A Dosimetric Comparison of Electronic Compensation, Conventional Intensity Modulated Radiotherapy, and Tomotherapy in Patients With Early-Stage Carcinoma of the Left Breast

doi:10.1016/j.ijrobp.2007.04.026

International Journal of Radiation OncologyBiologyPhysics

Volume 68, Issue 5, 1 August 2007, Pages 1505-1511

https://doi.org/10.1016/j.ijrobp.2007.04.026 Get rights and content

Purpose: Intensity modulated radiation therapy (IMRT) has been shown to significantly reduce dose to normal tissue while maintaining coverage of the clinical target volume (CTV) in patients with intact breast cancer. We compared delivery of whole breast irradiation utilizing three techniques: electronic tissue compensation (ECOMP), inverse-planned dynamic multileaf collimation IMRT (DMLC), and tomotherapy (TOMO).

Patients and Methods: Ten patients with early stage, left-sided breast cancer were selected for planning. CTV was defined as breast encompassed in a standard tangent field minus the superficial 5 mm from the skin edge. Normal tissue contours included the heart, lungs, and contralateral breast. Plans included delivery of 45 Gy in 25 fractions and were normalized to ensure ≥95% coverage of the CTV. Isodose distributions and dose–volume histograms for CTV and normal tissue were compared between plans. The time it took to plan each patient excluding contouring, as well as number of monitor units (MUs) required to execute each plan were additionally tabulated.

Results: The TOMO plans resulted in significantly greater heterogeneity (CTV V₁₁₅) versus ECOMP (p = 0.0029). The ECOMP plans resulted in significantly lower doses to heart, lung, and contralateral breast when compared with TOMO plans. The ECOMP plans were generated in the shortest time (12 min) and resulted in the lowest number of MUs when compared with DMLC (p = 0.002, p < 0.0001) and TOMO (p = 0.0015, p < 0.0001).

Conclusions: The ECOMP plans produced superior dose distributions in both the CTV and normal tissue when compared with TOMO or DMLC plans. In addition, ECOMP plans resulted in the lowest number of MUs and labor cost.

Introduction

The use of intensity modulated radiation therapy (IMRT) to treat the whole breast after breast-conserving surgery has been shown to improve both dose homogeneity and target coverage as well as to reduce dose to normal tissue when compared with conventional treatment (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22). Published techniques defined as IMRT for breast irradiation vary widely, from segmental multileaf collimation to inversely planned treatment using cost constraints for targets and normal structures (23). Reported techniques also vary in the degree to which they achieve target coverage and sparing of normal tissue, the time involved for planning, and the amount of low dose radiation contamination to structures that are routinely spared with standard planning (24).

In addition to advances made in the ability to deliver more conformal radiation doses, recent technologic advances now provide the ability for image-guided therapy providing improved localization of structures and thus more accurate treatment delivery. Image-guided IMRT options such as helical tomotherapy and topotherapy have recently been described as a means of delivering partial breast irradiation and whole-breast irradiation respectively (25, 26).

This dosimetric study of whole breast irradiation utilized three different IMRT techniques: dynamic multileaf collimation electronic tissue compensation (ECOMP), inverse-planned dynamic multileaf collimation IMRT (DMLC), and helical tomotherapy (TOMO), and was performed to compare target coverage and dose homogeneity, normal tissue sparing, low dose spillage to nontarget structures, and plan generation labor cost.

Section snippets

Patient population

Ten patients with early stage (T1N0), left-sided breast cancer, status post-lumpectomy and sentinel lymph node biopsy that had been treated with radiation therapy using standard wedged tangential fields in our department were randomly chosen to compare the three different planning approaches. Patients underwent virtual simulation according to our standard protocol positioned supine on a breast board with the left arm extended above the head, and the head turned to the right. Radioopaque wires

Target coverage

The mean CTV volume was 440 cc (range, 150–874 cc). Average cumulative DVHs for the CTV for each technique are shown in Figure 1. For all plans evaluated, and for all patients, the 95% isodose line covered more than 99% of the CTV. However, the TOMO plans resulted in much greater dose heterogeneity, best seen at CTV V₁₁₅, where larger volumes received significantly higher doses as compared with ECOMP plans (p = 0.003), and demonstrated a trend when compared with DMLC plans (p = 0.098).

Discussion

This dosimetric study explored three IMRT techniques to determine whether one would provide a clear advantage according to three factors: homogenous coverage of CTV and avoidance of normal tissue, low dose spill to critical structures, and whole-body radiation exposure during treatment, and labor-intensiveness of planning.

Our results demonstrate equivalent target coverage and improved dose homogeneity with ECOMP plans. Tomotherapy additionally resulted in significantly greater dose

Conclusions

In our dosimetric comparison of three IMRT techniques in 10 patients with left-sided early-stage breast cancer, the ECOMP technique provided homogeneous target coverage while maintaining low doses to normal tissue. In addition, delivery of this technique required the fewest number of monitor units reducing total radiation exposure, avoided low dose spill of radiation to structures at risk for second malignancy, and was attractive from a labor standpoint with an average planning time of 12 min.

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: Conflict of interest: none.

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Physics contributionA Dosimetric Comparison of Electronic Compensation, Conventional Intensity Modulated Radiotherapy, and Tomotherapy in Patients With Early-Stage Carcinoma of the Left Breast

Introduction

Section snippets

Patient population

Target coverage

Discussion

Conclusions

Radiother Oncol

Radiother Oncol

Radiother Oncol

Radiother Oncol

Radiother Oncol

Med Dosim

Int J Radiat Oncol Biol Phys

Radiother Oncol

Int J Radiat Oncol Biol Phys

Radiother Oncol

Radiother Oncol

Radiother Oncol

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Semin Radiat Oncol

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Lancet

Int J Radiat Oncol Biol Phys

Physics contribution
A Dosimetric Comparison of Electronic Compensation, Conventional Intensity Modulated Radiotherapy, and Tomotherapy in Patients With Early-Stage Carcinoma of the Left Breast