F.J. Lagerwaard

Tumor location cannot predict the mobility of lung tumors: a 3D analysis of data generated from multiple CT scans.

PURPOSEnThere is limited information available on the three-dimensional (3D) motion of lung tumors. Data derived from multiple planning computed tomographic (CT) scans were used to characterize the 3D movement of small peripheral lung tumors.nnnMETHODS AND MATERIALSnA total of 29 data sets from patients with Stage I non-small-cell lung cancer (NSCLC), each of which consisted of three rapid and three slow planning CT scans, were analyzed. All six scans were coregistered, and contoured gross tumor volumes (GTVs) were expanded by 5 mm to derive clinical target volumes (CTVs). Two-dimensional and 3D displacement vectors of the individual CTVs, relative to an optimal CTV derived from all six scans, were generated. Tumor mobility was correlated with location. Three-dimensional margins, which had to be added to individual CTVs to ensure coverage of optimal CTVs, were determined.nnnRESULTSnNo significant correlation was observed between the anatomic location of tumors and the extent of mobility in the x, y, and z axes. However, supradiaphragmatic lesions exhibited more mobility, particularly in the craniocaudal direction. The addition of a 3D margin of 5 mm to a single slow CTV ensured full coverage of the optimal CTV.nnnCONCLUSIONSnLung tumors demonstrate significant mobility in all directions, and this did not closely correlate with anatomic location. Individualized assessment of tumor mobility remains necessary, and is possible when the CTV derived from a single slow scan is used for radiotherapy planning.

Are multiple CT scans required for planning curative radiotherapy in lung tumors of the lower lobe

PURPOSEnLung tumors located in the lower lobe are the most mobile. Multiple computed tomographic (CT) scans, which had been performed for radiotherapy planning, were analyzed to determine the minimal number of required scans.nnnMETHODS AND MATERIALSnSix spiral CT scans (3 rapid and 3 slow) from 7 such patients were coregistered. Reproducibility of target volumes was defined as the ratio between the overlapping and encompassing volume (COM/SUM) from scans derived using one technique. Volumetric and dosimetric analyses were performed.nnnRESULTSnSlow CT scans generated larger and more reproducible target volumes than rapid planning scans, with a mean COM/SUM ratio of 71.9 +/- 8.7% and 58.0 +/- 12.7%, respectively. When only a single slow CT scan was used for planning, the addition of a symmetrical 3D margin of 5 mm ensured 99% coverage of the optimal target volume, which was derived from summation of target volumes from all six scans.nnnCONCLUSIONnPlanning target volumes (PTVs) derived from a single slow CT scan plus a 5-mm margin covered the optimal PTVs generated from six scans. Although these slow PTVs were larger, the increase in V(20) (the volume of lung tissue receiving a dose > or = 20 Gy) was limited. This indicates that only two CT scans, i.e., a full rapid scan of the entire thorax and a limited slow scan, are necessary for treatment planning in peripheral lung cancers.

High-dose, high-precision treatment options for boosting cancer of the nasopharynx

PURPOSEnThe aim of the study is to define the role and type of high-dose, high-precision radiation therapy for boosting early staged T1,2a, but in particular locally advanced, T2b-4, nasopharyngeal cancer (NPC).nnnMATERIALS AND METHODSnNinety-one patients with primary stage I-IVB NPC, were treated between 1991 and 2000 with 60-70Gy external beam radiation therapy (ERT) followed by 11-18Gy endocavitary brachytherapy (ECBT) boost. In 1996, for stage III-IVB disease, cisplatinum (CDDP)-based neoadjuvant chemotherapy (CHT) was introduced per protocol. Patients were analyzed for local control and overall survival. For a subset of 18 patients, a magnetic resonance imaging (MRI) scan at 46Gy was obtained. After matching with pre-treatment computed tomogram, patients (response) were graded into four categories; i.e. LD (T1,2a, with limited disease, i.e. disease confined to nasopharynx), LRD (T2b, with limited residual disease), ERD (T2b, with extensive residual disease), or patients initially diagnosed with T3,4 tumors. Dose distributions for ECBT (Plato-BPS v. 13.3, Nucletron) were compared to parallel-opposed three-dimensional conformal radiation therapy (Cadplan, Varian Dosetek v. 3.1), intensity modulated radiation therapy (IMRT) (Helios, Varian) and stereotactic radiotherapy (SRT) (X-plan, Radionics v. 2.02).nnnRESULTSnFor stage T1,2N0,1 tumors, at 2 years local control of 96% and overall survival of 80% were observed. For the poorest subset of patients, well/moderate/poorly differentiated T3,4 tumors, local control and overall survival at 2 years with CHT were 67 and 67%, respectively, vs. local control of 20% and overall survival of 12% without CHT. For LD and LRD, conformal target coverage and optimal sparing can be obtained with brachytherapy. For T2b-ERD and T3,4 tumors, these planning goals are better achieved with SRT and/or IMRT.nnnCONCLUSIONSnThe dosimetric findings, ease of application of the brachytherapy procedure, and the clinical results in early staged NPC, necessitates ERT combined with brachytherapy boost to be the therapy of preference for LD and LRD. For locally advanced T3,4 tumors, our current protocol indicates neoadjuvant chemotherapy in conjunction with high cumulative doses of radiotherapy (81Gy); IMRT and/or SRT to be the preferred technique for boosting the primary tumor.

