Role of computed tomography and [18F] fluorodeoxyglucose positron emission tomography image fusion in conformal radiotherapy of non-small cell lung cancer: a comparison with standard techniques with and without elective nodal irradiation.

AIMS AND BACKGROUND: Mediastinal elective node irradiation (ENI) in patients with non-small cell lung cancer candidate to radical radiotherapy is controversial. In this study, the impact of co-registered [18F]fluorodeoxyglucose-positron emission tomography (PET) and standard computed tomography (CT) on definition of target volumes and toxicity parameters was evaluated, by comparison with standard CT-based simulation with and without ENI. METHODS: CT-based gross tumor volume (GTVCT) was first contoured by a single observer without knowledge of PET results. Subsequently, the integrated GTV based on PET/CT coregistered images (GTVPET/CT) was defined. Each patient was planned according to three different treatment techniques: 1) radiotherapy with ENI using the CT data set alone (ENI plan); 2) radiotherapy without ENI using the CT data set alone (no ENI plan); 3) radiotherapy without ENI using PET/CT fusion data set (PET plan). Rival plans were compared for each patient with respect to dose to the normal tissues (spinal cord, healthy lungs, heart and esophagus). RESULTS: The addition of PET-modified TNM staging in 10/21 enrolled patients (48%); 3/21 were shifted to palliative treatment due to detection of metastatic disease or large tumor not amenable to high-dose radiotherapy. In 7/18 (39%) patients treated with radical radiotherapy, a significant (> or =25%) change in volume between GTVCT and GTVPET/CT was observed. For all the organs at risk, ENI plans had dose values significantly greater than no-ENI and PET plans. Comparing no ENI and PET plans, no statistically significant difference was observed, except for maximum point dose to the spinal cord Dmax, which was significantly lower in PET plans. Notably, even in patients in whom PET/CT planning resulted in an increased GTV, toxicity parameters were fairly acceptable, and always more favorable than with ENI plans. CONCLUSIONS: Our study suggests that [18F]-fluorodeoxyglucose-PET should be integrated in no-ENI techniques, as it improves target volume delineation without a major increase in predicted toxicity.

Target delineation in post-operative radiotherapy of brain gliomas: interobserver variability and impact of image registration of MR(pre-operative) images on treatment planning CT scans.

BACKGROUND AND PURPOSE: To investigate the interobserver variability of intracranial tumour delineation on computed tomography (CT) scans using pre-operative MR hardcopies (CT+MR(conv)) or CT-MR (pre-operative) registered images (CT+MR(matched)). PATIENTS AND METHODS: Five physicians outlined the 'initial' clinical tumour volume (CTV0) of seven patients affected by HGG and candidates for radiotherapy (RT) after radical resection. The observers performed on screen-tumour delineation using post-operative CT images of the patients in the treatment position and pre-operative MR radiographs (CT+MR(conv)); they also outlined CTV0 with both CT and corresponding MR axial image on screen (CT+MR(matched)). The accuracy of the image fusion was quantitatively assessed. An analysis was conducted to assess the variability among the five observers in CT+MR(conv) and CT+MR(matched) modality. RESULTS: The registration accuracy in 3D space is always less than 3.7 mm. The concordance index was significantly better in CT+MR(matched) (47.4+/-12.4%) than in CT+MR(conv) (14.1+/-12.7%) modality (P<0.02). The intersecting volumes represent 67+/-15 and 24+/-18% of the patient mean volume for CT+MR(matched) and CT+MR(conv), respectively (P<0.02). CONCLUSIONS: The use of CT and MR registered imaging reduces interobserver variability in target volume delineation for post-operative irradiation of HGG; smaller margins around target volume could be adopted in defining irradiation technique.

Rectal and bladder motion during conformal radiotherapy after radical prostatectomy.

