Which technique of positioning and immobilization is better for breast cancer patients in postmastectomy IMRT, single‐pole or double‐pole immobilization?

Abstract Purpose Our purpose was to explore which immobilization is more suitable for clinical practice in postmastectomy intensity modulation radiotherapy, the single‐pole position or the double‐pole position? Methods Patients treated with postmastectomy intensity modulation radiotherapy were eligible. They were selected randomly for single‐pole position or double‐pole position. Dose–volume histogram (DVH) was used to evaluate plans. After their first radiotherapy, the physicians asked a question about the comfort level of their position. The dosimetric parameters, comfort levels, and reproducibility of the two immobilization techniques were collected and analyzed after all patients had finished the whole radiotherapy. Results Totally, 94 patients were enrolled. Of these, 54 patients were treated with the single‐pole position, 28 (51.9%)had left‐sided lesions. While 40 patients were treated with the double‐pole position, 20 (50%) had left‐sided lesions. Patients’ characteristics in two groups were comparable. The single‐pole and double‐pole immobilizations had similar conformity (0.60 ± 0.05 vs 0.60 ± 0.06, P = 0.887) and homogeneity index (0.14 ± 0.03 vs 0.13 ± 0.03, P = 0.407). Compared to single‐pole position, double‐pole position typically increased the mean dose, V 20, and V 30 of heart (P < 0.05). Moreover, patients in the single‐pole group felt more comfortable than another group (P < 0.05). There was no difference in reproducibility between the two groups (P > 0.05). Conclusions Single‐pole position seems to be more comfortable and can reduce dose coverage to heart. Both devices allow for reproducible setup and acceptable dosimetry.


2.B | Radiotherapy
All patients underwent standard exposure and were supinated on the breast bracket with both arms extended above their head. Their heads were turned to the contralateral side of the affected breast as much as they could.
2.B.1 | Single-pole position (Fig. 2) 1. The single pole was on the ipsilateral side of the head.
2. The arm on the treatment side abducted to 90°with both hands gripping the single pole. Hoses filled with computed tomography (CT) contrast agent were used to mark the caudal border, lateral border, and the cranial border of the target volume, as well as the mastectomy scar area. The caudal border was defined as 1 cm below the margin of the contralateral mammary gland. The lateral border was at the mid-axillary line.
The cranial border of the chest wall skin was the infraclavicular edge.
The ipsilateral chest wall below the clavicle was covered with a 5 mm thermoplastic mold to reduce setup errors.
A large-aperture CT-simulation was performed in the treatment position on the breast bracket. The CT scan was performed using a 5-mm slice thickness, with scanning range running from the base of the skull to the lower edge of the liver. The CT images were exported to the Pinnacle 9.2 Treatment Planning System for clinical contouring of target volume. The clinical target volume (CTV) was defined to consist of ipsilateral chest wall, mastectomy scar, the supraclavicular and infraclavicular lymphatic drainage areas. Each CTV of the chest wall and regional lymph node were delineated according to breast cancer atlas for radiation therapy planning consensus definitions of the Radiation Therapy Oncology Group (RTOG). 5 The borders of the CTV for chest wall were as follows: (a) the cranial border was marked at inferior border of the clavicular head; (b) the caudal border was marked at the contralateral inframammary fold; (c) the anterior border was 2 mm below the skin surface; (d) the posterior border was rib-pleural interface; (e) the lateral border was at the mid-axillary line; (6) the medial border was the ipsilateral sternocostal junction. The chest wall CTV was expanded XIANG ET AL.
| 169 by 5 mm to construct planning target volume (PTV), while still conserving 2 mm under the skin surface integrity. Organs at risk (OARs) including bilateral lungs, heart and spinal cord, and contralateral breast were contoured. The heart was contoured along with pericardial sac. The superior aspect (or base) of the contour began at the level of the inferior aspect of the pulmonary artery passing the midline and extended inferiorly to the apex of the heart. 6 Our department utilized a multiple beam integrated plan, and a simplified IMRT plan was generated using Pinnacle treatment planning software (version 9.2). All plans were optimized to cover the entirety of the PTVs and spare surrounding normal tissues as much as possible. For the purpose of improving skin sparing dose and avoiding calculation errors of a dose built-up area, a daily 5-mm bolus was placed on the chest wall of each patient. The optimization process started with dose-volume constraints such as: (a) 95% of PTV receiving 50 Gy in 25 fractions; (b) the percent volume of PTV receiving 110% prescription dose was ≤5%; (c) ≤1% of the spinal cord received ≤40 Gy; (d) ≤30-35% of the ipsilateral lung was exposed to ≤20 Gy; (e) ≤20% of the total lung got ≤20 Gy; (f) the heart mean dose remaining at ≤10 Gy for left-sided lesions and ≤6 Gy for right-sided lesions. The priority was high for PTV, heart, and lung constraints relative to other structures. We always restricted the dose to hearts and lungs under the dose-volume constraints first, and then guaranteed the PTV dose next. Optimization proceeded until no further improvement was seen. All treatments were delivered T A B L E 1 Patients' characters.

