Radiation Dose to Critical Cardiac Structures from Three-Dimensional Conformal Radiation Therapy (3D-CRT), Intensity-Modulated Radiation Therapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT) Techniques for Left-Sided Breast Cancer

A comparison of the radiation exposure to the left anterior descending artery (LAD) and left ventricle (LV) was performed for twenty-three left breast cancer patients. For each participant, two tangential fields 3D-CRT, two- and seven-field IMRT and two and four partial arcs VMAT plans were created. Dose constraints for CTV, ipsilateral lung and heart were followed. The V40Gy, V30Gy, Dav of LAD and V23Gy, V5Gy, Dav of LV were calculated and extracted from the plans. Parametric and non-parametric tests were applied to compare the parameters derived from the five treatment techniques. All generated plans fulfilled the dose constraints. The Dav ranges of the LAD and LV from all examined techniques were 11.77-14.73 Gy and 5.37-6.40 Gy, respectively. The V40Gy and V30Gy ranges of the LAD were 2.90-12.91% and 10.80-18.51%, respectively. The V23Gy and V5Gy of the LV were 4.29-7.43% and 18.24-30.05%, respectively. The VMAT plans and seven-field IMRT significantly reduced the V40Gy, V30Gy of LAD and V23Gy of LV compared with the two-field treatments (p < 0.05). However, 3D-CRT plans provided statistically lower values for V5Gy of LV over the other techniques (p < 0.05). The presented results provide a detailed dataset of the radiation burden of two critical cardiac structures from five radiotherapy techniques.

Comparison of setup accuracy of optical surface image versus orthogonal x-ray images for VMAT of the left breast using deep-inspiration breath-hold

To compare the setup accuracy of optical surface image (OSI) versus orthogonal x-ray images (2DkV) using cone beam computed tomography (CBCT) as ground truth for radiotherapy of left breast cancer in deep-inspiration breath-hold (DIBH). Ten left breast DIBH patients treated with volumetric modulated arc therapy (VMAT) were studied retrospectively. OSI, 2DkV, and CBCT were acquired weekly at treatment setup. OSI, 2DkV, and CBCT were registered to planning CT or planning DRR based on a breast surface region of interest (ROI), bony anatomy (chestwall and sternum), and both bony anatomy and breast surface, respectively. These registrations provided couch shifts for each imaging system. The setup errors, or the difference in couch shifts between OSI and CBCT were compared to those between 2DkV and CBCT. A second OSI was acquired during last beam delivery to evaluate intrafraction motion. The median absolute setup errors were (0.21, 0.27, 0.23 cm, 0.6°, 1.3°, 1.0°) for OSI, and (0.26, 0.24, 0.18 cm, 0.9°, 1.0°, 0.6°) for 2DkV in vertical, longitudinal and lateral translations, and in rotation, roll and pitch, respectively. None of the setup errors was significantly different between OSI and 2DkV. For both systems, the systematic and random setup errors were ≤0.6 cm and ≤1.5° in all directions. Nevertheless, larger setup errors were observed in some sessions in both systems. There was no correlation between OSI and CBCT whereas there was modest correlation between 2DkV and CBCT. The intrafraction motion in DIBH detected by OSI was small with median absolute translations <0.2 cm, and rotations ≤0.4°. Though OSI showed comparable and small setup errors as 2DkV, it showed no correlation with CBCT. We concluded that to achieve accurate setup for both bony anatomy and breast surface, daily 2DkV can't be omitted following OSI for left breast patients treated with DIBH VMAT.

Application of tangent-arc technology for deep inspiration breath-hold radiotherapy in left-sided breast cancer

Objective

To explore the advantages of dosimetry and the treatment efficiency of tangent-arc technology in deep inspiration breath-hold radiotherapy for breast cancer.

Methods

Forty patients with left-sided breast cancer who were treated in our hospital from May 2020 to June 2021 were randomly selected and divided into two groups. The first group's plan was a continuous semi-arc that started at 145° ( ± 5°) and stopped at 325° ( ± 5°). The other group's plan, defined as the tangent-arc plan, had two arcs: the first arc started at 145° ( ± 5°) and stopped at 85° ( ± 5°), and the second arc started at 25° ( ± 5°) and stopped at 325° ( ± 5°). We compared the target dose, dose in organs at risk (OARs), and treatment time between the two groups.

