Failure patterns of locoregional recurrence after reducing target volumes in patients with nasopharyngeal carcinoma receiving adaptive replanning during intensity-modulated radiotherapy: a single-center experience in China

BACKGROUND

Previous researches have demonstrated that adaptive replanning during intensity-modulated radiation therapy (IMRT) could enhance the prognosis of patients with nasopharyngeal carcinoma (NPC). However, the delineation of replanning target volumes remains unclear. This study aimed to evaluate the feasibility of reducing target volumes through adaptive replanning during IMRT by analyzing long-term survival outcomes and failure patterns of locoregional recurrence in NPC.

METHODS

This study enrolled consecutive NPC patients who received IMRT at our hospital between August 2011 and April 2018. Patients with initially diagnosed, histologically verified, non-metastatic nasopharyngeal cancer were eligible for participation in this study. The location and extent of locoregional recurrences were transferred to pretreatment planning computed tomography for dosimetry analysis.

RESULTS

Among 274 patients, 100 (36.5%) received IMRT without replanning and 174 (63.5%) received IMRT with replanning. Five-year rates of locoregional recurrence-free survival (LRFS) were 90.1% (95%CI, 84.8% to 95.4%) and 80.8% (95%CI, 72.0% to 89.6%) for patients with and without replanning, P = 0.045. There were 17 locoregional recurrences in 15 patients among patients with replanning, of which 1 (5.9%) was out-field and 16 (94.1%) were in-field. Among patients without replanning, 19 patients developed locoregional recurrences, of which 1 (5.3%) was out-field, 2 (10.5%) were marginal, and 16 (84.2%) were in-field.

CONCLUSIONS

In-field failure inside the high dose area was the most common locoregional recurrent pattern for non-metastatic NPC. Adapting the target volumes and modifying the radiation dose prescribed to the area of tumor reduction during IMRT was feasible and would not cause additional recurrence in the shrunken area.

Adaptive radiation therapy of breast cancer by repeated imaging during irradiation

Breast cancer is the most frequent cancer among females and also a leading cause of cancer related mortality worldwide. A multimodality treatment approach may be utilized for optimal management of patients with combinations of surgery, radiation therapy (RT) and systemic treatment. RT composes an integral part of breast conserving treatment, and is typically used after breast conserving surgery to improve local control. Recent years have witnessed significant improvements in the discipline of radiation oncology which allow for more focused and precise treatment delivery. Adaptive radiation therapy (ART) is among the most important RT techniques which may be utilized for redesigning of treatment plans to account for dynamic changes in tumor size and anatomy during the course of irradiation. In the context of breast cancer, ART may serve as an excellent tool for patients receiving breast irradiation followed by a sequential boost to the tumor bed. Primary benefits of ART include more precise boost localization and potential for improved normal tissue sparing with adapted boost target volumes particularly in the setting of seroma reduction during the course of irradiation. Herein, we provide a concise review of ART for breast cancer in light of the literature.

Evaluation of the effectiveness of novel single-intervention adaptive radiotherapy strategies based on daily dose accumulation

Parotid gland (PG) shrinkage and neck volume reduction during radiotherapy of head and neck (H&N) cancer patients is a clinical issue that has prompted interest in adaptive radiotherapy (ART). This study focuses on the difference between planned dose and delivered dose and the possible effects of an efficient replanning strategy during the course of treatment. Six patients with H&N cancer treated by tomotherapy were retrospectively enrolled. Thirty daily dose distributions (D_MVCT) were calculated on pretreatment megavoltage computed tomography (MVCT) scans. Deformable Image Registration which matched daily MVCT with treatment planning kilovoltage computed tomography was performed. Using the resulting deformation vector field, all daily D_MVCT were deformed to the planning kilovoltage computed tomography and resulting doses were accumulated voxel per voxel. Cumulative D_MVCT was compared to planned dose distribution performing γ-analysis (2 mm, 2% of 2.2 Gy). Two single-intervention ART strategies were executed on the 18th fraction whose previous data had suggested to be a suitable timepoint for a single replanning intervention: (1) replanning on the original target and deformed organ at risks (OARs) (a "safer" approach regarding tumor coverage) and (2) replanning on both deformed target and deformed OARs. D_MVCT showed differences between planned and delivered doses (3D-γ 2mm/2%-passing rate = 85 ± 1%, p < 0.001). Voxel by voxel dose accumulation showed an increase in average dose of warped PG of 3.0 Gy ± 3.3 Gy. With ART the average dose of warped PG decreased by 3.2 Gy ± 1.7 Gy in comparison to delivered dose without replanning when both target and OARs were deformed. Average dose of warped PG decreased by 2.0 Gy ± 1.4 Gy when only OARs were deformed. Anatomical variations lead to increased doses to PGs. Efficient single-intervention ART-strategies with replanning on the 18th MVCT result a reduced PG dose. A strategy with deformation of both target and OAR resulted in the lowest PG dose, while formally maintaining PTV coverage. Deformation of only OAR nevertheless reduces PG dose and has less uncertainties regarding PTV coverage.

