Three-Dimensional Conformal Versus Intensitymodulated Radiation Therapy Planning For Left Breast, Chest Wall And Supraclavicular Fossa Of Cancer Patients

Abstract

Introduction: The use of radiation therapy has led to the instance where breast cancer now has a favourable prognosis post-surgery. For later stage breast cancer, radiation therapy is performed post-mastectomy. In the Oncology Department, University of the Free State, the use of radiation therapy post-mastectomy is a standard treatment technique and it includes the axillary nodes as well as the supraclavicular nodes, where indicated. The planning technique for radiation therapy has changed with the introduction of Intensity Modulated Radiotherapy (IMRT) for many cancer treatments. In this study, the use of IMRT for breast cancer was compared to 3-dimensional conformal radiation therapy (3D-CRT) for post-mastectomy breast cancer patients that include the supraclavicular fossa on the left-side. The left-side was selected to indicate the dose to the heart specifically. The study questioned how 3D-CRT planning compare with IMRT planning for post mastectomy patients receiving radiation therapy to the left chest wall and supraclavicular fossa. Aim: The aim of the research study was to compare 3D-CRT- with IMRT treatment planning techniques for the treatment delivery of post-mastectomy, left breast, chest wall and supraclavicular fossa for cancer patients. The objectives were to compare (i) the dose coverage for the planned target volumes (PTV), (ii) clinical target volumes (CTV), (iii) the dose received by organs at risk (OAR) and (vi) the dose volume histograms (DVH) created for each patient’s plans. Methodology: The retrospective study was conducted between January 2019 and June 2020 in the Oncology Department, University of the Free State, after having obtained ethical approval. The study was conducted in four stages: 1) contouring and delineation of structures, 2) generating 3D-CRT plans for 30 patients, 3) generating 30 IMRT plans and 4) comparing the data from the DVH’s. A pilot study was conducted in order to confirm the reliability and validity of methods and materials utilised. The patients’ scans were utilised to draw in the PTV, CTV and the OAR by an oncologist. The 3D-CRT plans were generated by the researcher on the XiO treatment planning system© (TPS) (Version 4.33.02) and the computed medical system (CMS) Elekta Software. The IMRT plans were derived from the Monaco© treatment planning system (V5.11.02). Both the 3D-CRT plans as well as the IMRT plans were compared on the Monaco planning system. The plans were compared for PTV and CTV dose coverage and dose delivered to the OAR. The plans were approved by an oncologist for reliability. The data was captured on a Microsoft Excel spreadsheet and analysed by a statistician. Results: Twenty-six of the thirty patients’ scans conformed to the inclusion criteria and were used to create the IMRT plans for comparison with the existing 3D-CRT plans. Four of the IMRT plans were excluded due to unacceptable dose coverage for either the PTV coverage or OAR. The PTV coverage for the 105% dose was higher for the IMRT plans with 1.1% versus 0.2% for the 3D-CRT plans. The 95% dose to the PTV was superior for the IMRT plans with 7.7% for IMRT versus 32.9% for 3D-CRT plans. The CTV coverage for the 3D-CRT plans and the IMRT plans had mean values of 0.3% and 1.1% for the 105%, respectively. The 3D-CRT plans had a mean difference of -0.8% and fewer areas of 105% to the PTV compared to the IMRT plans. The 3DCRT plans produced areas of less than 95% dose with a mean of 14.5%, whereas the IMRT plans had a mean dose of 0.9%. The V22 for the 3D-CRT to the heart was higher compared to IMRT with 7.7% versus 2.1%. The mean heart dose was less for 3D-CRT with 4.9Gy versus 5.4Gy for IMRT. The mean dose to the oesophagus was less for the 3D-CRT with 5.1Gy versus 9.3Gy for IMRT. The maximum dose was less for the 3D-CRT with 34.6Gy versus 39.4Gy for IMRT. The percentage of both lungs receiving 18.87Gy was less for IMRT plans with 13.7% versus 16.1% for 3D-CRT plans. The percentage of left lung receiving 18.87Gy was less for the IMRT plans with 28.1% versus 33.5% for 3D-CRT plans. The maximum dose to the left humeral head was less for IMRT with 34.6Gy versus 37.4Gy for 3D-CRT. The percentage of 5Gy to the right breast was less for 3D-CRT versus IMRT with 3.5% versus 11.4%, respectively. The dose to the spinal cord was less for IMRT with 13.3Gy versus 22.6Gy for the 3D-CRT. The percentage of the dose delivered to the normal tissue that received 5Gy was less for 3D-CRT plans with 12.9% versus 24.9% for IMRT plans. Conclusion: This comparative study demonstrated that the IMRT planning technique for post mastectomy, left breast cancer patients had superior PTV coverage and OAR sparing compared to the 3D-CRT planning technique. The IMRT planning technique did however have larger areas of normal tissue and contralateral breast tissue with low dose radiation. It should be noted though that this low dose radiation is a concern for secondary malignancies. The study limitations include the use of a single isocenter for the 3D-CRT plans, which limited the field size when the mastectomy scar extended beyond the mid-axillary line, in turn limiting the dose to the PTV dose coverage for both 3D-CRT and IMRT plans, respectively. The 7-field IMRT planning technique was utilised in this study. However there are 9- and 11- field IMRT planning techniques that could contribute more to this study. The use of 9- to 11-field IMRT plans could benefit and expand this study for a more in-depth comparison of different 3D-CRT and IMRT approaches. In future, the use of breathing techniques, such as deep inspiration breath hold or inspiration gating, should be considered when using IMRT planning techniques for breast cancer treatment.