Detecting anomalies in a deliberately biased tomotherapy plan: Comparison of two patient-specific quality assurance processes involving ArcCHECK® and Gafchromic® EBT3 films.

PURPOSE: This work proposes a comparative evaluation of two of our patient-specific quality assurance processes involving ArcCHECK® (Sun Nuclear) and Gafchromic® EBT3 films (Ashland) in order to determine which detector is able to most effectively detect an anomaly in a deliberately biased tomotherapy plan. MATERIAL AND METHODS: A complex clinical head and neck tomotherapy plan was deliberately biased by introducing six errors: multileaf collimator leaf positional errors by leaving one and two central leafs closed during the whole treatment, initial radiation angle errors (+0.5° and +1.0°) and multileaf collimator leafs opening time errors (+0.5% and +1.0%). For each error-induced plan, comparison of ArcCHECK® with Gafchromic® EBT3 films (20.3×25.4cm2) was performed through two methods: a dose matrices subtraction study and a gamma index analysis. RESULTS: The dose matrices subtraction study shows that our ArcCHECK® processing is able to detect all the six induced errors contrary to the one using films, which are only able to detect the two biases involving multileaf collimator leaf positional errors. The gamma index analysis confirms the previous method, since it shows all six errors induced in the reference plan seem to be widely detected with ArcCHECK® with the more restrictive 1%/1mm gamma criterion, whereas films may only be able to detect biases in relation to multileaf collimator leaf positional errors. It also shows the common 3%/3mm gamma criterion does not allow deciding between both detectors in the detection of the six induced biases. CONCLUSION: Both comparative methods showed ArcCHECK® processing is more suitable to detect the six errors introduced in the reference treatment plan.

[Comparison of three dosimetric techniques for lung tumor irradiation]. / Analyse des contraintes dosimétriques obtenues par trois techniques d'irradiation de tumeurs pulmonaires.

PURPOSE: Comparison of three dosimetric techniques of lung tumor delineation to integrate tumor motion during breathing. PATIENTS AND METHODS: Nineteen patients with T1-3N0M0 malignant lung tumor were treated with definitive chemoradiotherapy (14 cases) or pre-surgery chemoradiation. Doses were, respectively, 66 and 46Gy. CT-scan for delineation was performed during three phases of breathing: free breathing and deep breath-hold inspiration and expiration. GTV (gross tumor volume) was delineated on the three sequences. The classic technique included GTV from the free-breathing sequence plus a CTV (clinical target volume) margin of 5 to 8mm plus a PTV (planning target volume) margin of 7 to 10mm (including ITV [internal target volume] margin and set-up margin). The gating-like technique included GTV from the deep breath-hold inspiration sequence plus a CTV margin of 5 to 8mm plus a PTV margin of 2mm. The three-volume technique, included GTV as a result of the fusion of GTVs from the three sequences plus a CTV margin of 5 to 8mm plus a PTV margin of 2mm. Dosimetry was calculated for the three PTVs, if possible, with the same fields number and position. Dose constraints and rules were imposed to accept dosimetries: firstly spinal cord maximal dose less than 45Gy, followed by V95 % for PTV greater than or equal to 95 %, and V20 GY(Gy) for lung less than or equal to 30 %, V30 GY(Gy) for lung less than or equal to 20 %. RESULTS: GTVs were not statistically different between the three methods of delineation. PTVs were significantly lower with the gating-like technique. V95% of the PTV were not different between the three techniques. With the classic-, the gating-like- and the 3-volume techniques, dosimetry was considered as acceptable, respectively in 15, 18 and 15 cases. Comparisons of constraint values showed that the gating-like method gave the best results. In the case of pre-operative management, the gating-like method allowed the best results even for the V95% values. However, in the absence of gating device or without the possibility to use it, the 3-volume method allowed to take into account more precisely the organ motion than the classical technique. CONCLUSION: The 3-volume method can be done. It is a good method to take into account the organ motions. However, the gating-like method gives the best results leading to propose its use even for pre-operative patients with upper tumors.

[Diagnostic and treatment delays do not modify the treatment outcome of patients with multiform glioblastoma]. / Les délais au diagnostic et à la mise en traitement n'altèrent pas les résultats des traitements délivrés aux patients atteints de glioblastome.

PURPOSE: To assess waiting time effect in patient with multiform glioblastoma (GBM) treated with 3D conformal planned postoperative radiotherapy and to investigate the impact of chemotherapy as first adjuvant treatment. PATIENTS AND METHODS: We retrospectively analyzed 94 consecutive patients with histologically proven GBM. Surgery was considered as macroscopically complete in 33 cases (35%). Median irradiation dose was 60 Gy (8-63, mean 56 Gy). Dose per fractions was 1.8 Gy (five patients), 2 Gy (76 patients) and 2.7 Gy (13 patients). Forty patients received adjuvant pre-radiotherapy chemotherapy as intra-operative carmustine (nine patients) and adjuvant five-day protocol temozolomide alone (31 patients) or with cisplatinum (two patients). All patients received only one chemotherapy cycle. RESULTS: There were 56 males and 38 females. Median age was 62.1 years old (7-82, mean: 59.2 year). Median follow-up was nine months (1-49). For overall patients, median waiting time between fist clinical sign and start of the non surgical treatment was 68 days ((3-274, mean: 81.9 days). For those who received chemotherapy as first treatment, this waiting time was 54 days (3-221, mean 68.3 days). For overall patients, median waiting time between surgery and beginning of radiotherapy was 46 days (8-401, mean 59.3 days). For patients who did not receive chemotherapy as first adjuvant treatment this waiting time was 46 days (-278, mean 55.4 days). Median local control was 14.5 months. Six, 12-, 18-, and 24-month local control rates were 75.6+/-4.6%, 57.6+/-6.2%, and 36.7+/-8% and 27.6+/-8.2%, respectively. According to multivariate analysis, we retrieved two independent prognostic factors of local control, macroscopically total removal of the tumor [RR=2.85, IC 95% (1.3-6.5), p=0.012] and irradiation dose above 60 Gy, [RR=3.14, IC 95% (1.5-6.6), p=0.002]. Median overall survival was 14.3 months. Six-, 12-, 18, and 24-month overall survival rates were 84+/-3.9%, 55.1+/-5.9%, 34.2+/-6.3% and 30.4+/-6.7%, respectively. There was no independent prognostic factor. CONCLUSION: In our series neither waiting times nor adjuvant immediate chemotherapy were prognosticator of local control and overall survival outcome of patients with glioblastoma.

[New technologies in lung cancer radiotherapy]. / Techniques innovantes en radiothérapie des cancers bronchopulmonaires.

Since ten years, lung cancer radiotherapy improved thanks to capacities of imagery, softwares, hardwares which allowed developing and transforming drastically radiotherapy procedures. Improvements were performed in all steps of the lung treatment, immobilization, three dimensional imagery, delineation of the targets and organs at risk, simulation and ballistic, dose calculation, daily set-up, breathing control, and treatment verifications. Furthermore, new technology implies technical adjustments but also a change of physicians and physicists minds.