Alain Noel

Detection of errors in individual patients in radiotherapy by systematic in vivo dosimetry

Abstract We report 5 years of systematic measurements of the dose delivered to each patient undergoing radiotherapy treatment with photon beams in order to detect any systematic error that may have escaped the different checks performed at each step of planning and calculation prior to the first treatment session, or may have arisen during the set-up or the treatment delivery. For each patient the target-absorbed dose is derived from the entrance and exit doses measured by silicon diodes, on the beam axis at the patients skin. Depending on the discrepancies observed between the measured and expected doses we have set decision levels for the corrective actions to be taken. In addition these measurements allow us to obtain information on the overall accuracy or on the quality of a specific treatment. During 5 years, 7519 patients have been measured and 79 errors were detected. Half could have induced a variation of over 10% in the dose delivered. Seventy-eight out of 79 errors were of human origin. As part of an overall quality assurance programme, it is of the utmost importance to check the dose delivered for each patient undergoing radiotherapy treatment in order to avoid systematic underdosing or overdosing.

Complications following definitive irradiation for cancers of the oral cavity and the oropharynx (in a series of 1134 patients)

PURPOSE To study the rate and severity of complications in a series of 1134 patients treated by definitive irradiation for tumors of the oral cavity (772 cases) or the oropharynx (361 cases). METHODS AND MATERIALS Patients were staged as 29.5% T1, 42% T2, 26% T3, 2.5% T4-Tx, and 74.5% N0 tumors. We treated 364 patients with brachytherapy only (192Ir) for the primary lesion. External irradiation and brachytherapy were combined for 770 patients. RESULTS The results included local control and survival. Out of 1134 patients, 330 had 376 complications. Grade 1 complications occurred in 20% of the patients, Grade 2 in 9%; Grade 3 in 4%; and Grade 4 in 0.2%. Of the Grade 1 complications, 78% were soft tissue and only 24% were bone complications. For the more severe grades (2, 3, and 4), there were 56 soft tissue complications and 90 bone complications out of 1340 patients. The statistical analysis included tumor-related factors and treatment-related factors. For the first two factors, only tumor location was significant. The treatment-related factors significant for complications were studied in univariate and multivariate study. This multivariate study confirmed that for soft tissue complications dose rate and volume treated were important (p < 0.001). It also confirmed that for bone complications, total dose > 80 Gy, dose rate > 0.7 Gy/h, and the absence of leaded protection of the mandible were all important factors. CONCLUSION This statistical study should allow future reduction of severe complications (Grades 2, 3, 4), if treatment factors inducing them can be taken into account. This is not always possible for very large tumors.

Indications, techniques and results of postoperative brachytherapy in cancer of the oral cavity

Abstract Purpose/objective : We tried to reduce the number of local recurrences after surgery and external beam irradiation (EBI) in carcinoma of the oral cavity, when margins were positive or close. Material and methods : From 1980 to 1992, we treated 97 cases of carcinomas of the oral cavity by postoperative brachytherapy. Surgery was combined with EBI + brachytherapy in 51 cases and with brachytherapy alone in 46 cases. We treated 29 T1, 34 T2, 30 T3T4 and four Tx (73% were N0 at first examination and 23% had positive nodes). The type of surgery is analysed. Brachytherapy was performed in one or two planes along the surgical scar. If the mandibular rim was resected, especially when the tongue or the remaining floor were sutured to the internal face of the inferior lip or to the buccal mucosa, the bridge technique was used. To decrease the dose to the inferior part of the mandible, the bridge was modified thanks to experimental dosimetry. Results : At 5 years, the local control (LC) is 89%, the locoregional control (LRC) 82%, the specific survival (SS) 74% and the overall survival (OS) 67%. Complications : We noted 19% of grade 1 (minor), 12% of grade 2 (moderate) and 6% of grade 3 (major) complications. Conclusion : Compared with the results of the literature, we think that postoperative brachytherapy can improve classical radiosurgical results in selected cases with a risk of local recurrence.

