

Validation of an in vivo transit dosimetry algorithm using Monte Carlo simulations and ionization chamber measurements.

Transit dosimetry is a safety tool based on the transit images acquired during treatment. Forward-projection transit dosimetry software, as PerFRACTION, compares the transit images acquired with an expected image calculated from the DICOM plan, the CT, and the structure set. This work aims to validate PerFRACTION expected transit dose using PRIMO Monte Carlo simulations and ionization chamber measurements, and propose a methodology based on MPPG5a report. The validation process was divided into three groups of tests according to MPPG5a: basic dose validation, IMRT dose validation, and heterogeneity correction validation. For the basic dose validation, the fields used were the nine fields needed to calibrate PerFRACTION and three jaws-defined. For the IMRT dose validation, seven sweeping gaps fields, the MLC transmission and 29 IMRT fields from 10 breast treatment plans were measured. For the heterogeneity validation, the transit dose of these fields was studied using three phantoms: 10, 30, and a 3cm cork slab placed between 10cm of solid water. The PerFRACTION expected doses were compared with PRIMO Monte Carlo simulation results and ionization chamber measurements. Using the 10cm solid water phantom, for the basic validation fields, the root mean square (RMS) of the difference between PerFRACTION and PRIMO simulations was 0.6%. In the IMRT fields, the RMS of the difference was 1.2%. When comparing respect ionization chamber measurements, the RMS of the difference was 1.0% both for the basic and the IMRT validation. The average passing rate with a γ(2%/2mm, TH=20%) criterion between PRIMO dose distribution and PerFRACTION expected dose was 96.0%±5.8%. We validated PerFRACTION calculated transit dose with PRIMO Monte Carlo and ionization chamber measurements adapting the methodology of the MMPG5a report. The methodology presented can be applied to validate other forward-projection transit dosimetry software.

Dosimetric and radiobiological comparison between conventional and hypofractionated breast treatment plans using the Halcyon system.

The objective of this research is to compare the efficacy of conventional and hypofractionated radiotherapy treatment plans for breast cancer patients, with a specific focus on the unique features of the Halcyon system. The study collected and analyzed dose volume histogram (DVH) data for two groups of treatment plans implemented using the Halcyon system. The first group consisted of 19 patients who received conventional fractionated (CF) treatment with a total dose of 50 Gy in 25 fractions, while the second group comprised 9 patients who received hypofractionated (HF) treatment with a total dose of 42.56 Gy in 16 fractions. The DVH data was used to calculate various parameters, including tumor control probability (TCP), normal tissue complication probability (NTCP), and equivalent uniform dose (EUD), using radiobiological models. The results indicated that the CF plan resulted in higher TCP but lower NTCP for the lungs compared to the HF plan. The EUD for the HF plan was approximately 49 Gy (114% of its total dose) while that for the CF plan was around 53 Gy (107% of its total dose). The analysis suggests that while the CF plan is better at controlling tumors, it is not as effective as the HF plan in minimizing side effects. Additionally, it is suggested that there may be an optimal configuration for the HF plan that can provide the same or higher EUD than the CF plan.

Experience in the Treatment of Breast Cancer Using Tunnel Type Linear Accelerator

Purpose: Describes the features of dosimetric planning for breast cancer and conducts statistics analysis of the radiation treatment planning results, while taking into account 2.5 years of work experience on the Halcyon linear accelerator at the Irkutsk Regional Cancer Center.
 Materials and methods: Varian Halcyon tunnel type linear accelerator and Varian TrueBeam C-arm linear accelerator were used for breast irradiation. Treatment planning was performed in the Eclipse planning system, Acuros dose calculation algorithm. The experience of using the specified equipment and developments in the field of radiation treatment planning using the Halcyon system are presented.
 Results: Developed an approach to planning breast radiation at the Halcyon linear accelerator. A retrospective analysis of 84 radiation treatment plans on linear accelerators of various types was carried out. Breast treatment plans for Halcyon linear accelerator have equal dosimetric parameters in comparison to the TrueBeam treatment plans.
 Conclusion: Linear accelerator Halcyon can be used for treating breast cancer if staff understands specifics of treatment planning and treatment delivery.

