MOPA — Medical Oncology Prior Authorization - Local Development build (v0.1.1-snapshot-080926) built by the FHIR (HL7® FHIR® Standard) Build Tools. See the Directory of published versions

Regimen Modeling

Overview

For oncology prior authorization, the selected clinical unit is not a single medication order. It is the coordinated anti-cancer regimen: disease context, treatment intent, regimen components, timing, sequential phases, and the clinical facts that justify the regimen.

This IG defines two complementary profiles that separate the definition of a regimen from its instantiation as a patient-specific order.

The PlanDefinition / RequestGroup Separation

PlanDefinition     ← canonical, reusable regimen protocol (not patient-specific)
       ↑
  (instantiatesCanonical — OPTIONAL; omit when no canonical definition exists)
       ↑
RequestGroup       ← patient-specific ordered regimen instance (CDS Hooks payload) [REQUIRED]
       ↓
MedicationRequest  ← component orders (available at order-sign)

AntiCancerRegimenPlanDefinition

The canonical regimen definition carries:

• type = order-set — identifies this as an order set, not a clinical pathway
• subject[x] — the target cancer population (e.g., breast cancer); this is the canonical declaration of what cancer type the regimen is designed for
• action[+] — one action per regimen component (drug or phase)

AntiCancerRegimenRequestGroup

The patient-specific ordered instance carries:

• instantiatesCanonical (Must Support) — canonical URL of the PlanDefinition being ordered, when a published definition exists; MAY be omitted when the regimen originates from a local order-set without a canonical definition
• extension[category] (Must Support, 0..*) — repeated Da Vinci CRD ext-request-category values for patient-specific ordering categories. The optional category/treatmentIntent and category/lineOfTherapy reslices constrain that same extension to CodeableConcept and require bindings to RegimenIntentVS and TreatmentLineVS, respectively. CRD 2.2.1 needs a proposed RequestGroup extension-context expansion before this use is available in the base CRD specification.
• action[+] — ordered components with cycle-day timing and phase sequencing

Treatment intent and line of therapy are patient-specific CodeableConcept categories on the RequestGroup. Both semantic slices serialize with the CRD extension URL; their constraint profiles provide the distinct required terminology bindings. No companion Observation is used.

Cycle Day Timing

Each action declares which day(s) of the cycle the drug is administered using the local regimen-days-of-cycle extension on action.timingTiming. This is a temporary local semantic pending an official timing-daysOfCycle context expansion. The action.timingTiming.repeat carries the machine-computable cycle period.

{
  "id": "paclitaxel-action",
  "title": "Paclitaxel",
  "timingTiming": {
    "repeat": { "period": 7, "periodUnit": "d" },
    "extension": [{
      "url": "http://hl7.org/fhir/us/codex-mopa/StructureDefinition/regimen-days-of-cycle",
      "extension": [{ "url": "day", "valueInteger": 1 }]
    }]
  },
  "resource": { "reference": "MedicationRequest/paclitaxel-order" }
}

Sequential Phase Ordering

For multi-phase regimens (e.g., AC→T: dose-dense doxorubicin/cyclophosphamide followed by paclitaxel), top-level action groups represent phases. action.relatedAction with relationship = after-end declares that the second phase begins after the first completes.

{
  "id": "t-phase",
  "title": "T Phase — Paclitaxel",
  "relatedAction": [{
    "actionId": "ac-phase",
    "relationship": "after-end"
  }]
}

Note on NCPDP Structured Sig

NCPDP Structured Sig encodes per-drug dispensing instructions and maps to MedicationRequest.dosageInstruction. It is compatible with this model at the leaf level (within each component MedicationRequest action) but is not a substitute for the RequestGroup layer. NCPDP Structured Sig has no concept of cycle day, cross-drug phase sequencing, or inter-drug ordering (relatedAction); those constructs live exclusively in the RequestGroup. For oral oncology agents dispensed via retail pharmacy (e.g., capecitabine, palbociclib), NCPDP SCRIPT remains the e-prescribing channel, but cycle context still belongs on the RequestGroup action.

Examples

See Example: Paclitaxel + Trastuzumab (concurrent, weekly) and Example: ddAC→T (sequential phases).