Appeal type: Experimental/Investigational
Decision: Upheld

A 71-year-old male has requested coverage for past proton beam radiation therapy provided for treatment of his metastatic colon cancer to the liver.  Findings:  Two physician reviewers found that the patient has undergone partial colectomy and adjuvant 5-FU Leucovorin chemotherapy. He was subsequently diagnosed with liver metastases after he was noted to have an elevated CEA. He underwent radiofrequency ablation (RFA) after which he developed a recurrence in the treated sites and underwent a partial liver resection. Computed tomography (CT) imaging and PET/CT imaging revealed a recurrence in the liver. He was evaluated for possible treatment with radiation therapy for his solitary liver metastasis, and was offered proton therapy. A letter from the provider states that proton therapy is medically necessary to the isolated recurrence from solitary liver metastasis. The plan is to deliver 70 Gy in 10 fractions with curative intent. Proton therapy is necessary in order to spare normal liver as well as the surrounding normal organs.  Standard radiation is delivered with a linear accelerator (LINAC), which delivers photon therapy, while protons are generated from a cyclotron. The difference between proton and photon irradiation is that the protons stop abruptly in the tissue (Bragg peak) so there is less exit dose through normal tissue. The use of proton therapy is an accepted radiation technology that has proven efficacy and tolerability. Certain conditions such as base of skull chordomas and chondrosarcomas, and pediatric central nervous system (CNS) malignancies are likely best treated with proton therapy, due to the sharp dose fall off, allowing high dose delivery to the tumor, while relatively sparing the neighboring normal tissue. However, the issue of whether proton therapy provides any benefit over conventional radiation therapy in other tumors remains unsettled. Oligometastases are defined as a state of metastatic disease few in number and extent. This patient, with a solitary metastatic liver lesion, would be considered to have oligometastases. The rationale for treating oligometastases with local therapy (i.e. radiation or surgery) is to prolong disease control as well as quality of life by improved cancer control (Timmerman, et al). Numerous studies have published outcomes of using hypofractionated radiation for liver oligometastases with reports of prolonged disease-free survival after radiation, with approximately 20-30% of patients surviving many years (Katz, et al). For this patient, stereotactic body radiation therapy (SBRT) for a solitary oligmetastasis would be the standard of care and consistent with the treatment recommendations from the American Society of Therapeutic Radiation Oncology (ASTRO) model policy statement. While proton therapy is a potential alternative to SBRT, there is a paucity of peer reviewed medical literature describing its use for this indication. By virtue of its improved targeting accuracy, SBRT may be superior to proton therapy without stereotactic localization in terms of improved targeting and allowing higher fractional dose delivery. On review of the additional records and imaging provided for review, the proton beam therapy may have been effective, but was not clinically indicated for this patients solitary liver metastasis over conventional treatment with SBRT. In a patient declining surgery, as in this case, certainly radiation is appropriate. However, the standard approach is to use SBRT.