Investigator decided to not go forward with the study.

Unresectable (including metastatic) conventional chondrosarcoma requires high dose radiation for local control. Radiation Oncologists have traditionally used long radiation courses and concern for toxicity to surrounding organs at risk. Stereotactic body radiation therapy (SBRT) has the ability to deliver high doses of radiation in a manner that may improve clinical response but has size limitations. SBRT delivered with lattice radiotherapy (LRT) may safely dose escalate smaller portions of the tumor and also provide improved cancer control. This study is to evaluate the safety and initial efficacy of this treatment approach.

Inclusion Criteria:

• Histologically or cytologically confirmed conventional chondrosarcoma.

• At least one, large targetable lesion defined as: 1 lesion that can be accurately measured in at least one dimension (longest diameter to be recorded) as ≥ 45 mm with radiographic imaging or with calipers by clinical exam.

• Deemed metastatic and/or unresectable by multidisciplinary review. Patients with prior resection with gross residual disease that are subsequently deemed ineligible for further resection are allowed.

• Patients that have had prior chemotherapy are allowed

• At least 14 years of age

• ECOG performance status ≤ 2

• Normal bone marrow and organ function as defined below:

  • Leukocytes ≥ 3,000/mcL
  • Absolute neutrophil count ≥ 1,500/mcl
  • Platelets ≥ 100,000/mcl

• Radiotherapy is known to be teratogenic. For this reason women of childbearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control, abstinence) prior to study entry and for the duration of study participation. Should a woman become pregnant or suspect she is pregnant while participating in this study, she must inform her treating physician immediately. Men treated or enrolled on this protocol must also agree to use adequate contraception prior to the study, for the duration of the study, and 6 months after completion of the study

• Ability to understand and willingness to sign an IRB approved written informed consent document (or that of legally authorized representative, if applicable).

Exclusion Criteria:

• Dedifferentiated chondrosarcoma and extra-skeletal myxoid chondrosarcoma are excluded.
• Patients with greater than 5 measurable metastatic lesions as determined by multidisciplinary review are excluded
• Prior radiotherapy that overlaps with any planned site of protocol radiotherapy.
• Currently receiving any systemic cancer therapy agents. Systemic therapy prior to radiotherapy or planned after radiotherapy delivery are allowed at the discretion of the treating radiation oncologist.
• Pregnant and/or breastfeeding. Women of childbearing potential must have a negative pregnancy test within 20 days of study entry.
• Patients with HIV are eligible unless their CD4+ T-cell counts are < 350 cells/mcL or they have a history of AIDS-defining opportunistic infection within the 12 months prior to registration. Concurrent treatment with effective ART according to DHHS treatment guidelines is recommended. Recommend exclusion of specific ART agents based on predicted drug-drug interactions (i.e. for sensitive CYP3A4 substrates, concurrent strong CYP3A4 inhibitors (ritonavir and cobicistat) or inducers (efavirenz) should be contraindicated).