ABPS Radiation Oncology cheat sheet

Early-stage glottic cancer (T1N0) is typically managed with single-modality therapy: either transoral laser microsurgery or definitive radiotherapy (~63 Gy at 2.25 Gy/fraction); adding neck dissection is not routine for N0.

For locally advanced NSCLC, concurrent chemoradiotherapy is standard; conventionally fractionated dose is 60 Gy in 30 fractions, and dose escalation beyond 60 Gy has not improved survival in randomized trials.

Prostate cancer risk stratification uses PSA, Gleason/Grade Group, and T stage; dose-escalated EBRT (≥76-78 Gy conventional) or brachytherapy boost improves biochemical control in intermediate/high-risk disease.

Breast-conserving surgery is followed by whole-breast RT (typically 40-42.5 Gy in 15-16 fractions or ~50 Gy in 25 fractions) with a tumor-bed boost for higher-risk features; hypofractionation is standard for most patients.

Rectal cancer with T3/T4 or node-positive disease receives neoadjuvant therapy (chemoradiation or total neoadjuvant therapy) before surgery; short-course RT (25 Gy in 5 fractions) is an alternative for selected patients.

Head and neck squamous cell carcinoma with involved margins or extranodal extension receives postoperative RT with concurrent cisplatin; adjuvant RT alone is used when risk factors are absent.

HPV-positive oropharyngeal cancer has substantially better prognosis than HPV-negative disease and is the subject of de-escalation trials; staging differs (AJCC 8th edition).

Multidisciplinary tumor board review before definitive local therapy is standard for complex presentations; treatment decisions integrate stage, performance status, and patient preference.

The linear-quadratic model: surviving fraction SF = exp(-(αD + βD²)); α/β is the dose at which linear and quadratic contributions are equal.

Typical α/β values: ~10 Gy for early-responding tumors and acute effects; ~3 Gy for late-responding normal tissues (e.g., spinal cord, lung).

The 4 R's of radiobiology: repair (of sublethal damage), repopulation, redistribution (cell cycle), and reoxygenation.

The biologically effective dose (BED) = nd(1 + d/(α/β)); equivalent dose in 2-Gy fractions (EQD2) = BED/(1 + 2/(α/β)).

Oxygen enhancement ratio (OER) is approximately 2.5-3.0; hypoxic cells are 2.5-3 times more radioresistant than well-oxygenated cells.

The target theory and cell survival curves: D0 is the dose reducing survival by 1/e on the exponential portion; Dq and n describe the shoulder.

Repopulation during fractionated RT (accelerated repopulation) can require dose compensation; this underlies accelerated fractionation strategies in head and neck cancer.

Late effects follow the α/β ≈ 3 Gy model and are more sensitive to fraction size than acute effects; this drives constraints on dose per fraction.

Absorbed dose is measured in gray (Gy); 1 Gy = 1 J/kg. Equivalent and effective doses use sievert (Sv) with radiation and tissue weighting factors.

Photoelectric effect dominates at low photon energies and scales approximately with Z³/E³; Compton scattering dominates in the megavoltage range for tissue-like materials.

The inverse square law: dose rate falls as 1/r² from a point source; used for source strength and distance calculations.

Percent depth dose (PDD) increases with energy and field size and decreases with depth; tissue-air ratio and tissue-phantom ratio are used for isocentric calculations.

Half-value layer (HVL) = 0.693/μ; tenth-value layer = ln(10)/μ; used for shielding and attenuation calculations.

Monitor unit calculation for a linear accelerator uses output factor, PDD or TMR, inverse square, and field-size factors; independent MU checks are a required QA step.

Brachytherapy dosimetry uses the AAPM TG-43 formalism: dose rate = Sk · Λ · (G(r,θ)/G(r0,θ0)) · g(r) · F(r,θ).

Radioactive decay: A = A0·e^(−λt); half-life t½ = ln2/λ. Common isotopes: I-125 (59.4 d), Pd-103 (17 d), Cs-131 (9.7 d), Ir-192 (73.8 d).

3D conformal RT uses forward planning; IMRT/VMAT use inverse optimization with dose-volume objectives and constraints.

VMAT delivers dose during continuous gantry rotation with dynamic MLC; it typically reduces monitor units and treatment time versus fixed-field IMRT.

SBRT uses high dose per fraction (e.g., 8-20 Gy) in few fractions with steep dose gradients; accurate immobilization and image guidance are required.

Image-guided RT (CBCT, kV, MV, or surface imaging) reduces setup error; PTV margins account for setup uncertainty plus internal motion.

Dose-volume constraints (e.g., spinal cord Dmax, parotid mean dose, lung V20) are derived from QUANTEC and institutional data and drive plan evaluation.

AAPM TG-218 addresses IMRT QA: measurement-based or independent calculation-based verification with gamma analysis (typically 3%/2 mm) and action limits.

AAPM TG-142 defines linac QA tolerances: daily output constancy, monthly mechanical checks, and annual full calibration; tolerances depend on technique (e.g., SRS/SBRT tighter).