Investigation of the effects on dose calculations of correction-based algorithms in different tissue medium

The aim of this study is to determine the effects of correction-based algorithms on dose distributions in the inhomogeneous medium and dosimetric parameters depending on the algorithms preferred in breast and lung treatment plans. In the treatment planning system (TPS) in which the Pencil Beam Convolution (PBC) dose calculation algorithm is used, dose calculations were performed in different correction-based algorithms Modified Batho and Equivalent Tissue-Air Ratio (ETAR) for soft tissue, bone and air medium. Rectilinear virtual phantoms were created in TPS for soft tissue, bone and air materials, and deep dose values and dose distribution profiles at lateral depth were obtained. Intensity modulated radiotherapy (IMRT) treatment planning technique was applied to 20 patients with breast and lung cancer diagnosis on computed tomography (CT) sections, and dose calculations were performed. Different dosimetric parameters obtained within the target volume were calculated. Although the effects of correction-based algorithms on dose values depending on the depth and dose distribution profiles in lateral depth were calculated below 1% in dose calculations performed on soft tissue virtual phantom, dose profiles were obtained as approximately 20% in bone and air medium. It was concluded that correction-based algorithms in the different inhomogeneous mediums have a significant effect on the dose values calculated in TPS.

Comparison of the dosimetric accuracy of proton breast treatment plans delivered with SGRT and CBCT setups.

PurposeTo compare the dosimetric accuracy of surface‐guided radiation therapy (SGRT) and cone‐beam computed tomography (CBCT) setups in proton breast treatment plans.MethodsData from 30 patients were retrospectively analyzed in this IRB‐approved study. Patients were prescribed 4256–5040 cGy in 16–28 fractions. CBCT and AlignRT (SGRT; Vision RT Ltd.) were used for treatment setup during the first three fractions, then daily AlignRT and weekly CBCT thereafter. Each patient underwent a quality assurance CT (QA‐CT) scan midway through the treatment course to assess anatomical and dosimetric changes. To emulate the SGRT and CBCT setups during treatment, the planning CT and QA‐CT images were registered in two ways: (1) by registering the volume within the CTs covered by the CBCT field of view; and (2) by contouring and registering the surface surveyed by the AlignRT system. The original plan was copied onto these two datasets and the dose was recalculated. The clinical treatment volume (CTV): V95%; heart: V25Gy, V15Gy, and mean dose; and ipsilateral lung: V20Gy, V10Gy, and V5Gy, were recorded. Multi and univariate analyses of variance were performed to assess the differences in dose metric values between the planning CT and the SGRT and CBCT setups.ResultsThe CTV V95% and lung V20Gy, V10Gy, and V5Gy dose metrics were all significantly (p < 0.01) lower on the QA‐CT in both the CBCT and SGRT setup. The differences were not clinically significant and were, on average, 1.4–1.6% lower for CTV V95% and 1.8%–6.0% lower for the lung dose metrics. When comparing the lung and CTV V95% dose metrics between the CBCT and SGRT setups, no significant difference was observed. This indicates that the SGRT setup provides similar dosimetric accuracy as CBCT.ConclusionThis study supports the daily use of SGRT systems for the accurate dose delivery of proton breast treatment plans.

Clinical Experience With Machine Learning-Based Automated Treatment Planning for Whole Breast Radiation Therapy

