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.

Postoperative Concurrent Chemoradiotherapy Versus Radiotherapy Alone for Advanced Oral Cavity Cancer in the Era of Modern Radiation Techniques

Background/Purpose

Surgery followed by postoperative radiotherapy (RT) has been considered the standard treatment for oral cavity squamous cell carcinoma (OCSCC) of advanced stages or with adverse prognostic factors. In this study, we compared the outcomes in patients with OCSCC who received postoperative concurrent chemoradiotherapy (CCRT) or postoperative RT alone using modern RT techniques.

Methods

A total of 275 patients with OCSCC treated between 2002 and 2018 were retrospectively analyzed. Adverse prognostic factor was defined as extranodal extension (ENE), microscopically involved surgical margin, involvement of ≥2 lymph nodes, perineural disease, and/or lymphovascular invasion (LVI). In total, 148 patients (54%) received CCRT and 127 patients (46%) received RT alone. More patients in the CCRT group had N3 disease and stage IVB disease (46.6% vs. 10.2%, p<0.001), ENE (56.1% vs. 15.7%, p<0.001), LVI (28.4% vs. 13.4%, p=0.033).

Results

With a median follow-up of 40 (range, 5–203) months, there were no significant differences in the 5-year overall survival (OS) and PFS between treatment groups. In the subgroup analysis according to high risk, the concurrent use of chemotherapy showed significantly improved OS in patients with ENE (HR 0.39, p=0.003).

Conclusion

Our retrospective study showed that postoperative CCRT group had comparable survival outcomes to those in the RT alone group for advanced OCSCC in the era of modern RT techniques and indicated that concurrent chemotherapy should be administered to patients with ENE. Prospective randomized studies for confirmation are needed.

Clinical Implementation and Initial Experience of Real-Time Motion Tracking With Jaws and Multileaf Collimator During Helical Tomotherapy Delivery

PURPOSE

This work reports the clinical implementation of a real-time motion tracking and correction system using dynamic multileaf collimator and jaws during helical tomotherapy delivery (Synchrony on Radixact; Accuray, Inc).

METHODS AND MATERIALS

The first clinical Synchrony on Radixact system was recently installed and tested at our institution. Various clinical workflows, including fiducial implantation, computed tomography simulation, treatment planning, delivery quality assurance, treatment simulation, and delivery, for both fiducial-free and fiducial-based motion tracking methods were developed. Treatment planning and delivery data from initial patients, including dosimetric benefits, real-time target detection, model building, motion tracking accuracy, delivery smoothness, and extra dose from real-time radiographic imaging, were analyzed.

RESULTS

The Synchrony on Radixact system was tested to be within its performance specifications and has been used to treat 10 lung (fiducial-free) and 5 prostate (fiducial-based) patients with cancer so far in our clinic. The success of these treatments, especially for fiducial-free tracking, depends on multiple factors, including careful selection of the patient, appropriate setting of system parameters, appropriate positioning of the patient and skin markers, and use of treatment simulation. For the lung tumor cases, difficulties in model building, due primarily to the changes of target detectability or respiration patterns, were observed, which led to important system upgrades, including the addition of a treatment delivery simulation capability. Motion tracking metrics for all treated patients were within specifications, for example, (1) delivery quality assurance passing rates >95%; (2) extra dose from radiograph <0.5% of the prescription dose; and (3) average Potential Diff, measured Δ, and Rigid Body were within 6.5, 2.9, and 3.9 mm, respectively.

CONCLUSIONS

Practical workflows for the use of the first clinical motion tracking and correction system in helical tomotherapy delivery have been developed, and the system has now been successfully implemented in our clinic for treating patients with lung and prostate cancer.

Cyberknife, Helical Tomotherapy and Rapid Arc SIB-SBRT Treatment Plan Comparison for Carcinoma Prostate

Background:

This study was conducted to dosimetrically compare plan quality of Simultaneous Integrated Boost – Stereotactic Body Radiotherapy (SIB-SBRT) generated for different techniques such as Cyberknife (CK), Helical Tomotherapy (HT) and RapidArc (RA) for carcinoma prostate with same treatment margins.

Materials and Methods:

SIB-SBRT plans were generated for CK, HT and RA for thirteen CT data sets. The dose prescription was 45Gy in 5 fractions to GTV45 and 37.5Gy in 5 fractions to PTV37.5. The plan quality evaluation of the three techniques was done by comparing the DVH parameters, conformity index (CI) and gradient index (GI). For OAR’s mean, maximum dose and dose volumes were compared for bladder, rectum and bilateral femoral heads. The number of Monitor Units (MU) delivered and Beam-on time (BOT) were also compared.

Results:

D_2%, D_50% and D_Mean to GTV45 was significantly higher in the CK compared to HT and RA (CK vs HT: p values, <0.001, 0.002 and 0.003; CK vs RA: p values, 0.001, 0.004 and 0.004) respectively. RA gives a better gradient index compared to CK and HT. Conformity indices of the RA plans were better than the CK plans (P<0.001). Normal tissue and integral dose delivered to the patient in HT and CK were found to be significantly higher than RA. The average number of MU’s and BOT were significantly higher in CK (p<0.001).

Conclusion:

Using the same treatment margins and dose constraints, RA achieved better target dose distribution and sparing of critical structures compared to CK and HT. RA seemed to be the optimal planning technique for SIB-SBRT treatment of carcinoma prostate.