Evaluation of the Diagnostic Performance of Tomosynthesis in Fractures of the Wrist

OBJECTIVE The purpose of our study was to define the diagnostic value of tomosynthesis compared with standard radiography and CT in wrist injuries. MATERIALS AND METHODS One hundred consecutive patients with acute wrist trauma were investigated with standard radiography, tomosynthesis, and CT. Reference results were those obtained with CT; follow-up monitoring of the patients; and, in some cases, MRI (n=13). Three readers interpreted the findings independently, each using a PACS workstation, and categorized the cases into four groups: fracture of the radius, fracture of the scaphoid, fracture of another bone, and absence of fracture. RESULTS Fifty-seven percent of the patients had a fracture. The interobserver kappa value varied between 0.54 and 0.59 for standard radiography, between 0.66 and 0.69 for tomosynthesis, and between 0.84 and 0.89 for CT. The sensitivity of standard radiography varied between 61% and 80% and specificity between 65% and 83%. The sensitivity of tomosynthesis ranged between 77% and 87%, and specificity between 76% and 82%. Ranges of sensitivity and specificity for CT were 93-95%, and 86-95%, respectively. CONCLUSION The diagnostic value of tomosynthesis is superior to that of standard radiography but inferior to that of CT.

Qualitative estimation of pelvic organ interactions and their consequences on prostate motion : Study on a deceased person

In an attempt to have better targeting of the prostate during radiotherapy it is necessary to understand the mechanical interactions between bladder, rectum, and prostate and estimate their consequences on prostate motion. For this, the volumes of bladder, rectum, and lungs were modified concomitantly on a deceased person. A CT acquisition was performed for each of these different pelvic configurations (36 acquisitions). An increase in the volume of the bladder or lungs induces a compression of tissues of the pelvic area from its supero-anterior (S-A) to infero-posterior (I-P) side. Conversely, an increase of rectum volume induces a compression from the I-P to the S-A side of the pelvic region. These compressive actions can be added or subtracted from each other, depending on their amplitudes and directions. Prostate motion occurs when a movement of the rectum is observed (this movement depends, itself, on lungs and bladder volume). The maximum movement of prostate is 9 mm considering maximal bladder or rectal action, and 11 mm considering maximum lung action. In some other cases, opposition of compressive effects can lead to stasis of the prostate. Based on the volumes of bladder, rectum, and lungs, it is possible to qualitatively estimate the movement of organs of the pelvic area. The best way to reduce prostate movement is to recommend the patient to have an empty rectum, with either full bladder and/or full lungs.

Dosimetric Consequences of Breath-Hold Respiration in Conformal Radiotherapy of Esophageal Cancer

The objective of this paper is to study the dosimetric impact of respiratory gated radiotherapy in locally advanced esophageal carcinomaand to define the optimal respiratory phase for this treatment. The study included 8 consecutive patients with squamous-cell carcinoma (SCC) or histologically proved adenocarcinoma, for both at least T3-T4 NX or TX N1 M0 stage. Informed consent was obtained before beginning the study. Three spiral scans were performed in breath-hold respiration: one acquisition in end expiration (EBH), one in end inspiration (IBH) and one in deep inspiration breathhold (DIBH); and one acquisition was performed in Free Breathing (FB). A 3 mm-margin was defined as Internal Target Volume (ITV) on FB CT-scan. No ITV was applied on EBH, IBH and DIBH CT-scan. Target volumes were analyzed and we performed dosimetric comparisons on DVH data of each CT-scan for PTV and Organs at Risk (OAR) (Conformity Index, V(dose), D(mean), Equivalent Uniform Dose). DIBH and IBH correlated with a 32% (p=0.77) and 20% (p=0.52) decrease in lung V(20) respectively as compared to FB (13.5%and 15.6% respectively versus 19.9%). DIBH and IBH correlated with a 25% (p=0.25) and 17% (p=0.39) decrease in cardiac V(40) respectively, as compared with FB (16.9% and 18.9% respectively versus 22.7%). For spinal cord irradiation, the minimum dose was obtained in IBH (36.5 Gy). Conformal radiotherapy with respiratory gating for esophageal cancer decreases the irradiated dose to OAR. We suggest that DIBH technique should be used when irradiation is performed using the spirometric system. In the Tidal Volume, the inspiration phase is the most favourable and should be chosen for irradiation with a free breathing gating system.

