A dose planning study for cardiac and lung dose sparing techniques in left breast cancer radiotherapy: Can free breathing helical tomotherapy be considered as an alternative for deep inspiration breath hold?

Purpose: To investigate the possibility to be able to offer left sided breast cancer patients, not suitable for DIBH, an organ at risk saving treatment. Materials and Methods: Twenty patients receiving radiotherapy for left breast cancer in DIBH were enrolled in the study. Planning CT scans were acquired in the same supine treatment position in FB and DIBH. 3DCRT_DIBH plans were designed and optimized using two parallel opposed tangent beams (with some additional segments) for the breast and chest wall and anterior-posterior fields for regional lymph nodes irradiation. Additionally, FB helical tomotherapy plans were optimized to minimize heart and lung dose. All forty plans were optimized with at least 95% of the total CTV covered by the 95% of prescribed dose of 50 Gy in 25 fractions. Results: HT_FB plans showed significantly better dose homogeneity and conformity compared to the 3DCRT_DIBH specially for regional nodal irradiation. The heart mean dose was almost comparable in 3DCRT_DIBH and HT_FB while the volume (%) of the heart receiving 25 Gy had a statistically significant reduction from 7.90 ± 3.33 in 3DCRT_DIBH to 0.88 ± 0.66 in HT_FB. HT_FB was also more effective in left descending artery (LAD) mean dose reduction about 100% from 30.83 ± 9.2 Gy to 9.7 ± 3.1. The ipsilateral lung volume receiving 20 Gy has a further reduction of 43 % in HT_FB compared with 3DCRT_DIBH. For low dose comparison, 3DCRT_DIBH was superior for contralateral organ sparing compared to the HT_FB due to the limited angle for dose delivery. Conclusion: For patients who cannot be a candidate for DIBH for any reason, HT in free breathing may be a good alternative and provides heart and ipsilateral lung dose sparing, however with the cost of increased dose to contralateral breast and lung.

Dosimetric Evaluation of Cardiac Structures on Left Breast Cancer Radiotherapy: Impact of Movement, Dose Calculation Algorithm and Treatment Technique.

Background: Breast cancer is the most frequently diagnosed and leading cause of cancer-related deaths among females. The treatment of breast cancer with radiotherapy, albeit effective, has been shown to be toxic to the heart, resulting in an elevated risk of cardiovascular disease and associated fatalities. Methods: In this study, we evaluated the impact of respiratory movement, treatment plans and dose calculation algorithm on the dose delivered to the heart and its substructures during left breast radiotherapy over a cohort of 10 patients. We did this through three image sets, four different treatment plans and the employment of three algorithms on the same treatment plan. The dose parameters were then employed to estimate the impact on the 9-year excess cumulative risk for acute cardiac events by applying the model proposed by Darby. Results: The left ventricle was the structure most irradiated. Due to the lack of four-dimensional computed tomography (4DCT), we used a set of images called phase-average CT that correspond to the average of the images from the respiratory cycle (exhale, exhale 50%, inhale, inhale 50%). When considering these images, nearly 10% of the heart received more than 5 Gy and doses were on average 27% higher when compared to free breathing images. Deep inspiration breath-hold plans reduced cardiac dose for nine out of 10 patients and reduced mean heart dose in about 50% when compared to reference plans. We also found that the implementation of deep inspiration breath-hold would reduce the relative lifetime risk of ischemic heart disease to 10%, in comparison to 21% from the reference plan. Conclusion: Our findings illustrate the importance of a more accurate determination of the dose and its consideration in cardiologists' consultation, a factor often overlooked during clinical examination. They also motivate the evaluation of the dose to the heart substructures to derive new heart dose constraints, and a more mindful and individualized clinical practice depending on the treatment employed.

Dosimetric Comparison of the Heart and Left Anterior Descending Artery in Patients With Left Breast Cancer Treated With Three-Dimensional Conformal and Intensity-Modulated Radiotherapy.

