Dosimetric and clinical advantages of deep inspiration breath-hold (DIBH) during radiotherapy of breast cancer

Evaluation of helical tomotherapy as an alternative for left-sided breast cancer patients not compliant with deep inspiration breath hold

Purpose

The aim of this study is to investigate, from a dosimetric perspective, whether helical Tomotherapy (HT) during free breathing (FB) can serve as an alternative technique for treating left-sided breast cancer patients who are unable to comply with the deep inspiration breath hold (DIBH) technique.

Material and Methods

For this purpose, the CT images of 20 left breast-only cancer patients acquired in both FB and DIBH phases were utilized. The left breast was contoured as the target volume, while the heart, LAD, ipsilateral and contralateral lungs, and contralateral breast were contoured as organs at risk on the CT images obtained in both DIBH and FB. Planning with the volumetric modulated arc therapy (VMAT) technique was performed on the CT scans obtained in the DIBH (VMAT-DIBH), while planning with the HT technique was carried out on the CT scans obtained in the FB (HT-FB). Subsequently, dosimetric comparison of the plans were done in terms of target coverage and preservation of normal tissues.

Results

Both techniques achieved the desired target coverage; however, in terms of D2, Vpres values, Conformity Number (CN), and Homogeneity Index (HI), the HT-FB technique was found to be superior. While the mean doses to the heart were similar for both techniques, doses to the LAD and left lung were found to be superior in plans generated with the HT-FB technique. When compared in terms of contralateral breast and right lung protection, VMAT-DIBH technique was found to be significantly superior.

Conclusion

The treatment of left breast-only patients with the HT-FB technique has been observed to provide similar heart protection and better LAD and ipsilateral lung protection compared to the VMAT-DIBH technique without compromising target coverage. However, when the HT-FB technique is used, doses to the contralateral lung and contralateral breast should be carefully evaluated.

Evaluation of conventional IMRT and VMAT strategies for postmastectomy radiation therapy after immediate implant-based reconstruction using the new ESTRO-ACROP contouring guidelines

This study evaluated the usability of conventional templates based on the new contour guidelines of the European Society of Radiation and Oncology and Advisory Committee in Radiation Oncology Practice (ESTRO-ACROP) for treatment plans of postmastectomy radiotherapy after immediate implant-based reconstruction. Intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) plans generated with two different treatment planning systems (TPSs, Eclipse and Monaco) were examined. Six computed tomography scans of patients aged 35-54 years were retrospectively analysed who had undergone mastectomy and breast reconstruction using silicone implants after being diagnosed with left breast cancer. Six radiation oncologists participated in this study, and each of them contoured the target volume of one left breast using conventional contour (CTV-CONV) and new contour (CTV-ESTRO) methods. This study showed that compared with CTV-CONV, using CTV-ESTRO with objectives and cost functions similar to those of TPSs worsened the target volume coverage and increased the total number of monitor units. Considering the organs at risk, CTV-ESTRO tended to increase the mean dose delivered to the contralateral lung. It is concluded that the approach used for the new ESTRO-ACROP contour method cannot be applied in a manner similar to that for the conventional breast contour method, implying that the new ESTRO-ACROP contour method may require more time for improving plans for a given treatment.

Dosimetry impact of distinct gating strategies in cine MR image-guided breath-hold pancreatic cancer radiotherapy

PURPOSE

To investigate the dosimetry effects of different gating strategies in cine magnetic resonance imaging (MRI)-guided breath-hold pancreatic cancer radiotherapy.

METHODS

Two cine MRI-based gating strategies were investigated： a tumor contour-based gating strategy at a gating threshold of 0-5% and a tumor displacement-based gating strategy at a gating threshold of 3-5 mm. The cine MRI videos were obtained from 17 pancreatic cancer patients who received MRI-guided radiation therapy. We calculated the tumor displacement in each cine MR frame that satisfied the gating threshold and obtained the proportion of frames with different displacements. We generated IMRT and VMAT plans using a 33 Gy prescription, and motion plans were generated by adding up all isocenter-shift plans corresponding to different tumor displacements. The dose parameters of GTV, PTV, and organs at risk (OAR) were compared between the original and motion plans.

RESULTS

In both gating strategies, the difference was significant in PTV coverage but not in GTV coverage between the original and motion plans. OAR dose parameters deteriorate with increasing gating threshold. The beam duty cycle increased from 19.5±14.3% (median 18.0%) to 60.8±15.6% (61.1%) for gating thresholds from 0% to 5% in tumor contour-based gating and from 51.7±11.5% (49.7%) to 67.3±12.4% (67.1%) for gating thresholds from 3 to 5 mm in tumor displacement-based gating.

CONCLUSION

In tumor contour-based gating strategy, the dose delivery accuracy deteriorates while the dose delivery efficiency improves with increasing gating thresholds. To ensure treatment efficiency, the gating threshold might be no less than 3%. A threshold up to 5% may be acceptable in terms of the GTV coverage. The displacement-based gating strategy may serve as a potential alternative to the tumor contour based gating strategy, in which the gating threshold of approximately 4 mm might be a good choice for reasonably balancing the dose delivery accuracy and efficiency.

Carbon-fiber alternative to the commercial gating surrogate for the Varian Truebeam™

BACKGROUND

In this study we present the Tracking Accessory 3 (TA3) as an alternative to the commercial gating block (GB) surrogate for the Varian Truebeam™ gating system (TGS). The TGS requires three visible reflectors to track the surrogate, presenting an opportunity for a surrogate to be made with less material and thus smaller dosimetric footprint than the commercial four reflector model.

MATERIALS AND METHODS

Relative dose and depth dose profiles below the TA3 and the GB were measured with radiosensitive film. Accuracy and reproducibility of the detected motion amplitude for three TA3s and one GB were determined using a respiratory phantom with surrogate to determine the camera's tracking volume. Clinical performance was evaluated prospectively in 10 breast cancer patients treated with deep inspiration breath hold monitored with TA3 and compared to previously published results. Non-parametric statistics were applied to test for significance.

RESULTS AND CONCLUSIONS

Surface doses were increased up to 94% and 187% for the TA3 and GB, respectively, compared to no surrogate. The surface area influenced by at least 25% increase in dose was 12 cm2 and 105 cm2 for the TA3 and GB, respectively. The water equivalent thickness of the surrogates was found to be 1 mm for the TA3 and 3 mm for GB. The difference in measured amplitude were <0.2 mm for TA3 compared to the GB. The TA3s and GB were detected at all extremes of the clinically relevant tracking volume of the TGS. Clinical performance showed no significant differences. The TA3 caused less surface dose increase compared to the commercial GB. In the tested range all surrogates measured motion amplitude within 0.2 mm of reference value, which is not a clinically relevant difference. The TA3 showed no significant differences in clinical performance to similarly positioned surrogates.

Regional nodal irradiation in breast cancer patients: Effects of deep inspiration breath hold on the internal mammary chain location

The purpose of this study was to investigate the impact of deep inspiration breath hold (DIBH) on the positioning of thoracic structures and provide treatment planning recommendations for internal mammary chain (IMC) irradiation in breast cancer patients. Thirty-two breast cancer patients from our database underwent both DIBH and free breathing (FB) treatment planning. Contouring of the axillary lymph node clinical target volumes (CTVs: level I, II, III, IV, and IMC according to ESTRO), the internal mammary artery (IMA), the heart, and the left anterior descending artery (LAD) was performed. The following were then analyzed: the distance between the IMA and the heart, the craniocaudal distance in which IMC-CTV and heart coexist, the craniocaudal distance between the lower end of the of level III and IV and the upper end of the heart. Several significant geometric differences were observed between DIBH and FB that explain the efficacy of the DIBH for regional nodal irradiation. In >80% of patients the cranial origin of the LAD lies below the lower edge of the IMC-CTV in DIBH. In addition the slices in which the heart/LAD and IMC-CTV coexist decrease during DIBH. The IMA-heart distance is significantly larger in DIBH. Also the craniocaudal distance between the lower border of the CTV level III and IV and the upper border of the heart is larger in DIBH. The observed mechanisms during DIBH contribute significantly to the dose reduction in regional nodal irradiation. To further enhance the benefits of DIBH for the irradiation of the IMC-CTV, it is recommended to implement steep dose gradients in the caudal plane.

Cardiorespiratory dose comparison among six radiotherapy regimens for patients with left-sided breast cancer

There is uncertainty regarding the benefits and drawbacks of various radiation protocols for the treatment of left-sided breast cancer. To address this issue, we conducted a Bayesian network analysis. First, we searched several electronic databases for eligible literature. Next, we pooled the data from twelve studies concerning three-dimensional conformal radiation therapy (3D-CRT), intensity modulated radiation therapy (IMRT), and volumetric modulated arc therapy (VMAT), combined with either deep inspiratory breath-holding (DIBH) or free-breathing (FB) modalities. The integrated cardiac and pulmonary dosimetric indexes for all included treatments were compared using Bayesian networks. A direct meta-analysis indicated that for the two methods of 3D-CRT and IMRT, DIBH technology was more effective than FB in reducing the radiation dose to the heart and lungs. Additionally, according to the network results, DIBH was superior to FB in all six treatment options, regardless of whether the plan was 3D-CRT, IMRT, or VMAT. Besides, the combined data indicated that the FB-3D-CRT regimen had the weakest dosimetric advantage of all the treatments. Excluding FB-3D-CRT, each of the other five treatments had its own specific benefits. This is the first Bayesian study of several radiotherapy regimens for breast cancer patients on the left side, and the findings can be used to select appropriate radiotherapy programs for breast cancer patients.

