Evaluation and Improving Treatment Plans of Gated Radiotherapy in Left-Sided Breast Cancer Patients Using Respiratory Motion Management System for Deep Inspiration Breath-Hold (DIBH)

Background: One essential part of treating breast cancer is radiation therapy. Patients with breast cancer are more likely to develop cardiac problems and die if they accidentally expose their hearts to radiation. In order to minimize radiation exposure to the heart, the deep inspiration breath-hold technique (DIBH) has been implemented into clinical practice. This study aimed to assess the use of the Varian Respiratory Motion Management System (RGSC) for radiation application in DIBH, with a focus on dosimetric plan comparison and treatment planning during free breathing (FB) and DIBH

Methods and Material: This prospective clinical trial comprised 100 patients with left-sided breast cancer who had undergone breast-conserving surgery. Gating control and the RGS system were employed for therapy application. Analytical anisotropic algorithm (AAA) was used to generate dual treatment plans after CT data were obtained in FB and DIBH. Using the Dose Volume Histogram (DVH), dosimetric output parameters of organs at risk were compared.

Results: The RGSC is connected to the LINAC systems and enables con- tinuous, touchless respiratory motion tracking using a camera. After each patient underwent dual treatment planning, 50 patients received treatment in Intensity Modulated Radiotherapy (IMRT) using DIBH, while 50 more patients received treatment in IMRT using Free Breath (FB). The mean cardiac dose reduction for DIBH in these patients was 7.23 to 3.41 Gy when compared to FB.

Conclusion: The current data demonstrate that RT could greatly lower mean doses to the heart and high-dose locations by implementing the DIBH approach.

Introduction

Like other nations throughout the world, breast cancer is among the most prevalent diseases in Bangladesh. Although breast cancer is most common in women, it can occasionally affect men as well [1]–[3]. Between 2018 and 2024, Combined Military Hospital (CMH) treated about 2500 patients with radiation therapy; of these, 21% had breast cancer, 9.8% had cancer on the right side, and 11.2% had cancer on the left. The majority of the patients (70%) were between the ages of 34 and 53. Of them, we have chosen 100 patients with left-sided breast cancer for this study. Fifty of the patients have radiation therapy using the Deep Inspiration Breath-hold technique (DIBH), and another fifty patients receive free breathing (FB).

One of the most useful techniques for lowering the cardiac and lung dose during left-side breast irradiation is deep inspiration breath hold, or DIBH [4]–[6]. The method is based on the fact that the diaphragm’s thickening and the lungs’ expansion during inhalation cause the heart to move away from the chest wall [7]–[10] (see Fig. 1).

Fig. 1. FB (a), DIBH (b), and combined CT (c) image showing heart to target volume distance.

The most widely used and well-documented method for heart sparing is called deep inspiration breath-hold, or DIBH [8]. It is regarded as a reliable and safe method of breast irradiation with good PTV coverage that exhibits encouraging outcomes in lowering late cardiac toxicities [11]–[13].

To irradiate the PTV volume, intensity-modulated radiation therapy (IMRT) treatment planning has been completed [14], [15]. An improved method for conformal therapy and three-dimensional treatment planning is called IMRT. It can induce condensation and optimize the delivery of irradiation to volumes with uneven shapes [16]. In particular, a number of studies showed that radiation exposure to cardiac tissue raises the risk of cardiac mortality and cardiovascular illness. As a matter of fact, the risk of major coronary events increased by 4%–16% with every Gray (Gy) of mean heart dose (MHD) [14]. The cardiac dosage for hypofractionation left breast irradiation decreased by 25.4% in DIBH. The mean dosage to the heart was considerably lower in DIBH for cardiac doses [17], [18].

Due to the heart’s close proximity to the target or targets, this is especially concerning for patients with left-sided breast cancer or those undergoing regional nodal irradiation. The majority of the evidence on radiation-induced cardiac damage comes from research done before three-dimensional conformal radiotherapy (3DCRT) was widely used [5]. However, since 3DCRT was implemented, radiation procedures have advanced, resulting in more accurate, conformal treatments. For locoregional left-sided breast radiation, volumetric modulated arc therapy (VMAT), an IMRT approach, has demonstrated benefits comparable to those of static gantry IMRT in a significantly shorter amount of time.

Modern photon approaches such as IMRT and VMAT require careful consideration since low-dose scatter is sacrificed for high-dose conformance and organ at-risk sparing [19]. Deep inspiration breath hold, or DIBH, can also help lower cardiac dosages [20], [21]. For patients who are appropriately chosen the first time around, tangential breast irradiation with the Active Breathing control (ABC) device and DIBH approach has the potential to drastically reduce irradiated heart volume.

