Comparison of Incidental Radiation Dose to Axilla and Internal Mammary Nodal Area by Conventional, 3DCRT, and IMRT Technique in Carcinoma of Breast

Purpose: To quantify the incidental radiation dose delivered to axilla and internal mammary nodal (IMN) area by Conventional Tangential Radiation Therapy (CRT), 3 Dimensional Conformal Radiation Therapy (3DCRT) and Intensity Modulated Radiation Therapy (IMRT). Methods and Materials: We prospectively evaluated incidental radiation to axilla in twenty cases of breast cancer treated with adjuvant radiation therapy. Three plans were generated for each case, comprising CRT, 3DCRT and IMRT tangents. Radiation doses to axillary levels I, II, III, and IMN areas were evaluated for mean dose, V95, V80 and V50. Comparisons were made using ANOVA. Results: The mean volume and range of the axillary level I, II, III, and IMN were 61.1 cc and 142-57 cc; 42.6 cc and 61-21cc; 19.5 cc and 34-15 cc; 13.2 cc and 21-9 cc respectively. The mean dose to axilla by 3 techniques (by IMRT, 3DCRT and CRT) to Level I, II, III, and IMN were 75%, 53%, 38%, and 61% vs. 81%, 64%, 44% and 77% vs. 92%, 86%, 53% and 92% respectively (p<0.05). The V95 values (volume receiving 95% of dose) for the three techniques were 43%, 39%, 17% and 49% by IMRT: 40%, 45%, 21% and 59% by 3DCRT; 72%, 61%, 24% and 65% by CRT (IMRT vs. 3DCRT for level II axilla, IMRT vs. CRT and 3DCRT vs. CRT-p<0.05) The V80 were 49%, 53%, 29%, and 57% by IMRT; 55%, 47%, 34% and 68% by 3DCRT; 85%, 77%, 44% and 69% by CT (IMRT vs. 3DCRT for level III axilla and IMN, IMRT vs. CRT and 3DCRT vs. CRT -p<0.05). The V50 values were 75%, 65%, 41% and 66% by IMRT; 82%, 53%, 57% and 84% by 3DCRT; 94%, 89%, 42% and 90% by CRT (IMRT vs. 3DCRT, IMRT vs. CRT, and 3DCRT vs. CRP–p<0.05). Conclusion: Axillary and internal mammary nodal areas receive substantial amount of incidental radiation doses with all the three techniques; however, conformal techniques (IMRT, 3DCRT) deliver significantly lesser incidental radiation to lower axilla than CRT technique.