Assessing setup errors and shifting margins for planning target volume in head, neck, and breast cancer

Incidence of local breast cancer recurrence with delayed radiation therapy

BACKGROUND

The purpose of this research was to examine the probability of ipsilateral breast cancer recurrence in individuals whose RT was delayed after the first chemotherapy and surgery.

PURPOSE

To analyze the effect of delaying RT for breast cancer patients (by more than 6 weeks after treatment).

METHODOLOGY

A retrospective analysis comprised 136 female breast cancer patients treated at the Baghdad Centre for Radiation Oncology and Nuclear Medicine from 2021 to May 2022. External beam radiation was started more than 6 weeks after chemotherapy was finished for all patients who also had surgery. Clinical examination and ultrasound were part of the follow-up process.

RESULTS

Patients' ages varied from 28 to 71, and the majority (83%) had a mastectomy. The majority of cases (95.5%) were diagnosed as invasive ductal carcinoma on histopathology, with 49.6% being at stage 2 and 42.6% being at stage 3. Seventy-six percent of patients tested positive for hormones. Although 10 patients (7.35%) acquired distant metastases within 5 years, only 2 (1.47%) had local recurrence because of the delay in RT. Specifically, 91.1% had complete local control with no evidence of disease spread.

CONCLUSION

Delaying RT by more than 6 weeks in patients with breast cancer did not substantially affect local control, according to the results of a new research, the first of its type in Iraq.

Planning target volume margin in head and neck cancer patients undergoing radiation therapy: Estimations derived from own data and literature

Planning target volume (PTV) to deliver the desired dose to the clinical target volume (CTV) accounts for systematic (∑) and random (σ) errors during the planning and execution of intensity modulated radiation therapy (IMRT). As these errors vary at different departments, this study was conducted to determine the 3-dimensional PTV (PTV3D) margins for head and neck cancer (HNC) at our center. The same was also estimated from reported studies for a comparative assessment. A total of 77 patients with HNCs undergoing IMRT were included. Of these, 39 patients received radical RT and 38 received postoperative IMRT. An extended no action level protocol was implemented using on-board imaging. Shifts in the mediolateral (ML), anteroposterior (AP), and superoinferior (SI) directions of each patient were recorded for every fraction. PTV margins in each direction (ML, AP, SI) and PTV3D were calculated using van Herk's equation. Weighted PTV3D was also computed from the ∑ and σ errors in each direction published in the literature for HNC. Our patients were staged T2-4 (66/77) and N0 (39/77). In all, 2280 on-board images were acquired, and daily shifts in each direction were recorded. The PTV margins in the ML, AP, and SI directions were computed as 3.2 mm, 2.9 mm, and 2.6 mm, respectively. The PTV3D margin was estimated to be 6.5 mm. This compared well with the weighted median PTV3D of 7.2 mm (range: 3.2 to 9.9) computed from the 16 studies reported in the literature. To ensure ≥95% CTV dose coverage in 90% of HNC patients, PTV3D margin for our department was estimated as 6.5 mm. This agrees with the weighted median PTV3D margin of 7.2 mm computed from the 16 published studies in HNCs. Site-specific PTV3D margin estimations should be an integral component of the quality assurance protocol of each department to ensure adequate coverage of dose to CTV during IMRT.