RAMB - Setembro 2017

hen

730

ssoc

ras

2017; 63(9):729-732

dosage form is known as conformal technique. The soft-

ware shows the radiation dose distribution inside the

patient’s body and creates dose-intensity graphs on each

target organ or volume. It is thus possible to know the

potential toxicity of these organs and whether the tumor

is being adequately treated.

Even though the conformal technique allows for dose

assessment at irradiated site, sparing healthy organs, it

does not provide ways of protecting tissues in close con-

tact with irradiation treatment targets. The intensity-

modulated radiation beam technique was developed to

solve this problem. It allows the prescribed dose to “fit”

within the contour of the site to be irradiated, allowing

maximum protection of areas not intended for treatment.

In the thoracic region, which houses several radiation-

sensitive organs, such as the heart, esophagus, spinal cord,

and lungs, conformal radiotherapy is the minimally rec-

ommended technique for patient safety.

Based on clinical experience with complications of ra-

diotherapy, a dose-limiting standard according to the volume

of a normal organ was created and published in 2010, the

Quantitative Analysis of Normal Tissue Effects in the Clin-

ic (Quantec).

The recommendation was developed by the

joint work of several researchers, authors, reviewers and

support professionals. It is currently recommended through-

out the world as a practical guide to performing radio-

therapy on all parts of the body. Such dose quantification

can only be established from the shaped technique.

For the reasons given above, conventional radiother-

apy has been abandoned whenever the treatment site is

close to radiation-sensitive organs (for example, the chest),

since this technique does not provide any information

on dose distribution in these organs. In this case, both

the locoregional control of the disease is dose-dependent

and appears to be directly related to survival,

and re-

sidual lung function after treatment seems to be an im-

portant factor related to quality of life in survivors.

1. I

there

superiority

dose

distribution

for

irradiation

lung

cancer with

intensity

modulated

radiation

therapy

(IMRT)

compared

conformal

radiotherapy

There are no prospective phase III studies comparing

conformal radiation therapy and IMRT for any chest

cancer. Therefore, other factors should be weighed and

considered to choose the best radiotherapy technique.

These factors include, for example: dosimetric advantage,

technology accessibility, financial aspects, and decision

to escalate the dose or maintain the restriction of doses

released on a critical organ.

IMRT can improve the physical and biological con-

formability of the dose and enable its scaling within the

target volume, which makes it possible to release higher

doses to target subvolumes such as the hypoxic areas or

those capturing high SUV on PET-CT, with no need to

increase the number of fractions, and maintaining a low

dose exposure to healthy tissues.

Virtual simulation studies have shown that IMRTmay

be more appropriate than conformal radiotherapy for pa-

tients with large tumor volumes and difficult position

within the thoracic anatomy, cases in which protection of

normal surrounding structures is a priority. These studies

presented a 7% reduction in the irradiated lung volume

with more than 10 Gy, and 10% with more than 20 Gy.

Volumes of heart and esophagus irradiated with up to 50

Gy, as well as volumes of lung tissue irradiated between

10 and 40 Gy, were also reduced with IMRT compared to

conformal radiotherapy.

(D)

For bronchial neoplasms close to critical organs

(esophagus, heart, brachial plexus), IMRT may have do-

simetric advantages compared to 3DCRT.

(D)

Other points to consider include: IMRT can release

greater low dose volumes in areas of healthy lung, it may

result in failures outside the therapeutic margin leading

to differences in sterilization of lymph nodes inciden-

tally not included in the target volume, and the lower

dose rate may be less lethal for neoplastic cells.

2. I

there

less

toxicity

the

use

IMRT

relation

conformal

radiotherapy

for

lung

cancer

Toxicity related to radiotherapy external to primary lung

tumors can be temporally divided into acute or late. An-

atomically, it is divided into pulmonary and esophageal,

because these are the main organs to manifest adverse

reactions to radiation.

Comparing IMRT with conformal radiotherapy of

lung tumors, two studies had as their main toxicity out-

come, i.e., pulmonary toxicity:

1. A retrospective study of 290 patients showed that at

month 6, treatment-related grade ≥ 3 pneumonitis

rates reached 8% (95CI 4-19%) with IMRT and 22%

(95CI 17-29%) with conformal radiation therapy. At

month 12, treatment-related grade ≥ 3 pneumonitis

rates reached 8% (95CI 4-19%) with IMRT and 32%

(95CI 26-40%) with conformal radiation therapy

(p=0.002).

(B)

2. Another retrospective study with 409 patients being

treated reported a significant difference (p=0.017),

both 6 and 12 months after radiation, in favor of IMRT