[Influence of active breathing control on the dose distribution in the target of forward whole-breast intensity-modulated radiotherapy after breast conserving surgery].
OBJECTIVE
To explore the influence of intrafraction and interfraction target displacement on the dose distribution in the target of forward whole-breast intensity-modulated radiotherapy (IMRT) assisted by active breathing control (ABC).


METHODS
Each of the selected patient who had received breast conserving surgery was immobilized and received the primary CT simulation assisted by ABC device to get five sets of CT images in three different breathing status, including free breathing (FB) (one set), moderate deep inspiration breathing hold (mDIBH)(two sets) and deep expiration breathing hold (DEBH) (2 sets). After 10 to 15 fractions of radiation, the repeated CT simulation was completed and the same five sets of CT images were obtained at FB, mDIBH, and DEBH, respectively. In the Pinnacle3 treatment planning system, the forward IMRT planning was completed on the first set of mDIBH CT images from the primary CT simulation, and the planning was separately copied by the special system order to the second set of CT images from the primary CT simulation and to the first set of CT images from the repeated CT simulation, keeping the primary angle, direction, size and shape of the MLC field and prescribed dose un-changed. the volumes covered by selected high dose area in the selected segment were compared.


RESULTS
In the planning based on the first set of mDIBH CT images from the primary CT simulation, the volume irradiated by equal and more than 103% of prescribed dose in the segment was (1.16 +/- 0.39) cm3, and the volumes were (3.88 +/- 1.07) cm3 and (51.66 +/- 8.68) cm3 in the plannings copied from the first set of mDIBH CT images from the primary CT simulation respectively to the second set of CT images from the primary CT simulation and first set of CT images from the repeat CT simulation, the difference of the volume in the two plannings based on the two set mDIBH CT image from the primary CT simulation was not statistically significant (t = -1.672, P = 0.103). The difference of the volume in the two plannings based on the two sets of mDIBH CT images respectively from the primary and repeat CT simulations had a significant difference (t = -5.728, P < 0.01).


CONCLUSIONS
If the same threshold of mDIBH is maintained during IMRT after breast conserving surgery, the influence of the intrafraction target displacement on the dose distribution is not significant. However, if set-up error is not adjusted, the interfraction change of position of the segment given to cover the high dose area in the IMRT planning will be significant, resulting in a significant change of dose distribution in the breast.
Li
Jian-bin
JB
Shandong Cancer Hospital, Jinan 250117, China. lijianbin@msn.com
Wang
Jin-guo
JG
Lu
Jie
J
Xu
Min
M
Shao
Qian
Q
Fan
Ting-yong
TY
Ma
Zhi-fang
ZF
Sun
Tao
T
Liang
Chao-qian
CQ
D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy* / Q000601:surgery; D018270:Carcinoma, Ductal, Breast / Q000000981:diagnostic imaging / Q000532:radiotherapy* / Q000601:surgery; D018275:Carcinoma, Lobular / Q000000981:diagnostic imaging / Q000532:radiotherapy / Q000601:surgery; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D015412:Mastectomy, Segmental; D011184:Postoperative Period; D011859:Radiography; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012119:Respiration; D055425:Respiratory-Gated Imaging Techniques / Q000379:methods