Comparison among four immobilization devices for whole breast irradiation with Helical Tomotherapy

Upright patient positioning for gantry-free breast radiotherapy: feasibility tests using a robotic chair and specialised bras

For external beam radiotherapy using photons or particles, upright patient positioning on a rotating, robotic chair (a gantry-less system) could offer substantial cost savings. In this study, we considered the feasibility of upright breast radiotherapy using a robotic radiotherapy chair, for (i) a cohort of 9 patients who received conventional supine radiotherapy using photons for a diagnosis of primary breast cancer, plus (ii) 7 healthy volunteers, selected to have relatively large bra cup sizes. We studied: overall body positioning, arm positioning, beam access, breast reproducibility, and comfort. Amongst the healthy volunteer cohort, the impact of specialised radiotherapy bras upon inframammary skinfolds (ISF) was also determined, for upright treatment positions. In conclusion, upright body positioning for breast radiotherapy appears to be comfortable and feasible. Of the 9 patients who received conventional, supine radiotherapy (mean age 63.5 years, maximum age 90 years), 7 reported that they preferred upright positioning. Radiotherapy bras were effective in reducing/eliminating ISF for upright body positions, including for very large breasted volunteers. For upright proton radiotherapy to the breast, beam access should be straightforward, even for arms-down treatments, as en-face field directions are typically used. For photon radiotherapy, additional research is now required to investigate beam paths and whether, for certain patients, additional immobilisation will be required to keep the contralateral breast free from exposure. Future research should also investigate arm supports custom-designed for upright radiotherapy.

In Silico Studies of the Impact of Rotational Errors on Translation Shifts and Dose Distribution in Image-Guided Radiotherapy

Objective: To compare the 6-dimensional errors of different immobilization devices and body regions based on 3-dimensional cone beam computed tomography for image-guided radiotherapy and to further quantitatively evaluate the impact of rotational corrections on translational shifts and dose distribution based on anthropomorphic phantoms. Materials and Methods: Two hundred ninety patients with cone beam computed tomographies from 3835 fractions were retrospectively analyzed for brain, head & neck, chest, abdomen, pelvis, and breast cases. A phantom experiment was conducted to investigate the impact of rotational errors on translational shifts using cone beam computed tomography and the registration system. For the dosimetry study, pitch rotations were simulated by adjusting the breast bracket by ±2.5°. Roll and yaw rotations were simulated by rotating the gantry and couch in the planning system by ±3.0°, respectively. The original plan for the breast region was designed in the computed tomography image space without rotation. With the same planning parameters, the original plan was transplanted into the image space with different rotations for dose recalculation. The effect of these errors on the breast target and organs at risk was assessed by dose-volume histograms. Results: Most of the mean rotational errors in the breast region were >1°. A single uncorrected yaw of 3° caused a change of 2.9 mm in longitudinal translation. A phantom study for the breast region demonstrated that when the pitch rotations were -2.5° and 2.5° and roll and yaw were both 3°, the reductions in the planning target volumes-V_{50 Gy} were 20.07% and 29.58% of the original values, respectively. When the pitch rotation was +2.5°, the left lung V_{5 Gy} and heart Dmean were 7.49% and 165.76 Gy larger, respectively, than the original values. Conclusions: Uncorrected rotations may cause changes in the values and directions of translational shifts. Rotational corrections may improve the patient setup and dose distribution accuracy.

Clinical utility of a new immobilization method in image-guided intensity-modulated radiotherapy for breast cancer patients after radical mastectomy

OBJECTIVE

To investigate clinical utility of a new immobilization method in image-guided intensity-modulated radiotherapy (IMRT) for breast cancer patients after radical mastectomy.

MATERIALS AND METHODS

Forty patients with breast cancer who underwent radical mastectomy and postoperative IMRT were prospectively enrolled. The patients were randomly and equally divided into two groups using both a carbon-fiber support board and a hollowed-out cervicothoracic thermoplastic mask (Group A) and using only the board (Group B). An iSCOUT image-guided system was used for acquiring and correcting pretreatment setup errors for each treatment fraction. Initial setup errors and residual errors were obtained by aligning iSCOUT images with digitally reconstructed radiograph (DRR) images generated from planning CT. Totally 600 initial and residual errors were compared and analyzed between two groups, and the planning target volume (PTV) margins before and after the image-guided correction were calculated.