PurposeThe machine learning–based automated treatment planning (MLAP) tool has been developed and evaluated for breast radiation therapy planning at our institution. We implemented MLAP for patient treatment and assessed our clinical experience for its performance. Methods and MaterialsA total of 102 patients of breast or chest wall treatment plans were prospectively evaluated with institutional review board approval. A human planner executed MLAP to create an auto-plan via automation of fluence maps generation. If judged necessary, a planner further fine-tuned the fluence maps to reach a final plan. Planners recorded the time required for auto-planning and manual modification. Target (ie, breast or chest wall and nodes) coverage and dose homogeneity were compared between the auto-plan and final plan. ResultsCases without nodes (n = 71) showed negligible (<1%) differences for target coverage and dose homogeneity between the auto-plan and final plan. Cases with nodes (n = 31) also showed negligible difference for target coverage. However, mean ± standard deviation of volume receiving 105% of the prescribed dose and maximum dose were reduced from 43.0% ± 26.3% to 39.4% ± 23.7% and 119.7% ± 9.5% to 114.4% ± 8.8% from auto-plan to final plan, respectively, all with P ≤ .01 for cases with nodes (n = 31). Mean ± standard deviation time spent for auto-plans and additional fluence modification for final plans were 12.1 ± 9.3 and 13.1 ± 12.9 minutes, respectively, for cases without nodes, and 16.4 ± 9.7 and 26.4 ± 16.4 minutes, respectively, for cases with nodes. ConclusionsThe MLAP tool has been successfully implemented for routine clinical practice and has significantly improved planning efficiency. Clinical experience indicates that auto-plans are sufficient for target coverage, but improvement is warranted to reduce high dose volume for cases with nodal irradiation. This study demonstrates the clinical implementation of auto-planning for patient treatment and the significant importance of integrating human experience and feedback to improve MLAP for better clinical translation.

Dosimetric assessment of brass mesh bolus and transparent polymer-gel type bolus for commonly used breast treatment delivery techniques

We investigated skin dose enhancements of brass mesh bolus (BMB) and a recently developed transparent polymer-gel bolus (PGB) for clinically relevant breast treatment delivery techniques. The dose enhancement of the breast surface with BMB and PGB were compared to that of tissue-equivalent bolus. Three breast treatment plans were generated on CT scans of an anthropomorphic chest phantom: tangential step-and-shoot 3D conformal (3DCRT) planned using Field-in-Field (FiF), tangential sliding-window 3DCRT using Electronic Compensator (EC), and volumetric modulated arc therapy (VMAT). All plans were created using 6 MV photons and a prescription dose (Rx) of 180 cGy per fraction. Skin doses of all 3 plans were measured with radiochromic films, separately delivered in triplicate. Each plan was delivered to the phantom without bolus, and then with BMB (1 or 2 layers; 3 or 10 mm tissue-equivalent), PGB, and Superflab (3, 5, and 10 mm tissue-equivalent). Doses were determined by reading the radiochromic films with a flatbed scanner, and analyzing the images using a calibration curve for each specific batch. For all bolus types and plans, surface doses averaged over the 3 measurements were between 88.4% and 107.4% of Rx. Without bolus, average measured skin doses were between 51.2% and 64.2% of Rx. Skin doses with BMB and PGB were comparable to that with tissue-equivalent bolus. Over all 3 treatment delivery techniques, using BMB resulted in average skin doses of 92.8% and 102.1% for 1- and 2 layers, respectively, and using PGB results in average skin doses of 94.8%, 98.2%, and 99.7% for 3, 5, and 10-mm tissue-equivalent, respectively. The average measured skin doses with BMB and PGB agreed within ± 3% compared to the tissue-equivalent thickness bolus. We concluded that BMB and PGB are clinically equivalent in skin dose enhancement for breast treatment as the 3, 5, and 10 mm tissue-equivalent bolus.

Commissioning and performance testing of the first prototype of AlignRT InBore™ a Halcyon™ and Ethos™-dedicated surface guided radiation therapy platform.