Clinical applicability of deep learning-based respiratory signal prediction models for four-dimensional radiation therapy

For accurate respiration gated radiation therapy, compensation for the beam latency of the beam control system is necessary. Therefore, we evaluate deep learning models for predicting patient respiration signals and investigate their clinical feasibility. Herein, long short-term memory (LSTM), bidirectional LSTM (Bi-LSTM), and the Transformer are evaluated. Among the 540 respiration signals, 60 signals are used as test data. Each of the remaining 480 signals was spilt into training and validation data in a 7:3 ratio. A total of 1000 ms of the signal sequence (T_s) is entered to the models, and the signal at 500 ms afterward (P_t) is predicted (standard training condition). The accuracy measures are: (1) root mean square error (RMSE) and Pearson correlation coefficient (CC), (2) accuracy dependency on T_s and P_t, (3) respiratory pattern dependency, and (4) error for 30% and 70% of the respiration gating for a 5 mm tumor motion for latencies of 300, 500, and 700 ms. Under standard conditions, the Transformer model exhibits the highest accuracy with an RMSE and CC of 0.1554 and 0.9768, respectively. An increase in T_s improves accuracy, whereas an increase in P_t decreases accuracy. An evaluation of the regularity of the respiratory signals reveals that the lowest predictive accuracy is achieved with irregular amplitude patterns. For 30% and 70% of the phases, the average error of the three models is <1.4 mm for a latency of 500 ms and >2.0 mm for a latency of 700 ms. The prediction accuracy of the Transformer is superior to LSTM and Bi-LSTM. Thus, the three models have clinically applicable accuracies for a latency <500 ms for 10 mm of regular tumor motion. The clinical acceptability of the deep learning models depends on the inherent latency and the strategy for reducing the irregularity of respiration.

Heart Sparing Radiotherapy Techniques in Breast Cancer: A Focus on Deep Inspiration Breath Hold

Adjuvant radiation therapy is a critical component of breast cancer management. However, when breast cancer patients receive incidental radiation to the heart, there is an increased risk of cardiac disease and mortality. This is most common for patients with left-sided breast cancers and those receiving nodal irradiation as part of treatment. The overall risk of cardiac toxicity increases 4–16% with each Gray increase in mean heart radiation dose, with data suggesting that no lower limit exists which would eliminate cardiac risk entirely. Radiation techniques have improved over time, leading to lower cardiac radiation exposure than in the past. This decline is expected to reduce the incidence of radiation-induced heart dysfunction in patients. Deep inspiration breath hold (DIBH) is one such technique that was developed to reduce the risk of cardiac death and coronary events. DIBH is a non-invasive approach that capitalizes on the natural physiology of the respiratory cycle to increase the distance between the heart and the therapeutic target throughout the course of radiation therapy. DIBH has been shown to decrease the mean incidental radiation doses to the heart and left anterior descending coronary artery by approximately 20–70%. In this review, we summarize different techniques for DIBH and discuss recent data on this technique.

Deep inspiration breath-hold for patients with left-sided breast cancer - A one-fits-all approach? A prospective analysis of patient selection using dosimetrical and practical aspects

OBJECTIVE

To prospectively analyze the feasibility of an algorithm for patient preparation, treatment planning, and selection for deep inspiration breath-hold (DIBH) treatment of left-sided breast cancer.

METHODS

From February 2017 to July 2019, 135 patients with left-sided breast cancer were selected and prepared for radiotherapy in DIBH. 99 received radiotherapy for the breast alone and 36 for the breast including the lymphatic drainage (RNI). Treatment plans DIBH and free breathing (FB) were calculated. Dosimetrical analyses were performed, and criteria were defined to assess whether a patient would dosimetrically profit from DIBH.

RESULTS

Of the 135 patients, 97 received a DIBH planning CT and 72 were selected for treatment in DIBH according to predefined criteria. When using DIBH, there was a mean reduction of the DmeanHeart of 2.8 Gy and DmeanLAD of 4.2 Gy. seven patients did not benefit from DIBH regarding DmeanHeart, 23 regarding DmeanLAD. For the left lung, the V20Gy was reduced by 4.9%, the V30Gy by 2.7% with 15 and 29 patients not benefiting from DIBH, respectively. In the 25 patients treated in FB, the benefit of DIBH would have been lower than for patients treated with DIBH (ΔDmeanHeart0.7 Gy vs 3.4 Gy).

CONCLUSION

Dosimetrically, DIBH is no "one-fits-all" approach. However, there is a statistically significant benefit when looking at a larger patient population. DIBH should be used for treatment of left-sided breast cancer in patients fit for DIBH.

ADVANCES IN KNOWLEDGE

This analysis offers a well-designed dosimetrical analysis in patients treated with DIBH radiotherapy in an "every day" cohort.

Evaluation of the dosimetric and radiobiological parameters in four radiotherapy regimens for synchronous bilateral breast cancer

This study is to investigate the optimal treatment option for synchronous bilateral breast cancer (SBBC) by comparing dosimetric and radiobiological parameters of intensity‐modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) plans using single and dual isocenters.

Twenty patients with SBBC without lymph node involvement were selected retrospectively. Four treatment plans were generated for each patient using the Eclipse treatment planning system (Varian Medical System, Palo Alto, CA, USA) following two delivery techniques with two isocenter conditions—IMRT using a single isocenter (IMRT_Iso1), VMAT using a single isocenter (VMAT_Iso1), IMRT using dual isocenters (IMRT_Iso2), and VMAT using dual isocenters (VMAT_Iso2). A dose of 42.56 Gy in 16 fractions was prescribed for the planning target volume (PTV). All plans were calculated using the Acuros XB algorithm and a photon optimizer for a 6‐MV beam of a Vital Beam linear accelerator. PTV‐related dosimetric parameters were analyzed. Further, the homogeneity index, conformity index, and conformation number were computed to evaluate plan quality. Dosimetric parameters were also measured for the organs at risk (OARs). In addition, the equivalent uniform dose corresponding to an equivalent dose related to a reference of 2 Gy per fraction, the tumor control probability, and the normal tissue complication probability were calculated based on the dose–volume histogram to investigate the radiobiological impact on PTV and OARs.

IMRT_Iso1 exhibited similar target coverage and a certain degree of dosimetric improvement in OAR sparing compared to the other techniques. It also exhibited some radiobiological improvement, albeit insignificant. Although IMRT_Iso1 significantly increased monitor unit compared to VMAT_Iso1, which is the best option in terms of delivery efficiency, there was only a 22% increase in delivery time. Therefore, in conclusion, IMRT_Iso1, the complete treatment of which can be completed using a single setup, is the most effective method for treating SBBC.

Comparison of Deep Inspiration Breath Hold Versus Free Breathing in Radiotherapy for Left Sided Breast Cancer

Objectives

Modern breast cancer techniques, such as the deep inspiration breath-hold (DIBH) technique has been applied for left-sided breast cancer. Whether the DIBH regimen is the optimal solution for left-sided breast cancer remains unclear. This meta-analysis aims to elucidate the differences of DIBH and free-breathing (FB) for patients receiving radiotherapy for left-sided breast cancer and provide a practical reference for clinical practice.

Methods

Relevant research available on PubMed, Embase, Cochrane Library, and the Web of Science published before November 30, 2021 was independently and systematically examined by two investigators. Data were extracted from eligible studies for assessing their qualities and calculating the standardized mean difference (SMD) and 95% confidence intervals (CIs) using Review Manager software 5.4 (RevMan 5.4).

Results

Forty-one studies with a total of 3599 left-sided breast cancer patients were included in the meta-analysis. Compared with FB, DIBH reduced heart dose (D mean, D max, V30, V10, V5), left anterior descending branch (LAD) dose (D mean, D max), ipsilateral lung dose (D mean, V20, V10, V5), and heart volume significantly. Lung volume increased greatly, and a statistically significant difference. For contralateral breast mean dose, DIBH has no obvious advantage over FB. The funnel plot suggested this study has no significant publication bias.

Conclusions

Although DIBH has no obvious advantage over FB in contralateral breast mean dose, it can significantly reduce heart dose, LAD dose, ipsilateral lung dose, and heart volume. Conversely, it can remarkably increase the ipsilateral lung volume. This study suggests that soon DIBH could be more widely utilized in clinical practice because of its excellent dosimetric performance.

Nuclear medicine imaging methods of radiation-induced cardiotoxicity

Breast cancer survival is significantly improved over the past decades due to major improvements in anti-tumor therapies and the implementation of regular screening, which leads to early detection of breast cancer. Therefore, it is of utmost importance to prevent patients from long-term side effects, including radiotherapy-induced cardiotoxicity. Radiotherapy may contribute to damage of myocardial structures on the cellular level, which eventually could result in various types of cardiovascular problems, including coronary artery disease and (non-)ischemic cardiomyopathy, leading to heart failure. These cardiac complications of radiotherapy are preceded by alterations in myocardial perfusion and blood flow. Therefore, early detection of these alterations is important to prevent the progression of these pathophysiological processes. Several radionuclide imaging techniques may contribute to the early detection of these changes. Single-Photon Emission Computed Tomography (SPECT) cameras can be used to create Multigated Acquisition scans in order to assess the left ventricular systolic and diastolic function. Furthermore, SPECT cameras are used for myocardial perfusion imaging with radiopharmaceuticals such as ^99mTc-sestamibi and ^99mTc-tetrofosmin. Accurate quantitative measurement of myocardial blood flow (MBF), can be performed by Positron Emission Tomography (PET), as the uptake of some of the tracers used for PET-based MBF measurement almost creates a linear relationship with MBF, resulting in very accurate blood flow quantification. Furthermore, there are PET and SPECT tracers that can assess inflammation and denervation of the cardiac sympathetic nervous system. Research over the past decades has mainly focused on the long-term development of left ventricular impairment and perfusion defects. Considering laterality of the breast cancer, some early studies have shown that women irradiated for left-sided breast cancer are more prone to cardiotoxic side effects than women irradiated for right-sided breast cancer. The left-sided radiation field in these trials, which predominantly used older radiotherapy techniques without heart-sparing techniques, included a larger volume of the heart and left ventricle, leading to increased unavoidable radiation exposure to the heart due to the close proximity of the radiation treatment volume. Although radiotherapy for breast cancer exposes the heart to incidental radiation, several improvements and technical developments over the last decades resulted in continuous reduction of radiation dose and volume exposure to the heart. In addition, radiotherapy reduces loco-regional tumor recurrences and death from breast cancer and improves survival. Therefore, in the majority of patients, the benefits of radiotherapy outweigh the potential very low risk of cardiovascular adverse events after radiotherapy. This review addresses existing nuclear imaging techniques, which can be used to evaluate (long-term) effects of radiotherapy-induced mechanical cardiac dysfunction and discusses the potential use of more novel nuclear imaging techniques, which are promising in the assessment of early signs of cardiac dysfunction in selected irradiated breast cancer patients.

