The tumor core boost study: A feasibility study of radical dose escalation to the central part of large tumors with an integrated boost in the palliative treatment setting.

PURPOSE: For patients with large tumors palliative radiotherapy often is the only local treatment option. To prevent toxicity the administered doses are low. Dose escalation to the tumor could be an option to better smyptom control and prolong local control rates. In this prospective study we used a very pragmatic approach with a simultaneously integrated boost (SIB) to an almost geometrically defined tumor core to achieve this. The primary endpoint was to demonstrate feasibility. METHOD: Patients with solid tumors > 4 cm in diameter of different histologies were eligible in this single arm, prospective, multi-institutional clinical feasibility trial with two treatment concepts: 5â€¯× 5 Gy with an integrated boost to the tumor core of 5â€¯× 10 Gy or 10â€¯× 3 Gy with a boost of 10â€¯× 6 Gy. The objective of dose escalation in this study was to deliver a minimum dose of 150% of the prescribed dose to the gross tumor volume (GTV) tumor core and to reach a maximum of at least 200% in the tumor core. RESULTS: In all, 21 patients at three study sites were recruited between January 2019 and November 2020 and were almost evenly spread (9 to 12) between the two concepts. The treated planning target volumes (PTV) averaged 389.42 cm3 (range 49.4-1179.6 cm3). The corresponding core volumes were 72.85 cm3 on average (range 4.21-338.3 cm3). Dose escalation to the tumor core with mean doses of 167.7-207.7% related to the nonboost prescribed isodose led to PTV mean doses of 120.5-163.3%. Treatment delivery and short-term follow-up was successful in all patients. CONCLUSIONS: Palliative radiotherapy with SIB to the tumor core seems to be a feasible and well-tolerated treatment concept for large tumors. The applied high doses of up to 50 Gy in 5 fractions (or 60 Gy in 10 fractions) did not cause unexpected side effects in the 42 day follow-up period. Further research is needed for more information on efficacy and long-term toxicity.

Linac-Based Ultrahypofractionated Partial Breast Irradiation (APBI) in Low-Risk Breast Cancer: First Results of a Monoinstitutional Observational Analysis.

Purpose: For adjuvant radiotherapy of low-risk breast cancer after breast-conserving surgery, there have been many trials of hypofractionation and partial breast irradiation (PBI) over the years, with proven mild long-term toxicity. The aim of this study was to introduce a short-course dose-adapted concept, proven in whole breast irradiation (WBI) for use in accelerated partial breast irradiation (APBI), while monitoring dosimetric data and toxicity. Methods: From April 2020 to March 2022, 61 patients with low-risk breast cancer or ductal carcinoma in situ (DCIS) were treated at a single institution with percutaneous APBI of 26 Gy in five fractions every other day after breast-conserving surgery. Dosimetric data for target volume and organs at risk were determined retrospectively. Acute toxicity was evaluated. Results: The target volume of radiotherapy comprised an average of 19% of the ipsilateral mamma. The burden on the heart and lungs was very low. The mean cardiac dose during irradiation of the left breast was only 0.6 Gy. Two out of three patients remained without any acute side effects. Conclusions: Linac-based APBI is an attractive treatment option for patients with low-risk breast cancer in whom neither WBI nor complete omission of radiotherapy appears to be an adequate alternative.

Using a Further Planning MRI after Neoadjuvant Androgen Deprivation Therapy Significantly Reduces the Radiation Exposure of Organs at Risk in External Beam Radiotherapy of Prostate Cancer.

Radiotherapy for prostate cancer is often preceded by neoadjuvant androgen deprivation therapy (ADT), which leads to a reduction in the size of the prostate. This study examines whether it is relevant for treatment planning to acquire a second planning magnetic resonance imaging (MRI) after ADT (=MRI 2) or whether it can be planned without disadvantage based on an MRI acquired before starting ADT (=MRI 1). The imaging data for the radiotherapy treatment planning of 17 patients with prostate cancer who received two planning MRIs (before and after neoadjuvant ADT) were analyzed as follows: detailed comparable radiation plans were created separately, each based on the planning CT scan and either MRI 1 or MRI 2. After ADT for an average of 17.2 weeks, the prostate was reduced in size by an average of 24%. By using MRI 2 for treatment planning, the V60Gy of the rectum could be significantly relieved by an average of 15% with the same coverage of the target volume, and the V70Gy by as much as 33% (compared to using MRI 1 alone). Using a second MRI for treatment planning after neoadjuvant ADT in prostate cancer leads to a significant relief for the organs at risk, especially in the high dose range, with the same irradiation of the target volume, and should therefore be carried out regularly. Waiting for the prostate to shrink after a few months of ADT contributes to relief for the organs at risk and to lowering the toxicity. However, the use of reduced target volumes requires an image-guided application, and the oncological outcome needs to be verified in further studies.