To commission and assess the performance of AlignRT InBore™, a Halcyon™ and Ethos™-dedicated Surface Guided Radiation Therapy (SGRT) platform which combines ceiling-mounted cameras for patient setup and bore-mounted cameras for in-bore tracking. To check the potential impact of InBore™ cameras on dose delivery, 16 SRS, H&N, breast and pelvis patients' quality assurance (QA) treatment plans were measured with/without AlignRT InBore™ and using ArcCHECK® and SRS MapCHECK®. Impact on image quality was determined using Catphan® 540 phantom and considering all available MV and CBCT protocols (head, breast, chest and pelvis). The stability, accuracy and overall performance of AlignRT InBore™ was assessed using an MV Cube and anthropomorphic phantoms. Comparison of 2D dose distributions with/without AlignRT InBore™ showed no impact on treatment delivery for all 16 QA checks (p-value>0.25). 2D and CBCT images showed no artefacts or change in the contrast-to-noise ratio, resolution and noise values measured with Catphan® 540. Anti-collision sensors were unaffected by the bore-mounted cameras. Additionally, AlignRT InBore™ cameras allowed for motion detection with sub-0.5mm accuracy and sub-0.4mm stability with surface coverage of >50×60×35 cc. Accurate transition (sub-0.3mm) from virtual to treatment isocentres was achieved. Finally, Halcyon™ rotations during CBCT and beam delivery resulted in limited camera vibrations with translation uncertainty <0.5mm in left-right and anterior-posterior directions and <0.1mm in head-feet direction. AlignRT InBore™ provides SGRT setup and intrafraction monitoring capabilities with a performance comparable to standard SGRT solutions while having no adverse effect on Halcyon™.

Minimizing the V105 in Breast Irradiation Leads to Better Treatment Outcomes: A Retrospective Study

The aim of this study is to investigate what effects, if any, minimizing the V105 in whole breast irradiation has on cosmetic outcomes. Beginning July 2018, we implemented a quality measure for all breast treatment plans aimed at minimizing the V105. To that effect, a quality index, QI, is introduced and defined as follows: QI = V105/V95 A plan is deemed acceptable for treatment delivery if QI ≤ 0.3. The QI and clinical outcome of 33 consecutive breast patients treated between January 2017 and June 2018 were retrospectively reviewed and compared to 38 consecutive patients treated since QI was implemented. A three-level grading system is used to review the treating physician reported complications related to the treatment as stated in the follow-up notes: Grades I, II and III. Grade I, or good outcome, means nothing stands out in the follow-up note as complication related to the treatment. Grade II, or moderate, is assigned when a mild reaction to the treatment is reported while Grade III, or bad, indicates cases where the note describes significant irradiation related complications such as fibrosis. All patients were prescribed 4249.6 cGy in 16 fractions, or 5040 cGy in 28 fractions, followed by an electron boost to the tumor bed. The QI quality measure went from a mean of 0.5 prior to, to 0.24 post implementing the V105 minimization requirement. Using the three-level grading system described above, the results of our study are summarized in Table 1. For patients treated prior to QI implementation, the number of patients experiencing Grade III complications increases over time going from 15% at 1 month to 40% at 24 months. In the group of patients treated following the introduction of the QI, only one case of Grade III complication was reported at 1 month. At 6 months follow-up, there are no Grade III level outcomes reported while the proportion of Grade I level outcomes improve among the same group to reach 45. Grade III reported outcomes are equally distributed between patients receiving 4249.6 cGy and 5040 cGy. Based on our results so far, minimizing V105 does lead to better outcomes in breast radiation treatments. What’s more, they also seem to indicate that when such a volume is not minimized, patients that initially experienced moderate complications may see their severity increase over time.Abstract 2099; TableTreatment outcomes before and after implementing V105 minimization or QI ≤ 0.3Follow-up intervalBefore QI ImplementationAfter QI Implementation1 month6 months12 months24 months1 month6 months12 monthsNumber of Patients3322231038273Grade I18.18%9.09%30.43%50%28.95%44.44%100%Grade II66.67%63.64%39.13%10%68.42%55.56%0.0%Grade III15.15%27.27%30.43%40%2.63%0.0%0.0% Open table in a new tab

Retrospective analysis of portal dosimetry pre-treatment quality assurance of hybrid IMRT breast treatment plans