Reproducibility of deep inspiration breath-hold technique for left-side breast cancer with respiratory monitoring device, Abches

PURPOSE

This study aimed to evaluate the reproducibility of deep inspiration breath-hold (DIBH) using a respiratory control device, Abches, in patients with left-sided breast cancer.

MATERIAL AND METHODS

Abches comprises a main body, an indicator panel, and two fulcrums, one each on the chest and abdomen. Forty left side breast cancer patients treated with DIBH using abches were enrolled in this study. For all patients, CT images were taken three times to confirm the target position inside the body and to check the breath-hold reproducibility. Three anatomical points on the nipple, sternum, and heart were selected as measurement points on CT images. After measuring the coordinates, breath-hold reproducibility was defined as the mean of the absolute difference in the coordinates between the three CT images. The maximum differences were also investigated. In addition, the dice similarity coefficient (DSC) was calculated to examine the displacement of the heart volume in detail. Moreover, digitally reconstructed radiographs (DRRs) and linac graphs (LGs) were used to measure the positional accuracy of the chest and heart.

RESULTS

The reproducibility in all patients was within 0.75 mm for the nipple, 0.78 mm for the sternum, and 2.18 mm for the heart in each direction. Similarly, the maximum displacements for all patients were within 1.90 mm, 1.69 mm, and 4.75 mm, respectively, in each direction. For heart volume, the average DSC for all cases was 0.93 ± 0.01. The differences between the DRR and LG images were 1.70 ± 1.10 mm and 2.10 ± 1.60 mm, for the chest and heart, respectively.

CONCLUSION

Our study showed that DIBH using Abches can be performed with good target reproducibility of less than 3 mm with proper breath-hold practice, whereas the heartbeat-derived reproducibility of the cardiac position is poor and needs to be monitored carefully during treatment simulation.

Correlation of Optical Surface Respiratory Motion Signal and Internal Lung and Liver Tumor Motion: A Retrospective Single-Center Observational Study

Purpose: Surface-guided radiation therapy (SGRT) application has limitations. This study aimed to explore the relationship between patient characteristics and their external/internal correlation to qualitatively assess the external/internal correlation in a particular patient. Methods: Liver and lung cancer patients treated with radiotherapy in our institution were retrospectively analyzed. The external/internal correlation were calculated with Spearman correlation coefficient (SCC) and SCC after support vector regression (SVR) fitting (SCC_svr). The relationship between the external/internal correlation and magnitudes of motion of the tumor and external marker (A_i, A_e), tumor volume V_t, patient age, gender, and tumor location were explored. Results: The external/internal motions of liver and lung cancer patients were strongly correlated in the S-I direction, with mean SCC_svr values of 0.913 and 0.813. The correlation coefficients between the external/internal correlations and the patients’ characteristics (A_i, A_e, V_t, and age) were all smaller than 0.5; A_i, A_e and liver tumor volumes were positively correlated with the strength of the external/internal correlation, while lung tumor volumes and patient age were negative. The external/internal correlations in males and females were roughly equal, and the external/internal correlations in patients with peripheral lung cancers were stronger than those in patients with central lung cancers. Conclusion: The external/internal correlation shows great individual differences. The effects of A_i, A_e, V_t, and age are weakly to moderately correlated. Our results suggest the necessity of individualized assessment of patient's external/internal motion correlation prior to the application of SGRT technique for breath motion monitoring.

Target coverage and cardiopulmonary sparing with the updated ESTRO-ACROP contouring guidelines for postmastectomy radiation therapy after breast reconstruction: a treatment planning study using VMAT and proton PBS techniques

BACKGROUND

The European Society for Therapeutic Radiology and Oncology Advisory Committee in Radiation Oncology Practice (ESTRO-ACROP) recently released new contouring guidelines for postmastectomy radiation therapy (PMRT) after implant-based reconstruction (IBR). As compared to prior ESTRO guidelines, the new guidelines primarily redefined the chest wall (CW) target to exclude the breast prosthesis. In this study, we assessed the impact of these changes on treatment planning and dosimetric outcomes using volumetric-modulated arc therapy (VMAT) and proton pencil-beam scanning (PBS) therapy.

METHODS

We performed a treatment planning study of 10 women with left-sided breast cancer who underwent PMRT after IBR. All target structures were delineated first using standard (ESTRO) breast contouring guidelines and then separately using the new (ESTRO-ACROP) guidelines. Standard organs-at-risk (OARs) and cardiac substructures were contoured. Four sets of plans were generated: (1) VMAT using standard ESTRO contours, (2) VMAT using new ESTRO-ACROP contours, (3) PBS using standard contours, and (4) PBS using new contours.

RESULTS

VMAT plans using the new ESTRO-ACROP guidelines resulted in modest sparing of the left anterior descending coronary artery (LAD) (mean dose: 6.99 Gy standard ESTRO vs. 6.08 Gy new ESTRO-ACROP, p = 0.010) and ipsilateral lung (V₂₀: 21.66% vs 19.45%, p = 0.017), but similar exposure to the heart (mean dose: 4.6 Gy vs. 4.3 Gy, p = 0.513), with a trend toward higher contralateral lung (V₅: 31.0% vs 35.3%, p = 0.331) and CW doses (V₅: 31.9% vs 35.4%, p = 0.599). PBS plans using the new guidelines resulted in further sparing of the heart (mean dose: 1.05 Gy(RBE) vs. 0.54 Gy(RBE), p < 0.001), nearly all cardiac substructures (LAD mean dose: 2.01 Gy(RBE) vs. 0.66 Gy(RBE), p < 0.001), and ipsilateral lung (V₂₀: 16.22% vs 6.02%, p < 0.001).

CONCLUSIONS

PMRT after IBR using the new ESTRO-ACROP contouring guidelines with both VMAT and PBS therapy is associated with significant changes in exposure to several cardiopulmonary structures.

Impact of respiratory motion in dosimetric and clinical advantages for adjuvant left-sided breast radiotherapy

We investigated the organ-sparing effect of the deep inspiration breath hold (DIBH) technique among different levels of lung expansion for left-side breast radiotherapy. This retrospective study enrolled 30 patients who received adjuvant left breast radiotherapy after breast-conserving surgery (BCS). Simulation scans of both DIBH and deep breathing four-dimensional computed tomography (4DCT) were acquired, and three treatment plans were generated for each patient. One plan was based on the DIBH images, and the other two plans were based on the mid-lung expansion (ME) and initial lung expansion (IE) phases retrieved from 4DCT data sets. Dosimetric comparisons and normal tissue complication probability (NTCP) models were conducted. We used image registration for displacement analysis and sought potential factors related to the dose benefit of DIBH. The DIBH plans resulted significantly lower doses to the heart, left ventricle (LV) and left anterior descending coronary artery (LAD), including the high- to low-dose areas, followed by the ME plans and IE plans (p < 0.05). DIBH reduced the risk of long-term cardiac mortality by 40% and radiation pneumonitis of the left lung by 37.96% compared with the IE plans (p < 0.001). The reduction in the mean dose to the heart and LV significantly correlated with anterior displacement of the left lung. The DIBH technique is a feasible tool to provide dosimetric and clinical advantages for adjuvant left-sided breast radiotherapy. Breathing pattern and the level of lung expansion seem to play an important role.

Benefit of Deep Inspiratory Breath Hold for Right Breast Cancer When Regional Lymph Nodes Are Irradiated

BACKGROUND

Although deep inspiratory breath-hold (DIBH) is routinely used for left-sided breast cancers, its benefits for right-sided breast cancer (rBC) have yet to be established. We compared free-breathing (FB) and DIBH treatment plans for a cohort of rBC undergoing regional nodal irradiation (RNI) to determine its potential benefits.

METHODS AND MATERIALS

rBC patients considered for RNI (internal mammary nodal chains, supraclavicular field, with or without axilla) from October 2017 to May 2020 were included in this analysis. For each patient, FB versus DIBH plans were generated and dose volume histograms evaluated the following parameters: mean lung dose, ipsilateral lung V₂₀/V₅ (volumes of lung receiving 20 Gy and 5 Gy, respectively); mean heart dose and heart V₅ (volumes of heart receiving 5 Gy); liver V_{20 absolute} /V_{30 absolute} (absolute volume of liver receiving 20 Gy and 30 Gy, respectively), liver D_max, and total liver volume irradiated (TVI_liver). The dosimetric parameters were compared using Wilcoxon signed-rank testing.

RESULTS

Fifty-four patients were eligible for analysis, comparing 108 FB and DIBH plans. DIBH significantly decreased all lung and liver parameters: mean lung dose (19.7 Gy-16.2 Gy, P < .001), lung V₂₀ (40.7%-31.7%, P < .001), lung V₅ (61.2%-54.5%, P < .001), TVI_liver (1446 cc vs 1264 cc; P = .006) liver D_max (50.2 Gy vs 48.9 Gy; P = .023), liver V₂₀ (78.8-23.9 cc, P < .001), and liver V₃₀ (58.1-14.6 cc, P < .001) compared with FB. DIBH use did not significantly improve heart parameters, although the V_5Heart trended on significance (1.25-0.6, P = .067).

