open access

Vol 17, No 6 (2012)
Original research articles
Published online: 2012-11-01
Submitted: 2011-08-31
Get Citation

Exit fluence analysis using portal dosimetry in volumetric modulated arc therapy

Prabakar Sukumar, Sriram Padmanaban, Dhanabalan Rajasekaran, Muniyappan Kannan, Vivekanandan Nagarajan
DOI: 10.1016/j.rpor.2012.06.003
·
Rep Pract Oncol Radiother 2012;17(6):324-331.

open access

Vol 17, No 6 (2012)
Original research articles
Published online: 2012-11-01
Submitted: 2011-08-31

Abstract

Aim

In measuring exit fluences, there are several sources of deviations which include the changes in the entrance fluence, changes in the detector response and patient orientation or geometry. The purpose of this work is to quantify these sources of errors.

Background

The use of the volumetric modulated arc therapy treatment with the help of image guidance in radiotherapy results in high accuracy of delivering complex dose distributions while sparing critical organs. The transit dosimetry has the potential of Verifying dose delivery by the linac, Multileaf collimator positional accuracy and the calculation of dose to a patient or phantom.

Materials and methods

The quantification of errors caused by a machine delivery is done by comparing static and arc picket fence test for 30 days. A RapidArc plan, created for the pelvis site was delivered without and with Rando phantom and exit portal images were acquired. The day to day dose variation were analysed by comparing the daily exit dose images during the course of treatment. The gamma criterion used for analysis is 3% dose difference and 3[[ce:hsp sp="0.25"/]]mm distance to agreement with a threshold of 10% of maximum dose.

Results

The maximum standard deviation for the static and arc picket fence test fields were 0.19[[ce:hsp sp="0.25"/]]CU and 1.3[[ce:hsp sp="0.25"/]]CU, respectively. The delivery of the RapidArc plans without a phantom shows the maximum standard deviation of 1.85[[ce:hsp sp="0.25"/]]CU and the maximum gamma value of 0.59. The maximum gamma value for the RapidArc plan delivered with the phantom was found to be 1.2. The largest observed fluence deviation during the delivery to patient was 5.7% and the maximum standard deviation was 4.1[[ce:hsp sp="0.25"/]]CU.

Conclusion

It is found from this study that the variation due to patient anatomy and interfraction organ motion is significant.

Abstract

Aim

In measuring exit fluences, there are several sources of deviations which include the changes in the entrance fluence, changes in the detector response and patient orientation or geometry. The purpose of this work is to quantify these sources of errors.

Background

The use of the volumetric modulated arc therapy treatment with the help of image guidance in radiotherapy results in high accuracy of delivering complex dose distributions while sparing critical organs. The transit dosimetry has the potential of Verifying dose delivery by the linac, Multileaf collimator positional accuracy and the calculation of dose to a patient or phantom.

Materials and methods

The quantification of errors caused by a machine delivery is done by comparing static and arc picket fence test for 30 days. A RapidArc plan, created for the pelvis site was delivered without and with Rando phantom and exit portal images were acquired. The day to day dose variation were analysed by comparing the daily exit dose images during the course of treatment. The gamma criterion used for analysis is 3% dose difference and 3[[ce:hsp sp="0.25"/]]mm distance to agreement with a threshold of 10% of maximum dose.

Results

The maximum standard deviation for the static and arc picket fence test fields were 0.19[[ce:hsp sp="0.25"/]]CU and 1.3[[ce:hsp sp="0.25"/]]CU, respectively. The delivery of the RapidArc plans without a phantom shows the maximum standard deviation of 1.85[[ce:hsp sp="0.25"/]]CU and the maximum gamma value of 0.59. The maximum gamma value for the RapidArc plan delivered with the phantom was found to be 1.2. The largest observed fluence deviation during the delivery to patient was 5.7% and the maximum standard deviation was 4.1[[ce:hsp sp="0.25"/]]CU.

Conclusion

It is found from this study that the variation due to patient anatomy and interfraction organ motion is significant.

Get Citation

Keywords

RapidArc; Exit fluence; Gamma evaluation; EPID; Portal dosimetry

About this article
Title

Exit fluence analysis using portal dosimetry in volumetric modulated arc therapy

Journal

Reports of Practical Oncology and Radiotherapy

Issue

Vol 17, No 6 (2012)

Pages

324-331

Published online

2012-11-01

DOI

10.1016/j.rpor.2012.06.003

Bibliographic record

Rep Pract Oncol Radiother 2012;17(6):324-331.

Keywords

RapidArc
Exit fluence
Gamma evaluation
EPID
Portal dosimetry

Authors

Prabakar Sukumar
Sriram Padmanaban
Dhanabalan Rajasekaran
Muniyappan Kannan
Vivekanandan Nagarajan

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