Volumetric Modulated Arc Therapy Capabilities for Treating Lower-Extremity Skin Affected by Several Merkel Cell Carcinoma Nodules: When Technological Advances Effectively Achieve the Palliative Therapeutic Goal while Minimising the Risk of Potential Toxicities

Abstract

The peculiar and rare clinical condition below clearly requires a customized care approach in the context of personalized medicine. An 80-year-old female patient who was subjected in 2018 to surgical removal of a cutaneous Merkel cell carcinoma (MCC) nodule located on the posterior surface of the left thigh and to three subsequent palliative radiotherapy treatments developed a fourth relapse in October 2020, with fifteen nodular metastases located in the left thigh and leg. Since the overall macroscopic disease was still exclusively regionally located and microscopic spread was likely extended also to clinically negative skin of the thigh and leg, we performed an irradiation of the whole left lower extremity. For this purpose the total target (65.5 cm) was divided into three sub-volumes. Dose prescription was 30 Gy in 15 daily fractions. A sequential boost of 10 Gy in 5 daily fractions was planned for macroscopic nodules. Plans were calculated by means of volumetric modulated arc therapy (VMAT) with the field overlap technique. Thanks to this, we obtained a homogeneous dose distribution in the field junction region; avoidance structures were delineated in the central part of the thigh and leg with the aim of achieving an optimal superficial dose painting and to reduce bone exposure to radiation. This case study demonstrates that VMAT allows for a good dose coverage for circumferential cutaneous targets while sparing deeper organs at risk. A reproducible image-guided set-up is fundamental for an accurate and safe dose delivery. However, local treatments such as radiotherapy for very advanced MCC of the lower extremities might have limited impact due to the high probability of systemic progression, as illustrated in this case. Radiation is confirmed as being effective in preventing MCC nodule progression toward skin wounding.

Adjuvant Radiotherapy for Dissected Parotid Lymph Nodes Containing Merkel Cell Carcinoma from an Unknown Primary Skin Site: 2 Case Reports

“…The study showed that lymph node irradiation alone to the microscopic and macroscopic positive regional lymph nodes conferred an excellent regional control rate that was comparable to that of lymphadenectomy. Another study proved that lower dose ranges (30/40 Gy in 2 Gy/day/fractions) were sufficient to stably control extensive skin involvement of large body areas when symptom palliation was the primary goal of radiotherapy [ 22 ].…”

Case Report: Adjuvant image-guided radiation therapy reduces surgical invasiveness in malignant peripheral nerve sheath tumors

“…Sarcomas have traditionally been considered to be radioresitant; however, RT has now been routinely incorporated into sarcoma treatment regimens for more than a century ( 27 ). The introduction of newer RT modalities, such as IGRT, intensity modulation RT, volumetric modulated arc therapy, stereotactic RT, and proton-based RT has revolutionized the field of radiation oncology, while resulting in fewer toxicities ( 8 , 27 , 28 ). Given the locally aggressive nature of the tumor and risk of local and distant recurrence, several authors recommend surgery with concomitant radiotherapy as the standard of care for MPNSTs ( 3 , 4 , 14 , 29 – 32 ).…”

Introducing Radiotherapy in Metastatic Merkel Cell Carcinoma Patients with Limited Progression on Avelumab: An Effective Step against Primary and Secondary Immune Resistance?

“…Our GTVs ranged from 10 to 209 cc, while CTVs from 25 to 3744 cc. The largest CTV refers to the whole skin of the left lower limb of a patient in whom previous three RT courses had failed to prolong PFS, as described in [ 22 ]. Palliative doses were the most common, having been used in 6/8 patients: by delivering a 3 Gy/day fraction, a total dose of 30 Gy was administered to 5 patients and 36 Gy to another one.…”