CONCLUSIONS

This is the largest cohort to date analyzing DIBH for RNI-rBC. Our findings demonstrate significant improvement in all lung and liver parameters with DIBH, supporting its routine consideration for rBC patients undergoing comprehensive RNI.

Quantifying inter- and intra-fraction variations of breast cancer radiotherapy with skin dose measurements

Aim. The aim of the current study was to compare between the deep inspiration breath-hold (DIBH) technique and free-breathing (FB) method in the treatment delivery uncertainty of breast cancer radiotherapy using skin dose measurements.Methods. In a prospective manner, eighty patients were randomly selected for skin dose measurements, and they were assigned to two groups. DIBH (40 patients) and FB (40 patients). The systematic inter-fraction dose variation was quantified using the mean percentage error (MPE) between the average measured total dose per session in three consecutive sessions and the corresponding calculated point dose from the treatment planning system. The random inter-fraction dose variation was quantified using the standard deviation (SD) of the dose delivered by the medial or lateral tangential fields, or the total session dose in the three sessions (SD_MT, SD_LT, or SD_total, respectively). While the random intra-fraction dose variation was quantified using the SD of the dose difference between the medial and lateral tangential fields in three consecutive sessions (SD_MT-LT).Results. There was no statistically significant difference in MPE between the DIBH and FB groups (p = 0.583). Moreover, the mean SD_totaland SD_MTof the DIBH group were significantly lower than that of the FB group (2.75 ± 2.33 cGy versus 4.45 cGy ± 4.33, p = 0.048) and (1.94 ± 1.63 cGy versus 3.76 ± 3.42 cGy, p = 0.007), respectively. However, there was no significant difference in the mean SD_LTand SD_MT-LTbetween the two groups (p > 0.05).Conclusion. In addition to the advantage of reducing the cardiopulmonary radiation doses in left breast cancer, the DIBH technique could reduce the treatment delivery uncertainty compared to the FB method due to the significant reduction in the random inter-fraction dose variations.

The dosimetric benefit of in-advance respiratory training for deep inspiration breath holding is realized during daily treatment in left breast radiotherapy: A comparative retrospective study of serial surface motion tracking

Introduction

A novel approach of in‐advancepreparatory respiratory training and practice for deep inspiration breath holding (DIBH) has been shown to further reduce cardiac dose in breast cancer radiotherapy patients, enabled by deeper (extended) DIBH. Here we investigated the consistency and stability of such training‐induced extended DIBH after training completion and throughout the daily radiotherapy course.

Methods

Daily chestwall motion from real‐time surface tracking transponder data was analysed in 67 left breast radiotherapy patients treated in DIBH. Twenty‐seven received preparatory DIBH training/practice (_prepTrn) 1–2 weeks prior to CT simulation, resulting in an extended DIBH (_extDIBH) and reduced cardiac dose at simulation. Forty had only conventional immediate pre‐procedure DIBH instruction without _prepTrn and without extended DIBH (non‐Trn group). Day‐to‐day variability in chestwall excursion pattern during radiotherapy was compared among the groups.

Results

The average of daily maximum chestwall excursions was overall similar, 2.5 ± 0.6 mm for _prepTrn/_extDIBH vs. 2.9 ± 0.8 mm for non‐Trn patients (P = 0.24). Chestwall excursions beyond the 3‐mm tolerance threshold were less common in the _prepTrn/_extDIBH group (18.8% vs. 37.5% of all fractions within the respective groups, P = 0.038). Among patients with cardiopulmonary disease those with _prepTrn/_extDIBH had fewer chestwall excursions beyond 3 mm (9.4% vs. 46.7%, P = 0.023) and smaller average maximum excursions than non‐Trn patients (2.4 ± 0.3 vs. 3.0 ± 0.6 mm, P = 0.047, respectively).

Conclusion

Similar stability of daily DIBH among patients with and without preparatory training/practice suggests that the training‐induced extended DIBH and cardiac dose reductions were effectively sustained throughout the radiotherapy course. Training further reduced beyond‐tolerance chestwall excursions, particularly in patients with cardiopulmonary disease.

Dosimetric Comparison of Radiation Techniques for Comprehensive Regional Nodal Radiation Therapy for Left-Sided Breast Cancer: A Treatment Planning Study

Purpose

How modern cardiac sparing techniques and beam delivery systems using advanced x-ray and proton beam therapy (PBT) can reduce incidental radiation exposure doses to cardiac and pulmonary organs individually or in any combination is poorly investigated.

Methods

Among 15 patients with left-sided breast cancer, partial wide tangential 3D-conformal radiotherapy (3DCRT) delivered in conventional fractionation (CF) or hypofractionated (HF) schedules; PBT delivered in a CF schedule; and volumetric modulated arc therapy (VMAT) delivered in an HF schedule, each under continuous positive airway pressure (CPAP) and free-breathing (FB) conditions, were examined. Target volume coverage and doses to organs-at-risk (OARs) were calculated for each technique. Outcomes were compared with one-way analysis of variance and the Bonferroni test, with p-values <0.05 considered significant.

Results

Target volume coverage was within acceptable levels in all interventions, except for the internal mammary lymph node D95 (99% in PBT, 90% in VMAT-CPAP, 84% in VMAT-FB, and 74% in 3DCRT). The mean heart dose (MHD) was the lowest in PBT (<1 Gy) and VMAT-CPAP (2.2 Gy) and the highest in 3DCRT with CF/FB (7.8 Gy), respectively. The mean lung dose (MLD) was the highest in 3DCRT-CF-FB (20 Gy) and the lowest in both VMAT-HF-CPAP and PBT (approximately 5-6 Gy). VMAT-HF-CPAP and PBT delivered a comparable maximum dose to the left ascending artery (7.2 and 6.13 Gy, respectively).

Conclusions

Both proton and VMAT in combination with CPAP can minimize the radiation exposure to heart and lung with optimal target coverage in regional RT for left-sided breast cancer. The clinical relevance of these differences is yet to be elucidated. Continued efforts are needed to minimize radiation exposures during RT treatment to maximize its therapeutic index.

Individualised selection of left-sided breast cancer patients for proton therapy based on cost-effectiveness

INTRODUCTION

The significantly greater cost of proton therapy compared with X-ray therapy is frequently justified by the expected reduction in normal tissue toxicity. This is often true for indications such as paediatric and skull base cancers. However, the benefit is less clear for other more common indications such as breast cancer, and it is possible that the degree of benefit may vary widely between these patients. The aim of this work was to demonstrate a method of individualised selection of left-sided breast cancer patients for proton therapy based on cost-effectiveness of treatment.

METHODS

16 left-sided breast cancer patients had a treatment plan generated for the delivery of intensity-modulated proton therapy (IMPT) and of intensity-modulated photon therapy (IMRT) with the deep inspiration breath-hold (DIBH) technique. The resulting dosimetric data was used to predict probabilities of tumour control and toxicities for each patient. These probabilities were used in a Markov model to predict costs and the number of quality-adjusted life years expected as a result of each of the two treatments.

RESULTS

IMPT was not cost-effective for the majority of patients but was cost-effective where there was a greater risk reduction of second malignancies with IMPT.

CONCLUSION

The Markov model predicted that IMPT with DIBH was only cost-effective for selected left-sided breast cancer patients where IMRT resulted in a significantly greater dose to normal tissue. The presented model may serve as a means of evaluating the cost-effectiveness of IMPT on an individual patient basis.

Real-time liver tracking algorithm based on LSTM and SVR networks for use in surface-guided radiation therapy

Background

Surface-guided radiation therapy can be used to continuously monitor a patient’s surface motions during radiotherapy by a non-irradiating, noninvasive optical surface imaging technique. In this study, machine learning methods were applied to predict external respiratory motion signals and predict internal liver motion in this therapeutic context.

Methods

Seven groups of interrelated external/internal respiratory liver motion samples lasting from 5 to 6 min collected simultaneously were used as a dataset, D_v. Long short-term memory (LSTM) and support vector regression (SVR) networks were then used to establish external respiratory signal prediction models (LSTMpred/SVRpred) and external/internal respiratory motion correlation models (LSTMcorr/SVRcorr). These external prediction and external/internal correlation models were then combined into an integrated model. Finally, the LSTMcorr model was used to perform five groups of model updating experiments to confirm the necessity of continuously updating the external/internal correlation model. The root-mean-square error (RMSE), mean absolute error (MAE), and maximum absolute error (MAX_AE) were used to evaluate the performance of each model.

Results

The models established using the LSTM neural network performed better than those established using the SVR network in the tasks of predicting external respiratory signals for latency-compensation (RMSE < 0.5 mm at a latency of 450 ms) and predicting internal liver motion using external signals (RMSE < 0.6 mm). The prediction errors of the integrated model (RMSE ≤ 1.0 mm) were slightly higher than those of the external prediction and external/internal correlation models. The RMSE/MAE of the fifth model update was approximately ten times smaller than that of the first model update.

Conclusions

The LSTM networks outperform SVR networks at predicting external respiratory signals and internal liver motion because of LSTM’s strong ability to deal with time-dependencies. The LSTM-based integrated model performs well at predicting liver motion from external respiratory signals with system latencies of up to 450 ms. It is necessary to update the external/internal correlation model continuously.

