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ORIGINAL ARTICLE
Year : 2017  |  Volume : 13  |  Issue : 1  |  Page : 56-61

A dosimetric analysis of cardiac dose with or without active breath coordinator moderate deep inspiratory breath hold in left sided breast cancer radiotherapy


1 Department of Radiotherapy, Amrita School of Medicine, Amrita Viswa Vidyapeetham University, Ernakulam, Kerala, India
2 Department of Medical Physics, Amrita School of Medicine, Amrita Viswa Vidyapeetham University, Ernakulam, Kerala, India

Date of Web Publication16-May-2017

Correspondence Address:
Beena Kunheri
Amrita School of Medicine, Amrita Vishwa Vidyapeetham, Ernakulam, Kerala
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jcrt.JCRT_1414_16

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 > Abstract 

Background and Aim: Cardiac toxicity is a major concern for left breast tangential field irradiation. The left ventricle and left anterior descending (LAD) artery are suggested to be radiosensitive and radiation to these structures leads to late lethal cardiotoxicity. Moderate deep inspiration breath hold (mDIBH) during radiation treatment delivery helps in reducing the cardiac dose. This study compares dosimetric parameters of heart with and without active breath coordinator (ABC) mDIBH during tangential field breast cancer radiation.
Study Type: This is a dosimetric comparative study.
Materials and Methods: Forty-five consecutive patients with left-sided breast cancer who underwent breast-conserving surgery and adjuvant tangential field and radiotherapy with ABC mDIBH between November 2013 and September 2015 in our center were analyzed in this study. The ABC device was used for respiratory control and patients who could hold their breath for 20–30 s were considered for radiation with ABC mDIBH. Simulation scans of both free breathing (FB) and ABC mDIBH were done. Tangent field treatment plans with a dose prescription of 40 Gy/15 Fr were generated for each patient, in both scans. Target coverage, dose to the heart, LAD, and the left lung were documented with dose-volume histograms.
Results: Statistical Package for the Social Sciences, version 20 software, was used for analysis and the level of significance was set at P < 0.05. Mean heart dose was 308.5cGy with FB and 159cGy with ABC (P < 0.0001). Mean dose to the LAD was reduced by 53.81% (1320.64 cGy vs. 606.56 cGy, P < 0.001). Target coverage was equal in both the plans.
Conclusion: We report that the use of ABC mDIBH technique resulted in a significant reduction in cardiac dose and hence can be considered as a promising tool for cardiac sparing.

Keywords: ABC moderate deep inspiration breath hold, cardiac dose, radiotherapy, tangent field


How to cite this article:
Kunheri B, Kotne S, Nair SS, Makuny D. A dosimetric analysis of cardiac dose with or without active breath coordinator moderate deep inspiratory breath hold in left sided breast cancer radiotherapy. J Can Res Ther 2017;13:56-61

How to cite this URL:
Kunheri B, Kotne S, Nair SS, Makuny D. A dosimetric analysis of cardiac dose with or without active breath coordinator moderate deep inspiratory breath hold in left sided breast cancer radiotherapy. J Can Res Ther [serial online] 2017 [cited 2019 Nov 20];13:56-61. Available from: http://www.cancerjournal.net/text.asp?2017/13/1/56/206237


 > Introduction Top


Breast cancer comprises the most common type of cancer in females worldwide.[1] Radiation therapy (RT) is an integral part of breast cancer management after breast conservation surgery (BCS) and after mastectomy if risk factors are present.[2] According to the most recent Early Breast Cancer Trialists' Collaborative Group meta-analyses, adjuvant RT after BCS reduces the rate of breast cancer mortality compared to surgery alone.[3] However, as the survival improves for breast cancer patients, the long-term morbidity of RT becomes a concern.[4] Comprehensive RT for breast cancer targets the breast, chest wall, and lymph nodes when indicated. The proximity of these targets to critical structures can cause radiation-induced toxicity. The common late side effects of RT include fibrosis, telangiectasia, pigmentation of skin, and lymphedema. Rare but serious problems are cardiac and lung morbidity. Many studies had shown increased cardiac mortality and morbidity after breast radiotherapy and any dose to heart is significant.[4],[5],[6],[7],[8],[9],[10],[11]