Can errors in reconstructing pre-chemotherapy target volumes contribute to the inferiority of sequential chemoradiation in stage III non-small cell lung cancer (NSCLC)?

Concurrent chemo-radiotherapy (CT-RT) has been shown to be superior to sequential CT-RT for stage III non-small cell lung cancer (NSCLC). Pre-chemotherapy gross tumor volumes (GTV) are commonly contoured for sequential CT-RT and, as significant inter-clinician variability exists in defining GTVs for lung cancer, we postulated that the poorer local control observed with sequential CT-RT may partly be due to the larger errors in defining GTV after chemotherapy-induced tumor regression. Pre-and post-chemotherapy CT scans for RT planning (RTP) were performed in ten patients who received induction chemotherapy for NSCLC. Image registration of pre- and post-chemotherapy RTP scans was performed for all patients. GTVs were first contoured in the conventional manner by two clinicians, i.e. by visual reconstruction from hard copies of the pre-chemotherapy diagnostic CT scans (GTV-visual). A GTV-match was then contoured after image-registration, and the gold standard volume was considered to be the overlap of the GTV-match generated by both clinicians. The GTV-match was on average 31-40% larger than GTV-visual. The mean percentage of the gold standard, which was not covered by the GTV-visual was similar for both clinicians, i.e. 26.3+/-12.5 and 28.0+/-15.0%. The inter-clinician agreement in contouring improved after image registration. These data suggest that conventional visual contouring of pre-chemotherapy GTVs may fail to treat the actual pre-chemotherapy tumor volume, and thus confound studies evaluating optimal sequencing of chemo-radiotherapy in NSCLC.

(P36) Stereotactic MRI-Guided Adaptive Radiotherapy for Adrenal Metastases

Objectives: SABR for isolated adrenal metastases can result in high local control rates and long-term survival. However, the proximity of critical normal organs (OARs) limits the dose that can be delivered. We studied inter-fractional organ motion during MR-guided SABR for adrenal metastases, and evaluated the dosimetric advantages of daily online plan adaptation. Methods: 8 pts with adrenal metastasis underwent video-assisted, respiratory-gated SMART for a total of 41 fractions. For each fraction, a shallow breath-hold was performed, Contour deformation, PTV (GTV+3mm) expansion and planning structures were automatically generated according to the anatomy-of-the-day. Depending on tumor volume and OAR proximity either 5 x10Gy and 8 x7.5Gy. Treatment plans were generated using a novel strategy to minimize high doses to OARs. Inter-fractional changes in the stomach, bowel and duodenum were quantified according to the volume of OAR change (within a 3 cm from PTV), center of mass (COM) displacements and the maximum Hausdorff distance. We compared volumes of GTV and PTV receiving 95% of prescribed dose, and V35 for of all OARs (using paired t-tests). Results: In all patients, important inter-fractional changes were observed for each OAR. Mean COM displacements from baseline were 5.4 (range 1.9 – 9.8), 6.4 (range 1.1 – 18.2) and 6.6 (range 1.4 – 12.3) mm for the stomach, bowel and duodenum, respectively. Maximum OAR displacements were 34.1 mm, 28.2 mm and 23.4 mm for stomach, bowel and duodenum, respectively. Maximum volume changes for stomach, bowel and duodenum within a 3 cm distance from the PTV surface were 74.1, 58.9 and 27.8 cc, respectively. Baseline plans recalculated on the anatomy-of-the-day (defined as predicted plans) led to marked underdosage of target volumes and variable OAR sparing. In predicted plans, GTV and PTV objectives for V95% were unmet in 32% and 76% of all fractions, respectively. Plan reoptimization significantly improved target coverage, and the percentage of fractions not meeting the V95% objective was reduced to 12% and 39% for GTV and PTV, respectively (p<0.01). Re-optimized plans exhibited significantly better sparing of OAR and achieved a reduction of 2.1, 2.1 and 2.8 cc for stomach, bowel and duodenum at V35Gy, with respect to predicted plans (all: p<0.01). Conclusions: Despite breath-hold SABR delivery under MR-guidance, significant volumetric 1 2 3 4 2 Open Access Abstract