Ruth Williamson, MD
Radiation Oncology Physician · Pasadena, CA
Ruth Williamson, MD is a radiation oncology physician with a practice address in Pasadena, California, and NPI 1952486912, issued on Oct 26, 2006. Check the license (California G707B5C, as entered in NPPES) on the Medical Board of California; the Medicare figures below come from public CMS files.
- Name
- Ruth Williamson
- Credential
- MD
- Primary taxonomy
- Radiation Oncology Physician 2085R0001X
- License number
- G707B5C CA
Self-reported in NPPES; status is on the state search - Practice location
- 625 S Fair Oaks Ave Ste 100, Pasadena, CA 91105
- Phone
- (626) 397-5149
- Enumerated
- Oct 26, 2006
- Record last updated
- Oct 13, 2022
- Fax
- (310) 397-2147
- Medicaid ID
- GR0087110 CA
- Medicare enrollment
- Enrolled (PECOS I20100618000425); accepts Medicare assignment
- Medical or professional school
- University Of Southern California Keck School Of Medicine, 1989
- Entity
- Type 1 · individual
8 nearest radiation oncology physician records → All 735 in California → Look up another NPI →
Also registered at 625 S Fair Oaks Ave Ste 100
A shared address usually means a shared clinic or building; it does not show who employs whom.
- Ramona Kyaw, M.D.Radiation Oncology Physician1053494914
- Erika Winkler, MS, RD, CNSC, CSORegistered Dietitian1053947630
Verify Ruth Williamson in five checks
- 1IdentityNPI record in CMS NPPESNPI lookupConfirmed in NPPES
- 2LicenseActive license and public ordersMedical Board of California
Search for license G707B5CCheck the board - 3Other statesLicenses and actions elsewhereDocInfo (FSMB)Not checked
- 4ExclusionsMedicare and Medicaid bansHHS-OIG exclusion listNot checked
- 5CertificationBoard certificationABMS AOA NCCPA AANPNot checked
69% fewer Medicare Part D claims than the average radiation oncology physician in 2024
41 Medicare Part D claims for 31 beneficiaries, against an average of 134 among the 4,851 providers of this specialty who prescribed in Part D.
Most prescribed
- Clobetasol Propionate28 claims
Source: CMS Medicare Part D Prescribers by Provider and Drug, 2024 (data.cms.gov). Part D covers prescriptions for Medicare patients only; drugs with fewer than 11 claims are not published.
The practice group's MIPS final score for 2023 (Medicare payment program): 85.7 of 100
The Merit-based Incentive Payment System score is reported for the practice group, not for one clinician alone. Four categories are weighted into the final score; the average among 454,083 clinicians with a measured score was 83.5.
Source: CMS Quality Payment Program, MIPS performance year 2023, group reporting; category weights for 2023 (qpp.cms.gov).
Bills Medicare through one group practice
- Cedars-Sinai Medical Care FoundationPasadena, CA
Source: CMS Doctors and Clinicians National Downloadable File (the group practices a clinician bills Medicare through) (data.cms.gov).
Ruth Williamson among 735 radiation oncology physician records in California
Ruth Williamson, MD is one of 735 radiation oncology physician records with a practice address in California. 83% of them appear in a Medicare file (Part D prescribing, MIPS, Open Payments or Medicare group billing); this one does. Its NPI, issued in 2006, is newer than 16% of them.
- NPI issued2006 · 16% of these records are older, 55% newer
- In a Medicare fileYes · 83% of these records are
- In the CMS Doctors and Clinicians fileYes · 74% of these records are
- Graduated1989 · median 2005 among the 545 with a school on file
- Record last updated2022 · 55% of these records were not updated in five years or more
Source: CMS NPPES, file of Aug 9, 2026, every record with primary taxonomy 2085R0001X and a California practice address; Medicare files: CMS Part D Prescribers 2024, MIPS 2023, Open Payments 2024, Doctors and Clinicians (data.cms.gov).
Radiation Oncology Physician providers in California
There are 735 radiation oncology physician records in California.
All 735 in California → Every provider in Pasadena → Radiation Oncology Physician nationwide →
The 8 radiation oncology physician records with the nearest ZIP codes
- Ramona Kyaw, M.D.Pasadena, CA 911051053494914
- Linda Chak, M.D.San Marino, CA 911081275734956
- Benjamin Cahan, M.D.South Pasadena, CA 910301396034229
- Helen Chen, MDSouth Pasadena, CA 910301578546388
- Jason Liu, MDSouth Pasadena, CA 910301619537511
- Arya Amini, M.D.Duarte, CA 910101487910774
- Jose Bazan, MDDuarte, CA 910101851535504
- Savita Dandapani, M.D. , PH.D.Duarte, CA 910101619141751
Common questions
What is Ruth Williamson, MD's NPI number?
Ruth Williamson, MD's National Provider Identifier (NPI) is 1952486912, issued on Oct 26, 2006. An NPI identifies a provider in billing; it is not a license.
Where is Ruth Williamson, MD located?
The NPPES record lists a practice address at 625 S Fair Oaks Ave Ste 100, Pasadena, CA, 91105. Phone: (626) 397-5149. Providers update this record themselves, so call before visiting.
How can I verify Ruth Williamson, MD's license?
NPPES lists California license number G707B5C, as entered by the provider. Search the Medical Board of California at https://www.mbc.ca.gov/License-Verification/default.aspx. The NPPES record confirms identity only; the state search shows license status, expiration and public orders.
How much does Ruth Williamson, MD prescribe under Medicare Part D?
In 2024, Ruth Williamson, MD had 41 Medicare Part D claims for 31 beneficiaries; the average among radiation oncology physician prescribers was 134. Part D covers Medicare prescriptions only.
What is Ruth Williamson, MD's MIPS final score?
The 2023 MIPS final score is 85.7 of 100, reported for the practice group. The average among 454,083 clinicians with a measured score was 83.5.
Source: CMS National Plan and Provider Enumeration System (NPPES), file of Aug 9, 2026 (NPPES files on CMS.gov); NUCC Health Care Provider Taxonomy. Medicare files from data.cms.gov. An NPI identifies who bills; it is not a license.
Figures on PlainDoctor are read from the federal files each page names (CMS NPPES, Medicare Part D, MIPS, Open Payments; the HHS-OIG exclusion list only as counts) and from Census population estimates, with the file date shown beside them. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of Aug 9, 2026.