Impact of postoperative daily image-guided intensity-modulated radiotherapy on overall and local progression-free survival in patients with oral cavity cancer

Background

We compared the outcome of patients who received non-image-guided intensity-modulated radiotherapy (IMRT) with those who received helical tomotherapy (HT), a daily image-guided radiotherapy (IGRT), after surgery for oral cavity cancer (OCC).

Methods

During the period November 2006 to December 2013, a total of 152 postoperative OCC patients underwent either IMRT (n = 79) or daily IGRT (n = 73) 4 to 6 weeks after surgery. Patients in the IMRT group received 6 MV photon beams to 7 fields and those in the IGRT group received daily fractions of 1.8 or 2 Gy on five consecutive days.

Results

Patients who received daily IGRT had higher 5-year overall survival than those who received IMRT (87 % versus 48 %, p = 0.015). The local progression-free survival rate was also higher in patients who received IGRT (85 % versus 58 %, p = 0.006). More patients in the IGRT group completed the package of overall treatment time in ≤ 13 weeks and completed their course of radiation therapy in ≤ 8 weeks than patients in the IMRT group (89 % versus 68 %, p = 0.002; 84 % versus 58 %, p = 0.001), respectively. The rate of local failure in the primary tumor area was 24.0 % in the IMRT group and 6.8 % in the IGRT group. Among patients with primary local failure, the marginal failure rate was 52.6 % in the IMRT group and 0 % in the IGRT group.

Conclusions

For patients with locally advanced OCC, postoperative IGRT results in better overall survival, better local progression-free survival, less marginal failure and shorter overall treatment time than postoperative non-image-guided IMRT.

Dose-volume histogram comparison between static 5-field IMRT with 18-MV X-rays and helical tomotherapy with 6-MV X-rays

We treated prostate cancer patients with static 5-field intensity-modulated radiation therapy (IMRT) using linac 18-MV X-rays or tomotherapy with 6-MV X-rays. As X-ray energies differ, we hypothesized that 18-MV photon IMRT may be better for large patients and tomotherapy may be more suitable for small patients. Thus, we compared dose-volume parameters for the planning target volume (PTV) and organs at risk (OARs) in 59 patients with T1-3 N0M0 prostate cancer who had been treated using 5-field IMRT. For these same patients, tomotherapy plans were also prepared for comparison. In addition, plans of 18 patients who were actually treated with tomotherapy were analyzed. The evaluated parameters were homogeneity indicies and a conformity index for the PTVs, and D2 (dose received by 2% of the PTV in Gy), D98, Dmean and V10-70 Gy (%) for OARs. To evaluate differences by body size, patients with a known body mass index were grouped by that index ( <21; 21-25; and >25 kg/m(2)). For the PTV, all parameters were higher in the tomotherapy plans compared with the 5-field IMRT plans. For the rectum, V10 Gy and V60 Gy were higher, whereas V20 Gy and V30 Gy were lower in the tomotherapy plans. For the bladder, all parameters were higher in the tomotherapy plans. However, both plans were considered clinically acceptable. Similar trends were observed in 18 patients treated with tomotherapy. Obvious trends were not observed for body size. Tomotherapy provides equivalent dose distributions for PTVs and OARs compared with 18-MV 5-field IMRT. Tomotherapy could be used as a substitute for high-energy photon IMRT for prostate cancer regardless of body size.

Feasibility of prostate robotic radiation therapy on conventional C-arm linacs

PURPOSE

Significant dosimetric improvement for radiation therapy using optimized noncoplanar fields has been previously demonstrated. The purpose here is to study the feasibility of optimized robotic noncoplanar radiation therapy, termed 4π therapy, for prostate cancer treatments on a conventional C-arm linac.

METHODS AND MATERIALS

Twelve low-risk prostate cancer patients previously treated by 2-arc volumetric modulated arc therapy (VMAT) were selected. Forty gray in 5 fractions were prescribed to cover 95% of the prostate planning target volume (PTV). To replan by 4π therapy, a column generation method was used to optimize beam orientations and fluence. A total of 30 beams were selected for each patient.

RESULTS

Both planning methods provided adequate PTV coverage. Compared against VMAT plans, the 4π plan reduced the rectum V50%, V80%, V90%, D1cc, and the penile bulb maximum doses by 50%, 28%, 19% 11%, and 9% (P < .005), respectively, and the mean body dose was reduced from 2.07 Gy to 1.75 Gy (P = .0001). The bladder dose was only slightly reduced.

CONCLUSIONS

By optimizing beam angles and fluences in the noncoplanar solution space, superior prostate treatment plan quality was achieved compared against state of the art VMAT plans. The dosimetric potential for 4π therapy is established on an existing C-arm linac platform.

Management of high-risk localized prostate cancer

Traditionally, patients with high-risk localized prostate cancer have been an extremely challenging group to manage due to a significant likelihood of treatment failure and prostate cancer-specific mortality (PCSM). The results of multiple large, prospective, randomized trials have demonstrated that men with high-risk features who are treated in a multimodal fashion at the time of initial diagnosis have improved overall survival. Advances in local treatments such as dose-escalated radiotherapy in conjunction with androgen suppression and postprostatectomy adjuvant radiotherapy have also demonstrated benefits to this subset of patients. However, therapeutic enhancement with the addition of chemotherapy to the primary treatment regimen may help achieve optimal disease control.