Four Lost Fractions in a Head and Neck Schedule

The dominant issue is not the missing dose - it is the missing time.

• Accelerated repopulation. In head and neck cancer, clonogen proliferation accelerates after roughly the third to fourth week; a commonly cited working figure is that about 0.6 Gy of additional dose per lost treatment day is needed to offset the effect. Ms. L is in exactly that window, so an uncompensated 4-day gap is a real risk to local control.
• Fractionation sensitivity differs by tissue. Tumour BED with α/β ≈ 10: 66 Gy × (1 + 2.2/10) ≈ 80.5 Gy₁₀. Late-reacting tissue with α/β ≈ 3: 66 × (1 + 2.2/3) ≈ 114 Gy₃. Anything added to close the gap raises both - so a compensation that fixes the tumour BED can push the mandible, mucosa and pharyngeal constrictors past tolerance.
• Concurrent cisplatin already sensitises and already increases acute and late toxicity, so the acceptable margin for extra dose is smaller, not larger.
• Time is not fully recoverable. Restoring total dose does not restore the elapsed time; that requires compressing the remaining schedule (BID days, Saturday treatment).

So compensation is likely indicated, but it must be tumour-BED-driven and toxicity-limited - the oncologist's prescription, informed by my scheduling arithmetic.

It is radiobiologically defensible and logistically demanding.

• Recovering four 2.2 Gy fractions restores total dose to 66 Gy and BED₁₀ to ~80.5 Gy₁₀, and shortening overall time addresses repopulation directly - which a simple add-on at the end would not.
• Cost: each additional 2.2 Gy fraction adds ~3.8 Gy₃ of late BED. Four of them add ~15 Gy₃ on top of ~114 Gy₃, roughly a 13% increase to late-effect dose in a patient already receiving concurrent chemotherapy and with grade 2 mucositis. That is the trade-off the oncologist must own.

What I confirm before it goes on the board:

1. Interval ≥ 6 hours between the two daily fractions - enough for sublethal damage repair in late tissues. This drives slot times and transport.
2. Machine and staff cover for the Saturday and the BID days, with physics/QA sign-off on the altered schedule.
3. Same immobilisation and image guidance; with 6% weight loss and mucositis, the mask fit must be checked - a loose mask may mean a new CT and replan rather than simply compressing fractions.
4. Patient capacity: two visits a day, transport, nutrition and mucositis management. If she cannot tolerate it, the plan fails in practice even if it is correct on paper.
5. Documented consent for the altered fractionation.

It changes the order of operations: geometry before dose.

• A loose mask plus a new systematic shift (not random scatter) usually means anatomy has changed - 6% weight loss, resolving nodal mass, or both. Compensating a dose gap is pointless if the dose is being delivered to the wrong place, and a systematic 4 mm error repeated over the remaining compressed fractions multiplies the harm.
• My action: stop, escalate to the oncologist and physics before the next fraction, and recommend a repeat CT simulation and replan rather than pushing shifts on a mask that no longer fits. The 4-day machine downtime is the natural window to do it.
• This also reframes the compensation discussion: if the plan is being rebuilt anyway, the new plan can absorb part of the make-up dose in a way that respects the actual, current anatomy and the delivered dose so far (a composite of the first 22 fractions plus the new plan).
• Document the mask fit, the CBCT findings, the dates, and the decision. "The mask felt a bit loose" written retrospectively after a marginal recurrence is indefensible; a documented replan is not.