RESULTS

The initial setup errors of Group A and Group B were (3.14±3.07), (2.21±1.92), (2.45±1.92) mm and (3.14±2.97), (2.94±3.35), (2.80±2.47) mm in the left-right (LAT), superior-inferior (LONG), anterior-posterior (VERT) directions, respectively. The initial errors in Group A were smaller than those in Group B in the LONG direction (P < 0.05). No significant difference was found in the distribution of three initial error ranges (≤3 mm, 3-5 mm and > 5 mm) in each of the three translational directions for the two groups (P > 0.05). The residual errors of Group A and Group B were (1.74±1.03), (1.62±0.92), (1.66±0.91) mm and (1.70±0.97), (1.68±1.18), (1.58±0.98) mm in the three translational directions, respectively. No significant difference was found in the residual errors between two groups (P > 0.05). With the image-guided correction, PTV margins were reduced from 8.01, 5.44, 5.45 mm to 3.54, 2.99, 2.89 mm in three translational directions of Group A, respectively, and from 8.14, 10.89, 6.29 mm to 2.67, 3.64, 2.74 mm in those of Group B, respectively.

CONCLUSION

The use of hollowed-out cervicothoracic thermoplastic masks combined with a carbon-fiber support board showed better inter-fraction immobilization than the single use of the board in reducing longitudinal setup errors for breast cancer patients after radical mastectomy during IMRT treatment course, which has potential to reduce setup errors and improve the pretreatment immobilization accuracy for breast cancer IMRT after radical mastectomy.

Compare of Interfractional Setup Reproducibility Between Vacuum-Lock Bag and Thermoplastic Mask in Radiotherapy for Breast Cancer

Background: This study aimed to analyze the difference of setup reproducibility between Vacuum-lock bag and Thermoplastic mask in the radiotherapy for breast cancer. Methods: A total of 100 invasive breast carcinoma patients were collected, among whom 50 patients were immobilized with Vacuum-lock bag (VB group), and the other 50 patients were immobilized with Thermoplastic mask (TM group). Set up reproducibility in different axes and comfort levels between two groups at three treatment progress points during the radiation therapy were collected and analyzed. Results: The linear regression model showed that fixed device was an independent factor of radiotherapy setup error (SE). Further subgroup analysis based on different axes showed that the SE caused by the fixed device was obvious in all directions. The comfort level in the VB group was significantly larger than that in the TM group at the beginning of treatment, reduced as the treatment progress going on, and finally disappeared within three weeks. Conclusions: Thermoplastic mask could significantly reduce positioning errors in the radiotherapy of breast cancer. Although more discomfort was found in the TM group, it could be eliminated as the treatment progresses.

Comparing Accuracy of Thermoplastic Mask versus Commercial Bra for the Immobilization of Pendulous Breast During Radiation Therapy Treatment: A Retrospective Cohort Study

Purpose

This study aimed to compare thermoplastic mask with bra in terms of setup reproducibility and immobilization of pendulous breasts during radiation therapy (RT).

Methods and materials

Forty-two female patients with breast cancer treated with either intensity modulated RT or 3-dimensional conformal RT were retrospectively reviewed. Of these, 21 benefited from thermoplastic mask immobilization and 21 used a bra. Setup accuracy was evaluated using consecutive cone beam computed tomography/electronic portal imaging device sessions over the first 3 days before treatment (systematic setting), followed by weekly cone beam computed tomography/electronic portal imaging device (random settings), and compared with the reference image to calculate the corresponding translational shift (setup error) in the 3 planes. Average absolute shift values in both systematic and random settings were compared between the 2 groups. Accuracy was analyzed by comparing the percentage of pooled settings within ±0.05 and ±0.1 cm of the reference image.

Results

Compared with a bra, use of the mask was associated with a smaller longitudinal shift in systematic settings (difference in mean: 0.27 cm; P = .027; Mann-Whitney U test) and a lesser lateral shift in random setting (difference in mean: 0.19 cm; P = .005; Mann-Whitney U test). In the pooled systematic settings, the mask performed relatively better than the bra in the lateral and longitudinal planes, with no statistical significance. In pooled random settings, mask showed greater accuracy than bra in the lateral plane with 86.0% versus 58.9% accuracy at ±0.5 cm (P < .001) and 48.8% versus 21.7% accuracy at ±0.1 cm (P < .001), respectively. There was no significant difference in the incidence of radiodermatitis between the 2 groups. However, a hypofractionation regimen was associated with a lower incidence of radiodermatitis, and the severity of skin reactions was positively correlated with treatment dose (unstandardized regression coefficient: B = .001; correlation coefficient: r = .571; P < .001).

Conclusions

Masks provide superior reproducibility compared with commercially available bras.