Evaluation of volumetric modulated arc therapy for postmastectomy treatment.

PURPOSE: To examine the feasibility of volumetric modulated arc therapy (VMAT) for post mastectomy radiotherapy (PMRT). METHODS AND MATERIALS: Fifteen PMRT patients previously treated at our clinic with helical tomotherapy (HT) were identified for the study. Planning target volumes (PTV) included the chest wall and regional lymph nodes. A systematic approach to constructing VMAT that met the clinical goals was devised. VMAT plans were then constructed for each patient and compared with HT plans with which they had been treated. The resulting plans were compared on the basis of PTV coverage; dose homogeneity index (DHI) and conformity index (CI); dose to organs at risk (OAR); tumor control probability (TCP), normal tissue complication probability (NTCP) and secondary cancer complication probability (SCCP); and treatment delivery time. Differences were tested for significance using the paired Student's t-test. RESULTS: Both modalities produced clinically acceptable PMRT plans. VMAT plans showed better CI (p<0.01) and better OAR sparing at low doses than HT plans, particularly at doses less than 5 Gy. On the other hand, HT plans showed better DHI (p<0.01) and showed better OAR sparing at higher doses. Both modalities achieved nearly 100% tumor control probability and approximately 1% NTCP in the lungs and heart. VMAT showed lower SCCP than HT (p<0.01), though both plans showed higher SCCP values than conventional mixed beam (electron-photon) plans reported by our group previously. VMAT plans required 66.2% less time to deliver than HT. CONCLUSIONS: Both VMAT and HT provide acceptable treatment plans for PMRT. Both techniques are currently utilized at our institution.

Verification of calculated skin doses in postmastectomy helical tomotherapy.

PURPOSE: To verify the accuracy of calculated skin doses in helical tomotherapy for postmastectomy radiation therapy (PMRT). METHODS AND MATERIALS: In vivo thermoluminescent dosimeters (TLDs) were used to measure the skin dose at multiple points in each of 14 patients throughout the course of treatment on a TomoTherapy Hi·Art II system, for a total of 420 TLD measurements. Five patients were evaluated near the location of the mastectomy scar, whereas 9 patients were evaluated throughout the treatment volume. The measured dose at each location was compared with calculations from the treatment planning system. RESULTS: The mean difference and standard error of the mean difference between measurement and calculation for the scar measurements was -1.8% ± 0.2% (standard deviation [SD], 4.3%; range, -11.1% to 10.6%). The mean difference and standard error of the mean difference between measurement and calculation for measurements throughout the treatment volume was -3.0% ± 0.4% (SD, 4.7%; range, -18.4% to 12.6%). The mean difference and standard error of the mean difference between measurement and calculation for all measurements was -2.1% ± 0.2% (standard deviation, 4.5%: range, -18.4% to 12.6%). The mean difference between measured and calculated TLD doses was statistically significant at two standard deviations of the mean, but was not clinically significant (i.e., was <5%). However, 23% of the measured TLD doses differed from the calculated TLD doses by more than 5%. CONCLUSIONS: The mean of the measured TLD doses agreed with TomoTherapy calculated TLD doses within our clinical criterion of 5%.

Accelerated partial breast irradiation in early-stage breast cancer.

Whole-breast irradiation, as part of breast-conservation therapy (BCT), has well-established results, good cosmesis, and low toxicity. Results from the BCT trials suggest that the risk for ipsilateral breast cancer recurrence resides within close proximity to the original tumor site. This leads investigators to consider the role of an accelerated and more tumor bed-focused course of radiotherapy. Accelerated partial-breast irradiation (APBI) involves treating a limited volume of breast tissue, with dose of irradiation per fraction increased and the treatment time course decreased. Four currently available methods of APBI are interstitial brachytherapy, intracavitary brachytherapy, intraoperative radiotherapy, and three-dimensional conformal external-beam radiotherapy. Patient selection is critical. This review article presents some preliminary clinical observations and limitations that suggest a potential role for APBI as a more user-friendly mode for delivering radiotherapy after lumpectomy for early breast cancer.