Four-dimensional CT and respiratory gating or abdominal compression manage intrafraction motion for thoracic and upper-abdominal targets.

Prostate LDR brachytherapy uses permanent implants of I-125 (145 Gy monotherapy) or Pd-103 (125 Gy monotherapy); post-implant dosimetry is assessed by CT at ~30 days.

Cervical cancer definitive chemoradiation includes brachytherapy; MRI-guided adaptive brachytherapy uses the GEC-ESTRO target concept (GTVres, HR-CTV, IR-CTV) with EMBRACE dose-volume constraints.

High-dose-rate (HDR) brachytherapy uses a remote afterloader with a stepping Ir-192 source; treatments are fractionated, commonly 3-5 fractions for gynecologic implants.

Tandem-and-ovarian brachytherapy prescription is typically to Point A (historical) or to a volumetric HR-CTV dose (≥85-90 Gy EQD2 in EMBRACE).

Iodine-131 is used for differentiated thyroid cancer ablation; patients require thyroid hormone withdrawal or recombinant TSH and radiation safety instructions.

Yttrium-90 microspheres are used for hepatic tumors via transarterial delivery; pretreatment dosimetry uses MAA or partition-model calculations.

Radium-223 is an alpha-emitting agent for metastatic castration-resistant prostate cancer with bone metastases; it improves survival and reduces skeletal events.

Strontium-89 and samarium-153 are beta-emitting bone palliation agents; myelosuppression is the main toxicity, especially with concurrent chemotherapy.

Concurrent cisplatin with RT is a standard radiosensitizing regimen for head and neck and cervical cancers; nephrotoxicity, ototoxicity, and myelosuppression require monitoring.

Radiation recall is an inflammatory reaction in previously irradiated tissue triggered by systemic agents (e.g., doxorubicin, gemcitabine, taxanes); management is supportive.

Radiation-induced nausea and vomiting prophylaxis follows antiemetic guidelines (5-HT3 antagonist ± dexamethasone ± NK1 antagonist for high-risk regimens).

Oral mucositis prevention includes oral care and consideration of palifermin in selected high-risk patients; low-level laser therapy may reduce severity.

Radiation dermatitis is managed with gentle skin care, topical corticosteroids for pruritus, and avoidance of irritants; severe moist desquamation may require dressing changes.

Radiation pneumonitis presents 1-6 months post-thoracic RT with cough, dyspnea, and imaging changes; corticosteroids are the main treatment.

Lhermitte syndrome is a transient electric-shock sensation with neck flexion after cervical cord irradiation; it is usually self-limited.

Fertility preservation counseling should occur before pelvic or gonadal irradiation; options include sperm banking, oocyte/embryo cryopreservation, and ovarian transposition.

Bone metastasis palliation commonly uses 8 Gy in 1 fraction or 30 Gy in 10 fractions; single-fraction regimens have similar pain relief but higher retreatment rates.

Malignant spinal cord compression requires urgent corticosteroids (dexamethasone) and decompressive surgery or RT; RT alone is used when surgery is not feasible.

Superior vena cava syndrome from lung cancer or lymphoma is managed with urgent RT or stent placement; airway compromise requires emergent intervention.

Brain metastases are managed with whole-brain RT, stereotactic radiosurgery, or surgery depending on number, size, and performance status; hippocampal-sparing WBRT may preserve cognition.

Hemoptysis, dysphagia, and bleeding from advanced cancer can be palliated with short-course RT (e.g., 8-20 Gy in 1-5 fractions).

Hypercalcemia of malignancy is treated with IV fluids and bisphosphonates or denosumab; RT is used for painful bone lesions.

Febrile neutropenia requires prompt empiric broad-spectrum antibiotics; RT is generally held during acute infection.

Spinal cord compression dosing: 8 Gy single fraction, 20 Gy in 5 fractions, or 30 Gy in 10 fractions depending on prognosis and neurologic status.

The AAPM/RO-ILS and institutional incident learning systems should be used to report and analyze near-misses and adverse events; a just culture encourages reporting.

Time-out and pretreatment verification (patient ID, site, laterality, plan) are required safety steps before each treatment.

Informed consent must include discussion of benefits, risks, alternatives, and the option to decline; documentation is required.

Radiation safety principles: ALARA, time-distance-shielding, and compliance with NRC/state regulations for sealed sources and radiopharmaceuticals.

Pregnancy testing and counseling are required before pelvic RT in patients of childbearing potential; fetal dose estimation guides management.

Professional boundaries and conflicts of interest must be disclosed; financial relationships with industry are managed per institutional and ACCME policies.

Documentation of treatment parameters, dose constraints, and plan approval is a medical-legal requirement; peer review and chart rounds support quality.

Billing and coding for RT require accurate documentation of simulation, treatment delivery, and special procedures (e.g., IMRT, SBRT, brachytherapy) per CPT and payer rules.