How many radiation treatments are required for a young, otherwise healthy adult with stage I diffuse large B‑cell lymphoma (DLBCL) limited to a single cervical node who has received three cycles of R‑CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, prednisone) and now has a negative post‑treatment PET‑CT (positron emission tomography–computed tomography) (Deauville 1‑3)?

Radiation Therapy for Stage I DLBCL After 3 Cycles R-CHOP with Negative PET

For a young, healthy adult with stage I DLBCL limited to a single cervical node who achieved a negative PET-CT (Deauville 1-3) after 3 cycles of R-CHOP, consolidative involved-field radiotherapy at 30 Gy should be administered to optimize disease control and survival. 1

Evidence for Combined Modality Therapy in Limited-Stage DLBCL

The standard approach for localized DLBCL involves abbreviated chemotherapy followed by radiotherapy, based on Level I evidence:

• Randomized trials demonstrate superior outcomes with chemoradiotherapy versus chemotherapy alone in stage I-II DLBCL. The SWOG study showed patients receiving 3 cycles of CHOP plus radiotherapy had significantly better 5-year progression-free survival (77% vs 64%, p=0.03) and overall survival (82% vs 72%, p=0.02) compared to CHOP alone. 1

• The ECOG trial confirmed the benefit of consolidative radiotherapy in patients achieving complete remission after chemotherapy. Among 172 CR patients, 6-year disease-free survival was 73% with 30 Gy involved-field RT versus 56% with observation alone (p=0.05). 1

• Life-threatening toxicity was actually lower with combined modality therapy (61/200 patients) compared to chemotherapy alone (80/201 patients, p=0.06) in the SWOG trial, contradicting concerns about additive toxicity. 1

Specific Radiotherapy Recommendations

Dose and field:

• Administer 30 Gy involved-field radiotherapy to the initial site of disease (cervical node). 1
• This dose is standard for non-bulky limited-stage disease after abbreviated chemotherapy. 1

Timing:

• RT should be delivered after completion of the abbreviated chemotherapy course (typically 3-4 cycles). 1

Why PET-Negativity Does Not Eliminate the Need for RT

While your patient achieved an excellent metabolic response (Deauville 1-3), this does not obviate radiotherapy:

• The ESMO 2015 guidelines explicitly state that consolidation radiotherapy to initial non-bulky sites has no proven benefit in patients treated with rituximab when receiving the full 6 cycles of R-CHOP. 1

• However, this statement applies to patients receiving 6 cycles, not abbreviated 3-cycle regimens. The evidence supporting omission of RT is based on full-course chemotherapy. 1

• For abbreviated chemotherapy (3-4 cycles), radiotherapy remains standard regardless of interim PET results, as the randomized trials establishing this approach did not use PET-adapted strategies. 1

• Deauville score 4-5 after full R-CHOP predicts worse outcomes (5-year recurrence-free survival 66.8% vs 86.6%, p=0.041), but the prognostic value of interim PET after only 2-3 cycles is limited and should not guide treatment de-escalation. 2, 3

Critical Pitfalls to Avoid

Do not extrapolate data from 6-cycle regimens to abbreviated therapy:

• The evidence showing RT may be omitted applies only to patients receiving full 6-cycle R-CHOP, not 3-cycle regimens. 1
• Patients who fail to complete planned treatment have dramatically worse outcomes (5-year OS 26% for 1-3 cycles vs 76% for completed treatment). 4

Do not rely solely on interim PET to omit RT:

• Interim PET after 2 cycles of R-CHOP has limited prognostic value and is not validated for treatment de-escalation decisions. 3
• The prospective SAKK 38/07 trial showed interim PET-negative patients still had 2-year event-free survival of only 74-76%, not sufficient to justify omitting consolidative therapy. 3

Modern RT techniques minimize long-term toxicity:

• Involved-field RT at 30 Gy using contemporary techniques has low expected toxicity, making the risk-benefit ratio favorable even in young patients. 5

Treatment Algorithm Summary

For stage I DLBCL with single cervical node involvement:

1. Complete the planned abbreviated regimen: If only 3 cycles of R-CHOP were planned, this is appropriate for low-risk stage I disease. 1

2. Proceed with consolidative RT regardless of PET result: Administer 30 Gy involved-field RT to the cervical node region. 1

3. Do not extend chemotherapy to 6 cycles as a substitute for RT: The evidence base supports abbreviated chemo + RT, not extended chemo alone for stage I disease. 1

4. Consider multidisciplinary discussion only if contraindications to RT exist (e.g., prior neck irradiation, anatomic constraints), not based on PET-negativity alone. 5