Feasibility of Individualized, Model-guided Optimization of Proton Beam Treatment Planning in Patients With Low Grade Glioma (INDIGO)

Feasibility of Individualized, Model-guided Optimization of Proton Beam Treatment Planning in Patients With Low Grade Glioma

Prospective Phase II Trial to Assess Feasibility of Individualized, Model-guided Optimization of Proton Beam Treatment Planning in Patients With Low Grade Glioma Multicentric, Prospective Interventional, Randomized, Observer Blind Two Arm (Active Control), Parallel Group Investigator-initiated Phase II Trial

Low-grade glioma (LGG) represent typically slowly growing primary brain tumors with world health organization (WHO) grade I or II who affect young adults around their fourth decade. Radiological feature on MRI is a predominantly T2 hyperintense signal, LGG show typically no contrast uptake. Radiotherapy plays an important role in the treatment of LGG. However, not least because of the good prognosis with long term survivorship the timing of radiotherapy has been discussed controversially. In order to avoid long term sequelae such as neurocognitive impairment, malignant transformation or secondary neoplasms initiation was often postponed as long as possible

Since patients with low grade glioma are expected to become long-term survivors, the prevention of long-term sequelae is particularly important. In addition to disease progression, also treatment related side effects such as decline of neurocognitive function, endocrine impairment or sensorineural deficits can have a negative impact on patient's quality of life. Owing to the biophysical properties of protons with an inverse depth dose profile compared to photons and a steep dose fall of to the normal tissue, there is a strong rationale for the use of PRT in the treatment of patients with low-grade glioma. Although data from large randomized trials are still missing there is increasing evidence from smaller prospective trials and retrospective analyses that the expected advantages indeed transform into clinical advantages. However, in about 20 % of all patients, late contrast-enhancing brain lesions (CEBL) appear on follow-up MR images 6 - 24 months after treatment. At HIT in Heidelberg and at OncoRay in Dresden, CEBLs have been observed to occur at very distinct locations in the brain and relative to the treatment field. Retrospective analysis has elucidated potential key factors that lead to CEBL occurrence. However, avoidance of CEBLs is hardly feasible using conventional treatment planning strategies. Model-aided risk avoidance denotes the use of model-based CEBL risk calculations as an auxiliary tool for clinical treatment planning: Model-based risk calculations and risk reduction via software-based optimization help the clinician to minimize risk of CEBL occurrence during treatment planning.

Model-based NTCP is calculated after plan approval, however, no further adjustments are to be made to the approved treatment plan

Allocated to Control Calculation of normal tissue complication probability (NTCP) Model-guided replanning. Replanning is performed with Raysearch Raystation. Optimizations objectives are: the optimization objectives that control the maximum dose in the target volume employ a variable, LETd-dependent model for RBE that allows us to include the RBE-variations predicted by the NTCP model the periventricular volume, defined as the volume closer than 4 mm to the ventricular wall, is included into the optimization with a constraint on its Equivalent Uniform Dose (EUD) and with the variable RBE model described above. Thereby, the combined effect of the RBE variation and increased sensitivity of the periventricular volume, as predicted by the NTCP model, is included. The effectiveness of the re-planning is verified by a second NTCP computation.

observed within 24 months after Proton Beam Therapy (PRT) measured by quarterly contrast enhanced MRI of the brain

patient reported outcome according to points on the PRO-CTCAE questionaire, scored 0/1 for absent/present)

Inclusion Criteria: Age > 18 years histologically proven low-grade glioma indication for definitive or adjuvant radiotherapy ability to understand character and personal consequences of the clinical trial written informed consent Exclusion Criteria: previous cerebral irradiation contraindication for contrast-enhanced MRI neurofibromatosis participation in another clinical trial with competing objectives