Comprehensive commissioning and quality assurance validation of Ethos™ therapy

PURPOSE

Adaptive radiotherapy with the Ethos® therapy Varian system has been recently implemented at the Montpellier Cancer Institute, France. This article details the commissioning performed before the implementation of this new treatment planning system (TPS).

MATERIAL AND METHODS

To validate the golden beam data of the machine (Halcyon linear accelerator), percentage depth doses (PDD) and profiles were measured for several field sizes and at different depths with a microdiamond chamber. The final doses calculated for different plan types with the Ethos Acuros XB algorithm and the Halcyon Eclipse Analytic Anisotropic Algorithm were compared using the gamma index method. Lastly, for the patient quality assurance (QA) process, the patient treatment plan results obtained with the Mobius3D QA platform (Varian) were compared with the portal dosimetry results obtained with Epiqa (Epidos).

RESULTS

Minor differences were observed for the PDD and profile curves (mean difference of 0.2% and 2%, respectively). The χ index pass rate was above 98% for all measures using the 1%/1mm and 2%/2mm criteria for PDD and profile evaluations. The Ethos AXB algorithm was validated for every configuration (fixed fields, standard IMRT and VMAT fields, and clinical plans) with 2D/3D gamma index values>99%. Seventy-three 3-arcs-VMAT QA plans and 27 9-fields-IMRT QA plans were evaluated. Both showed excellent agreement with the TPS calculations (mean gamma pass rate higher than 99%). No difference was observed between IMRT and VMAT.

CONCLUSION

The beam delivery, the Ethos AXB algorithm, and the patient QA were comprehensively validated using independent tools.

Acceptance, commissioning and quality assurance of the MRIdian®: Site experience and three years follow-up

PURPOSE

This study presents the methodology and results of the acceptance and periodical quality controls on the MRIdian®.

MATERIALS AND METHODS

The impact of the magnetic field on other machines was investigated by controlling nearby linacs dose profiles. The image quality of the 0.345T MR scanner was evaluated, also assessing the integrated linear accelerator influence. The photon beams lateral and depth dose profiles were measured in motorized water tanks, along dose rate and output factors, and compared to Monte Carlo (MC) calculations. The isocenter position, gantry angles and multi-leaf collimator (MLC) position were controlled using film dosimetry. Gating latency and dosimetric accuracy were controlled with a dynamic phantom.

RESULTS

The magnetic field had no significant impact on other nearby linacs. Image quality was within tolerances and did not vary over time. Dose profiles measured showed good agreement with MC data, with maximum differences of 1.3% in-field. Output factors were within 0.8% of calculated values. Imaging and radiative isocenter matched within 0.9±0.4mm over all monthly controls. Gantry rotation was precise within -0.1±0.2°, with an isocenter variation of 1.4±0.3mm diameter. The average MLC position was within 0.4±0.1mm of theoretical value. Finally, the gating latency was 0.14±0.07sec and the gated dose within 0.3% of base value.

CONCLUSION

All results are within the tolerances fixed by ViewRay® and show low variations over 2 years, comforting the use of small margins and gating for high-dose adaptive treatments.

[Individual modification of the dose, volume and fractionation of breast radiotherapy]

Randomized trials demonstrated similar overall survival between mastectomy and breast-conservative surgery followed by adjuvant radiation therapy. Breast-conservative surgery, with adjuvant radiation therapy, with or without neoadjuvant systemic therapy has become the standard of care for women with early or locally advanced breast cancer. Nevertheless, certain cardiac, lung or cutaneous toxicities may alter the long-term body image and the quality of life of a limited number of patients who consider having had "overtreatment" or treatment outside the best knowledge of science. In case of low-risk breast cancer, several trials have evaluated the carcinologic outcome in absence of radiation therapy after breast-conservative surgery. Local recurrences increased in case of breast-conservative surgery alone but without impact on overall survival. Multiple debates have emerged in order to select the most appropriate evaluation criteria. Finally, a large consensus has considered that reducing local recurrences is important but with modern technologies and after identifying patients of individual radiosensitivity. Indeed, in case of a low absolute risk of local recurrence, radiation therapy techniques have been developed to allow a focal treatment especially for patients with high risk of developing late effects. This kind of compromise takes into account the reduction risk of local recurrences but also the probability of developing radiation-induced cutaneous sequelae. In the same way, for patients considered at high risk of recurrence, the huge volumes need specific techniques to better cover the targets while protecting the surrounding critic organs such as heart and lung. Intensity-modulated radiation therapy and the local high boost may help to decrease local recurrences of these more extended and aggressive diseases while considering the individual radiosensitivity that paves the way of long-term sequelae. In this article, we detail a personalized approach of breast radiation therapy considering the absolute risk of local recurrences and the probability of radiation-induced toxicity appearance.

