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BackgroundThe aim of this study is to examine the dosimetric influence of endorectal balloons (ERB) in rectal sparing in prostate cancer patients with implanted hydrogel rectum spacers treated with dose escalated/hypofractionated intensity modulated proton beam therapy (IMPT). MethodsTen patients with localised prostate cancer included in the ProRegPros study and treated at our centre were invastigated in this study. All patients underwent a placement of hydrogel rectum spacers before planning. Two planning CTs (with and without 120 cm3 fluid-filled ERB) were acquired for each patient. Dose prescription was set according to the used simultaneous integrated boost strategy with 72 Gray (Gy)/2.4 Gy/5 x weekly to prostate+1 cm of the seminal vesicle, and 60 Gy/2 Gy/5 x weekly to prostate+2 cm of the seminal vesicle. Planning with two lateral-opposed IMPT beams was performed in both CTs. Rectal dosimetry values including dose-volume statistics and normal tissue complication probability (NTCP) in both plans were compared (non-ERB plans vs. ERB plans).ResultsFor ERB plans compared to non-ERB, the reductions were 8.51 ± 5.25 Gy (RBE) (p= 0.000) and 15.76 ± 11.11Gy (P= 0.001) for the mean and the median rectal dose, respectively. No significant reductions in rectal volumes receiving high dose levels were found. The use of ERB resulted in significant reduction in rectal volume receiving 50 Gy (RBE), 40 Gy (RBE), 30 Gy (RBE), 20 Gy (RBE), and 10 Gy (RBE) with P values of 0.034, 0.008, 0.003, 0.001, and 0.001, respectively. For the anterior rectum, no differences between ERB and non-ERB plans were observed. For the posterior rectum, ERB reduced rectal volumes received 30 Gy (RBE), 20 Gy (RBE), and 10 Gy (RBE) with P values of 0.019, 0.003, and 0.001, respectively. No significant reductions in mean or median rectal toxicity (Late rectal bleeding ≥2, necrosis/stenosis, and Late rectal toxicity ≥ 3) were observed when using the ERB according to NTCP models.ConclusionThe ERB reduced rectal volumes exposed to intermediate/low dose levels. However, no significant reduction in rectal volumes receiving high/intermediate doses could be observed. No benefit but also no disadvantage of the ERB for late rectal toxicity was found according to available NTCP models.

Purpose Neuroblastoma (NB) is the most common extracranial solid malignancy during childhood. Despite a multimodal treatment approach, the prognosis of patients with metastatic NB is not satisfactory. Although radiotherapy (RT) has become an integral part of treatment of the primary tumor, the role of RT in osteomedullary lesions is not well defined. A retrospective analysis was conducted to evaluate the impact of RT for metastatic sites in children with high-risk NB. Methods All patients with stage 4 NB from the prospective, multicenter NB trials NB97 and NB2004 who received RT to metastatic sites during frontline treatment were included in this retrospective analysis. Results A total of 18 children were irradiated with a median dose of 36 Gray (Gy; range 20–45 Gy) to one or more (range 1–3) osteomedullary metastases with or without concomitant RT to the primary tumor site. The median follow-up time was 149 months (range 55–220) in survivors. At 5 years, local relapse-free survival (LRFS) at irradiated metastatic sites and metastases-free survival (MFS) at distant, non-irradiated site rates were 51.4 and 39.9%, respectively. The estimated overall survival (OS) rate at 5 years was 49.4%. No high-grade acute or late toxicity and no secondary malignancy was reported. Conclusion RT to metastases is feasible for patients with stage 4 NB. However, an impact of RT to residual metastatic sites on outcome was not found. Studies with larger cohorts or prospective trials would be desirable in order to elucidate the role of RT for metastases.

Pencil beam scanning (PBS) proton therapy enables better dose conformality for complex anatomical geometries than passive proton scattering techniques, but is more susceptible to organ motion. This becomes an issue when treating moving tumours in the thorax or abdomen. Novel four-dimensional treatment planning approaches have been developed to increase the robustness of PBS plans against motion. However, their efficacy still needs to be examined by means of 4D dynamically accumulated dose (4DDD) analyses. This study investigates the potential use of 4D robust optimisation to maintain sufficient target coverage in the presence of organ motion, while sparing surrounding healthy tissue, for hepatocellular carcinoma (HCC). The liver is particularly suited to study motion interplay effects since the treatment region exhibits smaller density gradients and more homogeneous tissue than targets in the thorax, making it less prone to range errors. A facility-specific beam time model, developed and experimentally validated previously, was used for the clinical evaluation. 4DDD analyses of eleven target volumes did not show a significant improvement of the target coverage using 4D robust optimisation, but a reduction of the dose to close-by organs at risk. Interplay effects were averaged out for the applied fractionation scheme of 15 fractions. Contrary to PBS, passive double scattering (DS) plans yielded homogeneous 4DDD dose distributions in a single fraction. But, in some cases, they exceeded organ at risk dose limits, which were only satisfied in PBS. The average normal liver dose could be decreased by almost 6% compared to non-robustly optimised PBS plans and by 16% compared to DS plans when implementing 4D robust optimisation. Except for some very small tumours with large motion amplitudes, 4D robustly optimised PBS plans were found to be clinically acceptable even without supplementary motion mitigation techniques.