Intensity modulated radiotherapy and 3D conformal radiotherapy for whole breast irradiation: a comparative dosimetric study and introduction of a novel qualitative index for plan evaluation, the normal tissue index

• Published in: Journal of medical radiation sciences Vol. 62; no. 3; pp. 184 - 191
• Main Authors: Yim, Jackie, Suttie, Clare, Bromley, Regina, Morgia, Marita, Lamoury, Gillian
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01-09-2015; John Wiley & Sons, Inc; John Wiley & Sons, Ltd
• Subjects: Breast cancer; Cancer therapies; DOSES; Dosimetry; HAZARDS; Heart; HYBRIDIZATION; INDEXES; intensity modulated radiotherapy; IRRADIATION; Lungs; MAMMARY GLANDS; NEOPLASMS; Original; PATIENTS; Planning; Radiation therapy; RADIOLOGY AND NUCLEAR MEDICINE; RADIOTHERAPY; Tumors; Breast cancer; intensity modulated radiotherapy
• ISSN: 2051-3895; 2051-3909
• DOI: 10.1002/jmrs.126

Introduction
We report on a retrospective dosimetric study, comparing 3D conformal radiotherapy (3DCRT) and hybrid intensity modulated radiotherapy (hIMRT). We evaluated plans based on their planning target volume coverage, dose homogeneity, dose to organs at risk (OARs) and exposure of normal tissue to radiation. The Homogeneity Index (HI) was used to assess the dose homogeneity in the target region, and we describe a new index, the normal tissue index (NTI), to assess the dose in the normal tissue inside the tangent treatment portal.
Methods
Plans were generated for 25 early‐stage breast cancer patients, using a hIMRT technique. These were compared with the 3DCRT plans of the treatment previously received by the patients. Plan quality was evaluated using the HI, NTI and dose to OARs.
Results
The hIMRT technique was significantly more homogenous than the 3DCRT technique, while maintaining target coverage. The hIMRT technique was also superior at minimising the amount of tissue receiving D105% and above (P < 0.0001). The ipsilateral lung and contralateral breast maximum were significantly lower in the hIMRT plans (P < 0.05 and P < 0.005), but the 3DCRT technique achieved a lower mean heart dose in left‐sided breast cancer patients (P < 0.05).
Conclusion
Hybrid intensity modulated radiotherapy plans achieved improved dose homogeneity compared to the 3DCRT plans and superior outcome with regard to dose to normal tissues. We propose that the addition of both HI and NTI in evaluating the quality of intensity modulated radiotherapy (IMRT) breast plans provides clinically relevant comparators which more accurately reflect the new paradigm of treatment goals and outcomes in the era of breast IMRT.
We report on a retrospective dosimetric study, comparing 3D conformal radiotherapy (3DCRT) and hybrid intensity modulated radiotherapy (hIMRT). In addition to plan evaluation based on planning target volume (PTV) coverage and dose to organs at risk (OARs), the Homogeneity Index (HI) was used to assess the dose homogeneity in the target region, and we describe a new index, the Normal Tissue Index (NTI), to assess the dose in the normal tissue inside the tangent treatment portal. We propose that the addition of both HI and NTI in evaluating the quality of IMRT breast plans provides clinically relevant comparators which more accurately reflect the new paradigm of treatment goals and outcomes in the era of breast IMRT.