Introduction: Primary mediastinal B-cell lymphoma (PMBCL) is a rare form of aggressive B-cell lymphoma with a predominant onset in young patients. The minimization of potential (late) side effects is of cardinal interest for these patients. An anticipation of the individual risk profile is desirable to counsel the patient on the putative impact of radiotherapy (RT). Methods: RT plans for a cohort of 25 patients with PMBCL were prospectively designed. One plan with two parallel- opposing fields (APPA) and another with volume-modulated arc therapy (VMAT) technique with 40 Gy in 2 Gy fractions each. Normal The normal tissue complication probability (NTCP) was calculated using the Lyman-–Kutcher-–Burman model for heart, lung and oesophageal toxicity. Results: APPA planning resulted in lower median doses (Dmedian) for the heart and lungs, whereas all other dose metrics for heart, lungs and esophagus were lower in VMAT planning. A significant difference in the mean NTCPs when comparing the APPA to VMAT plans was seen for increased cardiac mortality, pneumonitis and esophagitis. PTV size correlated with increased cardiac mortality and esophagitis in both plan variations and with pneumonitis for VMAT plans. Dmean, Dmedian, and V20Gy correlated with the risk for pneumonitis, and Dmean, Dmedian, and V1% with the risk for esophagitis in both variants. Conclusions: We showed decreased risk of different NTCPs for VMAT and APPA planning for thoracic toxicities. The use of an IMRT technique like VMAT showed advantages for several DVH metrics in organs at risk and should therefore be recommended for radiation treatment of PMBCL.

The importance of metastasis-directed radiotherapy is increasing in the management of oligometastatic prostate cancer. We evaluated different target volume and dose concepts for stereotactic body radiotherapy (SBRT) of spine bone metastases (BoM) from prostate cancer in a large European cohort. Data of prostate cancer patients receiving SBRT for spine BoM between 2010 and 2024 at 19 European cancer centers were retrospectively collected. Treatment volumes and dose concepts were analyzed regarding their impact on overall survival (OS), freedom from local recurrence (FFLR), biochemical recurrence-free survival (BRFS), and progression-free survival (PFS). With a median follow-up of 25.1 months (range: 1.4-77.2), 213 patients with 283 spine BoM were evaluated. 1-/3-year PFS with simultaneously integrated boost (SIB) were 85.7 %/73.9 % (BED₄ [Biologically effective dose with α/β-ratio = 4 Gy] ≥ 100 Gy) and for non-SIB concepts 81.2 %/45.5 % (BED₄ ≥ 100 Gy), respectively. 1-/3-year BRFS for SIB-treated BoM amounted to 81.7 %/68.4 % (BED₄ ≥ 100 Gy) and for non-SIB 78.3 %/43.6 % (BED₄ ≥ 100 Gy). OS was not significantly different for the evaluated dose and target volume concepts. For FFLR a significant difference was observed favoring BED₄ ≥ 100 Gy. In multivariable analysis, following factors were positively associated with both PFS and BRFS: BED₄ for GTV_mean dose and SIB concept. Adverse events were very low, with fracture rates of 2.2 %. This multicenter cohort analysis showed that SBRT of spine BoM from prostate cancer is an effective and well-tolerated treatment. Both BED and usage of a SIB concept were associated with improved PFS and BRFS. Prospective studies are needed to confirm these findings and further standardize SBRT concepts.

