1. Introduction Materials & Methods Results Conclusion
CHALLENGES AND DIFFERENCES IN EXTERNAL RADIATION THERAPY FOR RETINOBLASTOMA;
FROM STANDARD TECHNIQUES TO NEW DEVELOPMENT AREAS
(A REVIEW OF DIFFERENT RADIATION TECHNIQUES)
CHALLENGES AND DIFFERENCES IN EXTERNAL RADIATION THERAPY FOR RETINOBLASTOMA; FROM STANDARD TECHNIQUES TO NEW DEVELOPMENT AREAS
(A REVIEW OF DIFFERENT RADIATION TECHNIQUES)
Ayşe HİÇSÖNMEZ1, Yıldız GÜNEY2, Ayşen DİZMAN2, Bahar DİRİCAN3, Yakup ARSLAN4,Tuğba ATAKUL4, Hasan UYSAL2,
Kaan GÜNDÜZ5, Nurdan TAÇYILDIZ6, Emel ÜNAL6, Handan DİNÇASLAN6,  Meltem NALCA ANDRIEU7,
ONKO Ankara Oncology Center, TURKEY1
Ankara Oncology Hospital Department of Radiation Oncology ,TURKEY2
Ankara Gülhane Military Medical Academy Department of Radiation Oncology , TURKEY3
Ankara University School of Medicine, Department of Radiation Oncology, Ankara, TURKEY4
Ankara University School of Medicine Department of Ophthalmology ,TURKEY5
Ankara University School of Medicine Department of Pediatric Oncology ,TURKEY6
Near East University Faculty of Medicine, Department of Radiation Oncology, TURKISH REPUBLIC OF NORTHERN CYPRUS7
Introduction
Technique
V95% (%)
PTV min (Gy)
PTV max (Gy)
PTV mean (Gy)
V99%(%)
(2)
Dmax (%)
(3)
Electron technique 99 28 49
41.7 98
136
Wedge Pair (2LFT)
100 31 39
36.8 95
106.8
Conformal
(CRT) 34 38 37 97
102.3
IMRT
99.5 30
97.3
103.5
Helical tomotherapy
29.4
39.3
36.7
109.3
SBRT
32.6
40.9
38.1
98.5
112.2
Technique
Orbital bone
V15 Gy
V20 Gy
V25Gy
Mean dose
(Gy)
Electron technique 68 63 58 24
Wedge Pair(2LFT) 75 57 48 23
Conformal
(CRT) 92
87.7
75.6
28.4
IMRT 80 65 46
23.1
Helical tomotherapy 76 66
SBRT
21.7
12.9
6.75
8.71
Retinoblastoma is the most common intraocular malignant tumor of early childhood. The proximity between the retina and the other structures of the visual system, which are sensitive to radiation, poses a challenge for radiotherapy planning. There is increasing interest in new techniques of external radiotherapy for pediatric patients. The purpose of this study is to calculate the treatment plans and to compare the dose distributions and dose-volume histograms (DVH) for six external radiotherapy techniques for the treatment of retinoblastoma as well as the intensity modulated radiotherapy (IMRT) and fractionated stereotactic radiotherapy .
Abbreviations: CRT, conformal technique; IMRT, intensity Table 2. Dose volume histogram (DVH) analysis for orbital bone for the 6 delivery techniques listing V15 Gy, V20 Gy, and V25 Gy.
Abbreviations: CRT, conformal technique; IMRT, intensity modulated radiation therapy; SBRT, stereotactic external beam radiotherapy.
Table 1. Dose volume histogram (DVH) analysis for the planning target volume (PTV) of the 6 delivery techniques, listing V95% and V99% normalized to the PTV, Dmax normalized to the prescription dose of 36 Gy, and the conformity indices CI95% and CI100%.
LACRIMAL GLAND
BODY-PTV
Technique
V30
Mean
MEAN(Gy)
(cc)
Electron (ET)
%50
38.6
1.9
1886.7
Wedge Pair (2LFT)
%100 36 2
Conformal
(CRT)
% 100
36.7
2.2
IMRT
% 45
29.9
2.3
Helical tomotherapy
36.24 3
SBRT
% 78.85
31.7
Technique
Brain
V5 Gy
Brain V10 Gy
Brain V15Gy
Electron technique 5 2 1
Wedge Pair (2LFT) 9
6.8
1.8
Conformal
(CRT) 11 3
IMRT
2.5
Helical tomotherapy 20
4.6
SBRT
6.2
2.8
1.2
Materials & Methods
The right eye of a 2-year-old female patient with bilateral retinoblastoma was enucleated and the left eye underwent external radiotherapy after chemoreduction and focal therapies failed. Treatment plans for patient were developed using six techniques including Six treatment techniques were planned for comparison in this study. The prescribed dose was 36 Gy / 180 cGy / fraction. The 6 techniques were as follows:
An in-face electron technique, anterior 6 MeV electron field, without lens block;
An anterior and lateral wedge photon technique (2LFT); 6 MV photon, 2 fields;
Three-dimensional conformal (6 fields) technique (CRT), 6 MV photon, 6 coplanar beams at Varian Clinac® DHX;
An inverse plan intensity modulated radiation therapy (IMRT);
Tomotherapy; and
Stereotactic external beam radiotherapy with Cyberknife® (SBRT).
Table 3: Dose volume histogram (DVH) analysis for brain for the 6 delivery techniques listing V5 Gy, V10 Gy, and V15 Gy in cm3.
Table 4. Comparison of the dose delivered to the lacrimal gland and body-PTV.
Results
All techniques except the in-face electron technique provided similar target coverage. The electron technique had the highest planning target volume dose gradient. When the conformal plan is compared with IMRT and SBRT, there was no significant difference for PTV dose distribution. For the IMRT, tomotherapy and SBRT, volume 95% of the PTV was covered 99.5% , 99.2% and 99.2% of the prescribed dose respectively. The mean volume of ipsilateral bony orbit receiving more than 20 Gy, a suggested threshold for bone growth inhibition. The V20 Gy was 73% for the ET,57% for the LFT, 87% for the CRT, 65% for the IMRT, 66% for the tomotherapy, 2.7% for the SBRT.
Conclusion
With more sophisticated radiation therapy planning and delivery techniques, an advantage has been achieved over the other techniques. This work supports the potential use of IMRT and SBRT to spare normal tissues in these patients. .
Corresponding Author Ayşe Hiçsönmez,ONKO Ankara Oncology Center,