|Helical Tomotherapy for Routine Breast Cancer
Radiation Therapy: Feasibility and Initial Clinical Experience
D. Henrich, IJROBP Volume 69, Issue 3, Pages S236-S237 (1 November 2007)
University of Wisconsin, Madison, WI
Helical tomotherapy is an effective means of delivering image-guided IMRT with documented success in dosimetrically challenging cases where conformal avoidance is a priority. It is valuable in delivering image-guided IMRT for prostate cancer as well as more esoteric clinical situations such as stereotactic body radiation therapy. However, its practicality in routine breast conserving therapy and chest wall irradiation has been questioned. Here we present our experience with helical tomotherapy in a small tomotherapy-only facility for routine breast cancer radiotherapy.
The first 21 consecutive breast cancer cases treated with helical tomotherapy were included in this study. Two were post-mastectomy and the chest wall was irradiated; 3 had DCIS; the remaining 16 had T1 or T2, N0 or N1(micro), M0 invasive breast cancers. Nodal irradiation was not administered in this cohort of patients. All were planned with a simultaneous-in-field boost technique with the whole breast or chest wall receiving 1.8 Gy daily. Modal prescriptions for DCIS and invasive cancer were 46.8 Gy to the entire breast and 58.76 to the lumpectomy region in 26 fractions. Post-mastectomy patients were prescribed 50.4 Gy to the entire chest wall and 59.36 Gy to the scar in 28 fractions. The entire breast or chest wall was contoured in every case and used for both treatment planning and for aiding daily set-up. Megavoltage CT imaging was done before each administered fraction. The general guide for daily set-up was the external breast or chest contour as seen on MVCT, which was then matched to the simulation CT contours.
Dose homogeneity to the whole breast was excellent without the hot or cold spots seen with our “tangent” field technique. DVH's showed effective reduction of high dose to critical structures (heart and lung) although a greater volume of these organs received low dose compared to what is typical with tangential beams. MVCT images proved efficient and practical for aiding set-up. The lumpectomy cavity was visible on MVCT in every case where it was clearly visible on simulation CT and further aided in patient set-up. In one case there was obvious discrepancy between the simulation breast contour and the tomotherapy MVCT due to a dramatic reduction in the lumpectomy seroma and this patient was re-simulated before further treatment was administered. Limited field of view imaging reduced MVCT imaging time and was routinely employed after the first 3 patients. Mean MVCT imaging time using a limited field of view was 90 seconds. The mean beam-on time was 7 to 8 minutes. Overall treatment time including set-up, MVCT, readjustment and treatment was typically 20 minutes. No patients required treatment breaks and none had any >grade 2 adverse acute effects.
Helical tomotherapy appears to be an efficient and practical means of administering radiation therapy for routine breast-conserving therapy and post-mastectomy chest wall irradiation. The simultaneous in-field boost technique reduces the duration of the overall course with no observed increase in acute effects. Daily MVCT imaging is valuable in aiding set-up and engenders greater confidence that the planned IMRT is truly being delivered. MVCT can also visualize cases where seroma or overall breast size has changed since simulation, thereby identifying cases where replanning might be prudent.