Next, the Real-time Position Management (RPM) system was used to track the anterior-posterior (AP) motion of the abdomen while breath-holding was being done. Subsequently, surface-guided DIBH technology for left-sided breast cancer radiation therapy was launched. A surface-guided radiation therapy (SGRT) system continuously tracked the patient’s vertical motion throughout each treatment session, and an audio-visual patient feedback system was used to automate gating control (beam on/off). Using the Respiratory Gating System (RGSC) with IMRT, we observed in our study the advantages of DIBH over FB.

For patients with left-sided breast cancer or those receiving regional nodal irradiation, this is of special concern due to the proximity of the heart to the target(s). In previous studies, they used somewhat outdated technology like (ABC, RPM, and 3DCRT) [22]. The majority of the evidence on radiation-induced cardiac damage comes from research done before three-dimensional conformal radiotherapy (3DCRT) was widely used. However, since 3DCRT was implemented, radiation procedures have advanced, resulting in more accurate, conformal treatments.

For locoregional left-sided breast radiation, volumetric modulated arc therapy (VMAT), an IMRT approach, has demonstrated benefits comparable to those of static gantry IMRT in a significantly shorter amount of time [23]. Current photon approaches such as VMAT and IMRT require careful consideration since low-dose scatter is sacrificed for high-dose conformance and organ at-risk sparing. Deep inspiration breath hold, or DIBH, can also help lower cardiac dosages [17], [20]–[23]. For well-chosen patients, the first time around during tangential breast irradiation, the Active Breathing control (ABC) device and DIBH approach have the potential to dramatically reduce irradiated heart volume [24], [25].

The Real-time Position Management (RPM) system was used to track abdominal anterior-posterior (AP) motion while breath-holding was being done [26]. Following that, surface-guided DIBH treatment for left-sided breast cancer was introduced. A surface-guided radiation therapy (SGRT) system continuously tracked the patient’s vertical motion throughout each treatment session, and an audio-visual patient feedback system was used to automate gating control (beam on/off) [27]. In contrast to earlier research, which used somewhat antiquated technologies such as ABC, RPM, and 3DCRT, our study examined the advantages of DIBH versus FB when employing a Respiratory Gating System (RGSC) with IMRT.

Materials

Immobilization Devices

The Breast Board, Wing Board, Headrest, Index Bar, Tilting Base Plate, Foot Rest, and Breast Mask were used for patient setup.

Respiratory Gating System

Four dots Marker, Detection Camera, and Execution Monitor were used for motion management (see Fig. 2).

Fig. 2. DIBH tracking web form use for CT data accusation and treatment delivery.

PET-CT Simulator

Biograph mCT, Siemence Healthcare Ltd. (20 Slice) machine was used for image acquisition.

Treatment Planning System

The treatment planning was done using Varian Eclipse v15.1 Algorithm (AAA).

Method

Patient Selection

The Combined Military Hospital’s Cancer Center in Dhaka, Bangladesh, provided the data. Every patient had supraclavicular (SC) full breast irradiation (WBI) using tangential fields. The recommended dosage for the PTV breast (breast or thoracic wall), lymph nodes (LN), and intramammary lymph node chain (IMN) was 40.05 Gy in 15 fractions, or 2.67 Gy each fraction. Every patient with left-sided breast cancer who could hold their breath for at least 30 seconds while using 70% to 80% of their maximum inspiratory capacity was taken into consideration. Twenty seconds was chosen as the minimum for each hold time criterion.

Experimental Group (N1)

50 patients were treated with the DIBH technique.

Experimental Group (N2)

50 patients were treated with a free-breathing (FB) system.

Sample Selection

Subjects were selected prospectively and randomly following the inclusion and exclusion criteria mentioned below.

Inclusion and Exclusion Criteria

The inclusion criteria for the study required participants to be 18 years or older, of either sex and diagnosed with either metastatic or non-metastatic disease. However, pregnant women were excluded from the study.

Sample Size

50 individuals with breast cancer on the left side were included in this investigation. Both the free-breathing (FB) system and the DIBH approach were measured. (DiBH group sample size: N1, free-breathing (FB) group sample size: N2). The sample size for both groups was 50 patients. The z-test is usually used for larger sample sizes, while the t-test is appropriate for smaller sample sizes (usually less than 30 per group).

Training Session

The patient’s inspiration level for treatment and the length of the breath hold were determined during the training session. To track the patient’s respiratory motion, an RGSC infrared four-dot marker was positioned in the middle of the patient’s chest, directly over the diaphragm. The patients were instructed to exhale freely, then to inhale and hold their breath for at least thirty seconds at a comfortable level that was somewhat less than their maximal inspiration capacity. It was intended to repeat this cycle two or three times in a row. The rehearsal was captured on camera. A lower and an upper threshold were applied to the respiratory signal to define the gating window after a comfortable deep inspiration level was achieved. A moveable bar was positioned to track the patient’s chest movements, guaranteeing the deep inspiration amplitude could be repeated. For the purpose of treatment planning, a CT scan was carried out in these circumstances.