The necessity of using deep inspiration breath-hold in the radiotherapy of left breast cancer patients who undergo the UK FAST trial

Aim : The purpose of the current study was to compare between deep inspiration breath-hold (DIBH) and free-breathing (FB) method in the setup reproducibility and to perform a dosimetric comparison between both methods in left-sided breast cancer patients who undergo the UK FAST trial. Materials and methods : The online matching correction data were retrospectively collected for 50 patients treated with the FAST trial. They were equally divided into DIBH and FB groups to compare between both methods in the setup reproducibility and create the appropriate planning target volume (PTV) margin. Ten patients out of the fifty were scanned in DIBH and FB to perform a dosimetric comparison with the strict acceptance criteria of the FAST trial. Results : All heart dosimetric parameters of the DIBH was significantly lower than that of FB (p < 0.001), and the lung V30% of DIBH plans was significantly lower than FB plans (p = 0.03). There was no statistically significant difference between the two methods in the other organs at risk doses. To fulfill the heart and lung constraints in FB plans, the PTV V90% was reduced by 3.4%, and three plans would not attain the PTV acceptance criteria. There was no significant difference between the systematic or random setup errors between both methods except the left-right random shift was significantly lower in DIBH cases (p = 0.004). The calculated PTV margins were (4 mm, 3 mm, and 4 mm) for DIBH group, and (5 mm, 6 mm, and 8 mm) for FB group in the anterior-posterior, superior-inferior, and left-right shifts, respectively. Conclusion : It is highly warranted to treat left-sided breast cancer patients with the DIBH technique when the UK FAST trial is employed for treatment.

Identifying breast cancer patients who gain the most dosimetric benefit from deep inspiration breath hold radiotherapy

INTRODUCTION

Deep inspiration breath hold (DIBH) has been proven to reduce cardiac dose for women receiving left breast and chest wall radiation therapy. However, it utilises extra departmental resources and patient exertion. The aim of this exploratory study was to investigate if any factors existed that could identify breast cancer patients who may benefit most from DIBH, to facilitate appropriate utilisation of departmental resources.

METHODS

Left-sided breast cancer patients aged 18-70 years, and right-sided breast cancer patients with internal mammary nodes included, were recruited. DIBH and free breathing (FB) plans were created for all patients. Patient demographic and clinical history were recorded. Variables including lung threshold value, lung volume, patient separation, maximum heart in field, volume of planning target volume (PTV), heart dose, ipsilateral lung dose were compared between plans.

RESULTS

Plans for 31 patients were analysed. No correlations were found between lung threshold value or patient separation and cardiac dose. Moderate to strong correlations were found with BMI, PTV volume and lung volume change however no definitive thresholds were determined. A significant difference was found in the maximum heart in field between DIBH and FB (P < 0.001) with those patients with greater than 0.7 cm heart in the field on the FB scan demonstrating greater reductions in mean heart dose.

CONCLUSION

Maximum heart in the field of greater than 0.7 cm in FB could be a potential factor to identify patients who may benefit most from DIBH. This factor warrants investigation in a larger patient cohort to test its validity.

Characterisation of Time-of-Flight (ToF) imaging system for application in monitoring deep inspiration breath-hold radiotherapy (DIBH-RT)

The purpose of this study is to develop a method for characterisation of time-of-flight (ToF) imaging system for application in deep inspiration breath-hold radiotherapy (DIBH-RT). The performance of an Argos 3D P330 ToF camera (Bluetechnix, Austria) was studied for patient surface monitoring during DIBH-RT using a phantom to simulate the intra-patient and inter-patient stability of the camera. Patient setup error was also simulated by positioning the phantom at predefined shift positions (2, 5 and 10 mm) from the isocentre. The localisation accuracy of the phantom was measured using ToF imaging system and repeated using CBCT imaging alone (CBCT) and simultaneously using ToF imaging during CBCT imaging (ToF-CBCT). The mean and SD of the setup errors obtained from each of the imaging methods were calculated. Student t-test was used to compare the mean setup errors. Correlation and Bland-Altman analysis were also performed. The intra-and inter-patient stability of the camera were within 0.31 mm and 0.74 mm, respectively. The localisation accuracy in terms of the mean ±SD of the measured setup errors were 0.34 ± 0.98 mm, 0.12 ± 0.34 mm, and −0.24 ± 1.42 mm for ToF, CBCT and ToF-CBCT imaging, respectively. A strong correlation was seen between the phantom position and the measured position using ToF (r = 0.96), CBCT (r = 0.99) as well as ToF-CBCT (r = 0.92) imaging. The limits of agreement from Bland Altman analysis between the phantom position and ToF, CBCT and ToF-CBCT measured positions were −1.52, 2.31 mm, −0.55, 0.78 mm; and −3.03, 2.55 mm, respectively. The sensor shows good stability and high accuracy comparable to similar sensors in the market. The method developed is useful for characterisation of an optical surface imaging system for application in monitoring DIBH-RT.

Continuous positive airway pressure with deep inspiration breath hold in left-sided breast radiation therapy

A dosimetric study to evaluate the use of continuous positive airway pressure (CPAP), with free-breathing (CPAP-FB) or with deep inspiration breath hold (DIBH-CPAP) an adjunct and alternative to DIBH to reduce heart and lung dose in the radiation therapy (RT) of breast cancer planned for left side RT with regional nodes and internal mammary. A retrospective analysis of 10 left-sided breast cancer patients whose heart or lung dose constraints were not met after RT planning based on FB or DIBH simulations and were referred for CPAP-based planning. All patients were simulated using FB, DIBH, CPAP-FB, and CPAP-DIBH. Treatment plans were calculated to cover the breast/chest wall and regional nodes using tangential field-in-field technique (FiF). Dose-volume parameters for heart, ipsilateral lung, and contralateral breast were compared using the Wilcoxon signed-rank test. For all RT plans, mean heart dose (Gy) was lower for treatment plans with CPAP: CPAP-FB (mean 3.4 vs 7.4, p = 0.001) and CPAP-DIBH (mean 2.5 vs 7.4, p = 0.006) compared to FB alone. CPAP-DIBH also significantly reduced MHD as compared to DIBH alone (mean 2.5 vs 4.3 Gy, p = 0.013). CPAP-DIBH significantly reduced mean lung dose as compared to both FB (mean 14.4 vs 20.1, p = 0.005) and DIBH alone (mean 14.4 vs 17.4, p = 0.007). Eight of 10 patients did not meet ipsilateral lung V20Gy dose constraints (≥35% of lung receiving 20 Gy) in either the free breathing or DIBH plans, whereas 8 out of 10 met lung V20Gy goal constraints (≤30% of lung receiving 20 Gy) in the CPAP-DIBH plans. Based on the outcomes of our study, CPAP could be a strategy for reducing lung and heart dose, both in patients not able to execute DIBH and as an adjunct in those not deriving sufficient dose reduction from DIBH alone.

Dosimetry and Feasibility Studies of Volumetric Modulated Arc Therapy With Deep Inspiration Breath-Hold Using Optical Surface Management System for Left-Sided Breast Cancer Patients

Background

During radiotherapy (RT) procedure of breast cancer, portions of the heart and lung will receive some radiation dose, which may result in acute and late toxicities. In the current study, we report the experience of our single institution with organs at risk (OARs)–sparing RT with deep inspiration breath hold (DIBH) using an Optical Surface Management System (OSMS) and compare the dosimetric parameters with that of free breathing (FB).

Patients and Methods

Forty-eight cases diagnosed as early stage left-sided breast cancer scheduled for postoperative RT were enrolled. The OSMS was used to monitor the breathing magnitude and track the real-time respiratory status, which can control a stable lung and heart volume during RT delivery under DIBH. We did the dosimetric analysis of the heart, left anterior descending (LAD) coronary artery, lungs, and contralateral breast under FB and DIBH plans.

Results

Compared with FB–volumetric-modulated arc therapy (FB-VMAT), DIBH-VMAT resulted in significantly changed volumes to the heart and lungs receiving irradiation dose. The average mean heart dose and average D2%, V₅, and V₁₀ showed significant differences between the DIBH and FB techniques. For the LAD coronary artery, we found significantly reduced average mean dose, D2%, and V₁₀ with DIBH. Similar results were also found in the lungs and contralateral breast. The use of flattening-filter–free decreased treatment time compared with the flat beam mode in our VMAT (p < 0.05). For the 48 patients, there were no significant differences in the lateral, longitudinal, and vertical directions between OSMS and cone beam CT.

Conclusions

DIBH-VMAT with OSMS is very feasible in daily practice with excellent patient compliance in our single-center experience. Note that OSMS is an effective tool that may allow easier-to-achieve precise positioning and better and shorter position-verify time. Meanwhile, compared with FB, DIBH was characterized by lower doses to OARs, which may reduce the probability of cardiac and pulmonary complications in the future.

Dosimetric comparison of volumetric-modulated arc therapy and helical tomotherapy for adjuvant treatment of bilateral breast cancer

Purpose:

Dosimetric comparison between volumetric-modulated arc therapy (VMAT) and helical tomotherapy (HT) in the treatment of bilateral breast cancer (BBC).

Materials and methods:

Ten patients treated on HT were selected retrospectively. Dose prescription was 50 Gy in 25 fractions to breast/chest wall and supraclavicular fossa (SCF) while tumour bed was simultaneously boosted to 61 Gy in 25 fractions. VMAT plans were made with four mono-isocentric partial arcs. The monitoring unit (MU) and treatment time were used to quantify the treatment efficiency. Target volumes were compared for homogeneity index (HI), conformity index (CI) while organs at risk (OARs) were compared for relevant dose volumes and integral doses (IDs).

Result:

For targets, no significant difference is observed between VMAT and HT in CI but VMAT could give better HI. The mean lung dose, V20 and V5 is 10·6 Gy versus 8·4 Gy (p-value 0·03), 12% versus 11·5% (p-value 0·5) and 78·1% versus 43·4% (p-value 0·005), respectively. The mean heart dose, V30 and V5 is 4·9 Gy versus 4·7 Gy (p-value 0·88), 0·5% versus 1·5% (p-value 0·18) and 26·2% versus 22·8% (p-value 0·4). Integral dose (ID) for the whole body and heart are comparable: 289 Gy kg versus 299 Gy kg (p-value 0·24) and 2·9 Gy kg versus 2·8 Gy kg (p-value 0·80). ID for lungs was significantly higher with VMAT: 7·9 Gy kg versus 6·3 Gy kg (p-value 0·03). There is a 53% reduction in treatment time and 78% in MU with VMAT against HT.

