ESTRO 2023 - Abstract Book

S2098

Digital Posters

ESTRO 2023

PO-2329 Role of deep inspiration breath hold on post-operative radiotherapy of right-sided breast cancer

B.I. Torno 1 , N. Abella 2 , C.J. Villafuerte 2 , M.M. Lopez 2

1 Perpetual Help Medical Center- Las Pinas, Radiation Oncology, Las Pinas, Philippines; 2 Perpetual Help Medical Center-Las Pinas, Radiation Oncology, Las Pinas, Philippines Purpose or Objective This study aims to establish the role of deep inspiration breath hold (DIBH) in reducing radiation dose exposure of the organs at risk (OARs) in right-sided breast cancer patients, namely the lungs, liver, and heart. Materials and Methods A total of 20 patients referred for post-operative locoregional radiotherapy (RT) were included in this study. Two Non- Contrast Computed Tomography (CT) data sets were acquired from each patient, one for the free breathing (FB) scan and another for the DIBH scan. Following the acquisition of CT data sets, the target volumes (chest wall and the regional nodes composed of the supraclavicular, axillary, and internal mammary lymph nodes), as well as the OARs (both and ipsilateral right lung, heart, and liver) for both CT data sets of each patient, were delineated. Single isocenter 3D-conformal RT plans were then formulated using the prescription dose as prescribed by their respective radiation oncologist, which ranges from 50 to 50.4 Gy given in 25-28 fractions over 5 to 6 weeks with or without a boost to the surgical scar and high-risk regional nodes. This was followed by the generation of dose-volume histograms (DVHs). From these DVHs, the volume receiving at least 95% (V95%) of the prescribed dose and the volume receiving at least 90% (V90%) for the target volume; the mean dose, volume receiving at least 10 Gy (V10Gy) and at least 20 Gy (V20Gy) for the liver; the mean dose and the volume receiving at least 5Gy (V5Gy) for the heart; the mean dose as well as the V20Gy of both and ipsilateral right lung; and the total and ipsilateral right lung volume for both the DIBH and FB RT plans of each patient were then recorded and were statistically compared. Results From the data gathered, this study showed a significant reduction in total lung mean V20 Gy, as well as all liver dose- volume parameters (mean dose, mean V10Gy, and mean V20Gy) for the DIBH RT plans compared to the FB RT plans. However, for the heart, a significantly higher mean dose, as well as mean V5Gy, has been noted for the DIBH RT plans. Despite this increase in cardiac exposure, the dose received by the heart is only minimal because our patients have a right- sided disease. Conclusion This study supports the use of the DIBH technique in right-sided breast cancer patients especially those undergoing post- operative locoregional radiotherapy. Purpose or Objective This study aims to establish the brachial plexus as one of the organs at risk (OARs) for breast cancer patients undergoing post-mastectomy locoregional radiotherapy followed by an axillary boost. Materials and Methods A total of 35 patients undergoing post-mastectomy locoregional radiotherapy were included in this study. Non-contrast Computed Tomography (CT) data sets were retrieved where the brachial plexus was contoured. Following the delineation of the brachial plexus, dose-volume histograms (DVHs) were then generated. From these DVHs, the radiotherapy plan maximum radiation dose (Dmax), brachial plexus Dmax, brachial plexus mean dose, and volume of the brachial plexus receiving at least 40 Gy (V40) was then recorded. Results From the data gathered, the brachial plexus overall mean Dmax was above the minimum dose constraint with a value of 61.74 Gy (SD=5.0) and its highest value being 73.42 Gy suggesting a high risk of radiation-induced brachial plexopathy. However, the mean V40 value of the brachial plexus was 6.42 cc (SD=1.62) ranging from 4.08 to 11.03 which was below the proposed value to be associated with an increased risk of paresthesia. Conclusion This study recommends contouring of the brachial plexus as one of OARs for breast cancer patients undergoing post- mastectomy locoregional radiotherapy followed by an axillary boost. PO-2330 Dose metrics of the brachial plexus in post-mastectomy radiotherapy of breast cancer B.I. Torno 1 , E. Reyes 1 1 Perpetual Help Medical Center-Las Pinas, Radiation Oncology, Las Pinas, Philippines

PO-2331 Evaluating efficiency of Vertical MLC VMAT plan for nasopharyngeal carcinoma

S.H. Chae 1 , S.J. Son 1

1 Seoul national university hospital, Radiation oncology, Seoul, Korea Republic of

Purpose or Objective