Terminology Techniques and Radiation Biology

Peruvian Hair Loss Treatment

Natural Treatment to get rid of Hair Loss

Get Instant Access

Any comparison of toxicity between the various methods of APBI is complicated by the distinctive dosimetry and radiation biology inherent in interstitial, intracavitary, or external beam techniques. Table 17.1 summarizes the four most commonly practiced APBI modalities in general terms of prescription points, fractionation schemes, total delivered dose, and a rough comparison of biological effective doses (BED) as calculated at the prescription point (which ignores critical dose gradients). The interpretation of toxicity data can be further complicated when one considers, for example, such operator-specific variables as the method of catheter placement for interstitial brachytherapy. Controlling for needle placement technique can be difficult as complex interstitial breast brachytherapy systems have tended to develop as institution-specific protocols that may entail the use of customized rigid templates (Das et al. 2004; Vicini et al. 1999), specialized devices to guide free-hand placement (Wazer et al. 1997), or CT-guided placement (Arthur et al. 2003). There are no clear data to suggest that there are differences in normal tissue toxicity related to specific interstitial brachytherapy techniques.

It is again important to emphasize that virtually all of the limited toxicity data currently available for APBI were derived from the use of brachytherapy with either interstitial or MammoSite techniques. Early data are becoming available for conformal external beam APBI but little exist for single fraction intraoperative applications of electrons or low-energy photons. As such, this chapter focuses primarily on studies of APBI by brachytherapy.

Prior to reviewing the results of clinical studies, it would be useful to briefly explain some terminology that has been employed to describe the dosimetric characteristics of both interstitial and MammoSite implants. The V100, V150, and V200 represent the volume of breast tissue encompassed by the 100%, 150%, and 200% isodose lines, respectively. The dose homogeneity index (DHI) has been defined as a method for evaluating the dosimetric quality of an implant (Wu et al. 1988). The higher the, the more uniform is the dose distribution within the treatment volume. Numerous methods have been

Table 17.1 A comparison of the common APBI modalities for prescription point, total dose, fraction-ation/dose-rate, and biological effective dose (BED)

APBI technique

Typical

Total

Fractionation

BED (Gy)

prescription point (PTV)

dose (Gy)

or dose rate

Normal tissue

Tumor

Interstitial brachytherapy

HDR

Tumor bed plus 1.5 cm

34

Ten fractions twice daily

72.5

45.6

LDR

Tumor bed plus 2.0 cm

45

50 cGy/h

75

54

MammoSite

1 cm from balloon surface

34

Ten fractions twice daily

72.5

45.6

3D conformai external beam

Tumor bed plus 2.5 cm

38.5

Ten fractions daily or twice daily

164.9

53.3

Intraoperative electrons

"Operative bed"

21

Single fraction

168

65.1

Intraoperative 50-kV photons

1 cm from surface of applicator

5

Single fraction

13.3

7.5

Table 17.2 RTOG/EORTC normal tissue late toxicity scoring criteria

Grade

Description

Skin

0

No change from baseline

1

Slight atrophy; pigmentation change; some hair loss

2

Patchy atrophy; moderate telangiectasia; total hair loss

3

Marked atrophy; macroscopic telangiectasia

4

Ulceration

Subcutaneous tissues

0

No change from baseline

1

Slight induration (fibrosis) and loss of subcutaneous fat

2

Moderate fibrosis (asymptomatic); slight field contracture; <10% linear reduction

3

Severe induration and loss of subcutaneous tissue; field contracture; >10% linear measurement

4

Necrosis

proposed to calculate the DHI, but the formula commonly used in the assessment of APBI brachytherapy (Edmundson et al. 2002) is:

DHI=(V100-V150)/V100

APBI brachytherapy has been delivered with both low dose-rate (LDR) and high doserate (HDR) techniques. Typically, LDR implants have been performed at a dose-rate of 40-60 cGy/h to a total dose of 45-60 Gy (Arthur et al. 2003; Kuerer et al. 2004; Kuske et al. 1998; Vicini et al. 1997). HDR implants have most commonly been prescribed to a total dose of 32-34 Gy at 3.4-4.0 Gy per fraction delivered twice daily.

The normal tissue toxicity end-points commonly evaluated after APBI are early and late changes to skin and subcutaneous tissues. These are scored using the established grading criteria of the RTOG/EORTC (Table 17.2). There is not a uniformly accepted scoring system for cosmetic outcome and, as such, there is considerable variability in the criteria applied across studies. In general, a four-tiered grading of excellent, good, fair, and poor has been applied in the majority of studies.

Was this article helpful?

0 0
How To Deal With Rosacea and Eczema

How To Deal With Rosacea and Eczema

Rosacea and Eczema are two skin conditions that are fairly commonly found throughout the world. Each of them is characterized by different features, and can be both discomfiting as well as result in undesirable appearance features. In a nutshell, theyre problems that many would want to deal with.

Get My Free Ebook


Post a comment