Left-sided breast radiotherapy is associated with increased risk of coronary artery disease.[9],[11],[12] The dose distribution in the heart is not homogeneous and the highest doses are likely to be delivered to the anterior heart, especially left anterior descending (LAD) artery, which is one of the typical sites of origin for ischemic heart disease.[13] The dose to the LAD which is suggested to be radiosensitive may play a role in lethal cardiotoxicity.[9],[13],[14] RT-related cardiotoxicity may be affected by several factors including volume of heart within radiation field, dose, fraction size, LAD, and left ventricular doses.[14],[15],[16],[17],[18] Moreover, cardiotoxicity of RT in breast cancer patients may further be enhanced by the use of some chemotherapeutic agents such as anthracyclines. Cardiac dose-volume parameters should be thoroughly optimized in breast cancer RT to avoid potential cardiac toxicities of treatment.

Improvements in techniques of RT have helped decrease cardiac doses over the years. Besides 3D-based planning and intensity modulation, nowadays, respiratory management strategies are also being used to reduce cardiac dose in breast cancer RT. Active breath coordinator (ABC) system, first developed by Wong et al., offers an effective respiratory management strategy which can be used to improve cardiac sparing in breast cancer RT with the advantages of separating heart and target by changing the internal anatomy with moderate deep inspiration breath hold (mDIBH).[19] The benefit with different techniques largely depends on the individual patient anatomy.

To analyze the proposed benefit with mDIBH, in our population, we have compared the dosimetric parameters with and without using ABC-mDIBH technique in left-sided breast cancer tangential irradiation.


 > Materials and Methods Top


Inclusion criteria

From December 2013 to August 2015, 45 consecutive patients with left-sided breast cancer after BCS or breast reconstruction who underwent tangential RT with ABC-mDIBH technique were included in this analysis. Inclusion criteria included age ≤65 years, Eastern Cooperative Oncology Group performance score 0–1, no previous RT to the breast, no history of any cardiac and lung disease, and patients with a comfortable breath hold duration of 20–25 s.

Radiation treatment workflow

Pretreatment patient education

All the patients were explained regarding ABC mDIBH procedure. Before simulation computed tomography (CT) scan, all patients were given training for 3 days with the ABC (Elekta) device to enhance patient compliance and to determine individual (mDIBH) levels, which was set at 75% of maximum inspiratory capacity.

Simulation and treatment planning

All patients were simulated in supine position with both arms above head, using a breast board. Palpable breast tissue and visible surgical scar were marked with radiopaque wires. After acquiring a steady breathing pattern, two sets of CT images were acquired for each patient with a slice thickness of 2.5 mm, one with mDIBH with ABC system and the other with free breathing (FB). Threshold for breath holding and breath hold duration were documented.

The gross tumor volume, clinical target volume (CTV), and organ at risk were delineated on the Monaco contouring station on both the scans as per the Radiation Therapy Oncology Group breast contouring guidelines for breast cancer. Treatment Planning was done using XiO Planning system [Figure 1] and [Figure 2]. To improve consistency, the same physician performed all contouring procedures and the same physicist performed the treatment planning procedures. All patients were planned to receive a whole breast dose of 40 Gy in 15 fractions as in START B protocol [20] using 6 MV photons.
Figure 1: Radiation plan in ABC moderate deep inspiration breath hold scan

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Figure 2: Radiation plan in free breathing scan

