Dosimetric comparison of three dimensional conformal radiation therapy versus intensity modulated radiation therapy...

Breast conserving surgery (BCS) is the standard treatment for stage I and II breast cancer. Multiple studies have shown that recurrences after lumpectomy occur mainly in or near the tumor bed. Use of accelerated partial breast irradiation (APBI) allows for significant reduction in the overall treatment time that results in increasing patient compliance and decreasing healthcare costs. We conducted a treatment planning study to evaluate the role of intensity modulated radiation therapy (IMRT) with regards to three-dimensional conformal radiation therapy (3DCRT) in APBI.

Computed tomography planning data sets of 33 patients (20 right sided and 13 left sided) with tumor size less than 3 cm and negative axillary lymph nodes were used for our study. Tumor location was upper outer, upper inner, central, lower inner, and lower outer quadrants in 10, 10, 5, 4 and 4 patients, respectively. Multiple 3DCRT and IMRT plans were created for each patient. Total dose of 38.5 Gy in 10 fractions were planned. Dosimetric analysis was done for the best 3DCRT and IMRT plans.

The target coverage has been achieved by both the methods but IMRT provided better coverage (P = 0.04) with improved conformity index (P = 0.01). Maximum doses were well controlled in IMRT to below 108% (P < 0.01). Heart V2 Gy (P < 0.01), lung V5 Gy (P = 0.01), lung V10 Gy (P = 0.02), contralateral breast V1 Gy (P < 0.01), contralateral lung V2 Gy (P < 0.01), and ipsilateral uninvolved breast (P < 0.01) doses were higher with 3DCRT compared to IMRT.

Dosimetrically, IMRT-APBI provided best target coverage with less dose to normal tissues compared with 3DCRT-APBI.