Purpose: The aim of this study is to evaluate the decrease
of EQD2 (biologically equivalent dose in 2 Gy fraction) with various overall
treatment time and its correlation with local control of tumour in the
treatment of nasopharyngeal carcinoma (NPC).
Materials and Methods: A retrospective study was carried out
on 69 NPC (stage II, III and IV) treated with fractionated High Dose Rate
(HDR)–Brachytherapy boost, following external beam radiation therapy and
chemotherapy in the period from May, 2009 to December, 2015. External radiation
therapy (EBRT) of all patients were given with a dose of 66 ± 4.5Gy in 2 Gy per
fraction. It was followed by HDR –Intra Luminal Radiotherapy (ILRT) after
having a gap. The total EQD2 prescribed was 84.8 (range:75.0 – 102.8Gy).
Results: EQD2 lost per day (in Gy) for the overall treatment
time of 75, 150, 250 and 350 days are 0.04, 0.10, 0.12 and 0.13 respectively.
Extra radiation dose required for maintaining the prescribed EQD2 for the
overall treatment time of 75, 100, 150, 250 and 350 days are estimated as 2.7,
5.9, 12.1, 24.7 and 37.2 Gy respectively. The probabilities of disease
recurrence within a median follow-up of 28 months (range 10 – 80 months) are
expected as 0.06, 0.30, 0.62 and 0.94 (p=0.05) for the above overall treatment
time. The relative risk of local recurrence of Stage IV NPC patient is about
2.8 times higher than stage III and stage III patients is about 2.0 times
higher than stage II patients.
Conclusions: The increase of overall treatment time may be
of different origin resulting in the fall of EQD2. It was observed that the
recurrence of disease is more significant (p>0.50) when the overall
treatment time is above 100 days where EQD2 lost becomes more than 0.07
Gy/day. Moreover, there is a significant
decline of tumour control probability when overall treatment time reaches 150
days or more and the EQD2 lost = or > 0.10Gy/day. The relative risk of
disease recurrence was observed highest with stage IV patients followed by
stage III patients and least with stage IINPC patients.
Author(s) Details:
B. Arunkumar Sharma,
Radiation Oncology Department, Regional Institute of Medical
Sciences, Imphal 795004, Manipur, India.
L.
Jaichand Singh,
Radiation
Oncology Department, Regional Institute of Medical Sciences, Imphal 795004,
Manipur, India.
Jayshree Ph.,
Department of Physiology, RIMS, Imphal 795004, India.
Gaurav Goswami,
Radiation Oncology Department, Regional Institute of Medical
Sciences, Imphal 795004, Manipur, India.
Y. Indibor Singh,
Radiation
Oncology Department, Regional Institute of Medical Sciences, Imphal 795004,
Manipur, India.
Th.
Tomcha Singh,
Radiation
Oncology Department, Regional Institute of Medical Sciences, Imphal 795004,
Manipur, India.
A. Ronibala Devi,
Radiation Oncology Department, Regional Institute of Medical
Sciences, Imphal 795004, Manipur, India.
Please see the link here: https://stm.bookpi.org/RUDHR-V5/article/view/14104
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