Optimization of dose distributions for adjuvant locoregional radiotherapy of gastric cancer by IMRT.
OBJECTIVE
Locoregional relapse is a problem frequently encountered with advanced gastric cancer. Data from the randomized Intergroup trial 116 suggest effectiveness of adjuvant radiochemotherapy, albeit with significant toxicity. The potential of intensity-modulated radiotherapy (IMRT) to reduce toxicity by significantly reducing maximum and median doses to organs at risk while still applying sufficient dose to the target volume in the upper abdomen was studied.


METHODS
For a typical configuration of target volumes and organs, a step-and-shoot IMRT plan (eight beam orientations), developed as a class solution for treatment of tumors in the upper abdomen (Figures 1 to 3), a conventional plan, a combination of the conventional plan with a kidney-sparing boost plan, and a conventional plan with noncoplanar ap and pa fields for improved kidney sparing were compared with respect to coverage of target volume and dose to organs at risk with a dose of 45 Gy delivered as the median dose to the target volume.


RESULTS
When using the conventional three-dimensionally planned box techniques, the right kidney could be kept below tolerance, but median dose to the left kidney amounted to between 14.8 and 26.9 Gy, depending on the plan. IMRT reduced the median dose to the left kidney to 10.5 Gy, while still keeping the dose to the right kidney < 8 Gy. Liver was spared better with IMRT. Dose to the lungs was not significantly different, and dose to the spinal cord was higher (but well below tolerance) with IMRT. The dose distribution within the target volume was less homogeneous than for the conventional plans. With regard to target coverage, > 90% of prescription dose were delivered to > 90% of target volume with IMRT (Table 1).


CONCLUSIONS
IMRT has the potential to deliver efficient doses to target volumes in the upper abdomen, while delivering dose to organs at risk in a more advantageous fashion than a conventional technique. For clinical implementation, the possibility of extensive organ motion in the upper abdomen has to be taken into account for treatment planning and patient positioning. The multitude of potential risks related to its application has to be the subject of thorough follow-up and further studies.
D000230:Adenocarcinoma / Q000532:radiotherapy* / Q000601:surgery; D000328:Adult; D000465:Algorithms; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005743:Gastrectomy; D006801:Humans; D021621:Imaging, Three-Dimensional; D007668:Kidney / Q000528:radiation effects; D008099:Liver / Q000528:radiation effects; D008168:Lung / Q000528:radiation effects; D011187:Posture; D011829:Radiation Dosage; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D018714:Radiotherapy, Adjuvant; D020266:Radiotherapy, Conformal / Q000009:adverse effects / Q000379:methods*; D018570:Risk Assessment; D012984:Software; D013116:Spinal Cord / Q000528:radiation effects; D013274:Stomach Neoplasms / Q000532:radiotherapy* / Q000601:surgery; D013997:Time Factors