الفهرس 
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Abstract
The aim of this study was to quantify the extent of set-up errors and to
develop a quality assurance program using port films in the radiation
oncology department; NCI, Cairo.
This pilot study included a sample of ten patients treated for malignant
diseases of the pelvic and the head and neck regions during the period
between April 2005 and October 2005. For each patient, a number of Kodak
EC-L port films was taken once weekly on the linear accelerator (6Mv)
using the double exposure technique. The total number of films was 108, 58
films for the pelvic region and 50 films for the head and neck region.
Port film visibility and assessment of set-up errors, whether subjectiveor objective, in both the pelvic and the head and neck regions were analyzed
by two senior staff and one junior radiation oncologists.
Port film visibility was assessed by the percentage of the number of
visible landmarks in the port film/ number of chosen landmarks in the
simulator films with scoring: excellent = 4/4, good = 3/4 and poor = 0-2/4.
In pelvic port films the visibility was as follows: 62%, 24% and 14% of
films were of excellent, good and poor visibility, respectively. However in
the head and neck films 68%, 26%, 6% of films were of excellent, good,
poor visibility, respectively.The rejection rate in pelvic port films was 29%, while in head and
neck port films it was 28%. Shielding blocks placement errors was the most
common cause of film rejection; 14% of all port films. A higher rejection
rate due to shielding errors was noted in the head and neck region; 72% of
rejected films, compared to that in the pelvic region; 29% of rejected films.
The second most common cause of films rejection was centering error ;12%
of all films taken. A much higher rejection rate due to centering errors was
noted in the pelvic region; 65% of rejected films, compared to the head and
neck region; 14% (P = 0.018).
In the pelvic region, there was slight predominance of errors in the cranio-caudal (CC) direction with a mean systematic error of 6.2 mm,
followed by the antero-posterior (AP) and medio-lateral (ML) directions (5
mm and 3.3 mm, respectively). While in the head and neck region, there was
predominance of errors in the AP and the CC directions; with a mean
systematic error of 4.9 mm. and 3.4 mm, respectively, followed by that in
the ML directions (1.8 mm). In the pelvic region, the 2D-vector errors mean
was 8.2 mm, while at the level of head and neck, the 2D-vector errors mean
was 6.7 mm.
The shifts in ML direction in the pelvic and the head and neck regions
were: ≤ 5 mm in 72% and 87%, 5 - 10 mm in 28% and 6.5% and >10 mm in
0% and 6.5% of films, respectively. The shifts in CC direction in the pelvic and the head and neck regions
were: ≤ 5 mm in 65.5% and 80%, 5 - 10 mm in 10% and 20% and > 10 mm
in 24.5% and 0% of films, respectively. (P = 0.0007) The shifts in AP direction in the pelvic and the head and neck regions
were: ≤ 5 mm in 52% and 60%, 5 - 10 mm in 38% and 34% and > 10 mm in
10% and 6% of films, respectively.
The 2D-vector errors in the pelvic and the head and neck regions
were: ≤ 5 mm in 33% and 44%, 5 - 10 mm in 34.5% and 42% and > 10 mm
in 32.5% and 14% of films, respectively. (P = 0.067)
The present study has confirmed the equal importance of porta
imaging in both the pelvic and the head and neck regions as a part of the
routine quality assurance program in radiation therapy, with the stress on theport films ability of detection and measurement of set-up errors and
eventually guidance of their correction.