Sequential Tomotherapy Intensity Modulated Radiation Therapy for Breast Cancer: Initial Clinical Experience

Purpose/Objective: There is increasing interest in intensity modulated radiation therapy (IMRT) as a modality for post operative treatment for breast cancer. Most breast IMRT techniques use compensator techniques or multiple static Multileaf collimator shaped fields. The application of Sequential Tomotherapy (ST) for breast IMRT is particularly important in light of recent interest in similar techniques such as Helical Tomotherapy (HT). The goal of this study was to evaluate the acute skin toxicity with Sequential Tomotherapy for breast IMRT. Materials/Methods: Twenty five consecutive patients were evaluated using a Sequential Tomotherapy based NOMOS PEACOCK System. All patients underwent conventional simulation followed by a CT for treatment planning. The breast and boost target volume was defined using skin markers, surgical clips, post operative lumpectomy scar and post operative seroma. Patients were treated with 6MV photons to 46-50Gy. Boost doses ranged from 7.2Gy- 12.6Gy. The rotational ST delivery is accomplished with binary collimators along the plane of rotation and allows for a large number of potential positions to create a beam arc. Indexing cephalad to caudad is done with an automated device, the Auto Crane. Treatment time with the MIMIC was 10-12 minutes. Results: The maximum skin toxicity was evaluated based on erythema, moist desquamation and dry desquamation. For the 25 patients treated with Sequential Tomotherapy, RTOG Toxicity Assessment was as follows: Grade 1 = 60%; Grade 2 = 20%, no RTOG Grade 3 or higher toxicity was observed. There was no moist desquamation in 60% of the patients; dry desquamation was seen in 25% of the patients. Moist desquamation was minimal and usually occurred in the axillary or inframmmary fold. Compared to patients treated with 3D techniques, the results are similar. Higher body mass index (BMI), greater than 30(obese) or larger cup size was not associated with increase in moist desquamation or toxicity. ST breast plans had higher mean breast and boost doses (51.7 breast ST, 53.0 boost ST vs. 49.6 breast 3D, 49.8 boost 3D) with a greater percentage of the breast receiving 120% of prescription (13% ST vs. 0.2% for 3D.) Depending upon the location of the high dose region, or clinical parameters a separate boost was not delivered, in other cases the prescription dose to the boost target was reduced. Dose homogeneity was very dependent on breast size and shape. Patients with very small breasts or very large breasts generally were unsuitable for this technique and were treated conventionally. Maximum contralateral breast dose for ST was reduced by 60%, ipsilateral lung dose was reduced by 40% and the mean cardiac dose was reduced by 39% when compared to conventional plans. Patient satisfaction with cosmesis at 6 month follow up was 94%. Conclusions: Sequential Tomotherapy is associated with low risk of acute skin toxicity for breast IMRT. Moist desquamation was minimal for all patients even with high BMI and/ or large breasted patients. Despite the higher mean breast and boost doses with Sequential Tomotherapy appreciable differences in cosmetic outcome were not seen. Doses to the lung, heart and contralateral breast are reduced with this techniques, similar to other IMRT techniques. As with all breast IMRT techniques, the impact of the reduced dose to regions of interest must be weighed against the potential for dose inhomogeneity. Sequential Tomotherapy is associated with higher integral dose to the breast and requires careful attention to patient selection, total breast and boost doses since a concomitant boost effect has been observed. Further evaluation and long term follow up will ultimately determine cosmetic outcome and the efficacy of this treatment option.

SSK25-09

Sequential Tomotherapy Intensity Modulated Radiation Therapy for Breast Cancer: Initial Clinical Experience