Evaluation of the Block Matching deformable registration algorithm in the field of head-and-neck adaptive radiotherapy

BACKGROUND AND PURPOSE To compare the accuracy of the Block Matching deformable registration (DIR) against rigid image registration (RIR) for head-and-neck multi-modal images CT to cone-beam CT (CBCT) registration. MATERIAL AND METHODS Planning-CT and weekly CBCT of 10 patients were used for this study. Several volumes, including medullary canal (MC), thyroid cartilage (TC), hyoid bone (HB) and submandibular gland (SMG) were transposed from CT to CBCT images using either DIR or RIR. Transposed volumes were compared with the manual delineation of these volumes on every CBCT. The parameters of similarity used for analysis were: Dice Similarity Index (DSI), 95%-Hausdorff Distance (95%-HD) and difference of volumes (cc). RESULTS With DIR, the major mean difference of volumes was -1.4 cc for MC, revealing limited under-segmentation. DIR limited variability of DSI and 95%-HD. It significantly improved DSI for TC and HB and 95%-HD for all structures but SMG. With DIR, mean 95%-HD (mm) was 3.01 ± 0.80, 5.33 ± 2.51, 4.99 ± 1.69, 3.07 ± 1.31 for MC, TC, HB and SMG, respectively. With RIR, it was 3.92 ± 1.86, 6.94 ± 3.98, 6.44 ± 3.37 and 3.41 ± 2.25, respectively. CONCLUSION Block Matching is a valid algorithm for deformable multi-modal CT to CBCT registration. Values of 95%-HD are useful for ongoing development of its application to the cumulative dose calculation.

Feasibility study of using statistical process control to optimize quality assurance in radiotherapy

Purpose – The purpose of this paper is to evaluate and improve the quality and the reliability of pre‐treatment quality controls of an efficient technique of radiotherapy called IMRT (intensity‐modulated radiation therapy). The aim is then to determine if the controls can be safely reduced while keeping an optimal level of quality.Design/methodology/approach – The statistical process control method (SPC) was applied to quality assurance in IMRT. In order to characterize prostate and head‐and‐neck treatment process variability, individual value control charts and moving‐range control charts were established.Findings – Control charts showed that prostate and head‐and‐neck treatment processes are only subject to random causes of variability, which means they are statistically controlled. It was proved that both processes are statistically stable and capable.Originality/value – The paper shows that SPC is an efficient method to objectively determine if quality controls can be reduced.

Dose Optimization and Reduction in CT of the Musculoskeletal System Including the Spine

Since its introduction in the 1970s, computerized tomography (CT) has played an important role in the diagnosis of musculoskeletal disorders. It rapidly became the examination of choice for the diagnosis of disc herniation, fractures, bone tumours and some developmental abnormalities. Although the image quality was altered by streak artefact associated with medical devices, CT was also indicated in postoperative imaging (Blum et al. 2000; Iochum et al. 2001; Cotten et al. 2002; Fayad et al. 2005a, 2005b).

Comparaison dosimétrique de la radiothérapie conformationnelle, la radiothérapie conformationnelle avec modulation d’intensité, la radiothérapie conformationnelle en conditions stéréotaxiques et la radiothérapie en conditions stéréotaxiques robotisée des tumeurs cérébrales bénignes

PURPOSE To compare several techniques in order to determine the best treatment for benign brain tumours. METHODS AND PATIENTS A retrospective study was performed for five patients who received 3D-conformal radiotherapy, intensity modulated radiotherapy or CyberKnife(®). These patients had a meningioma, a pituitary tumour, a craniopharyngioma or a neurinoma. In each case, these treatment plans were optimised and compared with the three other dosimetries. Radiobiological or positioning parameters were evaluated, as well as dosimetric parameters, in order to compare treatments with different characteristics. RESULTS The dosimetric parameters showed that the choice of treatment seemed to be determined mostly by tumour size, shape and proximity with organs at risk (not tumour localisation). Whereas the results showed no significant deviations with regards to the radiobiological parameters. Therefore, with these parameters, it was difficult to give priority to a treatment. CONCLUSIONS With regards to benign brain tumours of medium or large size, intensity modulated radiotherapy seemed the recommended treatment. It enabled to obtain a good ratio between efficacy and toxicity for tumours that are really close to organs at risk. Concerning small benign brain tumours, the CyberKnife(®) was probably the best treatment.