Dosimetric comparison of normal breathing and deep inspiration breath hold technique for synchronous bilateral breast cancer using 6MV flattened beam and flattening filter free beam

Evaluation of Cardiac Substructures Dose Sparing in Single and Dual Isocenter RapidArc™ Radiotherapy Planning for Synchronous Bilateral Breast Cancer

Purpose This study compares the dosimetry and dose sparing of cardiac substructures in single isocenter and dual isocenter RapidArc™ (Varian Medical Systems, Palo Alto, California, United States) radiotherapy planning for synchronous bilateral breast cancer. Methodology Six synchronous bilateral breast cancer (SBBC) patients received adjuvant radiation with the prescribed dose of 40.05 Gy in 15 fractions to the planning target volume (PTV) without local lymph nodal regions. PTVs and organs at risk (OARs), including both lungs, esophagus, spinal cord, heart, and left anterior descending coronary artery (LAD), both atria and ventricles were contoured. Single isocentric RapidArc (SIRA) and dual isocentric RapidArc (DIRA) plans were made for each patient and dosimetric differences between these two techniques were evaluated. Results There was no statistically significant difference in conformity index (CI) values between SIRA and DIRA plans, with 0.9681±0.01 and 0.9721±0.01 (p=0.505), respectively. SIRA planning showed superior homogeneity with homogeneity Index (HI) values of 0.0999±0.01 compared to DIRA planning with HI values of 0.1640±0.12 (p=0.230). The mean LAD dose of SIRA was valued higher than that of DIRA planning. Lower mean doses were obtained for both lungs in SIRA plans compared to DIRA plans. Meanwhile, doses to the right atrium, left atrium, left ventricle, right ventricle, and esophagus showed no statistical significance between these two techniques, except in the spinal cord. Conclusion Both SIRA and DIRA plans have satisfactory outcomes in sparing OARs. Meanwhile, SIRA techniques have less setup time and overall machine time.

Deep inspiration breath hold: dosimetric benefits to decrease cardiac dose during postoperative radiation therapy for breast cancer patients

Background

Postoperative radiation therapy (RT) is the standard treatment for almost all patients diagnosed with breast cancer. Even with modern RT techniques, parts of the heart may still receive higher doses than those recommended by clinically validated dose limit restrictions, especially when the left breast is irradiated. Deep inspiration breath hold (DIBH) may reduce irradiated cardiac volume compared to free breathing (FB) treatment. This study aimed to evaluate the dosimetric impact on the heart and left anterior descending coronary artery (LAD) in FB and DIBH RT planning in patients with left breast cancer.

Materials and methods

A retrospective cohort study of women diagnosed with left-sided breast cancer submitted to breast surgery followed by postoperative RT from 2015 to 2019. All patients were planned with FB and DIBH and hypofractionated dose prescription (40.05 Gy in 15 fractions).

Results

68 patients were included in the study. For the coverage of the planned target volume evaluation [planning target volume (PTV) eval] there was no significant difference between the DIBH versus FB planning. For the heart and LAD parameters, all constraints evaluated favored DIBH planning, with statistical significance. Regarding the heart, median V16.8 Gy was 2.56% in FB vs. 0% in DIBH (p < 0.001); median V8.8 Gy was 3.47% in FB vs. 0% in DIBH (p < 0.001) and the median of mean heart dose was 1.97 Gy in FB vs. 0.92 Gy in DIBH (p < 0.001). For the LAD constraints D2% < 42 Gy, the median dose was 34.87 Gy in FB versus 5.8 Gy in DIBH (p < 0.001); V16.8 Gy < 10%, the median was 15.87% in FB versus 0% in DIBH (p < 0.001) and the median of mean LAD dose was 8.13Gy in FB versus 2.92Gy in DIBH (p < 0.001).

Conclusions

The DIBH technique has consistently demonstrated a significant dose reduction in the heart and LAD in all evaluated constraints, while keeping the same dose coverage in the PTV eval.

Cardiac dose in the treatment of synchronous bilateral breast cancer patients between three different radiotherapy techniques (VMAT, IMRT, and 3D CRT)

PURPOSE

Synchronous bilateral irradiation of both mammary glands and chest wall is a challenging task due to technical difficulties and limited evidence supporting an optimal technique to improve treatment outcomes. We studied and compared the dosimetry data of three radiotherapy techniques to select the most optimal one.

METHODS

We compared three-dimensional conformal radiation treatment (3D CRT), intensity-modulated radiation therapy (IMRT), and volumetric modulated arc therapy (VMAT) during irradiation of synchronous bilateral breast cancer in nine patients followed by examination of dose distribution to the cardiac conduction system (SA node, AV node and Bundle of His), myocardium, lungs, left anterior descending artery (LADA) and right coronary artery (RCA) .

RESULTS

VMAT is the most sparing technique for SBBC treatment. Even though doses to the SA node, AV node and Bundle of His were higher with VMAT (D_mean were 3.75 ± 0.62, 2.58 ± 0.83 and 3.03 ± 1.18 Gy respectively) compared with 3D CRT (D_mean were 2.61 ± 0.66, 1.52 ± 0.38 and 1.88 ± 0.70 Gy respectively), this difference is statistically insignificant. Doses to the right and left lung (average D_mean = 12.65 ± 3.20 Gy, V_20Gy = 24.12 ± 6.25%), myocardium (D_mean = 5.33 ± 1.51 Gy, V_10Gy = 9.80 ± 3.83%, V_20Gy = 7.19 ± 3.15%, V_25Gy = 6.20 ± 2.93%), and LADA (D_mean = 10.04 ± 4.92 Gy, V_20Gy = 18.17 ± 13.24% and V_25Gy = 15.41 ± 12.19%) were highest with 3D CRT. The highest  D_mean in the cardiac conduction system (5.30 ± 2.23, 3.15 ± 1.61 and 3.89 ± 1.85 Gy respectively) was observed with IMRT, and a similar effect was noted in RCA (D_mean = 7.48 ± 2.11 Gy).

CONCLUSION

VMAT is the optimal and satisfactory radiation therapy technique for sparing organs at risk (OARs). With VMAT, a lower D_mean value was noted in the myocardium, LADA, and lungs. The use of 3D CRT significantly increases the dose of radiation reaching the lungs, myocardium, and LADA, which can subsequently cause cardiovascular and lung complications, but not in the cardiac conduction system.