Results

The target dose was similar between the continuous semiarc and tangent-arc groups. The V5 of the right lung was significantly different between the two groups (Dif 5.52, 95% confidence interval 1.92-9.13, t=3.10, P=0.004), with the patients in the continuous semi-arc and tangent-arc groups having lung V5 values of (9.16 ± 1.62)%, and (3.64 ± 0.73)%, respectively. The maximum dose to the spinal cord was (1835.88 ± 222.17) cGy in the continuous semi-arc group and (599.42 ± 153.91) cGy in the tangent-arc group, yielding a significant difference between the two groups (Dif 1236.46, 95% confidence interval 689.32-1783.6, t=4.57, P<0.001). The treatment times was (311.70 ± 60.45) s for patients in the continuous semi-arc group and (254.66 ± 40.73) s for patients in the tangent-arc group, and there was a significant difference in the mean number of treatment times between the two groups (Dif 57.04, 95% confidence interval 24.05-90.03, t=3.5, P=0.001).

Conclusion

Both the continuous semi-arc and tangent-arc plans met the clinical prescription dose requirements. The OARs received less radiation with the tangent-arc plan than the continuous semi-arc plan, especially for the lung (measured as V5) and the spinal cord (measured as the maximum dose). Tangent-arc plan took significantly less time than the continuous semi-arc, which can greatly improve treatment efficiency. Therefore, tangent-arc plans are superior continuous semi-arc plans for all cases.

Dosimetric impact of different multileaf collimators on cardiac and left anterior descending coronary artery dose reduction

Introduction

Radiotherapy (RT) may increase the dose of heart structure like left anterior descending coronary artery (LAD). The purpose of this paper was to evaluate the impact of various multileaf collimators (MLCs) in shielding organ at risks (OARs), especially LAD, of patients with left breast cancer.

Materials and Methods

Forty-five patients with left breast cancer were selected. The treatment plans were created applying three techniques for all patients. In the first plan (uncovered LAD), the treatment plan was made without considering LAD as OARs. In the two other plans, two MLCs with different leaf widths (6.8 mm and 5 mm) were used to shield the LAD. For all plans, MLC was shielded as much of OAR as possible without compromising planning target volume (PTV) coverage. Dosimetric parameters of the heart, LAD, and ipsilateral lung were assessed.

Results

Compared to other plans, the covered LAD plan 1(CL1) obtained lower lung, cardiac, and LAD doses with the same PTV coverage. On average, the mean heart dose decreased from 6.2 Gy to 5.4 Gy by CL1, and the average mean dose to the LAD was reduced from 36.4 Gy to 33.7 Gy, which was statistically significant. The average lung volume receiving >20 Gy was significantly reduced from 24.6% to 23.4%. Moreover, the results show that covered LAD plan 2(CL2) is less useful for shielding OARs compared to CL1.

Conclusion

CL1 plans may reduce OAR dose for patients without compromising the target coverage. Hence, the proper implementation of MLC can decrease the side effects of RT.

Predictors of cardiac dose sparing in deep inspiratory breath-hold technique for radiation of left breast cancer patients

Introduction

Radiation therapy to left breast cancer patients results in significant exposure to heart resulting in long-term cardiac morbidity. This exposure can be reduced by performing deep inspiratory breath-hold (DIBH) technique, however, patient selection criteria or predictive parameters are not routinely used which can identify patients who will have significant benefit with this technique. This study intends to find and use these predictive parameters measured on free-breathing (FB) simulation scan which can help to select such patients so as to develop our institutional protocol.

Methods

A total of 35 patients of left breast cancer postsurgery were recruited in the study. All patients underwent 2-3 sessions of DIBH coaching followed by planning computed tomography scan in both FB phase and DIBH phase. Various anatomical parameters such as cardiac contact distance parasagittal (CCDps), CCD axial, heart-chest distance (HCD), and D were measured on FB scan and were correlated with a mean heart dose achieved in DIBH scan.

Results

Dose to normal structures, namely heart and lung, was drastically reduced for DIBH scan over FB scan. V5, V10, and V20 of heart also followed a similar reduction. The mean dose to heart in FB scan was 5.34 Gy, while in DIBH scan, it was 2.79 Gy which was statistically significant. Among all the parameters measured, CCDps and D had a statistically significant positive correlation with the mean heart dose in DIBH phase while HCD had a negative correlation which was statistically significant.

Conclusion

Cardiac parameters on FB scan such as CCDps, HCD, and D predict the patients with usual cardiac risk who will benefit most with DIBH techniques setting an arbitrarily cutoff value.