Intrafraction Motion and Margin Assessment for Ethos Online Adaptive Radiotherapy Treatments of the Prostate and Seminal Vesicles.

Purpose: Online adaptive radiation therapy (OART) uses daily imaging to identify changes in the patient's anatomy and generate a new treatment plan adapted to these changes for each fraction. The aim of this study was to determine the intrafraction motion and planning target volume (PTV) margins required for an OART workflow on the Varian Ethos system. Methods and Materials: Sixty-five fractions from 13 previously treated OART patients were analyzed for this retrospective study. The prostate and seminal vesicles were contoured by a radiation oncologist on 2 cone beam computed tomography scans (CBCT) for each fraction, the initial CBCT at the start of the treatment session, and the verification CBCT immediately before beam-on. In part 1 of the study, PTVs of different sizes were defined on the initial CBCT, and the geometric overlap with the clinical target volume (CTV) on the verification CBCT was used to determine the optimal OART margin. This was performed with and without a patient realignment shift by registering the verification CBCT to the initial CBCT. In part 2 of the study, the margins determined in part 1 were used for simulated Ethos OART treatments on all 65 fractions. The resultant coverage to the CTV on the verification CBCT, was compared with an image guided radiation therapy (IGRT) workflow with 7-mm margins. Results: Part 1 of the study found, if a verification CBCT and shift is performed, a 4-mm margin on the prostate and 5 mm on the seminal vesicles resulted in 95% of the CTV covered by the PTV in >90% of fractions, and 98% of the CTV covered by the PTV in >80% of fractions. Part 2 of the study found when these margins were used in an Ethos OART workflow, they resulted in CTV coverage that was superior to an IGRT workflow with 7-mm margins. Conclusions: A 4mm prostate margin and 5-mm seminal vesicles margin in an OART workflow with verification imaging are adequate to ensure coverage on the Varian Ethos system. Larger margins may be required if using an OART workflow without verification imaging.

Concomitant intensity modulated boost during whole breast hypofractionated radiotherapy--a feasibility and toxicity study.

BACKGROUND: Breast cancer sensitivity to large fraction size may be enhanced using hypofractionated concomitant boost radiotherapy (CBRT), thereby shortening overall treatment time. This ethics approved, prospective single cohort feasibility study was designed to evaluate the dosimetry and toxicity of CBRT using an intensity-modulated radiotherapy (IMRT) technique, compared with a standard sequential boost technique (SBT). METHODS: Fifteen women (11 right-sided; 4 left-sided) received 42.4 Gy to the whole breast and an additional 10.08 Gy to the tumor bed in 16 daily fractions, using IMRT and standard dose constraints. Each patient was replanned with the SBT, using mixed photon-electrons. Clinical target volume (CTV), dose evaluation volume (DEV), and organs at risk (OAR) dose distributions were compared with the SBT. Toxicity and treatment times were prospectively recorded. RESULTS: All 15 CBRT plans achieved the desired CTV (V(49.9Gy) ≥ 99%) and DEV (V(49.9Gy) ≥ 95%), coverage of the boost, compared with only 10 (66.7%, p=0.03), and 12 (80%, p=0.125) SBT plans, respectively. Ipsilateral lung (p<0.0001), and heart (right-sided, p=0.001; left-sided, p=0.13) doses were lower. Grade 3 acute toxicity occurred in 1 (6.7%) patient. At 1 year, two (13.3%) additional patients had overall grade 2 late toxicity, compared with baseline. No grade 3-4 late toxicity was observed. CONCLUSIONS: CBRT using IMRT improved boost coverage and lowered OAR doses, compared with SBT. Toxicities were acceptable using a daily boost of 3.28 Gy. While resource utilization was greater, overall treatment time was reduced.

Three-dimensional volumetric analysis of irradiated lung with adjuvant breast irradiation.

PURPOSE: To retrospectively evaluate the dose-volume histogram data of irradiated lung in adjuvant breast radiotherapy (ABR) using a three-dimensional computed tomography (3D-CT)-guided planning technique; and to investigate the relationship between lung dose-volume data and traditionally used two-dimensional (2D) parameters, as well as their correlation with the incidence of steroid-requiring radiation pneumonitis (SRRP). METHODS AND MATERIALS: Patients beginning ABR between January 2005 and February 2006 were retrospectively reviewed. Patients included were women aged >or=18 years with ductal carcinoma in situ or Stage I-III invasive carcinoma, who received radiotherapy using a 3D-CT technique to the breast or chest wall (two-field radiotherapy [2FRT]) with or without supraclavicular irradiation (three-field radiotherapy [3FRT]), to 50 Gy in 25 fractions. A 10-Gy tumor-bed boost was allowed. Lung dose-volume histogram parameters (V(10), V(20), V(30), V(40)), 2D parameters (central lung depth [CLD], maximum lung depth [MLD], and lung length [LL]), and incidence of SRRP were reported. RESULTS: A total of 89 patients met the inclusion criteria: 51 had 2FRT, and 38 had 3FRT. With 2FRT, mean ipsilateral V(10), V(20), V(30), V(40) and CLD, MLD, LL were 20%, 14%, 11%, and 8% and 2.0 cm, 2.1 cm, and 14.6 cm, respectively, with strong correlation between CLD and ipsilateral V(10-V40) (R(2) = 0.73-0.83, p < 0.0005). With 3FRT, mean ipsilateral V(10), V(20), V(30), and V(40) were 30%, 22%, 17%, and 11%, but its correlation with 2D parameters was poor. With a median follow-up of 14.5 months, 1 case of SRRP was identified. CONCLUSIONS: With only 1 case of SRRP observed, our study is limited in its ability to provide definitive guidance, but it does provide a starting point for acceptable lung irradiation during ABR. Further prospective studies are warranted.