AbstractBackground:The purpose of this study is to evaluate the effectiveness and sensitivity of the Varian portal dosimetry (PD) system as a quality assurance (QA) tool for breast intensity-modulated radiation therapy (IMRT) treatment plans.Materials and methods:Four hundred portal dose images from 200 breast cancer patient IMRT treatment plans were analysed. The images were obtained using Varian PortalVision electronic portal imaging devices (EPIDs) on Varian TrueBeam Linacs. Three patient plans were selected, and the multi-leaf collimator (MLC) positions were randomly altered by a mean of 0·5, 1, 1·5 and 2 mm with a standard deviation of 0·1 mm on 50, 75 and 100% of control points. Using the improved/global gamma calculation algorithm with a low-dose threshold of 10% in the EPID, the change in gamma passing rates for 3%/3 mm, 2%/2 mm and 1%/1 mm criterion was analysed as a function of the introduced error. The changes in the dose distributions of clinical target volume and organ at risk due to MLC positioning errors were also analysed.Results:Symmetric and asymmetric breast or chest wall plan fields are different in delivery as well as in the QA. An average gamma passing rate of 99·8 ± 0·5 is presented for 3%/3 mm symmetric plans and 96·9 ± 4·5 is presented for 3%/3 mm asymmetric plans. An average gamma passing rate of 98·4 ± 4·3 is presented for 2%/2 mm symmetric plans and 89·7 ± 9·5 is presented for 2%/2 mm asymmetric plans. A large-induced error in MLC positioning (2·0 mm, 100% of control points) results in an insignificant change in dose that would be delivered to the patient. However, EPID portal dosimetry is sensitive enough to detect even the slightest change in MLC positioning error (0·5 mm, 50% of control points).Conclusions:Stricter pre-treatment QA action levels can be established for breast IMRT plans utilising EPID. For improved sensitivity, a multigamma criteria approach is recommended. The PD tool is sensitive enough to detect MLC positioning errors that contribute to even insignificant dose changes.

Application of retrospective data analysis to clinical protocol design: can the potential benefits of breath-hold techniques for breast radiotherapy be assessed without testing on patients?

The advantages, in terms of heart dose sparing, resulting from using a breath-hold technique when treating supine left breast radiotherapy patients are widely accepted, and increasing numbers of radiotherapy departments are implementing breath-hold techniques. However, due to differences in patient setup and treatment planning protocols between radiotherapy departments, it is important to assess the benefits of using a breath-hold technique within each department, before or during implementation. This study investigated the use of retrospective analysis of past patient treatment plans, as a means to identify the potential for breath-hold techniques to benefit patients. In-house "Treatment and Dose Assessor" code was used to complete a bulk retrospective evaluation of dose-volume metrics for 708 supine and 13 prone breast and chest wall radiotherapy treatments, that were planned using the same clinical protocols, which did not utilise a breath hold technique. For supine patients, results showed statistically significant differences between heart doses from left and right breast treatment plans, in the absence of significant differences between lung doses from left and right breast treatment plans, confirming the potential benefit of using a breath-hold technique for supine left breast radiotherapy patients. Fewer than 1% of the right breast treatment plans showed heart doses high enough to suggest a possible benefit from using a breath-hold technique. Approximately 50% of the prone left breast treatment plans included very low heart doses without intervention, and may therefore have shown no noticeable dosimetric benefit from the use of a breath hold. This study demonstrated the extent of information that can be obtained using retrospective data analysis, before or instead of obtaining multiple CT images of patients and completing a process of dual planning and prospective dose evaluation.

28 Contribution of transit dosimetry (EPID-based) and retrospective dose calculation in the patient’s real anatomy (kV-CBCT-based) for the estimation of the dose delivered to the patient (Preliminary study)

