ESTRO 2024 - Abstract Book

S960

Clinical - CNS

ESTRO 2024

1 The Gujarat Cancer and Research Institute, Radiation Oncology, Ahmedabad, India. 2 The Gujarat Cancer and Research Institute, Medical Oncology, Ahmedabad, India. 3 The Gujarat Cancer and Research Institute, Medical Physics, Ahmedabad, India

Purpose/Objective:

Tomo-based helical IMRT for Craniospinal Irradiation (CSI) provided an alternate treatment technique to improve target coverage and reduce dose to nearby OAR compared to conventional techniques. 1 – 3 The Aim of this study was To perform a dosimetric analysis on tomotherapy in craniospinal irradiation for better coverage, homogeneity, and conformality of the target, sparing of normal tissue in terms of maximum and mean doses by the study of acute toxicities and To identify technical, planning, and logistic difficulties like setup-errors during the execution of CSI planning. 4 – 12

Material/Methods:

It was a prospective observational single-arm study done at a Tertiary care centre. Twenty-four patients with various brain tumours that require treatment of the whole neuro-axial axis were included in this study. Patients between 2 to 70 years of age were included. All the patients had a Karnofsky performance scale index (KPS) between 60 to 100. The most common histology was medulloblastoma (n=14). The planning CT images were acquired of a “Somaton Confidence” model of “Siemens Healthineers” CT simulator with a 5 mm thickness of slice from vertex to upper 1/3rd thigh with proper immobilization using devices like thermoplastic casts and vacloks. Planning was done in Accuray Precision system V-2.0.1.1. Patients were contoured by the European Society of Paediatric Oncology guidelines. Helical IMRT and Direct IMRT planning were done with inverse planning. Spine boost plannings were done with Direct IMRT. The Median Width, Pitch and Modulation factor for CSI plans were 5 cm, 0.3 and 3 respectively. For brain boost plan, the values were 1 cm, 0.3 and 3 respectively and for spine boost plan, the values were 2.5 cm, 0.25 and 2.2 respectively. Anisotropic Analytical Algorithm (AAA) with 2.5 mm spatial resolution was used as the dose calculation algorithm. A Dosimetric analysis for the target by Dmean, Dmax, Conformality & homogeneity indexes (CI & HI), PTV V95%, hotspot (V107%) & cold spot inside PTV (< V90%) was performed. Low doses of Body minus PTV (V5Gy and V1Gy) were documented. Treatment was delivered on Tomotherapy Radixact X9 (Sunnyvale, USA). Acute side effects were assessed using the Common toxicity criteria grading system (CTCAE 4.0). The Median age was 15.5 years (14 pediatric & 10 adult). The mean CSI dose was 33.4Gy. Median dose per fraction was 1.8Gy. Twenty-one patients were given boost to the brain and 2 to the spine. Fifteen were given concurrent chemotherapy. The mean fractional MU (Monitor unit) for CSI was 1190.77 (Range: 5624.9 – 29160.68). The mean beam-on time was 666.3 seconds (Range: 323 – 1685.6). Comparison between Beam-on time and MU to the field width suggested when width of the field is increased, MU and beam Beam-on time is significantly reduced giving statistical correlation “pearson correlation coefficient” value of 0.861 (Range: -1 to +1). Mean PTV Coverage - Dmax: 35.5Gy (106%), Dmean: 33.02Gy (98.86%), V107%: 0.45cc (0.02% of PTV), V90%: 14.86cc (0.68% of PTV) Conformality Index (CI): 1.08 and Homogeneity Index (HI): 1.1 Low doses received by body minus PTV - V5Gy: 38.95% and V1Gy: 71.33% were reported. OARs dosimetry suggested acceptable dosimetry for most organs except lungs, V5Gy for bilateral lungs was >42% in 17 patients. However, V20Gy <31% and Dmean were acceptable. 8 patients received a mean dose to cochlea >45Gy who were given brain boost in the posterior fossa in which cochlea was covered in Results: