Analysis on the Effect of Field Width in the Delineation of Planning Target Volume for TomoTherapy.
- Author:
Ju Young SONG
1
;
Byung Sik NAH
;
Woong Ki CHUNG
;
Sung Ja AHN
;
Taek Keun NAM
;
Mee Sun YOON
;
Jae Uk JUNG
Author Information
1. Department of Radiation Oncology, Chonnam National University Medical School, Gwangju, Korea. jysong@jnu.ac.kr
- Publication Type:Original Article
- Keywords:
TomoTherapy;
Field width;
PTV (planning target volume);
Dose distribution
- MeSH:
Humans;
Jaw
- From:Korean Journal of Medical Physics
2010;21(4):323-331
- CountryRepublic of Korea
- Language:Korean
-
Abstract:
The Hi-Art system for TomoTherapy allows only three (1.0 cm, 2.5 cm, 5.0 cm) field widths and this can produce different dose distribution around the end of PTV (Planning target volume) in the direction of jaw movement. In this study, we investigated the effect of field width on the dose difference around the PTV using DQA (Delivery quality assurance) phantom and real clinical patient cases. In the analysis with DQA phantom, the calculated dose and irradiated films showed that the more dose was widely spreaded out in the end region of PTV as increase of field width. The 2.5 cm field width showed a 1.6 cm wider dose profile and the 5.0 cm field width showed a 4.2 cm wider dose profile compared with the 1.0 cm field width in the region of 50% of maximum dose. The analysis with four patient cases also showed the similar results with the DQA phantom which means that more dose was irradiated around the superior and inferior end of PTV as an increase of field width. The 5.0 cm field width produced the remarkable high dose distribution around the end region of PTV and we could evaluate the effect quantitatively with the calculation of DVH (Dose volume histogram) of the virtual PTVs which were delineated around the end of PTV in the direction of jaw variation. From these results, we could verify that the margin for PTV in the direction of table movement should be reduced compared with the conventional margin for PTV when the large field such as 5.0 cm was used in TomoTherapy.
