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Purpose: To evaluate the effect of breathing motion and setup error on the accuracy of treatment planning surface dose calculation for breast cancer treatments on helical Tomotherapy. Method and Materials: In‐vivo dosimetry with MOSFET detectors was performed on a cohort of patients treated for breast cancer on helical Tomotherapy. The detectors were placed under the 0.5‐cm tissue‐equivalent bolus used for patient treatments. The pre‐treatment MVCT images were used to localize the MOSFET detectors. Tomotherapy's Planned Adaptive software was used to compare the measurements against both the planned surface doses at the locations of the dosimeters as well as the recalculated doses based on the MVCT scan. This allowed for evaluation of the combined impact of breathing and setup error on the surface dose contribution, and the quantification of dosimetric accuracy of the Tomotherapy treatment planning system for breast cancer patients. Results: The differences between dose values at the locations of the dosimeters from the plan and those calculated from the MVCT image were on average within 1% of each other. The average dosimetric differences between measured and calculated doses were 7.8 and 8 percent for the planned and adaptive calculated doses, respectively. Overall, the treatment planning system overestimated the dose at the skin/bolus interface. Conclusion: The treatment planning system was previously shown to overestimate dose at a 5‐mm depth by about 4%. The possible setup error is taken into account by the adaptive software since it recalculates the dose distribution based on the MVCT image associated with the treatment for which the measurement was made. Since the setup error was shown to be within 1%, it is therefore estimated that the dosimetric consequence of breathing motion may be as high as 3%. Conflict of Interest: This work was partially supported by a grant from Tomotherapy, Inc.

Purpose: To compare the quality of treatment plans and delivery times for breast cancer patients with involved lymph‐nodes generated using Tomotherapy's emerging technology of variable jaw widths and couch speeds called “Dynamic Jaws and Dynamic Couch” (DJDC) against existing helical delivery with fixed jaw widths and couch speeds (FJFC). Methods: Five left‐sided breast‐cancer patients with involved lymph‐nodes were retrospectively planned using Tomotherapy's FJFC and DJDC techniques. Patients were CT‐scanned with a 5mm‐bolus and two planning target volumes (PTVs) were segmented. The main PTV included chest‐wall/breast plus lymph‐nodes minus superficial region while Flash‐PTV includes a 5‐mm‐thick superficial target plus bolus. Optimized plans were generated on the Hi‐Art‐II research platform using FJFC and DJDC techniques. All five plans have the same prescription dose of 50.4 Gy to the PTV while limiting Flash‐PTV to 45 Gy. Directional blocking was applied on contralateral breast and lung. Doses to heart, lungs, and contralateral breast were limited to reduce complication probabilities. Plans using DJDC were compared against those using FJFC for plan quality and delivery times. Results: Minimum and maximum doses for the PTV were the same for both techniques. Maximum dose for the PTV‐Flash was elevated by 2.5% for DJDC technique. Average mean doses to all critical structures were same within the margin of error. However, the volume receiving 5 Gy (V5Gy) of ipsilateral and contralateral lung was elevated in DJDC plans by 15% and 10%, respectively. Average V5Gy and V10Gy volumes of the contralateral breast were decreased by 17% and 5%, respectively, in DJDC plans. Average V25Gy and V35Gy volumes of the heart were also decreased by ∼2% in DJDC plans. Average delivery times for DJDC and FJFC technologies were 6.06±0.94 and 11.12±0.69 minutes, respectively. Conclusions: Tomotherapy's DJDC technology shortened the treatment times by 5 minutes while maintaining the plan quality of FJFC.