Selective boosting of tumor subvolumes

Area of Science:

• Radiation Oncology
• Medical Physics
• Cancer Biology

Background:

• Radiotherapy dose distribution is evolving beyond uniform delivery.
• Non-uniform doses are common in brachytherapy and stereotactic radiosurgery, often yielding good outcomes.
• Targeting specific tumor regions (e.g., hypoxic areas) with non-uniform doses may enhance tumor control probability (TCP).

Purpose of the Study:

• To investigate the impact of boosting specific tumor subvolumes with non-uniform doses.
• To model the effect of dose ratios up to 2 for various tumor subvolume proportions.
• To determine optimal boost dose ratios for increasing tumor control probability.

Main Methods:

• Utilized a standard linear-quadratic model to define tumor dose-response curves.
• Calculated tumor control probability (TCP) based on tumor volume, radiosensitivity (SF(2)), and dose for 50% tumor control (TCD(50)).
• Constructed TCP curves as a function of boost dose ratio and boosted tumor volume proportion.

Main Results:

• TCP increased significantly with both boost dose ratio and the proportion of tumor volume boosted.
• A plateau in TCP increase was observed around boost dose ratios of 1.2-1.3, except for boosting over 90% of the volume.
• Substantial TCP increases (up to 75%) were achievable in small tumors with steep dose-response slopes (gamma(50)).

Conclusions:

• Boost dose ratios exceeding 1.3 are rarely necessary or beneficial.
• Significant TCP increases (from 50% to 75%) are possible by boosting 60-80% of tumor volume.
• This approach may offer improved outcomes with a manageable increase in the risk of necrosis.