Background Adjuvant radiotherapy plays an important role in the management of breast cancer, along with surgery and chemotherapy. However, postoperative radiotherapy poses an increased risk of radiation-induced heart diseases in patients with left-sided breast cancer due to damage of the coronary arteries, which can cause myocardial fibrosis and coronary artery disease; however, there is a lack of sufficient evidence for it. Hence, the present study aimed to assess the dosimetric parameters of the heart and left anterior descending (LAD) coronary artery in patients with left breast cancer treated with three-dimensional conformal radiotherapy (3DCRT) and intensity-modulated radiotherapy (IMRT). Methodology This study included 20 patients with left-sided breast cancer treated between January and July 2019. Patients were equally divided into two groups as follows: group I included those treated with 3DCRT and group II included those treated with IMRT. Radiotherapy was administered to the chest wall and regional lymph nodes. The dose administered for the planning target volume was 50 Gy in 25 daily fractions over five weeks with 6 MV photons. Dosimetric parameters of planning tumor volume (PTV; V95%, V90%, Dmax, Dmin, Dmean, V53.5 Gy, conformity index, and homogeneity index) along with the heart (V5%, V30%, and Dmean) and LAD artery (mean and V25%) were evaluated. Dose-volume histograms were generated and compared. The LAD artery was contoured virtually retrospectively during the study to determine the dosimetric parameters; the dose to the LAD artery was not considered during planning. Results Dosimetric parameters of the PTV were similar for 3DCRT and IMRT; D95 (38.53 vs. 41.61 Gy), D90 (43.67 vs. 44.77 Gy), Dmean (48.3 vs. 48.72 Gy), conformity index (1.10 vs. 1.06), and homogeneity index (0.50 and 0.28) did not show a significant difference. The Dmean for the LAD artery was significantly higher than that for the heart on 3DCRT (23.66 Gy vs. 8.46 Gy; p < 0.0000) and IMRT (31.53 vs. 17.7 Gy; p < 0.0000). The V25 for the LAD artery was significantly higher than that for the heart on 3DCRT (40.27 vs. 14.13 Gy; p < 0.0024) and IMRT (66.21 vs. 27.74 Gy; p < 0.0002). Conclusions Radiation doses to the LAD artery and heart must be evaluated prior to radiotherapy in patients with left breast cancer. Long-term follow-up is needed to evaluate cardiac complications and their association with dosimetric parameters.

Optimization of heart block in the left-sided whole breast radiation treatments.

PURPOSE: Blocks have been used to protect heart from potential radiation damage in left-sided breast treatments. Since cardiac motion pattern may not be fully captured on conventional 3DCT or 4DCT simulation scans, this study was intended to investigate the optimization of the heart block design taking the cardiac motion into consideration. MATERIALS AND METHODS: Whole breast treatment plans using two opposed tangential fields were designed based on 4DCT simulation images for 10 left-sided breast cancer patients. Using an OBI system equipped to a Varian Linac, beam-eye viewed fluoroscopy images were acquired for each of the treatment beams after patient treatment setup, and the MLC heart blocks were overlaid onto the fluoroscopy images with an in-house software package. A non-rigid image registration and tracking algorithm was utilized to track the cardiac motion on the fluoroscopy images with minimal manual delineation for initialization, and the tracked cardiac motion information was used to optimize the heart block design to minimize the radiation damage to heart while avoiding the over-shielding that may lead to underdosing certain breast tissues. RESULTS: Twenty-three sets of fluoroscopy images were acquired on 23 different days of treatment for the 10 patients. As expected, heart moved under the influences of both respiratory and cardiac motion. It was observed that for 16 out of the 23 treatments, heart moved beyond the planed heart block into treatment fields and MLC had to be adjusted to fully block heart. The adjustment was made for all but one patient. The number of the adjusted MLC leaves ranged from 1 to 16 (mean = 10), and the MLC leaf position adjustment ranged from 2 to 10 mm (mean = 6 mm). The added heart block areas ranged from 3 to 1230 mm(2) (mean = 331 mm(2)). CONCLUSION: In left-sided whole breast radiation treatments, simulation CT (and 4DCT) based heart block design may not provide adequate heart protection for all the treatments. A fluoroscopy-based method has been developed to adaptively optimize the heart MLC block to achieve optimal heart protection.