To quantify the incidental radiation dose delivered to the axilla and internal mammary nodal (IMN) area by Conventional Tangential Radiation Therapy (CTRT), Three Dimensional Conformal Radiation Therapy (3DCRT) and Intensity Modulated Radiation Therapy (IMRT).
We prospectively evaluated incidental radiation to the axilla and IMN in fifty cases of breast cancer treated with adjuvant radiation therapy. Three plans were generated for each of cases, comprising of CTRT, 3DCRT and IMRT tangents. Radiation doses to axillary levels I, II, III, and IMN areas were evaluated for mean dose,V95, V90, V80 and V50. Statistical comparisons were made using ANOVA.
The mean volume (range) of the axillary level I, II, III, and IMN were 61.1 cc (57.3-142.7 cc); 42.6 cc (21.3-61.5 cc); 19.5 cc (15.3-34.5 cc); 13.2 cc (9.3-21.8 cc) respectively. The mean dose to axilla by IMRT to Level I, II, III, and IMN were 75%, 53%, 38% and 61%, by 3DCRT to Level I, II, III, and IMN were 81%, 64%, 44% and 77%, by CTRT to Level I, II, III, and IMN were 92%, 86%, 53% and 92% respectively (p < 0.05). The V95 values (volume receiving 95% of dose) for the three techniques to Level I, II, III, and IMN were 43%,3 9%, 17% and 49% by IMRT, 40%, 45%, 21%, and 59% by 3DCRT, 72%, 61%, 24%, and 65% by CTRT. The V80 values were 49%, 53%, 29%, and 57% by IMRT, 55%, 47%, 34% and 68% by 3DCRT, 85%, 77%, 44%, and 69% by CTRT. The V50 values were 75%, 65%, 41% and 66% by IMRT, 82%, 53%, 57% and 84% by 3DCRT, 94%, 89%, 42% and 90% by CTRT. On comparison both IMRT and 3DCRT was found to have statistically significant lower radiation dose to Axilla level I, II, III and IMN in comparision to CTRT ( p < 0.05). However, on comparing IMRT and 3DCRT, IMRT was found to give statistically significant lower radiation dose at V80 and V50 to Axillary level III and IMN area (p < 0.05).
Axillary and IMN areas receive substantial amount of incidental radiation doses with all the three techniques. Among the three techniques, dose to axilla and IMN is low in IMRT followed by 3DCRT and CTRT.Thus in cases where conformal radiation technique is used in low risk axillary nodes, constraints to the axillary areas should be followed as in critical organ group.
Clinical trial identification
All authors have declared no conflicts of interest.