Delineation of Margins for the Planning Target Volume (PTV) for Image-Guided Radiotherapy (IGRT) of Gastric Cancer Based on Intrafraction Motion

Background: Application of the image-guided radiotherapy (IGRT) system for gastric cancer involving daily verification of patient positioning on the treatment machine allows minimisation of geometrical errors as a consequence of intra- and inter-fraction motion. The purpose of this study was to define the intrafraction motion in gastric cancer patients during a treatment session based on the IGRT system and designation of margins around the clinical target volume CTV (internal target volume ITV) necessary to delineate the planning target volume (PTV). Methods: Twenty gastric cancer patients were analysed. The total radiation dose for each was 45Gy in 25 fractions within 5 weeks. The margins for the PTV were calculated according to van Herk (2004), Stroom and Heijmen (2002) and the International Commission on Radiation Units and Measurements (ICRU) Report 62 formulas based on craniocaudal (Y axis), laterolateral (X axis) and anteroposterior (Z axis) shifts. Results: Delineated margins for the PTV in gastric cancer with the three formulas applied were respectively 0.2, 0.2, and 0.2cm in the lateral plane, 0.3, 0.3, and 0.3cm in the craniocaudal plane and 0.3, 0.3, and 0.2cm in the anteroposterior plane. Conclusions: Recommended margins for the PTV in gastric cancer calculated in this study based on intrafraction motion are 0.3cm, 0.2cm and 0.3cm in the craniocaudal, lateral and anterioposterior directions, respectively. Use of the IGRT system corrects for the motions between factions and allows reduction in ITV-PTV margins. The main advantage of the smaller margins in comparison to the non-IGRT radiotherapy is a reduction in the probability of radiation complications.

Can we obtain planning goals for conformal techniques in neoadjuvant and adjuvant radiochemotherapy for gastric cancer patients?

AIM: The purpose of this study was to compare conformal radiotherapy techniques used in the treatment of gastric cancer patients. The study is dedicated to radiotherapy centres that have not introduced dynamic techniques in clinical practice. BACKGROUND: The implementation of multi-field technique can minimise the toxicity of treatment and improve dose distribution homogeneity in the target volume with simultaneous protection of organs at risk (OaRs). Treatment plan should be personalised for each patient by taking into account the planning target volume and anatomical conditions of the individual patient. MATERIALS AND METHODS: For each patient, four different three dimensional conformal plans were compared: 2-field plan, 3-field plan, non-coplanar 3-field plan and non-coplanar 4-field plan. Dose distributions in a volume of 107% of the reference dose, and OaRs such as the liver, kidneys, intestines, spinal cord, and heart were analysed. RESULTS: The mean volume of the patient body covered using the isodose of 107% was 3004.73 cm(3), 1454.28 cm(3), 1426.62 cm(3), 889.14 cm(3) for the 2-field, 3-field, non-coplanar 3-field and non-coplanar 4-field techniques, respectively. For all plans the minimum dose in the PTV volume was at least 95% of the reference dose. The QUANTEC protocol was used to investigate doses in OaRs. CONCLUSIONS: Comparison of 3D conformal radiotherapy techniques in gastric cancer patients indicates that none of the plans can fulfil simultaneously all of the criteria of the tolerance dose in the organs at risk. The implementation of the multi-field technique can minimise the toxicity of treatment and improve dose distribution homogeneity in the target volume with additional protection of organs at risk (OaRs).

Protection of organs at risk during neoadjuvant chemoradiotherapy for gastric cancer based on a comparison between conformal and intensity-modulated radiation therapy.