Introduction During an external photon radiotherapy treatment, transit dosimetry performed with the electronic portal imaging device (EPID) makes it possible to record a footprint of the irradiation beam passing through the patient to detect any deviations between predicted and delivered dose. These deviations are most often due to wrong patient positioning or anatomical changes. The on-board X-ray imaging system provides 3D patient imaging (kV-CBCT). Despite lower image quality than the planning CT (pCT), the kV-CBCT provides information on the positioning and anatomy of the patient at the time of the fraction. It is tempting to use this data for recalculation purposes in the planning system (TPS). The objective of this study is to evaluate the potential of the joint contribution of transit dosimetry and a posteriori dose calculation performed in the anatomy of the kV-CBCT of the day. Methods The study concerns breast treatment plans in RapidArc technique (RX 6MV) on a TrueBeamTM machine (Varian MS, Palo Alto, CA, USA). For each fraction, a kV-CBCT was performed before beam delivered and the EPID images acquired in transit condition (movie mode). A cumulative image over the length of the arc is reconstructed in terms of dose from the movie sequence, it is then compared with a predicted image calculated at the EPID level, from the RT-plan, in the same dose terms and transmission conditions. Image comparison is performed using γ -index maps (5%/4 mm; threshold 40%; overall) and GAI approval value (%). The 3D a posteriori dose calculation was performed using Eclipse TPS (Varian MS) with the PK-AAA algorithm on the pCT corrected from anatomical information of the kV-CBCT by an elastic registration (ISOgray-DOSIsoft). Results In this study the comparison of a predicted/acquired dose images with the gamma index criteria mainly leads to GAI approval values greater than 90%. The use of the kV-CBCT for a posteriori dose calculation, confirms the deviations detected with the EPID images comparison and allows a more precise quantification of the deviations in terms of dose, or irradiated volumes. The observed differences in dose are more or less marked depending on the patient, with a trend for larger differences on the target volumes (around 5–10%) than for organs at risk (around 2–5%). Conclusions This preliminary study of the complementarity between EPID transit dosimetry and a posteriori dose calculation in the kV-CBCT anatomy of the day, shows the relevance and consistency of the two approaches. Deviations detected from planning conditions in terms of dose delivered and volumes to be treated or spared can then be more easily interpreted and their causes better identified in clinical practice.

EP-1844: A dosimetric comparison of 3 types of breast treatment plans. 3D conformal, RapidArc and IMRT

EP-1844: A dosimetric comparison of 3 types of breast treatment plans. 3D conformal, RapidArc and IMRT

Increased Number of Beam Angles Is Associated With Higher Cardiac Dose in Adjuvant Fixed Gantry Intensity Modulated Radiation Therapy of Left-Sided Breast Cancer

Toanalyze the relationship between angle number and mean heart dose (MHD) in adjuvant fixed gantry intensity modulated radiation therapy (FG-IMRT) treatment of left-sided breast cancer as is currently practiced in the community. We performed a retrospective, multi-institutional review of women with left-sided breast cancer receiving adjuvant FG-IMRT between 2012 and 2014, encompassing 85 centers in 15 states. Bivariate and multivariate regression analyses were done to identify factors associated with MHD. Long-term cardiac risk was estimated according to a previously published model. Of the 538 women included, 284 had >2 gantry angle treatment plans (multi-angle), and 254 had 2 gantry angle (standard) plans. Median MHD was higher in patients with multi-angle plans compared with standard (median 475 vs 203cGy). Number of gantry angles was significantly associated with MHD, with multi-angle plans independently increasing MHD by 229cGy. Absolute risk of acute coronary events 20years after treatment was estimated as 7 excess events per 1000 women for standard plans, compared with 12 excess events for multi-angle plans. Fixed gantry IMRT breast treatment plans with >2 gantry angles were associated with increased MHD, which translated to an increased cardiac risk. Clinicians should account for this potential drawback in treatment technique when assessing overall plan quality.

Impact of physiological breathing motion for breast cancer radiotherapy with proton beam scanning – An in silico study

This study investigates the impact of breathing motion on proton breast treatment plans. Twelve patients with CT datasets acquired during breath-hold-at-inhalation (BHI), breath-hold-at-exhalation (BHE) and in free-breathing (FB) were included in the study. Proton plans were designed for the left breast for BHI and subsequently recalculated for BHE or designed for FB and recalculated for the extreme breath-hold phases. The plans were compared from the point of view of their target coverage and doses to organs-at-risk. The median amplitude of breathing motion determined from the positions of the sternum was 4.7mm (range 0.5–14.6mm). Breathing motion led to a degradation of the dose coverage of the target (heterogeneity index increased from 4–7% to 8–11%), but the degraded values of the dosimetric parameters of interest fulfilled the clinical criteria for plan acceptance. Exhalation decreased the lung burden [average dose 3.1–4.5Gy (RBE)], while inhalation increased it [average dose 5.8–6.8Gy (RBE)]. The individual values depended on the field arrangement. Smaller differences were seen for the heart [average dose 0.1–0.2Gy (RBE)] and the LAD [1.9–4.6Gy (RBE)]. Weak correlations were generally found between changes in dosimetric parameters and respiratory motion. The differences between dosimetric parameters for various breathing phases were small and their expected clinical impact is consequently quite small. The results indicated that the dosimetric parameters of the plans corresponding to the extreme breathing phases are little affected by breathing motion, thus suggesting that this motion might have little impact for the chosen beam orientations with scanned proton beams.