Outcome patterns for stereotactic body radiotherapy (SBRT) of bone oligometastases (BoM) especially for older patients are inadequately defined. We aimed to evaluate oncological outcomes and tolerability of SBRT for BoM in older patients. Patients ≥70 years treated with SBRT for BoM between 2010 and 2024 at 20 European centers were analyzed and compared to patients <70 years. Outcomes included local recurrence (LR)/ freedom from LR (FFLR), progression-free survival (PFS), overall survival (OS), and adverse events. 789 patients with 1079 BoM were analyzed. Median age was 68 years (range: 19-91), and 355 patients (45.0%) were ≥70 years. Most common primary tumors were prostate (57.4%), breast (13.8%), and lung cancers (10.5%). LR at 3 years was 9.3% (CI: 6.0-12.8%) in patients <70 years and 11.7% (CI: 7.1-16.8%) in patients ≥70 years (p = 0.39). Grade-3 adverse events occurred in 1.8% of patients <70 years and 1.4% ≥70 years. No grade-4/5 adverse events were observed. Fracture rates were 2.9% for patients <70 years, and 1.8% ≥70 years. A higher metastatic volume was associated with reduced FFLR (Hazard ratio [HR] 1.006; p = 0.02), PFS (HR 1.003; p = 0.05), and OS (HR 1.003; p = 0.04). A better performance status was related to improved PFS (HR 0.98; p < 0.01) and OS (HR 0.96; p < 0.001), while age was not a significant factor. This multicenter cohort analysis showed that SBRT of BoM is effective and well tolerated even in older patients. There were no significant differences in outcomes or side effects including fracture rates across patient age groups.

In recent years, ablative radiotherapy of primary and secondary liver tumors has become a highly regarded treatment option. We aimed to compare high-dose-rate interstitial brachytherapy (HDR-iBT) and stereotactic body radiotherapy (SBRT) in free breathing (FB) and deep inspiration breath hold (DIBH) in order to support future decisions on the appropriate radiation technique for liver tumors. Forty-two patients with 1-4 liver malignancies undergoing HDR-iBT with 1x15-20 Gy were included. Eighty-eight SBRT plans in DIBH or FB with a prescription dose of 3x12.5 Gy to the surrounding 67 % isodose were generated using the HDR-iBT-computed tomography. Dose-volume parameters according to ICRU91 regarding organs-at-risk (OAR), target coverage, generalized equivalent uniform dose (gEUD_2Gy), biological dose parameters, dose uniformity, conformity and plan quality indices were compared. The mean target doses for HDR-iBT were at least twice as high as in SBRT, but target coverage was significantly more conformal for SBRT and the gEUD_2Gy was higher (p < 0.001). The healthy tissue conformity indices (HTCI) for SBRT_FB and SBRT_DIBH were significantly higher than for HDR-iBT (p < 0.001). For all techniques, a significant positive correlation between HTCI and target volume size was found. HDR-iBT achieved lower mean and maximum doses for most investigated OAR-parameters. Comparing SBRT_DIBH and SBRT_FB, all OAR-parameters presented significantly lower values for SBRT_DIBH (p < 0.001). While SBRT_DIBH achieved a more conformal target coverage with both higher minimal doses and gEUD_2Gy, brachytherapy offered higher mean and maximal doses to the target volume and a better sparing of OAR, depending on optimal catheter positioning.

Monte Carlo simulations offer the highest accuracy for calculating dose distributions in radiation therapy (RT). Precise modeling of the Elekta Synergy linear accelerator (LINAC) with Agility multi-leaf collimator (MLC) is essential for accurate dose verification. The 6 MV flattened (FF) and FF-free (FFF) Elekta Synergy LINAC with Agility MLC was modeled using TOPASMC, providing an additional verification tool for patient dose distributions. An initial model was developed based on vendor specifications. The 160-leaf MLC was constructed from a computer-aided design mesh of a single leaf. Proprietary code was created to manage the placement and movement of the field-defining diaphragms. Using measurements of depth doses, dose profiles, and output factors in a water phantom for energies of 6 MV and 6 MV FFF across field sizes from 1 × 1 cm² to 36 × 36 cm², we adjusted the incident electron beam energy distribution, flattening filter geometry, jaw and MLC leaf geometry, and leaf-bank rotation. A DICOM interface between the treatment planning system and TOPAS was developed, and patient plans of increasing complexity were calculated using the model. The local gamma index pass rate (1%/1 mm for 1D, 2%/2 mm for 3D) was used to evaluate the agreement between reference and simulation. Over 99% of depth dose points and 92% of dose profile points passed the gamma criterion for all field sizes. The model accurately replicated the leaf-tip and tongue-and-groove effects. Calculated RT plans showed a gamma agreement between 87% and 99%, depending on the delivery technique. The developed model accurately replicates measured dose distributions and can be used to externally validate treatment plans, serving as an additional tool for secondary dose calculations.