Effectiveness of robust optimization against geometric uncertainties in TomoHelical planning for prostate cancer.

BACKGROUND: Geometrical uncertainties in patients can severely affect the quality of radiotherapy. PURPOSE: We evaluated the dosimetric efficacy of robust optimization for helical intensity-modulated radiotherapy (IMRT) planning in the presence of patient setup uncertainty and anatomical changes. METHODS: Two helical IMRT plans for 10 patients with localized prostate cancer were created using either minimax robust optimization (robust plan) or a conventional planning target volume (PTV) margin approach (PTV plan). Plan robustness was evaluated by creating perturbed dose plans with setup uncertainty from isocenter shifts and anatomical changes due to organ variation. The magnitudes of the geometrical uncertainties were based on the patient setup uncertainty considered during robust optimization, which was identical to the PTV margin. The homogeneity index, and target coverage (TC, defined as the V100% of the clinical target volume), and organs at risk (OAR; rectum and bladder) doses were analyzed for all nominal and perturbed plans. A statistical t-test was performed to evaluate the differences between the robust and PTV plans. RESULTS: Comparison of the nominal plans showed that the robust plans had lower OAR doses and a worse homogeneity index and TC than the PTV plans. The evaluations of robustness that considered setup errors more than the PTV margin demonstrated that the worst-case perturbed scenarios for robust plans had significantly higher TC while maintaining lower OAR doses. However, when anatomical changes were considered, improvement in TC from robust optimization was not observed in the worst-case perturbed plans. CONCLUSIONS: For helical IMRT planning in localized prostate cancer, robust optimization provides benefits over PTV margin-based planning, including better OAR sparing, and increased robustness against systematic patient-setup errors.

Treatment outcome for locally advanced non-small-cell lung cancer using TomoDirect plan and its characteristics compared to the TomoHelical plan.

INTRODUCTION: TomoDirect (TD) is an intensity-modulated radiotherapy system that uses a fixed gantry angle instead of the rotational beam delivery used in the TomoHelical (TH) system. This study was performed (1) to evaluate the treatment outcome of the TD plan for locally advanced non-small-cell lung cancer (NSCLC) and (2) to compare the characteristics of TD plans with those of TH plans. METHODS: Twenty-one patients with NSCLC were treated using the TD system. The prescribed dose was 40 Gy/20 Fx for the initial planning target volume (PTV), which included the gross tumour volume (GTV) and lymph node regions. A boost plan of 20 Gy/10 Fx was then applied, focusing on the GTV. For the planning study, matched TH plans of 40 Gy for the initial PTV were created for each patient, to meet the same dosimetric constraints specified in the TD plans. RESULTS: The 2-year overall survival, progression-free survival and local control rates were 47%, 45% and 74% respectively. Grade 2 treatment-related pneumonitis occurred in three (14%) patients. The planning study comparing TD and TH showed that dose distribution to GTV and PTV were not significantly different. The lung V5 Gy was lower in the TD plans than TH plans (46.4 ± 5.4 vs. 52.3 ± 8.5), while the V20 Gy was higher (26.2 ± 4 vs. 24 ± 4.3). The TD plans had a significantly shorter treatment time than TH plans (4.5 ± 1.3 min vs. 9.8 ± 1.5 min). CONCLUSIONS: TD is a clinically acceptable treatment option for NSCSL. The quality of the TD and TH plans are comparable.

Clinical and dosimetric predictors of late rectal bleeding of prostate cancer after TomoTherapy intensity modulated radiation therapy.

INTRODUCTION: Rectal bleeding after radiotherapy impacts the quality of life of long-term surviving prostate cancer patients. We sought to identify factors associated with late rectal bleeding following intensity modulated radiation therapy (IMRT) using TomoTherapy for prostate cancer. METHODS: We retrospectively analysed 82 patients with localised prostate cancer treated with TomoTherapy. Most patients (95.1%) received neoadjuvant and concurrent hormone therapy. Forty-two patients (51.2%) graded as high risk using D'Amico's classification underwent radiotherapy involving the pelvic nodal area. Late bleeding complications were quantified using the Common Terminology Criteria for Adverse Events v4.0. Multiple clinical and dosimetric factors were considered with reference to rectal bleeding. RESULTS: The median follow-up period was 538 (range, 128-904) days. Grades 1, 2 and 3 rectal bleeding were observed in 14 (17.1%), four (4.9%) and one (1.2%) patient respectively. In multivariate analysis, the following factors were significantly associated with Grade ≥1 late rectal bleeding: volume, mean dose (P = 0.012) and rectal V30 (P = 0.025), V40 (P = 0.011), V50 (P = 0.017) and V60 (P = 0.036). When exclusively considering Grade 2-3 rectal bleeding, significant associations were observed with the use of anticoagulants or antiaggregates (P = 0.007), rectal V30 (P = 0.021) and V40 (P = 0.041) in univariate analysis. CONCLUSIONS: Our results suggested that the intermediate rectal dose-volume (V30-V60) was a significant predictor for mild to severe late rectal bleeding (Grade ≥1). Rectal dose-volumes >V70, which represented the volume of the highest doses, were not predictive in this study.

Tangent field technique of TomoDirect improves dose distribution for whole-breast irradiation.

TomoDirect (TD) is an intensity-modulated radiotherapy system that uses a fixed gantry angle instead of rotational beam delivery. Here, we investigated the effect of the multiple beam technique of TomoDirect on dose distribution compared with commonly-used tangential beams. We included 45 consecutive patients with right breast cancer who underwent postoperative radiotherapy in our institute in the present study. Clinical target volume (CTV) was the whole right breast. The planning target volume (PTV) was created by expanding the CTV by a 0.5 cm margin. Paired TD plans were generated for each patient; a two-beam plan using paired tangential beams and a six-beam plan with four additional beams with modified gantry angles of ± 5° from the original tangential beam set. A prescribed dose of 50 Gy was defined for 50% isodoses of the PTV. The six-beam plan delivered significantly more homogeneous doses to the PTV than the two-beam plan; and the mean dose to the PTV in the six-beam plan more closely reflected the prescribed dose. V20Gy and mean dose to the right lung and mean dose to the whole body were also significantly decreased in the six-beam plan. However, duration of radiation exposure was 1 min longer in the six-beam plan than in the two-beam plan. The dose distribution to the target and organs at risk were improved with the six-beam plan relative to the two-beam plan without increasing the whole-body radiation dose. The six-beam plan using TD is a simple technique that can be routinely applied to whole-breast irradiation in clinical practice.