EVALUATING DIFFERENCES IN GAMMA INDEX OF INTENSITY MODULATED RADIOTHERAPY PATIENT SPECIFIC QUALITY ASSURANCE BY VARYING GRID SIZES IN PATIENT PLANNING

Author Name: 1. Rajesh.R 2. Dr Shanmukhappa B Kaginelli 3. Vadivel Muthu 4. Ramanand M L

Volume/Issue: 02/08

Country: India

DOI NO.: 08.2020-25662434 DOI Link: https://www.doi-ds.org/doilink/01.2022-61254425/UIJIR

Affiliation:

1. Sr. Medical Physicist, Narayana Hrudayalaya, Hospital, Mysore, Karnataka, India
2. Associate Professor, Division of Medical Physics, School of Life Sciences, JSS AHER, Mysore, Karnataka, India
3. Junior Scientific Officer, Gamma Knife Centre, NIMHANS Hospital, Bangalore, Karnataka, India
4. Sr. Physicist, K R Hospital, Mysore, Karnataka, India

ABSTRACT

Choosing an optimum grid size plays a vital role for planning in Radiotherapy cases. A minimal change of even 1mm of grid size can result in large variation in treatment planning and is reflected in quality assurance results also. The objective of this study was to estimate the variations in Gamma Index (GI) quality assurance results for patients undergoing Intensity Modulated Radiotherapy (IMRT) planning with varying grid sizes of 3mm, 5mm and 10mm respectively. We compared IMRT plans for 15 patients. 15 patients planned for IMRT were selected for this study. Out of that 5 were head and neck, 5 were pelvic and 5 were brain patients respectively. For each patient three plans were generated with three different grid sizes. The plan acceptance criteria were 95% of PTV should receive at least 95% of prescribed dose and 1% of PTV should not exceed 107% of prescribed dose. Dose for the organs at risk were respected as per the QUANTEC guidelines. After plan acceptance corresponding IMRT QA was executed by PTW 729 array detector. The gamma index results of each plan were recorded for the three different grid sizes. The passing criteria were kept being 3% dose difference and 3mm of distance to agreement for all cases. Statistical analysis used: Notable passing rate of Gamma Index result are observed for three different grid size plans. The passing criteria were kept ideal to be 3% Dose difference and 3mm distance of Distance To Agreement (DTA) for all cases We observed 3mm grid size has best passing result when compared with that of 5mm and 10mm. Using minimum and optimum grid size enhances good Patient plan and good IMRT patient specific quality assurance results.

Key words: Intensity Modulated Radiation Therapy, Patient Specific Quality Assurance, Gamma Index, Distance to Agreement, Linear accelerating Machine, Treatment Planning System, Planning Target Volume, Quantitative Analyses of Normal Tissue Effects in Clinics (QUANTEC). Key Message: It was observed in the study that using minimum grid size in TPS gives good dose calculation which results in significantly good passing QA result, when compared to larger grid spacing. So, choose the grid spacing optimum suitable for TPS planning faster and to get best QA result by determining their own grid size parameter in hospital in spite of using vendor’s specified values.