Directly Improving the Quality of Radiation Treatment Through Peer Review: A Cross-sectional Analysis of Cancer Centers Across a Provincial Cancer Program

To describe the outcomes of peer review across all 14 cancer centers in Ontario. We identified all peer-reviewed, curative treatment plans delivered in Ontario within a 3-month study period from 2013 to 2014 using a provincial cancer treatment database and collected additional data on the peer-review outcomes. Considerable variation was found in the proportion of peer-reviewed plans across the centers (average 70.2%, range 40.8%-99.2%). During the study period, 5561 curative plans underwent peer review. Of those, 184 plans (3.3%) had changes recommended. Of the 184 plans, the changes were major (defined as requiring repeat planning or having a major effect on planning or clinical outcomes, or both) in 40.2% and minor in 47.8%. For the remaining 12.0%, data were missing. The proportions of recommended changes varied among disease sites (0.0%-7.0%). The disease sites with the most recommended changes to treatment plans after peer review and with the greatest potential for benefit were the esophagus (7.0%), uterus (6.7%), upper limb (6.3%), cervix and lower limb (both 6.0%), head and neck and bilateral lung (both 5.9%), right supraclavicular lymph nodes (5.7%), rectum (5.3%), and spine (5.0%). Although the heart is an organ at risk in left-sided breast treatment plans, the proportions of recommended changes did not significantly differ between the left breast treatment plans (3.0%, 95% confidence interval 2.0%-4.5%) and right breast treatment plans (2.4%, 95% confidence interval 1.5%-3.8%). The recommended changes were more frequently made when peer review occurred before radiation therapy (3.8%) than during treatment (1.4%-2.8%; P=.0048). The proportion of plans with recommended changes was not significantly associated with patient volume (P=.23), peer-review performance (P=.36), or center academic status (P=.75). Peer review of treatment plans directly affects the quality of care by identifying important clinical and planning changes. Provincial strategies are underway to optimize its conduct in radiation oncology.

Flattening filter free technique in breath-hold treatments of left-sided breast cancer: The effect on beam-on time and dose distributions

Background and purposeThe use of flattening filter free (FFF) beams has potential to speed up deep-inspiration breath-hold treatments. In this study, the beam-on time and dose characteristics of left-sided breast treatment plans with FFF and flattened beams were evaluated. Material and methodsTwelve plans were generated for 20 patients. The techniques utilized were volumetric modulated arc therapy with two limited tangential arcs (tVMAT) and tangential intensity modulated radiotherapy with dynamic (dIMRT) as well as step-and-shoot (FinF) dose delivery. Each technique was planned with FFF and flattened beams with 6 and 10MV photons. All plans were irradiated and the beam-on times were measured. Dose characteristics of planning target volume (PTV) and organs at risk (OAR) were evaluated. ResultsThe mean beam-on times were reduced by 18–39% using FFF. Mean PTV dose coverage was least reduced with tVMAT (0.6–0.8%) compared to dIMRT (4%) and FinF (5.6–9.1%), when FFF beams were used instead of flattened beams. Only small differences were observed in OAR doses between equivalent plans (FFF vs. flattened). ConclusionsA significant reduction was observed in beam-on time when utilizing FFF beams with tVMAT, dIMRT and FinF. tVMAT was the only technique for which the use of FFF did not degrade the treatment plan dose distributions.

SU‐E‐J‐22: A Feasibility Study On KV‐Based Whole Breast Radiation Patient Setup

Purpose:In room kilovoltage x‐ray (kV) imaging provides higher contrast than Megavoltage (MV) imaging with faster acquisition time compared with on‐board cone‐beam computed tomography (CBCT), thus improving patient setup accuracy and efficiency. In this study we evaluated the clinical feasibility of utilizing kV imaging for whole breast radiation patient setup.Methods:For six breast cancer patients with whole breast treatment plans using two opposed tangential fields, MV‐based patient setup was conducted by aligning patient markers with in room lasers and MV portal images. Beam‐eye viewed kV images were acquired using Varian OBI system after the set up process. In house software was developed to transfer MLC blocks information overlaying onto kV images to demonstrate the field shape for verification. KV‐based patient digital shift was derived by performing rigid registration between kV image and the digitally reconstructed radiography (DRR) to align the bony structure. This digital shift between kV‐based and MV‐based setup was defined as setup deviation.Results:Six sets of kV images were acquired for breast patients. The mean setup deviation was 2.3mm, 2.2mm and 1.8mm for anterior‐posterior, superior‐inferior and left‐right direction respectively. The average setup deviation magnitude was 4.3±1.7mm for six patients. Patient with large breast had a larger setup deviation (4.4–6.2mm). There was no strong correlation between MV‐based shift and setup deviation.Conclusion:A preliminary clinical workflow for kV‐based whole breast radiation setup was established and tested. We observed setup deviation of the magnitude below than 5mm. With the benefit of providing higher contrast and MLC block overlaid on the images for treatment field verification, it is feasible to use kV imaging for breast patient setup.

Dosimetric evaluation of whole-breast radiation therapy: Clinical experience

Radiation therapy of the intact breast is the standard therapy for preventing local recurrence of early-stage breast cancer following breast conservation surgery. To improve patient standard of care, there is a need to define a consistent and transparent treatment path for all patients that reduces significance variations in the acceptability of treatment plans. There is lack of consistency among institutions or individuals about what is considered an acceptable treatment plan: target coverage vis-à-vis dose to organs at risk (OAR). Clinical trials usually resolve these issues, as the criteria for an acceptable plan within the trial (target coverage and doses to OAR) are well defined. We developed an institutional criterion for accepting breast treatment plans in 2006 after analyzing treatment data of approximately 200 patients. The purpose of this article is to report on the dosimetric review of 623 patients treated in the last 18 months to evaluate the effectiveness of the previously developed plan acceptability criteria and any possible changes necessary to further improve patient care. The mean patient age is 61.6 years (range: 25.2 to 93.0 years). The mean breast separation for all the patients is 21.0cm (range: 12.4 to 34.9cm), and the mean planning target volume (PTV_eval) (breast volume for evaluation) is 884.0cm3 (range: 73.6 to 3684.6cm3). Overall, 314 (50.4%) patients had the disease in the left breast and 309 (49.6%) had it in the right breast. A total of 147 (23.6%) patients were treated using the deep inspiration breath-hold (DIBH) technique. The mean normalized PTV_eval receiving at least 92% (V92% PD) and 95% (V95% PD) of the prescribed dose (PD) are more than 99% and 97%, respectively, for all patients. The mean normalized PTV_eval receiving at least 105% (V105% PD) of the PD is less than 1% for all groups. The mean homogeneity index (HI), uniformity index (UI), and conformity index (CI) for the PTV_eval are 0.09 (range: 0.05 to 0.15), 1.07 (range: 0.46 to 1.11), and 0.98 (range: 0.92 to 1.0), respectively. Our data confirm the significant advantage of using DIBH to reduce heart dose when compared with the free-breathing technique. The p values analyses of the results for the V5Gy, V10Gy, V15Gy, V20Gy, and V30Gy for the heart comparing DIBH and free-breathing techniques are well less than 0.05 (i.e., p < 0.05). However, similar analyses for the lung give values greater than 0.05 (i.e., p > 0.05), indicating that there is no significant difference in lung dose comparing the 2 treatment techniques.