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RADIOTHERAPY TECHNIQUES
OVERVIEW

Currently standard EBRT is based on the assessment of target
volumes to irradiate and organs at risk to protect in 3D-computed
tomography (CT) simulation plus multimodal images (e.g. positron
emission tomography-CT, magnetic resonance imaging).
[2-6]
Delivery of treatment should be based on intensity modulated
radiation therapy (IMRT) which involves the use of multiple
[7]
computer-aided beams of inhomogeneous radiation, allow dose
shaping the spatial shape of treatment volume, improving the
coverage of target area and the protection of healthy tissue
[Figure 1]. When using IMRT different treatment volumes (e.g.
Figure 1: Postoperative intensity modulated radiation therapy plan for an macroscopic tumor vs. elective nodal levels) receive a different
oral tongue squamous cell carcinoma pT2 pN1 M0. High dose encompass
risk volumes (blue: ipsilateral nodal bed. purple: tumor bed) while sparing dosage during the same fraction, without increasing the number
healthy organ: parotids glands (orange) spinal cord (green) mandible and of RT sessions, so the intensity of treatment is adjusted to each
larynx (courtesy of Dr. Enrique Miragall from Fundación ERESA)
volume of interest by dose gradients. IMRT compared with
[8]
[9]
traditional 2D-EBRT has been shown to improve toxicity and
survival in patients with head neck cancer.
[10]
Traditionally BT implant has been performed with low dose rate
(LDR) by inserting iridium needles ( Ir) mainly; this technique has
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been gradually displaced by the so-called high dose rate (HDR)
BT [Figure 2] due to its advantages of radiation protection of
medical personnel, better dose distribution and shorter duration
of treatment. However, the accelerated treatment and high
[11]
dose per fraction used in HDR could lead to a decrease in the
therapeutic ratio because of the risk of complications in extreme
[12]
cases. Liu et al. conducted a meta-analysis to compare
[13]
HDR BT vs. LDR BT in the treatment of OCSCC. No statistically
significant difference was found in the odds ratio (OR) between
the group of patients treated with LDR or HDR in terms of local
recurrence OR = 1.12, mortality OR = 1.01, and complications
grade 3-4 OR = 0.86.
The equivalent fractionation and total dosing between
LDR and HDR is unknown. Neither the Groupe Européen
de Curiethérapie-European Society for Radiotherapy and
[11]
Oncology (GEC-ESTRO) nor the American Brachytherapy
[14]
Society came to publish a consensus, although they
recommended not to exceed a dose 6 Gy per fraction. In
the comparative meta-analysis of Liu et al., the mean dose
[13]
administered was 66.17 Gy in LDR group and 50.75 Gy in the
HDR. Radiobiological studies suggest that the optimal dose for
exclusive HDR is about 50 Gy [15,16] consistent with data from Liu
et al. GEC-ESTRO has published recommendations for the
[17]
[13]
calculation of equivalent doses between different protocols and
BT techniques.
The main indication for combining EBRT and BT is the need
to irradiate the cervical lymph node chains when the risk of
involvement is significant due to the primary site, tumor
[18]
thickness greater than 4 mm and stage cT2-T3.
[19]
Stages I-II
Figure 2: High dose rate brachytherapy for oral tongue carcinoma. (A) In treating early OCSCC the best results were obtained when
showing external outward apperance of percutnaeous catheters for
afterloading technique; (B) digital radiographic reconstruction of the BT is part of the treatment, either exclusively or as tumor
implant for planning purposes; (C) computed tomography axial view overdose after EBRT. Evidence supporting this practice is
[11]
showing high isodoses lines covering tumor bed but sparing contralateral
tongue, mandible and lips (courtesy of Dr. José Luis Guinot from Instituto based entirely on retrospective series. Even with the advent of
Valenciano de Oncología) IMRT, BT administration is advantageous in terms of shaping and
Plast Aesthet Res || Volume 3 || May 25, 2016 159