Final answer:
Radiation therapy is the primary palliative measure for reducing tumor mass and relieving obstruction in stomach cancer patients.
Explanation:
Radiation therapy is the most likely palliative measure used to decrease tumor mass and relieve obstruction in clients with stomach cancer. It involves the use of ionizing radiation like X-rays to kill cancerous tissues, sparing normal tissues as much as possible. Proton therapy, while offering advantages like targeting only the tumor area, is less common due to cost and availability.
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