Parameters
Single-pole Double-pole P value

2.C | Conformity index (CI)
For determination of the conformity index of PTV, we used the following definition: where V Tref is the target volume covered by the 95% isodose line, V ref is the treated volume covered by the 95% isodose line and VT is the volume of target. The CI value range is 0-1, the greater value means the better conformity. 7

2.D | Homogeneity index (HI)
To determine the homogeneity index of PTV, we used the following where D median is the median dose to the TV, D 2 and D 98 are the maximum and minimum dose that covers 2% and 98% volume of the PTV on dose-volume histogram. Lower HI correlates with a more homogeneous target dose. 8

2.E | Comfort levels
Comfort refers to a sense of being in a physically and spiritually healthy and peaceful state. It means individual's body and mind are relaxed and satisfied, with no anxiety nor pain. 9 Comfort includes physical comfort, psychological comfort, social and cultural comfort, and a comfortable environment. 10 In some previous studies on comfort levels, researchers used visual analog scores to assess the patients' comfort levels. Hamilton  uncomfortable.) We collected the answers of the two groups and compared the differences in their respective comfort zones.

2.F | Reproducibility
When patients were first treated, they were immobilized according to the positioning mark provided by the CT simulator. An electronic portal imaging device (EPID) was used each week for real-time verification, and data about the patients' left-right (X), craniocaudal (Y), and ventrodorsal (Z) setup deviations were collected for analysis. We adopted the coordinate system used in the report ICRU 62, in which the X-axis represents the left and right direction, the Y-axis represents the cranial and caudal direction, and the Z-axis indicates the anterior and posterior direction. 12 The anterior, right, and caudal directions were defined as positive values, while the posterior, left, and cranial directions were defined as negative values. 12 Total 3D vector error was defined using the formula: 13 The larger the value of the total 3D vector, the greater would be the overall setup displacement. 14

2.G | Plan evaluation
For dosimetric analysis, the following parameters extracted from dose-volume histograms (DVHs) were used:   compare the comfort levels of the two groups. All measurement data were expressed as mean ± standard deviation (mean ± SD), P < 0.05 were considered statistically significant.

| RESULTS
Patients' characteristics of two groups and the proportion of leftsided and right-sided lesions per group (Table 1) have no significant differences, P > 0.05.    Table 4 presented setup deviations of left-right (X), craniocaudal (Y), ventrodorsal (Z), and total 3D vector error. There was no difference in X, Y, Z, and total 3D vector error between the two groups, P > 0.05.

3.D | Comfort levels
As for comfort levels, the single-pole position group had a higher comfort rate (81.5%) than that in double-pole position group (37.5%) (P < 0.05, Table 5).

| DISCUSSION
With the development of precision radiotherapy, the goal of radiotherapy is minimizing the risk of normal tissue damage while delivering a dose distribution that will result in a high level of local control. 15  radiotherapy, but it is expensive and has technical challenges of program implementation; therefore, it has not been widely adopted in clinical practice. 16  There are publications trying to have predictors of heart dose with various measurements. 19,20 Investigators used the cranial-caudal distance of the heart in contact with the anterior chest wall or the "4th Arch" metric to explore the influence of anatomic features in women at risk of cardiac exposure from whole breast radiotherapy. Therefore, the anatomy factors might affect the heart dose in the two positions. We would like to bring the anatomy features in our further study. However, our conclusion might be just a random result in the double-pole position, and further studies are needed to confirm our result.
In addition to the radiation dose and the reproducibility, the comfort levels of patients are also important. The diagnosis of breast cancer and the followed breast cancer treatments always made the patients felt anxious. Radiotherapy in itself is a stress factor for patients. 21 The first factor affecting patient compliance is anxiety, and the second one is physical discomfort. The more comfortable the patients felt, the lower levels of anxiety the patients presented.
So we also paid attention to identify the relationship between the setup devices and the patients' comfort. In Kolcaba's study, they used guided imagery to increase patients' comfort. Then, they designed a tool to measure the comfort levels of early breast cancer patients who underwent radiotherapy. 22 The