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Dose-volume parameters

Total lung volume (TLV), total cardiac volume, and maximum heart distance (MHD) were all documented in both scans for each patient. Dose-volume histograms (DVHs) were generated for all delineated structures in both plans. For the heart, mean dose (Dmean), maximum dose (Dmax), and percentage volumes receiving doses ≥5 Gy (V5), 10 Gy (V10), 15 Gy (V15), 20 Gy (V20), 25 Gy (V25), 30 Gy (V30), 35 Gy (V35), and 40 Gy (V40) were recorded. MHD is defined as the maximum perpendicular distance from the posterior border of the tangential field to the cardiac border. For the ipsilateral lung, Dmean, Dmax, and percentage volumes receiving doses ≥5 Gy (V5), 10 Gy (V10), 15 Gy (V15), 20 Gy (V20), 25 Gy (V25), 30 Gy (V30), 35 Gy (V35), and 40 Gy (V40) were recorded. For the LAD, Dmean and Dmax were recorded, and for the breast, D90%, D95%, Dmean, and Dmax were recorded. V20, mean lung dose (MLD), and TLV were calculated for both right and left lungs.

Statistical analysis

The Kolmogorov–Smirnov test was used to detect whether the variables were normally distributed or not. After the assessment of all variables for normal distribution, variables with normal distribution were analyzed using paired t-test while variables with nonnormal distributions were analyzed using Wilcoxon signed-rank test. In descriptive statistics, mean and standard deviation was used for normally distributed variables which were analyzed using the paired t-test. Statistical Package for the Social Sciences, version 20 software (IBM SPSS Statistics for Windows, Armonk, NY: IBM Corporation), was used for analysis and the level of significance was set at P< 0.05.

Ethical approval

This study was approved by the Institutional Review Board. All procedures performed involving human participants were in accordance with the ethical standards of the institutional and/or the National Research Committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. This is only a dosimetric comparison with no intervention in the actual treatment delivered, and patient identity was not revealed.


 > Results Top


All the 45 patients' data with ninety CT scans were analyzed. The median age was 45.2 years (29–62 years). Nine patients had Stage I (20%), 24 patients had Stage IIA (53.3%), eight patients had Stage IIB (17.8%), and four patients had Stage IIIA (8.9%) disease.

The mean threshold for breath holding was 1.33 L. The mean breath hold duration was 24.28 s. CT scans using mDIBH showed a significant larger TLV. The mean increase in the TLV was 73.98%. Smaller MHD was observed in mDIBH scan when compared with scans performed in FB. The mean MHD in FB and mDIBH scans was 2.37 cm and 1.3 cm, respectively.

The dose-volume parameters of the heart, LAD, left lung, both lungs, and CTV volume were compared for each patient using DVH generated for FB and mDIBH scans as shown in [Table 1],[Table 2],[Table 3]. The mDIBH with ABC technique significantly reduced Dmean and Dmax heart dose compared to FB. There was also a significant reduction in all the heart dose-volume parameters.
Table 1: Cardiac dose-volume parameters

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Table 2: Left lung dose-volume parameters

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Table 3: Dose-volume parameters of both lungs, left anterior descending, and breast

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The average mean heart dose (Dmean) was reduced from 308.5 cGy (with FB) to 159 cGy (with ABC) (P < 0.0001). The relative reduction in average mean heart dose was 45.3%. The average relative reduction in average Dmax heart dose was 12.94%. The corresponding relative reductions in the average maximum and mean doses to LAD were 37.3% and 53.81%, respectively.

The MLD with mDIBH was 608.75 cGy and with FB was 646.08 cGy which showed a nonsignificant reduction of 1.53%. The difference in the lung dose-volume parameters was not significant. There was no significant difference in the breast CTV target dose parameters in both plans.


 > Discussion Top


Late cardiac morbidity is a serious concern for left-sided breast cancer patients who receive tangential RT, especially in the younger age group. Hence, integration of respiratory motion management to reduce the cardiac dose has been widely studied in the past few years. Delivering treatment to left breast using ABC technique has been shown to reduce dose to both heart and LAD artery.

