ESTRO 2022 - Abstract Book

S231

Abstract book

ESTRO 2022

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). Results 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%, D1cm 3 for ipsilateral lung 37.8% vs. 48.2%, D1cm 3 for skin 54.9% vs. 84.3%, and for D1cm 3 for ribs 45.9% vs. 70.6% in favour of BT compared to CK. In case of H&N cancer the D 2cm 3 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 D2cm 3 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

Conclusion 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.

OC-0274 Validation of automated adjustments of clinical prostate brachytherapy treatment plans

F. Dohlmar 1 , Å. Carlsson Tedgren 1 , M. Sandborg 1 , B. Morén 2 , T. Larsson 2

1 Linköping University, Medical Radiation Physics, Department of Health, Medicine and Caring Sciences, Linköping, Sweden; 2 Linköping University, Department of Mathematics, Linköping, Sweden Purpose or Objective The treatment planning of high dose-rate (HDR) prostate brachytherapy can be performed by manual or automated methods. Automated treatment planning is prone to yield uneven distribution of dwelling times, giving rise to regions with high dose, often resolved by manual fine-tuning. Here, an earlier developed, in-house adjustment tool is used to improve clinical treatment plans upon spatial properties. A paired observer study was performed to validate the performance of the adjustment tool against the original clinical approved treatment plans.

Materials and Methods