Conclusion:

VMAT can generate clinically acceptable plans comparable to HT for BBC. HT shows better control over low dose spillage in lungs compared to VMAT thereby increasing ID to lungs. VMAT shows better homogeneity and efficient treatment delivery than HT.

Dosimetric and Radiobiological Comparison of Five Techniques for Postmastectomy Radiotherapy with Simultaneous Integrated Boost

Purpose

To compare five techniques for the postmastectomy radiotherapy (PMRT) with simultaneous integrated boost (SIB).

Materials and Methods

Twenty patients with left-sided breast cancer were retrospectively selected. Five treatment plans were created for each patient: TomoDirect (TD), unblocked helical TomoTherapy (unb-HT), blocked HT (b-HT), hybrid intensity-modulated radiotherapy (hy-IMRT), and fixed-field IMRT (ff-IMRT). A dose of 50.4 Gy in 28 fractions to PTV_total and 60.2 Gy in 28 fractions to PTV_boost were prescribed. The dosimetric parameters for targets and organs at risk (OARs), the normal tissue complication probability (NTCP), the second cancer complication probability (SCCP) for OARs, and the treatment efficiency were assessed and compared.

Results

TD plans and hy-IMRT plans had similar good dose coverage and homogeneity for both PTV_boost and PTV_total and superior dose sparing for the lungs and heart. The ff-IMRT plans had similar dosimetric results for the target volumes compared with the TD and hy-IMRT plans, but gave a relatively higher NTCP and SCCP for the lungs. The unb-HT plans exhibited the highest OAR mean dose, highest NTCP for the lungs (0.97 ± 1.25‰) and heart (4.58 ± 3.62%), and highest SCCP for the lungs (3.57 ± 0.05%) and contralateral breast (2.75 ± 0.29%) among all techniques. The b-HT plans significantly outperformed unb-HT plans with respect to the sparing of the lungs and heart. This technique also showed the best conformity index (0.73 ± 0.08) for PTV_boost and the optimal NTCP for the lungs (0.03 ± 0.03‰) and heart (0.61 ± 0.73%). Concerning the delivery efficiency, the hy-IMRT and ff-IMRT achieved much higher delivery efficiency compared with TomoTherapy plans.

Conclusion

Of the five techniques studied, TD and hy-IMRT are considered the preferable options for PMRT with SIB for left-sided breast cancer treatment and can be routinely applied in clinical practice.

Capacitive monitoring system for real-time respiratory motion monitoring during radiation therapy

Summary

This work introduces a novel capacitive‐sensing technology capable of detecting respiratory motion with high temporal frequency (200 Hz). The system does not require contact with the patient and has the capacity to sense motion through clothing or plastic immobilization devices.

Abstract

Purpose

This work presents and evaluates a novel capacitive monitoring system (CMS) technology for continuous detection of respiratory motion during radiation therapy. This modular system provides real‐time motion monitoring without any contact with the patient, ionizing radiation, or surrogates such as reflective markers on the skin.

Materials and methods

The novel prototype features an array of capacitive detectors that are sensitive to the position of the body and capable of high temporal frequency readout. Performance of this system was investigated in comparison to the RPM infrared (IR) monitoring system (Varian Medical Systems). The prototype included three (5 cm × 10 cm) capacitive copper sensors in one plane, located at a distance of 8–10 cm from the volunteer. Capacitive measurements were acquired for central and lateral‐to‐central locations during chest free‐breathing and abdominal breathing. The RPM IR data were acquired with the reflector block at corresponding positions simultaneously. The system was also tested during deep inspiration and expiration breath‐hold maneuvers.

Results

Capacitive monitoring system data demonstrate close agreement with the RPM status quo at all locations examined. Cross‐correlation analysis on RPM and CMS data showed an average absolute lag of 0.07 s (range: 0.03–0.23 s) for DIBH and DEBH data and 0.15 s (range: 0–0.43 s) for free‐breathing. Amplitude difference between the normalized CMS and RPM signal during chest and abdominal breathing was within 0.15 for 94.3% of the data points after synchronization. CMS performance was not affected when the subject was clothed.

Conclusion

This novel technology permits sensing of both free‐breathing and breath‐hold respiratory motion. It provides data comparable to the RPM system but without the need for an IR tracking camera in the treatment room or use of reflective markers on the patient.

Comparison of conventional and advanced radiotherapy techniques for left-sided breast cancer after breast conserving surgery

Whole breast radiotherapy (WBRT) after breast conserving surgery is the standard treatment to prevent recurrence and metastasis of early stage breast cancer. This study aims to compare seven WBRT techniques including conventional tangential, field-in-field (FIF), hybrid intensity-modulated radiotherapy (IMRT), IMRT, standard volumetric modulated arc therapy (STD-VMAT), noncoplanar VMAT (NC-VMAT), and multiple arc VMAT (MA-VMAT). Fifteen patients who were previously diagnosed with left-sided early stage breast cancer and treated in our clinic were selected for this study. WBRT plans were created for these patients and were evaluated based on target coverage and normal tissue toxicities. All techniques produced clinically acceptable WBRT plans. STD-VMAT delivered the lowest mean dose (1.1 ± 0.3 Gy) and the lowest maximum dose (7.3 ± 4.9 Gy) to contralateral breast, and the second lowest lifetime attributable risk (LAR) (4.1 ± 1.4%) of secondary contralateral breast cancer. MA-VMAT delivered the lowest mean dose to lungs (4.9 ± 0.9 Gy) and heart (5.5 ± 1.2 Gy), exhibited the lowest LAR (1.7 ± 0.3%) of secondary lung cancer, normal tissue complication probability (NTCP) (1.2 ± 0.2%) of pneumonitis, risk of coronary events (RCE) (10.3 ± 2.7%), and LAR (3.9 ± 1.3%) of secondary contralateral breast cancer. NC-VMAT plans provided the most conformal target coverage, the lowest maximum lung dose (46.2 ± 4.1 Gy) and heart dose (41.1 ± 5.4 Gy), and the second lowest LAR (1.8 ± 0.4%) of secondary lung cancer and RCE (10.5 ± 2.8%). MA-VMAT and NC-VMAT could be the preferred techniques for early stage breast cancer patients after breast conserving surgery.

Reducing Cardiac Radiation Dose From Breast Cancer Radiation Therapy With Breath Hold Training and Cognitive Behavioral Therapy

The delivery of radiation therapy shares many of the challenges encountered in imaging procedures. As in imaging, such as MRI, organ motion must be reduced to a minimum, often for lengthy time periods, to effectively target the tumor during imaging-guided therapy while reducing radiation dose to nearby normal tissues. For patients, radiation therapy is frequently a stress- and anxiety-provoking medical procedure, evoking fear from negative perceptions about irradiation, confinement from immobilization devices, claustrophobia, unease with equipment, physical discomfort, and overall cancer fear. Such stress can be a profound challenge for cancer patients' emotional coping and tolerance to treatment, and particularly interferes with advanced radiation therapy procedures where active, complex and repetitive high-level cooperation is often required from the patient.In breast cancer, the most common cancer in women worldwide, radiation therapy is an indispensable component of treatment to improve tumor control and outcome in both breast-conserving therapy for early-stage disease and in advanced-stage patients. High technological complexity and high patient cooperation is required to mitigate the known cardiac toxicity and mortality from breast cancer radiation by reducing the unintended radiation dose to the heart from left breast or left chest wall irradiation. To address this, radiation treatment in daily deep inspiration breath hold (DIBH), to create greater distance between the treatment target and the heart, is increasingly practiced. While holding the promise to decrease cardiac toxicity, DIBH procedures often augment patients' baseline stress and anxiety reaction toward radiation treatment. Patients are often overwhelmed by the physical and mental demands of daily DIBH, including the nonintuitive timed and sustained coordination of abdominal thoracic muscles for prolonged breath holding.While technologies, such as DIBH, have advanced to millimeter-precision in treatment delivery and motion tracking, the "human factor" of patients' ability to cooperate and perform has been addressed much less. Both are needed to optimally deliver advanced radiation therapy with minimized normal tissue effects, while alleviating physical and cognitive distress during this challenging phase of breast cancer therapy.This article discusses physical training and psychotherapeutic integrative health approaches, applied to radiation oncology, to leverage and augment the gains enabled by advanced technology-based high-precision radiation treatment in breast cancer. Such combinations of advanced technologies with training and cognitive integrative health interventions hold the promise to provide simple feasible and low-cost means to improve patient experience, emotional outcomes and quality of life, while optimizing patient performance for advanced imaging-guided treatment procedures - paving the way to improve cardiac outcomes in breast cancer survivors.

Dosimetric and clinical advantages of adapting the DIBH technique to hybrid solitary dynamic portal radiotherapy for left-sided chest-wall plus regional nodal irradiation

To evaluate the dosimetric and clinical advantages of using deep-inspiration breath-hold (DIBH) technique in hybrid solitary dynamic portal radiotherapy (hSDPRT) for left-sided chest-wall plus regional nodal irradiation and to demonstrate a simplified strategy for preclinical commissioning and calibration of DIBH-gating technique. Fifteen patients with left-sided breast cancer who underwent postmastectomy radiotherapy using hSDPRT were retrospectively evaluated. Two sets of planning-CT images were acquired for each patient, one with free/normal breathing and the other with DIBH. The hSDPRT plans were computed to deliver about 85% of the prescribed dose using static open fields and 15% of dose using a less complex solitary dynamic field. The dosimetric differences between the paired samples were compared using the Wilcoxon signed-rank test. For clinical commissioning of gated treatments, a respiratory simulator equipped with a microcontroller was programmed to simulate free-breathing and DIBH-patterns using a custom-developed android application. While both the hSDPRT plans displayed identical target coverage on both the image-sets, the DIBH technique resulted in statistically significant differences in various dose-volume metrics of heart, left-anterior-descending artery, and ipsilateral-lung structures. The hSDPRT plan with DIBH entails reduced total monitor unit (354.9 ± 13.6 MU) and breath-hold time ranging from 2.9 ± 0.3 to 13.7 ± 0.8 seconds/field, along with an acceptable impact on overall machine throughput. DIBH is a feasible method to effectively address the delivery uncertainty and produce substantial sparing of heart and lung when combined with hSDPRT. Streamlined procedures for commissioning and calibration of DIBH-gating technique are essential for more efficient clinical practice.