BACKGROUND AND PURPOSE: To investigate the extent and the impact of rectum and bladder motion during adjuvant conformal radiotherapy (3DCRT) after radical prostatectomy (RP). MATERIALS AND METHODS: Nine patients previously operated with RP and treated with early adjuvant 3DCRT were considered for this investigation. Weekly CT scans were collected during treatment (CT1-CTn, n=4-6) and were 3D matched using bony anatomy with the planning CT (CT0). A single observer drew the contours of rectum and bladder on all CTs. The CTV (prostate+/-seminal vesicles surgical bed) was contoured on CT0 by a single observer and a 4-field 3DCRT technique was planned: dose statistics/dose-volume histograms (DVH) of the rectum and bladder were calculated for each contour referred to CT0, CT1...CTn. Average DVHs during the treatment were then calculated and compared with the planned DVH. Cranial, caudal, anterior and posterior shifts of rectum and bladder were also assessed by lateral BEV projections. NTCP values for the rectum were also calculated using the Lyman-Kutcher model. RESULTS: Random variations of volume and DVHs due to variable filling content were found for the bladder; a trend of the bladder to be more empty during therapy with respect to CT0 was also found (median values: 45 cm3 vs. 79 cm3, P=0.02). Regarding the rectum, 6/9 patients showed an average DVH 'worse' than the planned one (up to 10-20%). BEV and volume analyses showed that the rectal volume decreased in 3/9 patients after the first week. In 6/9 patients a systematic anterior shift of the cranial half of the rectum was detected and found to be correlated with a corresponding shift of the posterior border of CTV contoured by five different observers. The average rectal NTCP during therapy was systematically higher than the NTCP referred to CT0 (average increase 1.2%; range 0.0-3.7%, for a 70 Gy ICRU dose, P=0.01). CONCLUSIONS: The impact of systematic uncertainty due to rectal wall motion seems to be relatively high for patients treated with adjuvant 3DCRT after RP. The detected trend of the rectum in migrating anteriorly during therapy is consistent with post-surgery settlement effects and/or some modification of rectum mobility due to irradiation. Rectal motion (and consequent shifts of CTV) was large at the half cranial portion of the rectum while it was very small below the flexure.

Anatomic variations due to radical prostatectomy. Impact on target volume definition and dose-volume parameters of rectum and bladder.

BACKGROUND AND PURPOSE: A quantitative estimate of the impact of prostatectomy on pelvic anatomy is unavailable, even if it would be an important prerequisite for a precise definition of clinical target volume (CTV) in post-prostatectomy radiotherapy. The purpose of this study was to investigate the impact of prostatectomy on the definition of CTV, on the position of bladder and rectum and their implications for three-dimensional conformal radiotherapy (3-D CRT). PATIENTS AND METHODS: Six patients eligible for radical retropubic prostatectomy were considered. Each patient underwent a planning CT between 1 week and 1 month before surgery (CTpre), and then CT was repeated in the same positioning 1-2 months after surgery (CTpost). For each patient the CT(pre/post) scans were matched; rectum, bladder and CTV were contoured on both CT scans for each patient by one observer. Two different CTVs were contoured: CTV1: prostate + seminal vesicles in CTpre; prostate + seminal vesicles surgical bed in CTpost; CTV2: prostate in CTpre; prostate surgical bed in CT(post). After image registration, the contours of rectum, bladder and CTV1/2 drawn on CTpost were transferred on CTpre. The corresponding planning target volumes (PTVs) were generated, and for each PTV, a conformal four field technique using 18-MV X-rays was planned. The volumes of CTV1, CTV2, PTV1, PTV2, rectum and bladder pre- and post-surgery were compared. Differences in 3-D position of these structures before and after surgery were analyzed by beam's eye view (BEV) images. Pre- and post-surgery dose-volume histograms (DVHs) of rectum and bladder were compared together with the fraction of rectum/bladder receiving at least 95% of the ICRU dose (V95), the treated volume (TV, body included in the 95% isodose) and the irradiated volume (IV, body included in the 50% isodose). RESULTS: For both CTV1 and CTV2, the volumes were significantly reduced after prostatectomy (average reduction around 30 cm3 for both; range 0-60 cm3). This reduction was mainly due to a more caudal definition of the cranial edge of CTV after prostatectomy (average difference for CTV2: 1.5 cm; range 0-2.5 cm). Concerning the bladder, a systematic posterior shift of the bladder base (average: 1.5 cm) was found and was correlated with a significant reduction of V95 for bladder (around 10 cm3; p = 0.03). V95 of the rectum, TV and IV also resulted to be significantly lower after surgery. The average reduction of V95 for the rectum was relatively small (2.5 cm3 of rectal wall). CONCLUSION: The impact of prostatectomy on CTV definition is high. A significant reduction of CTV, PTV, TV and IV may be expected after surgery with a consequent reduction of the portions of rectum/bladder irradiated with adjuvant radiotherapy.