This topic is covered poorly in most areas. The only useful information I could find was in the 5th edition of Perez & Brady
Neoadjuvant Radiotherapy
Radiobiological Basis
Neoadjuvant radiotherapy allows tumours to be treated in their 'natural state' before processess such as accelerated repopulation can be triggered by other treatment modalities. Hypoxia due to surgical changes is not present (although standard tumour hypoxia may be). Early side effects are generally more easily tolerated pre-operatively. In some cases, preoperative treatment requires smaller fields, leading to reduced volumes of normal tissue irradiated.
Advantages
- Increases potential for complete (R0) resection
- Treats potentially involved nodes early
- Eradication of disease outside the surgical field
- May be tolerated more easily than adjuvant radiotherapy
- Reduces the number of tumour clonagens in the surgical field, potentially reducing the potential for intraoperative seeding.
Disadvantages
- Delays surgery
- May interfere with wound healing after surgery
- Disruption of staging
Examples
Radiation is not used neoadjuvantly, in most cases, for Phase I tumour sites.
Other sites where it may be used include:
- Locally advanced rectal cancer
- Sarcoma
Adjuvant Radiotherapy
Radiobiological Basis
Surgery reduces the number of tumour clonagens significantly in most cases. A smaller number of clonagens means that radiation is likely to be more effective. Tumour hypoxia may also be reduced as smaller, subclinical sites are less likely to have developed significant hypoxia. Accelerated repopulation, early effects and increased volumes of treatment may cause problems with this approach.
Advantages
- Surgery occurs rapidly
- Pathological specimen not affected by radiotherapy changes
- Eradication of residual tumour cells in the surgical field
Disadvantages
- Delay in radiation until wound healing complete
- Changes in tumour bed may lead to increased hypoxia of surviving cells with corresponding radioresistance.
- Radiotherapy tolerated less well post-operatively
Examples
Most Phase 1 tumour sites utilise adjuvant radiotherapy as one form of treatment.
- Breast
- Adjuvant breast irradiation following wide local excision
- Chest wall irradiation following mastectomy (in selected cases)
- Regional lymph node irradiation following wide local excision or mastectomy
- Prostate
- Adjuvant radiotherapy is recommended when patients have positive margins or other high risk features (stage T3 and above)
- Head and Neck
- Radiotherapy may be delivered after primary excision when aggressive features or nodal involvement are present
- Lung
- Radiotherapy is sometimes given in situations of incomplete resection or to regional lymph nodes
- Skin
- Radiotherapy may be used when surgical margins are positive or shows aggressive features (perineural invasion, sclerosing basal cell cancer subtype)
- Regional nodes often require adjuvant radiotherapy when melanoma is treated.
Intraoperative Radiation
Intraoperative Radiation is the delivery of a radiation treatment during a surgical procedure (generally for the removal of the primary treatment). Electrons are the usual method of dose delivery.
Radiobiological Basis
- Smaller radiotherapy volume
- Minimal normal tissue side effects
- Increased dose to tumour site
Advantages
- Delivery of high dose boost to tumour bed with minimal normal tissue complications
Disadvantages
- Increased rate of peripheral neuropathy near treated sites
- Patient must be transferred to a radiotherapy bunker from the operating theatre
Extracorporeal Radiation
Extracorporeal radiation involves removing the tumour and surrounding normal tissue from the patient for irradiation, and then reimplanting the tissue. It is used for osteosarcoma, where removal of the bone would lead to unacceptable deformity or immobility.
Radiobiological Basis
By removing the tumour and surrounding tissues from the body, a very high dose can be delivered to the tumour and surrounding bed without risk of causing early or late effects in the other tissues of the body. Doses usually range from 200 - 300 Gy.
Advantages
- Very high dose delivered to the tumour
- Minimal side effects in remaining tissues
Disadvantages
- High rate of side effects in the removed tissue (avoided somewhat by replacement of bone with prostheses after dose delivered)
- Complicated surgical procedure
