Dosimetric analysis of intensity-modulated radiotherapy and three-dimensional conformal radiotherapy for chest wall irradiation in breast cancer patients

Patient and treatment-related factors that influence dose to heart and heart substructures in left-sided breast cancer radiotherapy

BACKGROUND

Cardiac substructures are critical organs at risk in left-sided breast cancer radiotherapy being often overlooked during treatment planning. The treatment technique plays an important role in diminishing dose to critical structures. This review aims to analyze the impact of treatment- and patient-related factors on heart substructure dosimetry and to identify the gaps in literature regarding dosimetric reporting of cardiac substructures.

METHODS

A systematic search of the literature was conducted in Medline/Pubmed database incorporating data published over the past 10 years, leading to 81 eligible studies. Treatment-related factors analyzed for their impact on patient outcome included the number of treatment fields, field geometry, treatment time and monitor units. Additionally, patient-related parameters such as breast size and tumor shape were considered for cardiac dosimetry evaluation.

RESULTS

Limited number of fields appeared to be an advantage for mean heart dose reduction when tangential IMRT versus multiple fields IMRT was evaluated. Larger breast size (910.20 ± 439.80 cm3) is linked to larger treatment fields and higher heart doses. Internal mammary node irradiation further escalates cardiac substructures dosimetry treated with 3DCRT and IMRT/VMAT. Proton therapy delivers lower mean heart dose regardless of breathing condition (free or respiratory-gated).

CONCLUSION

The management of treatment- and patient-related factors must be taken into account regardless of the treatment technique when evaluating cardiac dose. Furthermore, the gap found in the literature regarding heart toxicity assessment in left-sided breast cancer patients emphasizes the need for cardiac substructure contouring to better manage and control radiation-induced cardiac toxicities in this patient group.

Comparison of Dosimetric Parameters of Three- Dimensional Conformal Radiotherapy and Intensity- Modulated Radiotherapy in Breast Cancer Patients Undergoing Adjuvant Radiotherapy after Modified Radical Mastectomy

Introduction Adjuvant radiotherapy has an important role in preventing locoregional recurrences. But radiation-induced late sequelae have become an important area of concern. The ideal postmastectomy radiotherapy technique is an area of controversy. The present study was designed to compare two widely practiced conformal techniques, three-dimensional conformal radiotherapy (3DCRT) and intensity-modulated radiotherapy (IMRT), in terms of dosimetry.

Material and Methods A total of 50 postmodified radical mastectomy patients were selected and were randomized to treatment either by 3DCRT or IMRT technique. Two opposing tangential beams were used in 3DCRT plans whereas five to seven tangential beams were used for IMRT plans. The prescribed dose was 50 Gy in 25 fractions over 5 weeks. The dosimetric parameters were compared for planning target volume (PTV), lungs, heart, and left ventricle, opposite breast and esophagus.

Results The dosimetric parameters of PTV in terms of D95%, D90%, D50%, and Dmean showed no significant difference among both techniques. The IMRT technique had significantly better mean values of Dnear-min/D98% (45.56 vs. 37.92 Gy; p = 0.01) and Dnear-max/D2% (51.47 vs. 53.65 Gy; p < 0.001). Also, conformity index (1.07 vs. 1.29; p = 0.004) and homogeneity index (0.22 vs. 0.46; p = 0.003) were significantly better in IMRT arm.

The dosimetric parameters of ipsilateral lung were significantly higher in IMRT arm in terms of mean dose (19.92 vs. 14.69 Gy; p < 0.001) and low/medium dose regions (V5, V10, V13, V15, V20; p < 0.05). However, high-dose regions (V40) were significantly higher in 3DCRT arm (15.57 vs. 19.89 Gy; p = 0.02). In contralateral lung also, mean dose was significantly higher in IMRT technique (3.63 vs. 0.53 Gy; p < 0.0001) along with low-dose regions (V5, V10, V13, V15; p < 0.05) while V20 was comparable between both the arms.

In left-sided patients, the heart dose favored 3DCRT technique in terms of mean dose (17.33 vs. 8.51 Gy; p = 0.003), low/medium dose regions (V5, V10, V20; p < 0.05), and doses to partial/whole volumes (D33, D67, D100). But the high-dose regions (V25, V30, V40) were comparable between both the arms. The dosimetry of left ventricle also showed significantly lesser values of mean dose and V5 in 3DCRT technique (p < 0.0001).

The opposite breast also showed higher mean dose with IMRT technique (2.60 vs. 1.47 Gy; p = 0.009) along with higher V5 (11.60 vs. 3.83 Gy; p = 0.001). The dosimetric parameters of esophagus showed higher mean dose in IMRT technique (10.04 vs. 3.24 Gy; p < 0.0001) but the high-dose regions V35 and V50 were comparable between both the arms.

Conclusion A clear advantage could not be demonstrated with any of the techniques. The IMRT technique led to more conformal and homogenous dose distribution with reduction in high-dose regions in ipsilateral lung while the 3DCRT technique showed lesser mean dose to organs at risk (OARs). The exposure of large volumes of OARs to low doses in IMRT technique may translate to increased long-term radiation-induced complications. The shortcomings of 3DCRT technique can be overcome by using multiple subfields within tangential fields.

Optimization of autogenerated chest-wall radiation treatment plans developed for postmastectomy breast cancer patients in underserved clinics

Over the past decade, several strides have been made to improve the management of breast cancer in developing countries; however, there are still obstacles present. In the area of radiation therapy, these hurdles include limited access to radiotherapy treatment and scarcity of oncology specialists. In an effort to reduce inequities in cancer care while improving patient outcomes, our research is focused on developing automated postmastectomy radiation therapy (PMRT) plans for breast cancer patients in these underserved communities that can be further improved upon through treatment planning system (TPS) specific optimization guidelines. The automated planning tool utilized algorithms integrated with Varian's Eclipse TPS. The tool created PMRT plans that used monoisocentric tangents and supraclavicular (SCV) fields with a mix of high and low energy photon beams along with field-in-field (FIF) segments. The completed autogenerated PMRT plans were imported into Phillip's Pinnacle 9.10 and Varian's Eclipse 13.6 TPSs to be further improved through manual optimization; the time required to complete this step was measured and assessed. A senior dosimetrist, physicist, and physician evaluated the optimized plans for clinical acceptability. Guidelines were developed for the planning systems that can be implemented by personnel with either limited experience in radiation treatment planning or those with limited time to produce treatment plans. The autogenerated plans in conjunction with our guidelines have shown to significantly reduce the time required to produce a clinically acceptable PMRT plan from approximately 120 ± 60 minutes to just 13 ± 11 (Pinnacle) and 12 ± 7 (Eclipse) minutes, reducing the total uninterrupted treatment planning time by an average of 108 ± 51 minutes. The results from this research indicate that the autogenerated PMRT plans along with the optimization guidelines are a viable option to provide quality and clinically acceptable PMRT plans that are more efficient and consistent for postmastectomy breast cancer patients in severely underserved communities.