Dosimetric Verification of Gamma Passing Rate for Head and Neck Cases Treated with Intensity Modulated Radiation Therapy (IMRT) Treatment Planning Technique

Siham Sabah Abdullah

doi:10.21123/bsj.2021.18.4(suppl.).1514

Abstract

Each Intensity Modulated Radiation Therapy (IMRT) plan needs to be tested and verified before any treatment to check its quality. Octavius 4D-1500 phantom detector is a modern and qualified device for quality assurance procedure. This study aims to compare the common dosimetric criteria 3%/3 mm with 2%/2 mm for H&N plans for the IMRT technique. Twenty-five patients with head and neck (H&N) tumor were with 6MV x-ray photon beam using Monaco 5.1 treatment planning software and exported to Elekta synergy linear accelerator then tested for pretreatment verification study using Octavius 4D-1500 phantom detector. The difference between planned and measured dose were assessed by using local and global gamma index (GI) analysis method at threshold 10%. The DD/DTA criteria are performed with 3%/3 mm and 2%/2 mm. A significant difference is shown between the measured and calculated point dose for the treatment plans. A comparison made between the gamma passing rate between the 2%/2 mm and 3%/3 mm shows a significant difference for local and global which shows that the 2%/2 mm are more sensitive to dose variation than 3%/3 mm. The total monitor unit (MU) shows a negative linear relationship with both criteria and %GP types. A significant correlation is shown between the total MU and global %GP at 2%/2 mm criterion. The conclusion of the study indicates that 2%/2 mm criterion is more sensitive to the dose distribution changes than the 3%/3 mm. The total number of monitor units should be taken into consideration during the planning of H&N tumors using the IMRT plans.

Highlights

The modern radiation therapy treatment ofHead and Neck (H&N) tumors are done with a treatment planning technique named intensitymodulated radiation therapy or so-called Intensity Modulated Radiation Therapy (IMRT).The IMRT delivers the non-uniform intensity of eternal radiation across the beams to the target volume to optimize the composite dose distribution 1,2
Head and Neck (H&N) tumors are done with a treatment planning technique named intensitymodulated radiation therapy or so-called IMRT
The unit that measures the output dose from the linear accelerator machine is called the monitor unit (MU) which is equal to 100 Gy 4-6

Summary

Introduction

The modern radiation therapy treatment ofHead and Neck (H&N) tumors are done with a treatment planning technique named intensitymodulated radiation therapy or so-called IMRT.The IMRT delivers the non-uniform intensity of eternal radiation across the beams to the target volume to optimize the composite dose distribution 1,2. Head and Neck (H&N) tumors are done with a treatment planning technique named intensitymodulated radiation therapy or so-called IMRT. PTW (PTW, Freiburg, Germany) invent a device called Octavius 4D with 1500 cubic ion chambers distributed over the 27 × 27 cm[2] detector surfaces contain a place inserted with the 2D array. It uses software named Verisoft 7.1 software version. To assess the delivery accuracy and verify the IMRT plans, a gamma evaluation method adopted which is proposed by Low in 1998 7,8. Gamma evaluation is a practical method where its verification varies from one QA device to another[9]. The main difference between them occurs in the method of evaluating the dose difference[16,17,18]

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