Tibor Major1,2, Georgina Fröhlich3,4, Péter Ágoston1,2, Csaba Polgár1,2, Zoltán Takácsi-Nagy1,2
1National Institute of Oncology, Centre of Radiotherapy, Budapest, Hungary; 2Semmelweis University, Department of Oncology, Budapest, Hungary; 3National Insitute of Oncology, Centre of Radiotherapy, Budapest, Hungary; 4Eötvös Loránd University, Faculty of Science, Budapest, Hungary
Recently, the use of brachytherapy (BT) has been declining worldwide for various reasons. The aim of this presentation is to provide a dosimetric overview of the role of brachytherapy in the treatment of different anatomical sites of cancer patients in the era of advanced external beam radiotherapy (EBRT).
A systematic literature search was conducted and publications on dosimetrical comparison between BT and EBRT were collected. The studies were categorized and evaluated according to the tumour location. In addition, treatment plans with identical CT images and contours were created for BT, IMRT/VMAT and Cyberknife (CK) treatments for patients with breast, head&neck (H&N) and prostate cancer. Dosimetrical comparisons were performed with visual inspections of dose distributions and with dose-volume parameters. An emphasis was made on doses to organs at risk (OARs).
Fifty-three publications with at least treatment plans of five patients were collected and analysed. One study was found for brain and H&N, two for lung, three for liver, six for skin and eight for breast tumours. The most papers were published for gynaecological and prostate cancer (sixteen for both). In thirteen studies the EBRT, in thirty-three the BT clinical plan was used as a reference, and the virtual plan was generated for the alternative technique, while in six studies two separate patient cohorts were compared. In most studies BT performed better or as good as the most advanced EBRT techniques regarding doses to OARs, especially adjacent or close to the target volume. This statement was confirmed by our results for breast, H&N and prostate cancer (Figure 1-2.). For breast cases the mean values of V50 for non-target breast was 10.0% vs. 15.3%, D1cm3 for ipsilateral lung 37.8% vs. 48.2%, D1cm3 for skin 54.9% vs. 84.3%, and for D1cm3 for ribs 45.9% vs. 70.6% in favour of BT compared to CK. In case of H&N cancer the D2cm3 was 48.4% vs. 68.4% for mandible and 7.0% vs. 10.5% for ipsilateral salivary gland with BT and VMAT, respectively. For prostate cancer the EQD2 D2cm3 for the rectum and bladder was the lowest with the HDR BT (36 Gy and 51.4 Gy), compared to VMAT (66.7 Gy and 68.4 Gy) and Cyberknife (68.1 Gy and 78.9 Gy). With high-tech EBRT techniques (IMRT, VMAT, Tomotherapy, Cyberknife) higher dose coverage and better dose conformality can be achieved, but the integral dose to the body is generally lower with BT. The better OAR protection and larger dose inhomogeneity in BT is the direct consequence of the inverse square law, which is the main factor in forming the dose distribution in BT.
Figure 1. Comparative dose distributions of BT and Cyberknife for breast cancer
Figure 2. Comparative dose distributions of BT and VMAT for head&neck cancer
Despite its invasive nature and the widespread availability of high-tech EBRT techniques, brachytherapy still has a present and a future in the treatment of cancer patients, due to its favourable dosimetric characteristics.