CT Simulation for DIBH and FB Patients

Prior to the CT simulation, the patients were educated regarding the DIBH procedure. They were told to begin practicing breath-hold training multiple times a day at least one week prior to the CT simulation day. The patient was placed in the head-first supine posture, with both arms elevated above the head, using a wing-board immobilization device for the CT simulation and treatment. FB and DIBH patients were simulated using a PET-CT simulation machine (Biograph mCT, Siemence Healthcare Ltd., 20 Slice) prior to radiation therapy. For the purpose of ray seeking, the patient’s body was covered in four radiopaque markers and a radiopaque wire. The acquisition of CT images was done independently for the DIBH and FB patients. Respiratory motion was tracked using the Varian respiratory gating system (RGSC) system (Varian Medical Systems). To ensure that it did not obstruct the pathways of tangential rays, the RGS infrared four dots marker was positioned in the middle of the patient’s chest, on top of the diaphragm.

Treatment Planning

CT data was imported into the Digital Imaging and Communications in Medicine (DICOM) treatment planning system. The RTOG contouring atlas has been used to contour the PTV and OARs in both FB- and DIBH CT images. It was the senior radiation oncologist who contoured. This strategy was used to reduce the contouring uncertainties as much as feasible. PTV borders were established by including the chest wall in the PTV and adding an extra 1 cm of margin. The Varian treatment planning system, version 15.1, employed the Anisotropic Analytical Algorithm (AAA) in the Eclipse treatment planning system for calculating dosages. The planned CT scans were obtained during DIBH and FB and included slices of the whole chest spaced 2.5 mm apart. Using both CT data sets, treatment plans were developed in accordance with accepted practices. In most cases, 6 MV tangential opposing photon beams were employed. To increase target coverage, a combination of 6 and 10 MV photon beams was required for certain patients. Boluses were employed to adjust for dosage buildup in certain mastectomy patients whose fields were formed using millennium 120-leaf multileaf collimators. The target means of the two breathing conditions (FB and DIBH) were used to standardize the plans. Every target was managed based on internal standards for dose uniformity, which ranged from 95% to 107% of the recommended dosage. The sixth to ninth step and shoot fields are used in IMRT plans to properly design the plan (see Fig. 3).

Fig. 3. IMRT treatment Plan for FB (a) and DIBH (b) in lt side breast cancer.

Planning Dose Optimization

The dose volume histogram has been used to optimize dose planning (DVH). Lung dosage and heart dose have been computed. Heart mean dose (HMD), heart dosage at V25%, and heart dose at V30% have been taken into consideration for heart dose optimization. To optimize lung dose, lung mean dose (LMD) and lung dose at V20% have been explored (see Figs. 4 and 5).

Fig. 4. Dose Volume Histogram (DVH) for FB IMRT treatment plan.

Fig. 5. Dose Volume Histogram (DVH) for DIBH IMRT treatment plan.

Analysis

In this work, we examined the dosimetric parameters for patients receiving Intensity-Modulated Radiation Therapy (IMRT) for the left breast utilizing two distinct methods: Free Breathing (FB) and Deep Inspiration Breath Hold (DIBH). The analysis comprised 100 patients in total; 50 of them were treated with the DIBH approach, and the remaining 50 were treated with the FB technique.

Data Collection

• Information was gathered for the subsequent parameters:
• Measurements of Heart Doses (mean dose in Gy)
• Measurements of Ipsilateral Lung Doses (mean dose in Gy)
• V25 (Heart%): The volume of the heart that receives a minimum of 25% of the recommended dosage.
• Heart%, or V30, is the volume of the heart that receives at least 30% of the recommended dosage.
• V20 (Lung%): The volume of the ipsilateral lung that receives 20% or more of the recommended dosage.

Statistical Analysis

To compare the means of these parameters between the DIBH and FB groups, we used independent samples t-tests. Since it compares the means of two independent groups and ascertains whether there is a statistically significant difference between them, the t-test is applicable in this situation.

The t-tests were carried out using the Python programming language. The ttest_ind function of the scipy.stats library was used to determine the t-statistics and p-values.

Results

According to the RTOG dose constrain, the comparison of Lung doses and heart doses between DIBH and FB are presented in Tables I–V.