Evaluation of the heart and lung dosimetric parameters in deep inspiration breath hold using 3D Slicer

Purpose

The present study was conducted to compare dosimetric parameters for the heart and left lung between free breathing (FB) and deep inspiration breath hold (DIBH) and determine the most important potential factors associated with increasing the lung dose for left-sided breast radiotherapy using image analysis with 3D Slicer software.

Materials and Methods

Computed tomography-simulation scans in FB and DIBH were obtained from 17 patients with left-sided breast cancer. After contouring, three-dimensional conformal plans were generated for them. The prescribed dose was 50 Gy to the clinical target volume. In addition to the dosimetric parameters, the irradiated volumes and both displacement magnitudes and vectors for the heart and left lung were assessed using 3D Slicer software.

Results

The average of the heart mean dose (D_mean) decreased from 5.97 to 3.83 Gy and V₂₅ from 7.60% to 3.29% using DIBH (p < 0.001). Furthermore, the average of D_mean for the left lung was changed from 8.67 to 8.95 Gy (p = 0.389) and V₂₀ from 14.84% to 15.44% (p = 0.387). Both of the absolute and relative irradiated heart volumes decreased from 42.12 to 15.82 mL and 8.16% to 3.17%, respectively (p < 0.001); however, these parameters for the left lung increased from 124.32 to 223.27 mL (p < 0.001) and 13.33% to 13.99% (p = 0.350). In addition, the average of heart and left lung displacement magnitudes were calculated at 7.32 and 20.91 mm, respectively.

Conclusion

The DIBH is an effective technique in the reduction of the heart dose for tangentially treated left sided-breast cancer patients, without a detrimental effect on the left lung.

Liver dose reduction by deep inspiration breath hold technique in right-sided breast irradiation

Purpose

Deep inspiration breath hold (DIBH) is a well-established technique that enables efficient cardiac sparing in patients with left-sided breast cancer. The aim of the current study was to determine if DIBH is effective for reducing radiation exposure of of liver and other organs at risk in right breast radiotherapy (RT).

Materials and Methods

Twenty patients with right-sided breast cancer were enrolled in this study. Three-dimensional conformal RT plans were generated for each patient, with two different computed tomography scans of free breathing (FB) and DIBH. Nodes were contoured according to the Radiation Therapy Oncology Group contouring guidelines. Dose-volume histograms for the target volume coverage and organs at risk were evaluated and analyzed.

Results

DIBH plans showed significant reduction in mean liver dose (5.59 ± 2.07 Gy vs. 2.54 ± 1.40 Gy; p = 0.0003), V_20Gy (148.38 ± 73.05 vs. 64.19 ± 51.07 mL; p = 0.0003) and V_10Gy (195.34 ± 93.57 vs. 89.81 ± 57.28 mL; p = 0.0003) volumes compared with FB plans. Right lung doses were also significantly reduced in DIBH plans. Heart and left lung doses showed small but statistically significant improvement with application of the DIBH technique.

Conclusion

We report that the use of DIBH for right-sided breast cancer significantly reduces the radiation doses to the liver, lungs, and heart.

Cardio-Oncology: Vascular and Metabolic Perspectives: A Scientific Statement From the American Heart Association

Cardio-oncology has organically developed as a new discipline within cardiovascular medicine as a result of the cardiac and vascular adverse sequelae of the major advances in cancer treatment. Patients with cancer and cancer survivors are at increased risk of vascular disease for a number of reasons. First, many new cancer therapies, including several targeted therapies, are associated with vascular and metabolic complications. Second, cancer itself serves as a risk factor for vascular disease, especially by increasing the risk for thromboembolic events. Finally, recent data suggest that common modifiable and genetic risk factors predispose to both malignancies and cardiovascular disease. Vascular complications in patients with cancer represent a new challenge for the clinician and a new frontier for research and investigation. Indeed, vascular sequelae of novel targeted therapies may provide insights into vascular signaling in humans. Clinically, emerging challenges are best addressed by a multidisciplinary approach in which cardiovascular medicine specialists and vascular biologists work closely with oncologists in the care of patients with cancer and cancer survivors. This novel approach realizes the goal of providing superior care through the creation of cardio-oncology consultative services and the training of a new generation of cardiovascular specialists with a broad understanding of cancer treatments.

An effective patient training for deep inspiration breath hold technique of left-sided breast on computed tomography simulation procedure at King Chulalongkorn Memorial Hospital

Purpose

To observe the effectiveness of the practical instruction sheet and the educational video for left-sided breast treatment in a patient receiving deep inspiration breath hold (DIBH) technique. Two parameters, simulation time and patient satisfaction, were assessed through the questionnaire.

Methods

Two different approaches, which were the instruction sheet and educational video, were combinedly used to assist patients during DIBH procedures. The guideline was assigned at least 1 week before the simulation date. On the simulation day, patients would fill the questionnaire regarding their satisfaction with the DIBH instruction. The questionnaire was categorized into five levels: extremely satisfied to dissatisfied, sequentially. The patients were divided into four groups: not DIBH technique, DIBH without instruction materials, the DIBH with instruction sheet or educational video, and DIBH with both of instruction sheet and educational video.

Results

Total number of 112 cases of left-sided breast cancer were analyzed. The simulation time during DIBH procedure significantly reduced when patients followed the instruction. There was no significant difference in simulation time on the DIBH procedures between patient compliance via instruction sheet or educational video or even following both of them. The excellent level was found at 4.6 ± 0.1 and 4.5 ± 0.1, for patients coaching via instruction sheet as well as on the educational video, respectively.

Conclusion

Patient coaching before simulation could potentially reduce the lengthy time in the simulation process for DIBH technique. Practicing the DIBH technique before treatment is strongly advised.

Effects of Preparatory Coaching and Home Practice for Deep Inspiration Breath Hold on Cardiac Dose for Left Breast Radiation Therapy

AIMS

Deep inspiration breath hold (DIBH) reduces cardiac radiation exposure by creating cardiac-chest wall separation in breast cancer radiotherapy. DIBH requires sustaining chest wall expansion for up to 40 s and involves complex co-ordination of thoraco-abdominal muscles, which may not be intuitive to patients. We investigated the effect of in-advance preparatory DIBH coaching and home practice on cardiac doses.

MATERIALS AND METHODS

Successive patients from 1 February 2015 to 31 December 2016 with left-sided breast cancer who underwent tangential field radiotherapy utilising the DIBH technique were included. The study cohort consisted of patients treated by a physician who routinely provided DIBH coaching and home practice instructions at least 5 days before simulation. The control group included non-coached patients under another physician's care. Minimum, maximum and mean cardiac doses and V5, V10 and V30 from DIBH and free breathing simulation computed tomography scans were obtained from the planning system. DIBH and free breathing cardiac doses and volume exposures were compared between the coached and non-coached groups using the two-sample t-test, Fisher's exact test and the Mann-Whitney U-test.

RESULTS

Twenty-seven coached and 42 non-coached patients were identified. The DIBH maximum cardiac dose was lower in coached patients at 13.1 Gy compared with 19.4 Gy without coaching (P = 0.004). The percentage cardiac volume exposure in DIBH was lower in coached patients; the DIBH V10 was 0.5% without coaching and 0.1% with coaching (P = 0.005). There was also a trend towards lower DIBH V5 in the coached group compared with the non-coached group (1.2% versus 1.9%, P = 0.071). No significant differences in patient cardiopulmonary comorbidity factors that might influence cardiac doses were found between the groups.

CONCLUSIONS

Our results suggest that cardiac dose sparing can potentially be further improved with a 5 day regimen of preparatory DIBH coaching and in-advance home practice before simulation. These hypothesis-generating findings should be confirmed in a larger study.

Deep inspiration breath-hold intensity modulated radiation therapy in a large clinical series of 239 left-sided breast cancer patients: a dosimetric analysis of organs at risk doses and clinical feasibility from a single center experience

OBJECTIVE

To evaluate dose to organs at risk, target coverage and treatment compliance in left-sided breast cancer patients (LSBCP) treated with deep inspiration breath-hold (DIBH) and intensity modulated radiation therapy (IMRT) technique in a contest of daily clinical practice.

METHODS

A total of 280 consecutive LSBCP referred for adjuvant radiotherapy were systematically screened for suitability of DIBH technique. 239 were able to comply with the requirement for DIBH. Whole breast or chest wall were irradiated in DIBH, monitored by Varian RPM™ Respiratory Gating System, and two tangential inverse-planned beams with dynamic dose delivery. Dose prescription was 42.4 Gy/16 fractions in 205 patients and 50 Gy/25 fractions in 34. 23 patients received local and nodal treatment. Boost to tumor bed, of 10 Gy/5 fractions was used in 135 patients. Relevant dose metrics for heart, left anterior descending (LAD) coronary artery, lungs, contralateral breast and planning target volume were retrospectively analyzed.

RESULTS

The average mean heart dose (MHD) for all patients was 0.94 Gy and mean maximum LAD dose was 13.82 Gy. MHD and LAD maximum dose were significantly higher in patients treated with conventional fractionation whether expressed in absolute dose (1.44 vs 0.85 Gy, p < 0.0005 and 20.78 vs 12.45 Gy, p < 0.0005 respectively) or in equivalent doses of 2 Gy fractionation (0.88 vs 0.52 Gy, p =< 0.0005 and 17.68 vs 10.63 Gy, p = 0.0002 respectively). In 57 patients (23.8%) the maximum LAD dose was >20 Gy. Mean V20 ipsilateral lung dose was 8.5%. Mean doses of contralateral breast and lung were 0.13 Gy and 0.09 Gy respectively. Mean planning target volume V95% coverage was 96.1%. Compliance rate of DIBH technique was 84.5% (239/280).