The aim of the present study was to compare the techniques of dynamic intensity-modulated radiation therapy (IMRT) and three-dimensional conformal radiotherapy (3DCRT) in patients with gastric cancer. Implementation of the IMRT technique does not significantly affect the minimum and maximum dose levels in the planning target volume (PTV), but more effectively protects the critical organs. The study group consisted of 25 patients. The results of the analysis of the conformity index (CI) and the homogeneity index (HI) showed that the doses in the PTV regions were at a comparable level. The CI for the PTV was 0.95 for the 2-field technique, 0.95 for the 3-field technique, 0.96 for the 4-field technique and 0.94 for the IMRT technique. The CIs for these techniques for the clinical target volume (CTV) were 0.96, 0.96, 0.97 and 0.96, respectively, and the CIs for the gross tumor volume (GTV) were 0.99, 0.99, 0.99 and 0.98, respectively. The HI values for the PTV were 1.12 for the 2-field technique, 1.12 for the 3-field technique, 1.09 for the 4-field technique and 1.09 for the IMRT technique, and the HI values for the CTV were 1.12, 1.12, 1.09 and 1.08 for the same techniques, respectively. The HI values for the GTV were 1.09, 1.09, 1.07 and 1.06, respectively, which indicated significantly superior performance in the regions of healthy tissue. Statistical study was based on Friedman's rank analysis of variance to determine the level of reliability of the tested groups of variables (P<0.001). The present study demonstrated that the IMRT technique in the pre-operative radiotherapy of gastric cancer patients results in superior treatment tolerance and reduces the risk of damage to healthy tissue that is in close proximity to the irradiated area.

Dose distribution in bladder and surrounding normal tissues in relation to bladder volume in conformal radiotherapy for bladder cancer.

PURPOSE: To estimate bladder movements and changes in dose distribution in the bladder and surrounding tissues associated with changes in bladder filling and to estimate the internal treatment margins. METHODS AND MATERIALS: A total of 16 patients with bladder cancer underwent planning computed tomography scans with 80- and 150-mL bladder volumes. The bladder displacements associated with the change in volume were measured. Each patient had treatment plans constructed for a "partially empty" (80 mL) and a "partially full" (150 mL) bladder. An additional plan was constructed for tumor irradiation alone. A subsequent 9 patients underwent sequential weekly computed tomography scanning during radiotherapy to verify the bladder movements and estimate the internal margins. RESULTS: Bladder movements were mainly observed cranially, and the estimated internal margins were nonuniform and largest (>2 cm) anteriorly and cranially. The dose distribution in the bladder worsened if the bladder increased in volume: 70% of patients (11 of 16) would have had bladder underdosed to <95% of the prescribed dose. The dose distribution in the rectum and intestines was better with a "partially empty" bladder (volume that received >70%, 80%, and 90% of the prescribed dose was 23%, 20%, and 15% for the rectum and 162, 144, 123 cm(3) for the intestines, respectively) than with a "partially full" bladder (volume that received >70%, 80%, and 90% of the prescribed dose was 28%, 24%, and 18% for the rectum and 180, 158, 136 cm(3) for the intestines, respectively). The change in bladder filling during RT was significant for the dose distribution in the intestines. Tumor irradiation alone was significantly better than whole bladder irradiation in terms of organ sparing. CONCLUSION: The displacements of the bladder due to volume changes were mainly related to the upper wall. The internal margins should be nonuniform, with the largest margins cranially and anteriorly. The changes in bladder filling during RT could influence the dose distribution in the bladder and intestines. The dose distribution in the rectum and bowel was slightly better with a "partially empty" than with a "full" bladder.

Could lipid CH2/CH3 analysis by in vivo 1H MRS help in differentiation of tumor recurrence and post-radiation effects?

PURPOSE: To inspect the potential diagnostic role of in vivo 1H MRS lipid methylene CH2 to methyl CH3 signal ratio in differentiation of recurrent brain tumor from radiation injury. METHODS: Two patients--one with documented recurrence and the other without recurrence--were monitored by means of 1H MRS before and during two years after radiation therapy. The comparative group consisted of 20 patients with glial tumor recurrence diagnosed 2 years after the radiotherapy. RESULTS: In case of tumor recurrence, an increase of the lipid CH2/CH3 value is observed. In contrast, for the patient with no tumor recurrence and within the brain areas distant from the tumor the CH2/CH3 ratio reveals a negative correlation vs. time after irradiation. The Lip trend to increase on radiotherapy both at the tumor bed and within the non-involved areas lessens the value of Lip as a marker of tumor recurrence. CONCLUSION: The analysis of the lipid CH2/CH3 ratio may be useful in differentiation of the tumor recurrence from radiation response. The Lip signals observed in normally appearing brain tissue after radiotherapy could originate from the change of metabolism of irradiated cells.