Table I. T-test Results for Heart Dose (DMean) Measurements in Left Breast IMRT

Measurement	DIBH group	FB group
Sample size (n)	50	50
Mean (Gy)	3.41	7.23
Standard deviation (Gy)	0.33	0.83
t-statistic	−27.63
p-value	1.55 × 10−31 (< 0.0001)
Degrees of freedom	49
Significance level (α)	0.05

Table II. T-test Results for Ipsilateral Lung Mean Dose Measurements in Left Breast IMRT

Metric	DIBH group	FB group
Sample size (n)	50	50
Mean (Gy)	12.90	17.57
Standard deviation (Gy)	0.98	0.90
t-statistic	−23.24
p-value	4.10 × 10−28 (< 0.0001)
Degrees of freedom	49
Significance level (α)	0.05

Table III. T-test Results for Heart Dose (V25%) in Left Breast IMRT

Metric	DIBH group	FB group
Sample size (n)	50	50
Mean (%)	0.22	3.07
Standard deviation (%)	0.25	0.55
t-statistic	−30.95
p-value	7.96 × 10−34(< 0.0001)
Degrees of freedom	49
Significance level (α)	0.05

Table IV. T-test Results for Heart Dose (V30%) in Left Breast IMRT

Metric	DIBH Group	FB Group
Sample Size (n)	50	50
Mean (%)	0.03	1.09
Standard Deviation (%)	0.10	0.21
t-statistic	−32.55
p-value	7.60 × 10−35 (< 0.0001)
Degrees of Freedom	49
Significance Level (α)	0.05

Table V. T-test Results for Ipsilateral Lung Dose (V20%) in Left Breast IMRT

Metric	DIBH group	FB group
Sample size (n)	50	50
Mean (%)	21.06	26.10
Standard deviation (%)	1.20	1.07
t-statistic	−22.40
p-value	2.14 × 10−27 (< 0.0001)
Degrees of freedom	49
Significance level (α)	0.05

Discussion

The significant advantages of Deep Inspiration Breath Hold (DIBH) in lowering radiation exposure to vital organs are highlighted by a comparison of dose measurements for lung and heart tissues between FB (Free Breathing) and DIBH (Deep Inspiration Breath Hold) procedures. Given that the mean heart dosage with DIBH is 3.41 Gy instead of 7.23 Gy with FB, this indicates that the approach is efficient in reducing cardiac exposure (see Table I).

This decrease is consistent with research by Sakyanun et al. [5] and Yamauchi et al. [4], which emphasize the enhanced left anterior descending coronary artery and heart sparing associated with DIBH. Additionally, in line with studies from Lai et al. [9] and Bruzzaniti et al. [18], the volumes of the heart receiving high doses (V25 and V30) are significantly reduced with DIBH, who noted that the risk of cardiac problems is decreased by DIBH, which greatly lowers high-dose volumes (see Tables III and IV).

For pulmonary tissue, DIBH exhibits a definite benefit as well. In accordance with findings from Oechsner et al. [7] and Gaál et al. [8], who found lower lung doses and better dose distribution with DIBH, the average lung dosage with DIBH is 12.90 Gy, as opposed to 17.57 Gy with FB (see Tables I and V).

The results of Koivumäki et al. [13] and Xiao et al. [11], who highlighted the technique’s efficacy in avoiding exposure to high radiation doses and potentially lowering the risk of pulmonary problems, are further supported by the fact that the volume of the lung receiving 20 Gy is smaller with DIBH. Together, these results highlight the clinical benefits of DIBH in improving the safety and effectiveness of radiation therapy for left-sided breast cancer by lowering dose exposure to the heart and lungs.

Conclusion

The comparison of lung and heart dose estimations between FB (Free Breathing) and DIBH (Deep Inspiration Breath Hold) approaches shows that employing DIBH in radiation therapy has distinct advantages.

Heart Dose

In addition to volumes receiving lower radiation thresholds, such 5 Gy or 10 Gy, which are more pertinent for lowering the risk of cardiac toxicity, DIBH dramatically lowers the mean dose to the heart. Particularly for left-sided breast cancer, the significant decrease in heart dosage that comes with DIBH is essential for reducing the risk of long-term cardiac problems and enhancing the overall safety profile of radiation therapy.

Lung Dose

The amount of the lung receiving 20 Gy and the mean dose to the lung are both markedly reduced by DIBH. By lowering the chance of radiation-induced lung damage, this decrease improves patients’ long-term results.

The findings demonstrate how well DIBH works to lower radiation doses to the heart and lungs, which may improve patient outcomes and lower the chance of radiation-related adverse effects. These results provide compelling evidence for the use of DIBH as the recommended approach in radiation therapy, particularly for patients who are more likely to experience pulmonary or cardiac problems.