[The major debate: Micrometastases and breast cancer - To be for nodal irradiation]

Standard of care in breast cancer management is well-defined. However, some gray zones still exist, in particular adjuvant radiotherapy indications in case of pN1mi breast cancer. Here we propose to define their prognosis, to underpin the benefit of adjuvant treatments in such patients' management and to define lymphedema risk, which is the most common late side effect of locoregional treatments.

[Modalities and advantages of image guided radiation therapy of breast cancer in adjuvant setting]

In adjuvant setting, breast cancer radiotherapy volumes include whole mammary gland or chest wall, and when indicated, nodal area such as axilla, supraclavicular, and internal mammary chain. An accurate patients positioning is required due to some geometric complexity of target volumes closed to organs at risk as heart and lung. Image guided radiation therapy allows such accuracy. Here we propose a review on image guided radiotherapy for breast cancer.

Twin machines validation for VMAT treatments using electronic portal-imaging device: a multicenter study

Purpose

To verify the accuracy of volumetric arc therapy (VMAT) using the RapidArc™ device when switching patients from one single linear accelerator (linac) to a paired energy and mechanics "twin" linac without reoptimization of the original treatment plan.

Patients and Methods

Four centers using 8 linacs were involved in this study. Seventy-four patients previously treated with the 6MV photon RapidArc™ technique were selected for analysis, using 242 measurements. In each institution, all patients were planned on linac A, and their plans were verified both on linac A and on the twin linac B. Verifications were done using the amorphous silicium electronic portal imager (EPID) of the linacs and were analyzed with the EpiQa software (Epidos, Bratislavia, Slovakia). The gamma index formalism was used for validation with a double threshold of 3 % and 3 mm with a measurement resolution of 0.39 mm/pixel, and a smoothed resolution of approximately 2.5 mm.

Results

The number of points passing the gamma criteria between the measured and computed doses was 94.79 ± 2.57 % for linac A and 94.61 ± 2.46 % for linac B. Concerning the smoothed measurement analysis, 98.67 ± 1.26 % and 98.59 ± 1.20 % points passing the threshold were obtained for linacs A and B, respectively.

The difference between the 2 dose matrices acquired on the EPID was very small, with 99.92 ± 0.06 % of the points passing the criteria.

Conclusion

For linacs sharing the same mechanical and energy parameters, this study tends to indicate that patients may be safely switched from treatment with one linac to treatment with its twin linac using the same VMAT plan.

Concurrent or sequential letrozole with adjuvant breast radiotherapy: final results of the CO-HO-RT phase II randomized trial

BACKGROUND

We present here final clinical results of the COHORT trial and both translational sub-studies aiming at identifying patients at risk of radiation-induced subcutaneous fibrosis (RISF): (i) radiation-induced lymphocyte apoptosis (RILA) and (ii) candidates of certain single-nucleotide polymorphisms (SNPs).

PATIENTS AND METHODS

Post-menopausal patients with stage I-II breast cancer (n = 150) were enrolled and assigned to either concurrent (arm A) or sequential radiotherapy (RT)-letrozole (arm B). Among them, 121 were eligible for RILA and SNP assays. Grade ≥2 RISF were the primary end point. Secondary end points were lung and heart events and carcinologic outcome. RILA was performed to predict differences in RISF between individuals. A genome-wide association study was performed to identify SNPs associated with RILA and RISF. Analyses were done by intention to treat.

RESULTS

After a median follow-up of 74 months, 5 patients developed a grade ≥2 RISF. No significant difference was observed between arms A and B. Neither grade ≥2 lung nor symptomatic cardiac toxicity was observed. Median RILA value of the five patients who had grade ≥2 RISF was significantly lower compared with those who developed grade ≤1 RISF (6.9% versus 13%, P = 0.02). Two SNPs were identified as being significantly associated with RILA: rs1182531 (P = 4.2 × 10(-9)) and rs1182532 (P = 3.6 × 10(-8)); both located within the PHACTR3 gene on chromosome 20q13.33.

CONCLUSIONS

With long-term follow-up, letrozole can safely be delivered concomitantly with adjuvant breast RT. Translational sub-studies showed that high RILA values were correlated with patients who did not develop RISF.

REGISTERED CLINICAL TRIAL

NCT00208273.

[Radiomics: Definition and clinical development]

The ultimate goal in radiation oncology is to offer a personalized treatment to all patients indicated for radiotherapy. Radiomics is a tool that reinforces a deep analysis of tumors at the molecular aspect taking into account intrinsic susceptibility in a long-term follow-up. Radiomics allow qualitative and quantitative performance analyses with high throughput extraction of numeric radiologic data to obtain predictive or prognostic information from patients treated for cancer. A second approach is to define biological or constitutional that could change the practice. This technique included normal tissue individual susceptibility but also potential response of tumors under ionizing radiation treatment. These "omics" are biological and technical techniques leading to simultaneous novel identification and exploration a set of genes, lipids, proteins.