Lu et al. had shown that mDIBH could reduce the volume of heart by increasing the intrathoracic pressure, thereby increasing the distance between the heart and chest wall.[21]

Vikström et al. in their study with 17 patients had shown that respiratory gating with deep inspiration breath hold (DIBH) significantly reduces cardiac and pulmonary doses for tangentially treated left-sided breast cancer patients. The mean heart dose was reduced from 3.7 Gy to 1.7 Gy. The study also showed reduction in pulmonary doses from 12% to 10%.[22]

Aznar et al. in their review of 24 patients who received adjuvant RT for left-sided breast cancer indicated that both whole heart and LAD should be taken into account while delivering RT for breast cancer.[13] They reported that the arch of the LAD is considered to receive an unacceptably high dose when any part of the contoured volume receives 20 Gy or more. The whole LAD is considered to be receiving a high dose when over 10% of the contoured volume received 20 Gy or more. It has been suggested that if 5% of the heart receives 40 Gy, the risk of cardiac mortality exceeds 2%.

Lee et al. showed a statistically significant reduction in mean heart dose and LAD.[23] The mean heart doses with DIBH and FB were 2.52 Gy and 4.53 Gy, respectively. The mean LAD dose with DIBH was 16.01 Gy and with FB was 26.26 Gy, and all had P< 0.001. However, the mean left lung doses with DIBH and FB were 7.53 Gy and 8.03 Gy, respectively, which were not different significantly compared with FB.

Limitations of most of these earlier studies were small sample size and most of the authors commented that the absolute benefit in an individual patient is decided by the patients' chest wall and cardiac relationship. Published literature in this regard from our country and our continent is sparse and hence this well-powered dosimetric comparison was aimed to quantify the proposed benefit in our population.

In our study, we have analyzed 45 patients' dosimetric data. The patients in our study were younger with a median age of 45.2 years. The volume of the heart was smaller with mDIBH when compared to FB. There was a significant reduction in the mean heart dose with mDIBH (45.3%) when compared to FB. Our study showed a benefit of 53.81% reduction in the mean LAD dose when compared to FB. There was a 73% increase in mean TLV with mDIBH when compared to FB. However, there was no significant difference in the lung dose-volume parameters. Our study is well powered compared to other studies and it proves that mDIBH with ABC is feasible and effective in our population also.

Respiratory management for breast cancer patients is relatively easy to implement in clinical practice compared to other novel techniques such as intensity-modulated radiation therapy (IMRT) which has been favored as another alternative method in reducing cardiac doses. Low-dose spill to critical normal structures in IMRT can also be avoided using respiratory gating with mDIBH technique.

Since it is a dosimetric study, clinical endpoints in terms of cardiac morbidity and survival were not evaluated. Correlation of clinical outcome with cardiac dose-volume parameters in the future may enable to predict the dose reduction needed to reduce the cardiac morbidity and mortality in adjuvant left-sided breast cancer RT. Darby et al. from Oxford after a retrospective study concluded that rate of coronary event increases by 7.4% for increase of every 1 Gy to the heart [10,24] and NSABP 51 study recommended a mean cardiac dose of <4 Gy for left-sided breast irradiation, and both emphasize the need for cardiac dose reduction in breast cancer radiotherapy.


 > Conclusion Top


From this dosimetric comparison, we can conclude that mDIBH with ABC technique has a great impact on dose-volume parameters of heart and LAD. The mean heart dose and mean LAD dose showed a significant reduction of 45.3% and 53.81%, respectively, with ABC mDIBH technique. These reductions achieved are likely to result in reduced long-term cardiac morbidity and mortality. Therefore, respiratory management strategy is a promising tool which can be routinely implemented for the tangential field radiation treatment of patients with left-sided breast cancer.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
 > References Top

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Aznar MC, Korreman SS, Pedersen AN, Persson GF, Josipovic M, Specht L. Evaluation of dose to cardiac structures during breast irradiation. Br J Radiol 2011;84:743-6.  Back to cited text no. 13
    
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22.
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23.
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24.
Taylor CW, Wang Z, Macaulay E, Jagsi R, Duane F, Darby SC. Exposure of the heart in breast cancer radiation therapy: A systematic review of heart doses published during 2003 to 2013. Int J Radiat Oncol Biol Phys 2015;93:845-53.  Back to cited text no. 24
    


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