Prefer stereotactic radiotherapy over conventional RT unless specific constraints
STEP 1 — Gather Information
Confirm persistent disease after surgery and/or medical therapy (or medical therapy unavailable/unsuccessful/not tolerated); obtain postoperative MRI/CT to measure residual tumor volume and distance from optic chiasm; verify local availability of SRT equipment.
STEP 2 — Rule In / Rule Out
Is radiotherapy indicated for adjuvant treatment? If yes (persistent disease after surgery/medical therapy or medical therapy not an option), proceed to Step 3; if no, consider continued medical therapy or observation.
STEP 3 — Classify or Stratify
Assess three constraints: (1) SRT unavailable? (2) Significant residual tumor burden (e.g., volume >10 cm³ or invasive growth)? (3) Predicted optic chiasm dose >8 Gy (based on tumor‑chiasm distance and prescribed dose). If any constraint is present, classify as “conventional RT preferred”; otherwise classify as “SRT preferred”.
STEP 4 — Decide
If classified as “SRT preferred”, schedule stereotactic radiotherapy (single‑fraction or hypofractionated) per institutional protocol; if classified as “conventional RT preferred”, plan conventional fractionated radiotherapy (e.g., 45–50 Gy in 25 fractions) or consider alternative management.
Clinical Guardrails / Mimics / Pitfalls
Do not use SRT when predicted optic chiasm dose exceeds 8 Gy due to risk of radiation‑induced visual loss; avoid SRT in cases of large invasive tumor burden where conventional wider fields may be needed; ensure SRT planning includes dose‑volume constraints for optic apparatus; verify that residual tumor burden assessment uses contrast‑enhanced MRI; never omit dose calculation for optic chiasm when tumor is within 5 mm of the chiasm.
Concrete Clinical Example
A 48‑year‑old woman with acromegaly has persistent IGF‑1 elevation after transsphenoidal surgery and failed somatostatin ligand therapy. MRI shows a 0.8 cm³ residual tumor 4 mm from the optic chiasm; SRT is available. Dose‑prediction estimates 6 Gy to the chiasm (<8 Gy). No significant residual burden. Decision: proceed with SRT (single‑fraction 19 Gy).
Source: Acromegaly: An Endocrine Society Clinical Practice Guideline, Endocrine Society, 2014, DOI:10.1210/jc.2014-2700
TODO: consider adding scripts/calc.py for the endo-srt-over-conventional-rt-unless-constraints calculator