Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Purpose: To identify patients who are likely to benefit most from proton therapy, based on the potential reduction in normal tissue complication probability (NTCP) compared to photon therapy. The NTCP models required for this comparison were developed using clinical data on early side effects for patients with brain or prostate cancer having received proton therapy.

Material and methods: Eighty patients with primary brain tumours and 30 patients with adenocarcinoma of the prostate who received proton therapy were included in this study. For the brain tumour patients, the radiation-induced early toxicities alopecia, erythema, pain and fatigue were considered, while for prostate cancer proctitis, diarrhoea, urinary frequency, urgency and incontinence, obstructive symptoms and radiation-induced cystitis were investigated. The occurrence of these side effects was correlated with different dose-volume parameters of associated organs at risk. NTCP models were created using logistic regression. A retrospective comparative treatment planning study was conducted to predict the potential reduction in NTCP of proton therapy compared to volumetric modulated arc therapy using the created models. For patients with brain tumours different subgroups were defined to identify patient groups which show a particularly high reduction in the considered toxicities.

Results: For patients with primary brain tumours significant correlations between the occurrence of alopecia grade 2 as well as erythema grade ≥ 2 and the dose-volume parameters D5% and V25Gy of the skin were found. Plan comparison showed an average reduction in NTCP for alopecia grade 2 of more than 5 % (see figure) and for erythema grade ≥ 2 of about 5 % using proton therapy. For patients with a brain tumour located in the skull base, with a clinical target volume less than 115 cm³ or with a prescribed dose less than 60 Gy, a potential reduction in NTCP for alopecia grade 2 of about 10 % could be achieved. For patients with prostate cancer significant correlations between obstructive symptoms grade ≥ 1 and the dose parameter D30% of the bladder as well as radiation-induced cystitis grade ≥ 1 and D20% of the bladder were found. Plan comparison showed an average reduction in NTCP for obstructive symptoms ≥ grade 1 of about 25 % and for radiation-induced cystitis about 15 % using proton therapy.

Conclusion: We found significant correlations between the occurence of early toxicities and dose-volume parameters of associated organs at risk for patients with primary brain tumours or prostate cancer receiving proton therapy. A reduction of NTCP could be predicted for proton therapy based on comparative treatment planning. After validation, these results may be used to identify patients who are likely to benefit most from proton therapy, as suggested by the model-based approach [1].

[1] Langendijk JA et al. (2013) Radiother Oncol 107, 267 - 273.