CONCLUSION

DIBH and IMRT in daily clinical practice are feasible in high percentage of unselected patients and allows low levels of irradiation of organs at risk without compromising target coverage. However, despite low MHD a significant proportion of patients receives a maximum LAD dose superior to 20 Gy.

ADVANCES IN KNOWLEDGE

The value of MHD used exclusively is not able to describe entirely the risk of late heart toxicity, which can be better evaluated with the joint analysis of the maximum dose to LAD region. The vast majority of LSBCP referred to adjuvant radiotherapy in the setting of routine practice are able to comply with the requirement of DIBH.

Fraction-specific post-treatment quality assurance for active breath-hold radiation therapy

Purpose

The purpose of this study is to evaluate variation in the treatment hold pattern and quantify its dosimetric impact in breath-hold radiotherapy, using fraction-specific post-treatment quality assurance.

Material and Methods

A patient with lung mets treated using intensity-modulated radiation therapy (IMRT) with active breath coordinator (ABC) was recruited for the study. Treatment beam hold conditions were recorded for all the 25 fractions. The linearity and reproducibility of the dosimetric system were measured. Variation in the dose output of unmodulated open beam with beam hold was studied. Patient-specific quality assurance (PSQA) was performed with and without beam hold, and the results were compared to quantify the dosimetric impact of beam hold.

Results

There was a considerable amount of variation observed in the number of beam hold for the given field and the monitor unit at which the beam held. Linearity and reproducibility of the dosimetric system were found within the acceptable limits. The average difference over the 25 measurements was 0·044% (0·557 to −0·318%) with standard deviation of 0·248.

Conclusion

Patient comfort with the ABC system and responsiveness to the therapist communication help to maintain consistent breathing pattern, in turn consistent treatment delivery pattern. However, the magnitude of dosimetric error is much less than the acceptable limits recommended by IROC. The dosimetric error induced by the beam hold is over and above the dose difference observed in conventional PSQA.

Bragatston study protocol: a multicentre cohort study on automated quantification of cardiovascular calcifications on radiotherapy planning CT scans for cardiovascular risk prediction in patients with breast cancer

INTRODUCTION

Cardiovascular disease (CVD) is an important cause of death in breast cancer survivors. Some breast cancer treatments including anthracyclines, trastuzumab and radiotherapy can increase the risk of CVD, especially for patients with pre-existing CVD risk factors. Early identification of patients at increased CVD risk may allow switching to less cardiotoxic treatments, active surveillance or treatment of CVD risk factors. One of the strongest independent CVD risk factors is the presence and extent of coronary artery calcifications (CAC). In clinical practice, CAC are generally quantified on ECG-triggered cardiac CT scans. Patients with breast cancer treated with radiotherapy routinely undergo radiotherapy planning CT scans of the chest, and those scans could provide the opportunity to routinely assess CAC before a potentially cardiotoxic treatment. The Bragatston study aims to investigate the association between calcifications in the coronary arteries, aorta and heart valves (hereinafter called 'cardiovascular calcifications') measured automatically on planning CT scans of patients with breast cancer and CVD risk.

METHODS AND ANALYSIS

In a first step, we will optimise and validate a deep learning algorithm for automated quantification of cardiovascular calcifications on planning CT scans of patients with breast cancer. Then, in a multicentre cohort study (University Medical Center Utrecht, Utrecht, Erasmus MC Cancer Institute, Rotterdam and Radboudumc, Nijmegen, The Netherlands), the association between cardiovascular calcifications measured on planning CT scans of patients with breast cancer (n≈16 000) and incident (non-)fatal CVD events will be evaluated. To assess the added predictive value of these calcifications over traditional CVD risk factors and treatment characteristics, a case-cohort analysis will be performed among all cohort members diagnosed with a CVD event during follow-up (n≈200) and a random sample of the baseline cohort (n≈600).

ETHICS AND DISSEMINATION

The Institutional Review Boards of the participating hospitals decided that the Medical Research Involving Human Subjects Act does not apply. Findings will be published in peer-reviewed journals and presented at conferences.

TRIAL REGISTRATION NUMBER

NCT03206333.

A Retrospective Dosimetric Study of Radiotherapy Patients with Left-Sided Breast Cancer; Patient Selection Criteria for Deep Inspiration Breath Hold Technique

Background: Several studies have investigated cardiac dose reduction when utilizing the deep inspiration breath hold (DIBH) technique in patients undergoing radiotherapy for left-sided breast cancer. This paper aims to recommend potential selection criteria based on a retrospective single institute study of free breathing (FB) and DIBH computed tomography (CT) simulation planning scans. Methods: Dosimetric comparisons were performed retrospectively for 20 patients correlating the dose reduction and patient anatomical factors (anatomical variation of chest shape, chest wall separation, total lung volume (TLV) and others). Results: Paired t-tests demonstrated significant cardiac dose reduction for most patients but not all. Minimal cardiac dose reduction was observed for three patients using their DIBH plan, with one patient receiving a higher dose. Linear regression analysis identified a positive correlation between the patient’s TLV (on the FB CT simulation scan) and the magnitude of dosimetric benefit received (0.4045 R²). Conclusion: The TLV measured on a FB plan could potentially be utilised to predict cardiac exposure and assist with patient selection for DIBH. This is important in resource allocation, as DIBH may be unnecessarily recommended for some patients with little dosimetric benefit.

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.

Low cardiac and left anterior descending coronary artery dose achieved with left-sided multicatheter interstitial-accelerated partial breast irradiation

PURPOSE

Studies have shown that an additional mean dose of 1 Gy to the heart can increase the relative risk of cardiac events. The purpose of this study was to quantify the dose delivered to the heart and left anterior descending artery (LAD) in a series of patients with left-sided breast cancer (BC) or ductal carcinoma in situ treated with multicatheter-accelerated partial breast irradiation (MC-APBI) at a single institution.

METHODS AND MATERIALS

Patients with left-sided BC or ductal carcinoma in situ treated consecutively from 2005 to 2011 with MC-APBI were retrospectively identified. Cardiac and LAD contours were generated for each patient. Cardiac dosimetry and distance to the planning target volume were recorded. Patient health records were reviewed and cardiac events were recorded based on Common Terminology Criteria for Adverse Events version 4.0.

RESULTS

Twenty consecutive patients with left-sided BC treated with MC-APBI were retrospectively identified. Median followup was 41.4 months. Mean equivalent dose in 2 Gy fractions delivered to the heart and LAD were 1.3 (standard deviation: 0.7, range: 0.2-2.9) and 3.8 (standard deviation: 3.0, range: 0.4-11.3) Gy, respectively. There was an inverse linear relationship (R2 = 0.52) between heart-to-lumpectomy cavity distance and mean heart equivalent dose in 2 Gy fractions. One patient (5%) experienced symptomatic cardiac toxicity.

CONCLUSIONS

MC-APBI consistently delivers average doses to the heart and LAD that are similar to those achieved in most series with deep inspiration breath-hold and lower than free-breathing radiotherapy techniques. Distance from the heart to the lumpectomy cavity and the availability of other heart-sparing technologies should be considered to minimize the risk of cardiac toxicity.

Intrafractional motion management in external beam radiotherapy

The recent advancements in radiotherapy technologies have made delivery of the highly conformal dose to the target volume possible. With the increasing popularity of delivering high dose per fraction in modern radiotherapy schemes such as in stereotactic body radiotherapy and stereotactic body ablative therapy, high degree of treatment precision is essential. In order to achieve this, we have to overcome the potential difficulties caused by patient instability due to immobilization problems; patient anxiety and random motion due to prolonged treatment time; tumor deformation and baseline shift during a treatment course. This is even challenging for patients receiving radiotherapy in the chest and abdominal regions because it is affected by the patient's respiration which inevitably leads to tumor motion. Therefore, monitoring of intrafractional motion has become increasingly important in modern radiotherapy. Major intrafractional motion management strategies including integration of respiratory motion in treatment planning; breath-hold technique; forced shallow breathing with abdominal compression; respiratory gating and dynamic real-time tumor tracking have been developed. Successful intrafractional motion management is able to reduce the planning target margin and ensures planned dose delivery to the target and organs at risk. Meanwhile, the emergency of MRI-linear accelerator has facilitated radiation-free real-time monitoring of soft tissue during treatment and could be the future modality in motion management. This review article summarizes the various approaches that deal with intrafractional target, organs or patient motion with discussion of their advantages and limitations. In addition, the potential future advancements including MRI-based tumor tracking are also discussed.

Dosimetric evaluation and systematic review of radiation therapy techniques for early stage node-negative breast cancer treatment

Radiation therapy (RT) is essential in treating women with early stage breast cancer. Early stage node-negative breast cancer (ESNNBC) offers a good prognosis; hence, late effects of breast RT becomes increasingly important. Recent literature suggests a potential for an increase in cardiac and pulmonary events after RT. However, these studies have not taken into account the impact of newer and current RT techniques that are now available. Hence, this review aimed to evaluate the clinical evidence for each technique and determine the optimal radiation technique for ESNNBC treatment. Currently, six RT techniques are consistently used and studied: 1) prone positioning, 2) proton beam RT, 3) intensity-modulated RT, 4) breath-hold, 5) partial breast irradiation, and 6) intraoperative RT. These techniques show dosimetric promise. However, limited data on late cardiac and pulmonary events exist due to challenges in long-term follow-up. Moving forward, future studies are needed to validate the efficacy and clinical outcomes of these current techniques.