Effect of adaptive replanning in patients with locally advanced nasopharyngeal carcinoma treated by intensity-modulated radiotherapy: a propensity score matched analysis

PURPOSE

Limited data have been published regarding the effect of adaptive radiotherapy (ART) on clinical outcome in patients with nasopharyngeal carcinoma (NPC). We compared the long-term outcomes in patients with locally advanced NPC treated by adaptive intensity-modulated radiotherapy (IMRT) replanning versus IMRT.

METHODS

200 NPC patients with stage T3/T4 were included between October 2004 and November 2010. Patients in both treatment groups were matched using propensity score matching method at the ratio of 1:1. Clinical outcomes were analyzed with Kaplan-Meier method, log-rank test and Cox regression.

RESULTS

After matching, 132 patients (66 patients in each group) were included for analysis. The median follow-up for the IMRT replanning group was 70 months, while the IMRT group was 69 months. The 5-year local-regional recurrence-free survival (LRFS) rate was higher in IMRT replanning group (96.7 vs. 88.1 %, P = 0.022). No significant differences in distant metastasis-free survival (DMFS), progression-free survival (PFS) and overall survival (OS) were observed between the two groups. 21.2 % patients in IMRT replanning group and 28.8 % patients in IMRT group had distant metastasis. In multivariable analysis, IMRT replanning was identified as an independent prognostic factor for LRFS (hazard ratio 0.229; 95 % CI 0.062-0.854; P = 0.028), but not for DMFS, PFS and OS.

CONCLUSIONS

IMRT replanning provides an improved LRFS for stage T3/T4 NPC patients compared with IMRT. Distant metastasis remains the main pattern of treatment failure. No significant advantage was observed in DMFS, PFS and OS when adaptive replanning was used.

Optimal adaptive IMRT strategy to spare the parotid glands in oropharyngeal cancer

PURPOSE

In oropharyngeal cancer adaptive radiation therapy (ART), this study aimed to quantify the dosimetric benefit of numerous replanning strategies, defined by various numbers and timings of replannings, with regard to parotid gland (PG) sparing.

MATERIAL AND METHODS

Thirteen oropharyngeal cancer patients had one planning and then six weekly CT scans during the seven weeks of IMRT. Weekly doses were recalculated without replanning or with replanning to spare the PG. Sixty-three ART scenarios were simulated by considering all the combinations of numbers and timings of replanning. The PG cumulated doses corresponding to "standard" IMRT and ART scenarios were estimated and compared, either by calculating the average of weekly doses or using deformable image registration (DIR).

RESULTS

Considering average weekly doses, the mean PG overdose using standard IMRT, compared to the planned dose, was 4.1Gy. The mean dosimetric benefit of 6 replannings was 3.3Gy. Replanning at weeks 1, 1-5, 1-2-5, 1-2-4-5 and 1-2-4-5-6 produced the lowest PG mean doses, 94% of the maximum benefit being obtained with 3 replannings. The percentage of patients who had a benefit superior to 5Gy for the contralateral PG was 31% for the three-replannings strategy. The same conclusions were found using DIR.

CONCLUSION

Early replannings proved the most beneficial for PG sparing, three replannings (weeks 1-2-5), representing an attractive combination for ART in oropharyngeal cancer.